A comparison of strength properties of heat treated AISI ...

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Masters Theses Student Theses and Dissertations

1967

A comparison of strength properties of heat treated AISI 1065 A comparison of strength properties of heat treated AISI 1065

steels at high strength levels steels at high strength levels

Robert Lowell Hollenbeck

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Recommended Citation Recommended Citation Hollenbeck, Robert Lowell, "A comparison of strength properties of heat treated AISI 1065 steels at high strength levels" (1967). Masters Theses. 6168. https://scholarsmine.mst.edu/masters_theses/6168

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A COMPARIOON OF STRlllmTH PROPERTIES

OF HEAT '!'REATED AISI 1065 STEELS

AT HIGH STRENGTH LEVELS

BY

BOBlCRT L. HOLLENBECK _;93P -

129537A

THmSIS

submitted to the faoulty ot

THE UNIVERSITY OF MISSJURI AT ROLLA

in partial tul:f'1.l1ment ot the requirements tor the

Degree ot

MASTER OF salmi IN MI'1'ALLUBGICAL INGlNEEBING

Rolla, Missouri

1967

Approved by

~o/iCZ.l

1Yrt'

c/~ (AM""r)

~ :1S1 Oe1A.~\UN\

11

Six .!IS! c1065 steE?1s were heat treated and tensile tested in

order to eva1.uate their ductility at high strengtb levels. Heat

treating and tensile testing prooedures were developed. for use in

working with these steels at tensile strengths of 300,000 psi and

higher. The allstenitiUng procedure i,n the hardening operation _8found to af'f'eot thestrel'lgthand duotility of thebigh .tre~s&1n

pIes. RapidJ.y heating to the austen::ltiziDg tempera'Qure followed by

an immed1ate q,ue.,h produced better"propert.1es than slow be,ating

followed by a soaking period before the quench. However, it was

concluded that the carbon oontents of the steels studied (O.~

O.~) was too high to realize simultaneously very high strength

and appreciable duotility.

ill

The author is especially grateful to Dr. Fred K1sslinger tor

his advice and assistance given throughout the investigations am

in the preparation of this thesis.

The assistanee given by the Department ot Engineering Meobatdcs

in JII&k1ng the tensile testing facilities available and the assistance

and cooperationot the other members of thefaeulty of the Depdtment

of Met.al3.urgieaJ. Eng1neer1ng is grateMly aoknowledged.

The author un wishes to expre.s his gratitude to IDterlake

steel OorpentioR of Chioago. Dll.nois for denation of the steel

used in this study.

TABLB or CONTENTS

ABSTRACT • • • • • • • • • • • • • • • • • • • • • • • • • • • •

ACKNOWLBIGBJt1ENT •••••••• • • • • • • • • • • • • • • • •

LIST OF FIGURES ••••••••••••••••••••••••

LIST OF TABLES • • • • • • • • • • • • • • • • • • • • • • • • •

I. INTHOICCTION....... • • • • • • • • • •••••••

II. LITERATURE REVIEW • • • • • • • • • • • • • • • • • • • •

A. TEMPERING OF MARTENSITE •••••••••••••••

B. STRENGTHENING or MARTENSXTE •••••••••••••

III. EXPERJ:MENTAL PROClIlDURE • • • • • • • • • • • • • • • • • •

A.' STEELS srtJDIED • • • • • • • • • • • • • • • • • • • •

B. SAMPLE PREPARATION • • • • • • • • • • • • • • • • • •

C• HA:RI>ENING • • • • • • • • • • • • • • • • • • • • • •

D. TDlPERING .• • • • • • • • • • • • • • • • • • • • • •

E. TENSILE TESTING • • • • • • • • • • • • • • • • • • •

F. ELONGATION ••••••••••••••••••••••'p

IV. RESULTS •••••••••••••••••••••••••

A. STRENZTH PROPERTIES WITH SLOW HEATING • • • • • • • •

B. STRENGTH PROPERTIES WITH RAPID HEATING ••••••••

C. COMPARISON OF SIX STEELS • • • • • • • • • • • • • • •

v. DISCUSSION OF RESULTS ••••••••••••••••••

A. GENERAL •••••••••••••••••••••••

B. HARDENING TREATMENTS •••••••••••••••••

C. COMPARISON OF STEELS • • • • • • • • • • • • • • • • •

VI. CONCLUSIONS •••••••••••••••••••••••

BIBLIOGRAPHY • • • • • • • • .. • • • • • • • • • • • • • • • • •

VITA ••••••••••••••••••••••••••••••

iv

Page

i1

iii

v

vii

1

2

2

6

10

10

11

12

14

14

15

19

19

35

55

60

60

67

68

71

72

?4

FIGURES

1. Modified. Jaws

LIST OF FIGURES

.. . . .. . ...... -. . . . . .. • • •

Page

16

v

2. Templin Grip .Assembly With Expanding Dev1ce In Place

Against Dltts Of Jaws •• " . • • • 17

3. Hardnesses or Samples Of steel No. 5 Quenched From Various

Autrt.en1t1zing Temperatures IIrt:.o 7fl'F Oil, 140°F Oil And

700rWater ••••••••••• 1•••• • • • • • • • • 21

4. Tensile strength Of Six steels Austenitized At 1500°' For

15 Minutes A.md Tempered At 660°' ;0 .'. • • • • • •• •• 24

S. Tensile strength or S1x steele Austem.tized At 1500°' For

15 Minutes And Tempered At ;00°' •• • • • • • • • • •• 26

6. Tensile strength .AM Elongation On samples From steel No. :3

With Various Austenitizing Treatments • • • • • • • • •• 29

7. Tensile strength And. ,Elongation On Bamp1es From steel No. 4

With Various Auste:n:l.tizing Treatments • • • • • • • • •• 30

8. Tensile strength And ELongation On Samples FrGm steel No. 5

With Various Austemtizing Treatments. • • • • • • •

9. Effect Of Tempering '1'1111e On Tensile St:rength or steels

Tempered At 450°' • • • • • • • • • • • • • • • • • •

• •

• •

31

10. Effect or Tempering Treatments On Strength Properties Of

steel No. J • • • • • • • • • • • .. • • • • • •• • • •• 36

11. Tensile strength And Elongation On samples F:rom steels No. :3

And 4 Hardened With RApid Heating JinFu.rnace At 15;()OF • 41

L2. Tensile Strength And ELongation Of Samples Frem steels No. J

.AlXi 4 Hardened With Rapid HeatiDg In Furnace At 16,50°,. ~

FIGURES Page

13. Tensile st.rength Ani Elongation or S8mples From steels

No. 3 And 1+ HardenedWlth 1i?.apid Heating In Furnace

At 17.50°, • • • • • • • • • • • • • • • • • • • • • • ••14. Eft'ect Of Tempering Temperatu:re On strength Properties or

st.eels No. 1.~ , .And"4 • • •• •• • '.. ." • • • • ,,; •

15. Average Tensile strength- Am. llIlongatd:enOt Six steels

Hardened B,rRapidHeat4.ngtt'e1.500e, In A Furnace At

1550°, ••••••• • • • • • • • • • • • • • • •

• • •

• ••

• •

58

61

vii

LIST OF TABLES

TABLES

I. COlllpOsitiOn6 or steels stud:1ed • • • • • • • • • • • •

Page

10

II. Effect or Quench Media .And Austenitizing Temperature

On Average Hardness Of steel No.5. • • • • • • • • 20

III. If'teot or Austenitizing AM Tempering Treatments On

strength Properties With Slow Heating ••••••• 23

IV. Efrect Of AustenitiziDg Treatments On strength

Properties With Slow Heating • • • • • • • • • • • • 28

V. Eftect Of Tempering Treatments On strength Properties

Of S&mp~e8 Hardened With Slow Heating ••••••• .33

VI. strength Properties WithlW.p1d Heating In Furnaoe At

1550°' • • • • • • • • • • • • • • • • • • • • • • • .38

vn. streDgth Properties With Rapid Heating In Fumaoe At

1650°, •••• • • •••• • ••• • • • • • • • • • 39

VIII. strength Properties With Rapid Heating In FurDace At

17500, .. • • • • • • • • • • • • • • • • • • • • • • 40

IX. Effect Of Tempering Temperatv.re On strength Properties

or Samp1es Rapidly Heated ••••••••••••• 48

X. Effect ot Tempering On strel)gth Properties Of samples

Rapidly Heated In FUrnaoe At 1750°' •• • • • • • • 51

II. Effect Of Pretreatment (Austen::ltize At 1450°' And Jdr

CoDl) On strength Properties Ot samples Hardened In

:Fu.:r'Daee At 15500 r ••• • • • • • • • • • • • • • • 5.3

XII. stremgth Properties On samples Of Six steels Uniformly

HUdened By Rapidly Heating To 1500°' In Furnaoe At

1550°, • • • • • • • • • • • • • • • • • • • • • • • 56

1

I. INTRODUCTION

A. study aimed at investigating the ductillty of high strength

plain carbon steels was undertaken. Six steels of the AISI C 1065

grade with oarbon oontents between O.~ and 0.726)', were studied.

stronger materials are constantly-required to meet the demands

of modern technology. Often where high strength is required, alloy

steels must be used. because the particular applioation demands certain

qualities such as high toughness, retention of strength at high temp..

erature, corrosion resistance, weldability,etc. However, there are

applications where high strength is required and the other require

ments are less stringent. From the standpoint of economics in mater

ial usage, it is 'Worthwhile to investigate plain carbon steels in

order to determine their maximum useable tensile strength.

Plainoarbon steels are cODIl.11only used in the slow cooled condition.

In this study where very high tensile strength, 300 ksi (thousands of

pounds per square inch) a.nd. higher, are of interest, the quenohed and

tempered oondition was studied.

Chien (1)1 and Kisslinger (2) have studied high strength, heat

treated, plain carbon steels and found that tensile strengths of 300

ksi or higher can be obtained, but that some heats of ateel lose their

duotility when heat treated to high hardness.

The six steels that were available at the start of this work were

studied in order to develop a heat treating procedure that would pro

duoe their best properties and to determine whioh, if any, of these

steels was duotile at very high .strength levels.

1Numbers in parentheses refer to bibliographical entries.

2

II. LITERATURE REVIliCW

A. TEt-1PERING OF filARTENSITE

Tempering of martensite has been a subject of importance to steel

users since the discovery of the allotropic nature of iron. Light

microscope and X-ray work served to remove much of the mystery of the

hardening and subsequent tempering process of martensite. Not until

the early 1950's, however, was much of the true mechanism revealed and

adequately explained. In the early 1950's with the initiation of

widespread use of the electron microscope, new in-roads were made to

understanding the tempering process. Some discussion of the advances

reported in the literature is considered necessary.

While there exist oonflioting opinions ooncerning the exact

nature of the tempering prooess, it is still oustoinary to distinguish

three general stages in tempering steels:

1. Decomposition of martensite and formation of epsilon carbide

2. Transformation of retained austenite

3. Trans1tion of epsilon carbide to cementite.

In much of the literature attention is ooncentrated on the first and

third stages, but no marked distinction is made.

Kelly and Nutting (3) show that the shear transformation of

super-saturated austenite gives rise to two 'types of martensite:

low-carbon martensite is in the form of' needles or laths containing

dense dislooation networks, while high-carbon martensite is in the

form of internally tidnned plates. Both of these substructures are

known to e:rlst simultaneously in quenched steels throughout the range

of carbon contents. The extent to whioh either would e;xist in a. steel

of the carbon content being studied (approximately O..?~) co\D.d oon

ce!vably be dependent on the degree of homogen1.zation achieved in the

austenitizing operation. How' these substructures relate to the temp

ering prooess' am Subsequently affect the strength in quenohedste&ls

is discussed in the literature.

Teldn aM Kelly (4) in their work w.tth a"twinned or high' ce:rbon

form of martensite found that tempering ocourred. at temperatures as

low as 700F (20°0). Although too undeveloped to be definitely defined

as carbide, they observed what appeared to be a precipitate lying

between the twins after 18 months tempmng. For morepraotical. temp..

ering times (25 hours) aprecip1.tate first appeared at the temperature

of 210°F (100°0), but it was not dEtfin1.t~y'ident1tied~Aftertemp...

ering at 300°F (15000) £01"2 hours, this preoipitate was identif1edas

epsilon oarbide by diffraotion methods. They found that the epsilon

oarbide began to disappear "Whell tempe1"f.ng was o'arTiad: titit at 390°F

(200°0) ani, simultaneously, cementite began 'to' atJi)eu-.ms' oha.nge

from epsilon oarbide to oementite did notoo<s~ as a'direct transition,

but the cementite precipitated at looations different frOllt those df the

original. epsilon carbide. This last finding was corroooratedby Blguohi

et a1 (5) in transmission electron miorosoope work With a. steel con.

tairdng O.4~ea.rbon; however, Eguchi obsel"V'edthat' ep$i.lon oarbide

dissolved completely below 570°F (300°C) before oementite first appeared

at 6100 r (320°0).

In some of, the earlier work, Lement;et>a1'(6)' detenro.ned that the

temperature ranges over whioh the oarbide phases ex1sted in the' early

stages of tempering' overlapped. WOrking with high purity steels they

indi.cated,in theoase ofa 0~8os' cat'bOn conterxt;that the first 'stage

4

of tempering ended at 350 to 400°F (17.5 to 200°0). Thereafter, pt'o

gress!ve solut.1on of the epsilon oarbide network oocurred in the third

stage of temp&ring at 450 to .5000 F (230 to 260°0). This solution of

epsilon oarbide oocurred s1multaneQusJ.y 'With formatiortofeementd.te

platelets and globules wi:thin the martensite subgrains and films at

the subgrain boundaries. At least some overls.pping of the e:x:1stenoe

of epsilon oarbide andcamerxtite, then, was inc:l1oated; whereas, Eguobi

had noted a separation of the temperature ranges over wbi,oh the two

oarbides existed..

In regard to the observation by Lement and bis ooworke~s, it

should 'be noted. tha.t they did net have the advantage ~f transmission

microsoopy techniques fo·l' their investigati.ons ud that use of replioas

may not have revealed the specific nature of the oarbides. A1so, com

position is known to aff6lOt oarbide formation ohara.cterlstios s.nd

could have been responsible for the varyimg obseNat10'u.

Reisdolrl: (J?)and Baker et al (8) haveobse);'V'$d,a ms.rked retarding

of carbide preoip1tatiom. in high silioon steels at low tempering temp

eratures. other elements have an effeet on t9llJ1i>ering ra.tes, but no

other element has been singled out which shows the marked retarding

effect that silicon shows at low temperatures. Some evidcence exi;sts

that indicates silicon is combined in the epsilon oarbide. (7) SUCh

being the case, silioon oontent could well be a controlling factor in

the rate of dissolution of epsilon carbide~

The three stages of tempering stated at the beginnLng a.re a

general discription of tempering martensite in the low temperature

range. A more detailed description seems pos'sibleof the lowtempar...

ature temperingprooess tha.t can be e:lq>ected in steels suoh as thOse

in the liSI C 1065 grade be;l.ng studied, because reoent studies using

the electron microsoope haY, provided increased understanding 0$ the

nature of carbide formation in lllal"t.ensite.

The nature of carbide formation at low tempering temperatUres is

generally agreed upon. (3),(4),(5),(8) Agreement is less obvious with

regard to temperatures at which the various oarbides appear or dis

appear. The variation in oompositionsstl).died and in experimental

techniques probably accounts, to some extent, for the disag~eem9nt on

temperatures at whioh oarbides .appear aM disappear.

As previously rnantioneci, both a twinned ~,nd Q,. ctts].oC)ation sub..

structure oan be present in a Ciuenched plain carbon steel ~n the O.7~

oarbon range, but a greater percentage of the twinned substructure is

expeoted to be present. Tempering a twinneclSUobstructu,re in the

vioinity of 4000 F (~QOOC) can be expected to fom a, n~twork 01' fine

epsilon carbides ly,lng in a direotioJil acro.ss th~t~eP. ,pl:ates. At

this same temperature the first o$Illentite precipitates oan be expected.

to appear along the twin 'QQundarles. Temperl.ng at higher temperatures

of 500 to 5700 F (260 to 300°C) can be expected toenla);'ge the oemen

tite precipitates formed along the twin boUl'rlaries ani to completely

dissolve the epsilon carbides lying across the twins. Tempering at

750°F (400°C) should reduoe the number. of oementite precipitates,

slightly enlarge the surviving precipitates, an? reduoe the number of

twins present.

Any dislocation-substructured martensite present in a plain high

oarbon steel would be mofrf:, dfected in the temp~n1oture 1"a:t:1ge below,

500°F (260°C) where recovery would decrease the :1.ntensity of the. qi.~...

location tangles.

5

B. STRENGTHENING OF· l-1ARTENSITE

The precise meohanisms whioh influence the strength of martensite

are peroaps no better understood than the temperlngmeohanisms. Muoh

of the unoertainty Stems from the multiplicity of factors available

to produoe strengthening and frOm the probab1.lity that mal\V of these

factors oan be additive or cancelling when combined.

Kelly and Nutting (9) have studieci the contribution that 'iTarlous

factors make to hardness in martensite. Worldng with plain caroon

steels of O~20 and 0.80% earbon and iron--nickel-carbon alloys Gf 0.20

and 0.8~ carbon, they were ablato draw certain oQholusions regarding

the role of oarbon- in st1"engtherdng,asdetermined. by hardness•.. They

presented evidence showing that oarbon in solid solution aocounts for

only about half otthe strength oUserV'ed in a fully hardel'1ed 0.8~

carbon steel;' It was assumed, then, that a large portion otthe -add

i tional st1"engtb observed. in martens1te 'WaS provided by. some ·form of

carbide segregate ani matrix S'UbstNoture.

Carbide segregation is exceedingly dependent on carbon conoen

tration and ismamtest as precipitates in relation to ej.ther internal

twins which predominate in high-carbon martensite or to dislocations

which predominate in the needles or laths of low-oarbon martensite.

The internallytWlnned substructure in a plain carbon steel in the

0.70'f, oarbon range is believed to aftaot strength properties more than

is the dislocationsubstruoture because oftts a:£fecton ,:Qarbide mor

phology.

Carbide morphology-was discussed in the previous section with

regard to theea.rly sta.ges of tempering or high earbon steels. VaH.ous

irwestigators (3), (4) , (5) , (8) have reported experimental da;ta verltying

the formation of oarbides during tempering which lie both along twin

boundaries and. aorOss the twinned pla.tes~ Twin boundary precipitates

restriot the movement of dislooationsand act as barriers to slip.·

For twinned martensite to deform, a slip system must be operativ& such

that both the slip plane and slip direction are common to a pair of

twinned plates~ 'When carbide preoipitates lieaeross; 'in addition to

along the twin direotion, they look the only remaining defomation

system. This presumably accounts for much of' the hardness or high

oa.rbon martensite after tempering in the region or 400E)F (2000C)~

Kelly and. N1rt.ting (3) propose that the softening noted1nthe 400 to

750°' (200 to 400°0) rang$ does l'lot resultf'romcarbide growth, rather

to removal of twins.

Hardening of dislooatio:D-substrliCtured, low..oarbon martensite

seems to ooour by a mechanism qu1tedifferent than that for tldnned,

high-clWOOn ma.rt.ensite~ E2tperlmema1 evidence (9Y··h8ssh~'that

autotempering (oarbidepreoipitation during th~qlienOh) is p1"evalent

in plain, low oarlxm·st'ee1s. The temp~aturer at which a lOw-oarbon

austerdte begins to transform to martensite is relativelyhitJb.'in

comparison to the loW range tempering temperatures. This is believed

to p1"Ol110te the formation o£ a high density ot fine oaJ'bides, because

the density of the dislocations is high 'in this newly tomed marten

site am. mobility of the dislooations is relativ$ly" high at ,the Ms

temperature~ As the disloeations SW$9p threughthe material, oppor

tunity is provided for forming many nucleation sites. Thus, a. high

density of finely dispersed carbides is posSible Which woUld have a

strengthening effect on the ~ensite~ Work reported by Kelly arid

Nutting- (-9) ':showed aU'totempered Jnartensite to b~i signi.f'i~antlrHarder

7

8

than virgin martensite (oarbon completely in solid solution) of the

low..carbon type after both have been tempered. in the SB.lIle manner.

The strength of any steel 1s seen to result from aOQIl1'b1natiQn

of various factors. Carbon solid .solution strengthening aocounts for

approximately half of the strength of martensite tempered at low temp

erature. A large portion of the additional strength is dUe to oarbide

precipitates both of a ooherent andno:ncoherent nature w.1th dispersions

oommensurate 'With the partioular substru.oture -- dislooations or

internal tw1nning~ Grain si~e and elements in substitutional solid

solution are oonsideredto playa relatively minor role~ (9)

Carbon is known to have a greater hardeni.ng effect in the twinned

substruoture, both in solid solution and as oarbide preoipitate.

Therefore, it is important to oonsider the degree of achievement of a

twinned substruoture in a given steel.

Austenite with o.S~ or higher oarbon is oonsidered necessary to

produoe a predominantly twinned martensite. The extent to whioh this

substructure would be aohieved in a O.7~ oarbon, plain oarbon steel

should depend. largely on the degree of homogenization achieved :Ln the

austenitizing treatment~

The Bain (10) and Osborn (11) studies on rates of carbon movement

in spherodized and lamellar pearlitio steels indioate that approx

imately t-seoond is all the time that is required for oarbon to diffuse

the half lamellar distame in a coarse pearlite during auBtenitizing.

Using a 0.68% carbon steel Mima and Hon (12) found that the hardness

of martensite, .formed from austElnite whioh had been isothermally trans

fo;rmed from lamellar pearlite, was markedly dependent on austenltizing

temperature and time. Approximately 40 seconds were required to

develop full hardness at 1380°'(750°0) asoompared to 2 seconds at

14700 F (8000 e) and 1 second at 1560°' (850°C). Additionally, they

showed that the time to completely austenitize lamellar pearlite at

1380°' is approximately 300 seconds and at 1470°' the time is 100

seconds.

9

III. EXPERIMENTAL PROCEDURE

10

A. STEELS STUDIED

Six coils of 3/4-inch wide by 0.035 inch thick steal strip were

donated by Interlake steel Corporation. Each of the six coils was

taken from a different heat of steel approximating the USI C 1065

composition range. The compositions provided by the supplier are

~sted in Table Io

Table I. Compositions Of steels studied.

§!:eel No. 2- 4-

~c 0.70 0.71 0.65 0.72 0.64 ).76

<,tMn .80 .68 .70 .67 .66 .75

%p .009 .020 .014 .014 .014 .016

%8 .016 .040 .013 .008 .012 .012

~Si .05 .04 .05 .05 .05 .05

~Cu .01 .01 .01 .01 .01 .01

%Ni .01 .01 .01 .01 .01 .01

%Or .01 .01 .01 .01 .01 .01

%Mo .009 .005 .009 .005 .005 .005

%Sn .020 .006 .008 .008 .007 .008

%Al 0.005 0.005 0.005 0.00.5 0.005 0.005

These steels were described as "semi-ldlledtl and were hot rolled.

Metallographio examination revealed that the microstructures of

the steels as-received Were essentially cOll1'oletelv nsa:rlitia. RnmA

11

proeutectoid ferrite was observed in steels No. :3 and .5 which were

slightly lower in carbon content relative to the other steels. A very

thin, discontinuous layer of light etching ferrite was observed at the

exterior surfaoes of the strips. This indicated that some decarburi

zation had occurred during hot rolling.

B. SAMP.LE PREPARATION

1. Tensile

Samples were cut with a mechanical shear and identified by stamp

ing appropriate numbers near one end. Samples were cut to two lengths:

8 inches and 10 inches. The 10-inch sample was used for tensile tests

,in all except some of the preliminary work to establish heat treating

guidelines. The greater length permitted mo" aocurate measurement of

elongation. No sUrface preparation was pe,rformed since the material

was received with smooth, uniformly oxidized surfaoes.

Approximately 20 samples were tested with reduced sections machined

to a width of t-inch. Only these few samples were tested with reduoed

sections because no improvement was apparent in their test results.

All other specimens reported in this thesis were straight strip samples

with no reduced section.

2. Hardness

All of the tensile samples were tested for hardness with s. Rockwell

hardness testing machine. The ends of the samples were ground on a belt

grinder before ma1d.ng hardness tests. These ground areas were in or

beyond that portion of the sample gripped by the jaws during testing.

Some preliminary quenching experiments were done on .5-inch long

samples. These were used for comparing differ-ant quench media and were

12

hardness tested along their full length. No tensile testa were made on

these samples.

Samples for microhardness testing were mounted and metallograph

ically polished. A Kentron hardness testing machine with a Knoop

indentor and 100 gram load was used.

C. HARDENING

1. Slow Heati~

Samples wers hardened by austeniti zing in a preheated box type

furnace and quenching in warm oil. A protective atmosphere was not

used in the furnace.

The :f'Urnaoe was a Hen-Duty electrically heated, resistance type

furnaoe with internal diinensionat at inches high, 1) inches wide, and

41 inches deep. Temperature was oontrolled by means of a variable

temperatura-band Wbeelco controller which was f'ound to maintain tem

perature to :±-30r at· any given point in the work area., ThemaJdtllUm:

temperature variation along the length 'sf '8. l(A.inoh sample was approxi

matelyeoF.

Temperature was continuously monitored with a strip-chart recorder

oonneoted to a thermocouple 'With its hot junction placed on the hearth

near the oenter of' the sample. The recorder was checked against a

portable potentiometer using the same the1'1l1ocouple and a double-pole,

double-throw switoh connected to the thermocouple leads.

The oil quench bath was heated on a hotplate and mazLntained at

140;±-1SOF.

A wire loop was attaohed to each sample to facilitate handling.

The specimens were placed. indiv:ldually in the furnace on the clean

13

hearth and removed individually for quenching.

2. Rapid Heathy;

Rapid heating during austenization was aohieved by plaoing sa,m..

pIes in the f'urnace when its temperature was higher than the desired

austenitizing temperature~ The temperature of the sample was continu-

ously monitored during heating. .As soon as the sample reached the

desired austenttizing temperature, it was quickly removed from the hot

furnaoe and quenched.

Special. sample holders were prepa.red to implement. the rapid heat-

ing. The holders were prepared by attaching thermooouple insulators

to 3..foot long by S/32-inch diameter steel rods. Ch1'omel and alumel

thermooouple wires nre' threaded through the insulators and used to

hold the sample. Onethemooouple wire was welded to each end of the

sample. Thus, the s-ample Was suspemed by thewlres and served as the

hot junction of the themoo~)Uple; 'Compensat&d lead wirewasroo,l'Mected

to the thermooouple wires at the handle end of the holder. The other

ends of the lead wire wel'e oonnected toa potentiometer. Temperature

could be oontinuously mordtor'ed with this type holder as the sample

heated.

The same box type f'urnace was used for both rapid and slow heat

ing. However, the rapid heat!.ng procedure necessitated leaving the

door up (partially open) approrlmately one inch while the sample was

heating. Brick baffles were placed in the hrnaoe between the open, ' " " ,..' ,

door and the area used for hea:ting the samples in order to maintain a• ~ > ' " ."', .'

unifol'lll teniperature. Thetemperatve within the heatingchs..mber was. 0

found to vary no more than a.pproximately 12· F with this arra.ngement.

14

The temperature of the furnace near the middle of the sample was moni

tored with a thermocouple and the recorder during the rapid heating

experiments.

D. TEMPERING

Prior to tempering, loose seale and oil from the quench bath were

wiped off the samples and some of the samples were cheeked on an area

near their ends with a Rookwell hardness testing maohine to insure that

proper hardening had been achieved.

Tempering at the 350 and 4000 F temperatures was performed in an

oil bath tempering furnace. Temperature was found to be uniform

throughout the oil bath and to vary :i-3°F from the desired temperature

during the control oyole.

Tempering at temperatures above 400°F was performed in a forced

circulation air furnaoe. Temperature variation was ;;I;.5°F from the

desired temperature during the control oycle and the variation with

posttion was negligible.

All samples were tempered on the same day that they were hardened

unless speoifically noted otherwise.

E. TENSILE TESTING

statio tensile testing was performed u,nnga Baldld,n hydraulio

universal testing maohine whioh was equipped with Ternplin grips. The

machine had a load capaoity of 20,000 pounds. The high range on this

machine, full seale equal to 20,000 pounds load, was used for testing

all of the tensile specimens since the loads required to break them··

were near 9,000 pounds.

For the major!ty of the tests , the jaws used to pull the samples

15

'Were of a design with one gripping surface rigid and the opposite

gripping surface free to rotate approximately 10 degrees about, the. .

sample axis. In this configuration a uniform ''bite" was possible on

the Bample~ The pulling bars were equipped with ball and socket- joints

to minimize any tendeJ»Y to bend tl\l.e saw,ples during loading.

The regular jaws ~~soribed a~'f.e',..nd not hold samples which

were harder than about Roc~ 057 and th:as8;:sa.mples slipped during

loading. A set of old jaws was modified toall6w an insert cut from

a tile to grip the harder samples. A portion of the solid jaw was

ground down to aocommodate the insert (see Figure 1). In this manner

with a coarse file as one of the gripping surfaces, the haJ.oder samples

oould be puJJ..ed.

For all except the softest samples, an expanding device was fre

quently necessary to set the jaw teeth into the sample before applying

any load. The expanding de"4ce was me~,ely a :xns.obine bolt brazed to a

steel strap~ By placing the head of tae bolt on the butts of the jaws,

as shown in Figure 2, and unsorewing tbe nut, the jaws were forced

along the tapered slides in the grip assembly and forced to clamp the

sample.

Load was applied to the sample at -a rate 0f a.ppN:xim:a.tel.~'1500

pounds pe-r minute. Testing. was p&rformed ·at room temp~r&ture'i .

F. ELONGATION

Prior to tensile testing, each sample was scribe marked. Lines

were scribed across the sample at t-inch intervals. A special templet

whioh could be attached to the samples was made to facilitate this

work.

16

F.lgure 1. Modified Jaws: Top Shows Serra.ted Gripping SUrfaaes

Without File Insert. In Plaoe On the MGdified Solid Jaw t Bottom

Shows Depth or Ground-out Portion Of Solid Jaw To Aooommodate

A File Insert..

17

Figure 2. T8lIlPlin Grip Assembly With Expanding Device In Place Against

Butts or Jaws.

18

Af'ter tensile testing, elongation was measured on the broken sam

ple using a beam trammel and a metal scale with 0.01 inch divisions.

The longest distance between two scribed lines on the larger piece of

the tested sample was measured and used to ca.l.cula.te elongation~ The

elongation did not include the fracture nor the localized deformation

nea.r the fracture. Therefore, all elongation data reported are

uniform elongation outside the fracture area. of the sample.

19

IV.. RESULTS

A. STRENGTH PROPERTIES WITH SLOW HEATING

1. Hardness

steel No. 5 was used in a preliminary study whioh determined the

effeot of austenitizing temperature andquenohing medium on the hard

ening operation. samples were austenitized for 15 minutes at tempera

tures ranging from 1425 to 1525°F and quenched with three different

media: tap water at 70°F, oil at 700 Ft and oil at 1400 F.

Table n shows the a'terage hardnasses found in these samples.

Hardness was measured at fi:ve points along the length of each sample.

Qu.enching 'in oil at 140°F produoed the most uniform hardness through_

out the range of tamperatm:-es studied. Quenching in water at 70°F

produoed the least 'Unifonn hardness. The variation of hardness along

the length of these samples is shown in Figure :3. The more uniform

hardness of the samples quenched in the warm oil is apparent in this

figure.

The individual hardness values varied between RookweJ.l C63 and

c66 for the samples quenched in oil at 140°F while they varied between

C62.5 and C67 for the samples quenched in oil at 700F. The water

quenohed samples had baronesses between Rockwell C57 and c66. However,

the water quenched samples that had been austenitized at 1425 and

147SoF were relatively uniform With hardness spreads of only about

three points on the Rookwell C-scale.

The reason for the greater variation of hardness in some samples

quenched in water is not known. This variation was observed in two

separate runs. Water was ruled out a.s a suita.ble quenching mediura on

'l'ab~8n

.E

f'fe

et

orQ

uene

hM

ed

iaA

nd.Ansten1.:tizi~

Tem

pera

t'lU

'es

On

Ave

rag

eH

ard

ne

ssor

ste

el

No.

5

Que

nch

Med

ium

Oil

(14

0°1

)

Oil

(7rf

'F)

Wat

er(7

oGF)

1to

ekw

ell

CH

ard

ne

ssA

uste

niti

ziX

lKT

empe

ratU

re142seF-14~

14

75

!F15()()O~_~5GF

64.0

..64

.$64

.56

4.0

6/}.

0"."

.

65.0

.65.

5Qp

.O63

.563

.5-.

64.5

·60

.564

.562

.062

.5

~

-----a ----0----66D0e6 )(0 M, 11 011

~ 8 ~ MO-----.4 --.....----o~-6:3

21

Austemt1zing Temperatures, 0,• 1425 CJ 1500)(1450 ... 152501475

Oil At 140°,

rt 66..: 64G)

j 62

60 1-------&.1---1~t ---':2f:----3t:'.:-----:4~. -

nlstanoe Along .5-IDOh Sample, Inches

011 At 700 FD 66 -----,--- -----67~ ~ x· •.. ~ 0 B ~~~ ~ ~ ~ A

j :: L-~_.~~__.a.-__R~' ~~__--:+-__~._- 62.5

1 it 2t * 4

mstance Along .5-IDOh Sampl.., Inches

Water At 700,

r!66

.. 64 04 ~o 0e . • os• 13 0410 62 x

jA

60 ...

.58 )It x.

56.,1 it 2t 3ft

Dlstance Along .5-Inoh Sample. Inches

4

F.1.gure'~ Hardnesses or SImples Of' steel. No.5 Quenched From Variou8

Austemtiz1ng Temperatures Into 700' 011,140°' 01.l And 700.,

Water.

22

the basis of these results.

Oil at both of the temperatures studied was able to produce

maximum hardness, but oil at 140°F was seleoted for use in the later

work because it seemed to produce a more uniform hardness.

During the oourse of the later work, all six steels were found to

developma:ximwn hardness when quenched in oil at 140oF. samples were

spot checked before tempering and were oonsistently found to have

hardnesses of Rockwell 062 or higher.

2. T.ensile· streng!jh Ani Duotility. .

a. E1;elor.atolX Treatments. Table nI shows the results of

exploratory b.a.rd.ening a.ni tempering treatments of the six steels.

This work was intended, primarily to determine which of the six steels

was relativ$l.y duotile when heat treated to high tensile strengths.

For this work samples were austanitized at 15000 F for 15 minutes and

quenohed in warm oil. This austenitizing treatment was used to insure

that proper hardening would be aohieved in all.of the steels even

though the previous work on hardening showed that steel No. 5 oould

be fully hardened with lower temperatures.

Samples were tempered. at 600°F for 1, 2 and 4 hours•. F.1.gIU"e 4

shows tha.t steels No.3, 4, 5 ani 6 developed tensile stre~hs of

approximately 250 ksi (thousal'ld~ of pounds per square {nch} after

tempering for 1 hour and for 4 hours. steel No. 1:was noticAbly lower

in strength than were steels No. ), 4, 5 and 6 a.fter;temperiJlg· for 1

a:rrl 4 hours.ne tensile strength of steel No. 2teroed to be lllUoh

lowe,r than that. of the others for eaoh of the thre~ tempering ,times •.

S0lJl.9 of ~~ steelst viz. 2, 4, .5 ani 6; gave their lowest strength

Tab

lem

.E

Ueet

Of

Au8

t.em

:t.i

zing

And

Tem

peri

ng~8

On

str

en

gth

P1

"op

wti

esW

ith

Sle

wH

eati

ng

.

ste

el

No.

1st

ee1

No.

2S

tee1

No.

:3st

ee1

No.

4st

eel

No.

5st

ee1

No.

6

Har

den

ing

aT

em

pe

rin

gTS

bFb

Elb

TSF

lQ.

TSF

El.

TSF

El

TSF

El.

TsF

El.

Au

sten

itiz

e,

6000

,1

hr

22

18

°21

7c

°24

0s

°2

45

8°

253

s1

.024

60

°15

000,

-15

mip

2h

r24

3s

°1

60

00

24

2,8

0.5

224

s0

233

80

210

0°

4h

r2

20

80

20'0

c0

233

8o

,~'

,242

s1

.524

3s

1.5

238°

1s0

SOoo

,2

hr

114

00

54

00

176

00

175

e0

167

e0

127

e0

4h

r21

00

014

60

021

90

0'2

09

00

191

c0

142

c0

7h

r19

7c

°75

c0

202

C/s0

'25

00

024

8e

019

80

0

aA

:Usa

mp]

.es'

wer

e'qu

8Dch

edin

on

at

140°

'.b

TS

_T

.ns1

1.e

str

og

th,

1000

psi

F-

Fra

otu

re"

e.-

e1ea

vag

es

-sh

ea

rCJs

-m

ere

clea

vag

eth

an

shear

~-

mer

esh

ear

than

clea

vag

eE

l.-

Per

cen

tlll

':Ii:f

'orm

elo~atien

G1r

t.8id

eth

efl

oac

ture

ze..

...

N \..0)

Steel No.4 1,c 20)~4

d5p6

250

225

175

1.50 '-- -.&... .&-- L..-_

1 2 4

Tempering Time, Reurs

Figure 4. Tensile strength at Sb: Steels AustenLtized At 15000 F

For 15 Minutes AId .Te1I$pet'ed At 6000 r.

2.5

after 2 hours tampering while the others gave their highest strength

after 2 hours tempering. The reason for this was not clear.

Since tempering at 600°F aohieved strengths of only about 250 ksi,

the seoond set of samples was tempered at .5000 F in an attempt to

aohieve higher strengths. Tempering times were increased to include

7 hours because the work at 600°F indioated the strength of Borne of

the steels nIi.ght be higher after longer tampering. The data for these

samples are shown in Table III.

Figure .5 shows the results of temPering at 500°F. Scatter was

more pronoumed at this temperature- than at 600°F. The most sigmf'i-

cant fea.ture of theBe data was the apparent separat10m of the material

into two groups ~ steels, No.1, :3, 4 and .5 showed higher strength than

did steels No. 2 am 6 for a given tempering time. Also, the strength

data were relatively linear and increased with increasing tempering

time. strengths of approrlmate1y 2.50 ksi were developed in steels

No.. 4 and .5 afte-r tempering 7 hours, and appeared probable in steels

No. 1 and :3. The samples of Steels No. 1 and. 3 broke in the tensile

tester jaws at lower values.

As indicated in Table III, a change oocurred in the appearance of

the fraoture surfaces between the 500 and 600°F tempering treatments ..

All samples fractured in the cleavage mode at 500°F; whereas, the mode

° .of fracture was predominantly shear at 600 F. Significantly, only

steels No. 2 a.m 6 displayed a cleavage fraoture at 600°F. '

b. Austenitizing Treatments. On the basis of the exploratory

work, steels No. 3,'4 and .5 were selected for use in eValuating the

effeot of &ustenitizing treatments. A treatment was desired which

26

steel No.o 1)( 2~ 3CI 405p6

250

225

E 200s

A.. p

i~ 175

CD

i&-i

150)(

~p

/125

p

1002 4 7

Tempenlfll 'l'ime, Hours

F.lgure 5. Tensil.e strength Of S1X steels Austenltized At 15000,

Fer 15 Minutes .Ani Tempered At 500°'.

27

would develop tensile strengths of 300 ksi or more and uniform elong

ations of at least 3%.

Tabla IV lists the data generated with samples quenched from six

austenitizingtemperatures ranging from 1375 up to 15000 r using three

austenitirlng times: 10" 20 ard ;0 m:i,nutes. Lower austenitizing tem

peratures were included here than were studied in the above work on

hardentng~ The preliminary hardening work had not oompletely estab.

lished. the lowest possible austem.tirlng temperature, nor did it show

the effoot ot austeni.tizing temperature on the duotility of the steel •

.All samples were tempered at 600oFf3r 4 hours.

Figures 6, 7 and 8 present tensile strength and elongation data

plotted against austerdt1zing ti.me a.t the various teIl:q)eratures. The

highest tensile strengths "e~ aohieved in samples from steel No. 4

and. were obtained by austenitizing a.t 14500 F~ steels No. 3 and 5 also

showed their highest strength when austerdtized at 14500 F. Slightly

more than 3~ elong.a.tion was achieved by austenitizing at 14250 F f~r

20 ,minutes in eaoh of the three steels studiad, and austenitizing at

14500 F for 20 minutes produoed more than 3% elongation in steels lb. :3

aId 4.

Ta.ble rv shows that for the above series of teats inwbioh aus

tenitizing tmtInen:t was studied the mode of fraoture was shear for'

all three steels. > Mode of fraoture oorrelated to some extent with the

amount of elongation observed. Shear was assooiated with ductile

sam,ples am. oleavage with samples show.l.ng little or no elongation.

o ~ T!D'=Per:l.ng Trea.tmen:ts~The above study of austeni:tizing traat

ments indioated that the best hardening treatment might use 20 ro:l.;11U~es

Tab

J.eIV~

Eff

ect

Of

A.u

stem

.:t1.

z1ng

Tre

at.m

errt

sO

nst

reD

gth

P1"

oper

t1.e

aW

ith

Slo

wH

eati

ng

.

steel

No.

3st

eel

No

_4

steel

No.

5

Ha

rde

nil'

l$t

T~ri.~

.TS

EE

lT

SE

l!a.

TSE

E1

Aus

tem

.tiz

e,

137S

Of

-10

min

20m

inJO

min

.140

of7

-10

min

20m

in~O

min

14

Zh

-10

lIlin

.2Q

-lld

n:3

0xp

1n

~450eF

-10

min

ZO

min

JOm

in

1471

'F-

10m

inZO

1Ili

n30

min

1500

0F

-10

min

ZOm

in30

min

.~

*sa

mpi

ew

4ste

mp

ered

for

8h

ou

rs.

6000

,4

hr

250

s1

.225

28

1.2

249

81

.8

~8

25

0s

2.1

242

82.

3

2.54

82.

324

68

3.1

256

82

.3

258

82

.624

78

3.1

241

82w

3

247

s3-

324

18

1.3

244

82

.5

251

82

.1Z4

5s

1.6

242

s·3.

1

2.52

81

.424

0s

025

18

1.2

266

s2

.325

78

2.J

253

81

.6

258

s2.

J2,

54s3

.125

08

1.6

266

82

.126

68

3.1

'2f:J7

82

.0

264

82.

325

78

2.7

253

s2.

5

260

81

.925

8s

1.9

249

s3.

1

220

s0

211

s0

245

81

.6

257

83.

125

18

2.1

249

82.

3 *25

18

3.1

256

s3.

125

28

2.3

258

81

.52

57

82

•.'3

255

82

.1

255

83.

125

28

2.1

249

82.

3

252

82.

3·2

53

82•

.524

68

2.1

t\)

Q)

29

260Austerdtize, of

A 1375)( 1400o 142;l:l 14,50d 1475p 1500

10 20

.!uat.eJdt.,.."ng 1'1me, M1nutes

:~6). Ttta,dJ..,~:~ JLo:ng~tion On ~e. hom steel

No. :3 tilth V:¢o!'YAu,~t.1;r.iRg~tllelrt.,~ ~ ~.JI

6 0W~1'~e~red.t ·;001 'or 1+ ao~.

1~..t 255

gA

CD

1250E-4

265

260

245 I

til

£11----0------

30

Austenitize, ofA 1375~ 1400o 1425p 1450d 1475p 1500

10 20

Aus:teJd.tildtilg T.llme. In ~e" Ml.ml1~e",~

F.L~ 7. Terild.l. 6btr~,AM Elongat4on On SUples· From at,eel

,lb'. A,.'Wltii.<-Vu4.oUiI!S';A.u8teD1tisiDg 'l':reatmeJJt.s. m Semples

l We.L.f-.pe1"8ii. At· gorP, ,For 4Beurs.

260 AuBten1tize, 0,,6 1375)( 1400o 1425o 1450d 1475

255 p 1500

1iJ~..

1250

15 •G)

i .. .. .. ..~CD

E-4 24S <4

,2

1

10 20

Austen1tiztDg Time In Furnace, MinUte,

Figure 8. Tensile $re~* ELongation On Sb1p1el From steel

No•.~. With Vq;o,1l8 AustemUzing Treatment.. ill Samples

Were'1'em.pe1'i8d At ·dJfXPr For 4 Hours.

at 1450°'. Therefore, this was adopted as the austenitizing treatment

in a serles of experiments intended to show how the tempering treat..

ment affected strength properties. steels No.2, 3, 4, .5 and 6 were

used in t.hese experiments and the results are shown in Table V.

Since the results of the work reported in the exploratory treat~

menta (Table III )illdioated that strength improvement might be expected

with tempering times long&r than the 7 hours used there, a study was

made of the effect of tempering at 4.500 F for times up to 128 hours.

Tempering at 4.50°' was expected to yield higher strengths than were

achieved with tempering at .500 and 600°F in the exploratory work.

Figure 9 shows the tensile strength data obtained with salllples from

steels No.3, 4, .5 and 6.

Hi.gher strength was Qbta1ned in steels No. 3 and 4 than in steels

No. .5 and 6 throughout the range of tempering times. All steels sholited

a decline in tensile strength w.tth increasing tempering time except

steel No. :3 which showed its highest strength of appron.tnate1y 275 kai

after tempering 128 hours.

Elongation was nil for all samples except those of steel No .. 3

tempered 16 hours and. longer at 4500" as shown in Table V. The sample

from steel No. :3 tempered 128 hours was the only one of the series

which showed more than 1'% elongation. This particular saIllplealso

showed the highest strength of the series.

The increase of tensile strength with increased elongation might

have been an, indioationthat the material was notch sensitiva at low

tempering tijlp.peraturetJ. Therefore, the effect of tempering in the

range of temper~tu:res from 550 to ?OOoF for times up to 1 hour was

studied. steels No. 2 and :3 were seleoted for this work since on the

Tab

lev.

Etf

eet

Of

Tem

peri

ngT

reat

men

tsO

nst

ren

gth

Pro

pert

ies

Of'

Sam

ples

Hu

deD

8d

Wit

hS

low

Hea

tin

g.

steel

No.

2st

eel

No.

3ste

el

No.

4ste

al

No.

5ste

el

No.

6

i.rd

em

ng

-T~l'1P:

-TS

FE

l.fS

Fm

.-T

S-F

-E1

TSF

E1TS

FE

l

.(Ust

em.ti

Z9,

....14

50o F

';;'

20ll

lin

45

0G

.F8

hr

16h

r32

hr

64

hr

128

hr

o5

50

F1

0:m

in.

20m

in30

min

60

lJdn

600fJ

F1

0m

in20

min

30m

in6

0m

in

650°

F10

min

·20

min

30

min

>60

min

o70

0F

10

min

20m

in3

0m

in6

0m

in

*.S

amp

lew

ascra

ck

ed

.

176

00

261

c0

242

c0

11

80

026

8e

0.5

23~f

e0

16

7e

019

3c

025

2e

0.5

·26

7c

021

30

°17

3e

0189~.O.5

250~

018

6e

015

2e

027

6#

81

.72

25

*0

185

00

160

c0

150

00

27

8%

010

9c

026

8SP

016

4e

027

28

1.5

137

c0

265

s1

.0

214

c0

255

s0

234

e0

268

s1

.514

8c

0*25

1s

1.0

178

00

257

s1

.0

196

00

25

08

1.5

215

c0

248

s1

.225

70/&

1.2

246

s1

.225

5s2

.024

6s

2.0

263

sp1

.724

4s

2.0

251

s3

.324

0s

2.0

246

s2

.524

0s

1.7

170

s0*

231

s2

.5\M \,

,)

280

260

...i 220

~CD

! 200E-t

180

160

8 16 32

~ Steel No. ;0--0

Steel No. 6EI

128

T~.r1~ Time, Hours

Figure 9~ E:t'f'eetOi T~_ft._ On TensUestl'$ngth or steels

Tempered At 4500,~ AU Salnples Were Austenltlzed At 14;00'

FoJ:" 20 :Mi._tea.

35

basis of the previous work steel No.2 tended to show the least elong

ation and Steel No. :3 tended to show the highest elongation of the six

steels.

The data from steel No. 2 had a large amount of scatter, as shown

in Table V, and are oonsidered to be of questionable value.

The data from steel No. :3 are plotted in Figure 10 and show that

tensile strengths in the vicinity of 275 ksi were obtained by tempering

a.t 550oF. A. ~1.ativ~ly st\\&ll d$e'r~&.se in stt'engtb. was noted '\dth

increasing tempering time at eaoh tempering temperature. Elongation

varied between 1 and 2.5~ except at the 5S0oF temperature where no

elongation WAS measured even though tensile strength was high.

The dat8. in Table V indicated that no temper.tngtreatment was

likely to produce very high tensile strengths together with appreci

able duotility in samples hardened 8.ocording to what appeared to be

the best tret\tment with slow heating. If the desired higher properties

could be produced in these steels, it appeared that the hardening pro

oedure would have to be improved. :For this reason further work was

done on the ,"ustenitizing treatment and some work was done on pre

treatments.

B. STRENGTH PROPERTIES 'WITH RAPID liEATING

1. Austenit1zing Treatments

steels No. 3 and 4 were seleQt~ for further study or the effect

of austenitir.ing treatment on tensile properties of high strength

steel. steel No. :3 had the lowest oarbon content (o.6S~) relative to

the other steels. Furthermore, it bad been most thoroughly studied in

the above work on hardening and tempering. steel No .. 4 was highest in

280

... ....270

4

230

111..!l4 260..,g

)l

i~~Gl 250 e

i -----.-----0_ 6,50°,Gl 0

e-tIII

240

10 20 30 60

Tempering T1:me. M1nutes

Figure 10. Effect Of Tem:per11'Jg Tl"eatments On strength Propert.ies

Of steel No.3. All Samples Were Austem.Used At 14,50oF .Fer

20 Minutes.

37

carbon content (0.7210). Both steels showed oomparable tensile strength

and elongation in the above work and both had shown somewhat better

properties than the other steels. It ws.sassumed that these two steels

were most likely to respond to any improvement in the heat treating

prooedure.

The heating rate was studied to deter.m:Lne its effect on properties.

This was done by heating to the austenitiz.1,ng temperature in a furnace

at a temperatureabov& the austenitizing temperature. Table VI gives

the tensile strength and elongation of samples heated rapidly to tem

peratures of 1425, 1450 and 15000 F with the furnace at 1550°1. Tables

VII and VIII give the tensile data for samples austenitized at tempera

tures of 1450, 1500 and. 15500 F with the furnace at 16.50 and 17.500 F,

respectively.

For the 15500 F :t\1rnaoe t$l'llperature, the highest austenitizing

temperature studied was 15000 F since higher temperatures began to give

too slow heating. Austenitizing at 1425°' was included in the series

with the turnaoe at 1.550°' to provide heating times oomparable to those

obtained a.t the higher furnaoe tempepatures. The time required for e.

sample to heat to the austenit1zing temperature was a function of both

furnace temperature anddifferenoe batween furnaoe temperature and the

desired austerdtizing temperature.

a. :Fu1"na.ce At 15500 F. samples of stellU. Nl;). :3, when rap1dl.y

heated to temperatures of 1425, 1450 and 1.500°, in a furnaoe at 15500 F

and tempereq. at 550°F after warm oil quenching, developed tensile

strengths in the range trom 270 to 290 ksi, as shown in Figure 11.

A maxi.ll1um strength of 292 ksi was obtained 'by auste11itizing at 14500F

Tab

leV

I.st

ren

gth

Pro

pert

ies

Wit

hR

apid

Hea~ing

InF

urn

ace

At

1550

oF

.

'"

ste

el.

No.

3st

eel

No

.4.

Hardeni~

__

Tem

per

ing

_T

S~El.

TS

FE

l.

Auste~ti-ze

,14

2,5

F3

5se

eS-

14.5

00F

40se

c

15O

O&

F50

seo

55C1

'F10

min

2Om

i.n

60m

in

10m

in2

0P

dn

60m

in

10m

in2

0m

i.n60

llIi.n

288

s2

.028

9s

1.5

2'78

s1

.0

292

s1

.02

87

*1

.328

2If

1.1

290

s1

.428

4s

2.0

271

s1

.0

307

s1

.828

0sp

028

4s

0

302

o/e1

.8Z,

-,sp

0.8

286

s1.

3

294%

03

04

*1

.529

4s

1•.5

aA

ppro

::xim

a.t.

tim

ete

heat.

f.o

ai.1sten1t.izi~

tem

per

atu

re.

\oN CD

Tab

lem

.st

reD

gth

Pro

pert

ies

Wl:

thR

aJd,

dH

eatb

gIn

Fur

Dae

eA

t16

50",

.

ste

el

:NG.

3ste

el

No.

4

Hard

em

..T

EIm

lLe

ft_

TS

FE

lTS

Fn

Aus

tell

Jiti

.ze,

145€

)OF

2Sse

ea

1~r

30se

c

e15

50F

35se

c

550G

pt10

min

20

mn

60m

in

10

min

26m

in60

min

10

min

:2

0m

in60

min

293

s1

.327

7s

0.9

276

s1

.S

293·

s1

.328

2s

1.3

27.3

s1

.5

28

,s

1.7

277

s2

.026

9s

2.0

304

s0.

729

1s

0.6

292

s1

.5

308

s0

.8)0

1s

1.3

29

2s

1.0

248

s0

298

s1

.129

0s

1.5

a:A

ppro

xim

ate

t.im

eto

heat

toau

stem

.tiz

ing

tem

per

atu

re.

\..A

)'0

Tab

lem

r.str

en

gth

Pro

per

ties

Wit

hR

apid

Hea

ting

InF

nrna

ceA

t17

500

F.

steel

No.

3ste

el

No.

4

Har

deni

:Qg

Temperi~

TSF

El.

TSF

El.

.Au

sten

itiz

eJ14

5<PF

22sJ

1500

Gp-

2Sse

c

e15

50F

30se

c

55cP

F10

min

20

min

60m

in

10m

in2

0m

in60

mi.

n

10m

in20

mi.

n60

min

28

8s

1.0

281

s1

.027

7s

2.4

287

s1

!327

6s

1:7

273

s2

.3

290

s1

.727

5s

1.7

266

s1

.7

321

s1

.030

3s

1.7

291

s2

.0

313

"01

.330

4s

1.7

291

s2

.3

21

4%

030

5s

1.7

289

s1

.0

aA~'te

'tim

.to

hea

t·~

aust

en:t

Un

ng

't8

Dp

erat

ure

.

~ o

310

'00

~..

I 290

er-I

J280

270

'*l 2..s:l0:u 1I0~

10 20

41

--steel No. 4--- steel No. :3

Austen:1.tize, orlJ 1425)( 1450o 1,500

60

!empfU'd.ng Time, MLrmt.8s

F.l.gure 11. XensUe streDgth And. ELongation On SUJples Il'rom steels

No. , AlId 4 l!a1'd.enedWitb. Rapid Heat4ng In~• .At 1,55Qor•

.All Buap18s Were'fempereclAt 550°F.

42

oand tempering 10 minutes at 550 F. This strength oan be compared

direotly with the strength shown in Figure 10 for the same a.usteniti

zing temperature with slew heating. Suoh a oomparison indicates that

steel No. 3 improved by approximately 5~ in tensile strength when

hardened by rapid heating.

An improvement in the elongation of steel No. :3 also was obtained

by rapid hea.ting. Between 1 and 2$ elongation was obtained, oompared

to no elongation with slow heating, for the shorter tempering times.

Elongation tended to deorease from the values obtained at 10 and 20

minutes when tempering was oontinued for an hour in samples austerrl....

tized at 142S0F a.nd 15000 F; whereas, elongation inoreased oontiIl\\ously

with tempering time in samples austenitized at 14500 F.

A difference in fracture appearanoe between the rapidly heated.

and slowly heated samples of steel No.3 'Was observed at the iO-minute

tempering time at 550°F. Rapid heating produoed So predominantly shear

fraotUre while 'With slow heating the fraoture was predominantly oleavage

Rapidly heating sa.lIlples of steel No.4-to the austenitizing tem

perature in a furnaoe at 1550°' produced a greater increase in the ten-

sile strength than that observed in steel No.3. Figure 11 shows that

tensile strengths over 300 ksi were obtained with steel No. 4 after 10

minutes tempering. Direct oomparison of slowly and rapidly heated

samples of steel No.4-was not possible since no samples of steel No. l.j.

were tempered at 550°F in the work on slow heating. However, oomparing

the strengths shown in figure 11 with those in Figure 4, where temper

ing was done at 600°F instead of 5500 F, indicates that tensile strength

improvement might have been of the order of 2~. The tensile strength

of the sample rapidly heated to 15000 F ani tempered 1 hour at 550°F was

294 ksi, compared to 24,5 ksi for the ample slowly hes.ted to 15000 F

and tempered 1 hour at 600°F.

Elonga.tion in sa1l1ples of steel No 0 4 was between 1 and2¢except

on the samples austenitized at 14Z5°F and tempered for 20 and 60 min

utes 'Which showed no elongation.

b. Furnace At 1620 And 17,20°,. Figures 12 and 13 show the mech..

anical. properCies obtained with samples of steels No.3 and 4 'When

rapidly heated to the austenitizing temperature in a furnace at 1650

and 17500 F, respective+Y. At these higher furnace temperatures, whioh

gave faster heating rates, the austenitizing temperatures investigated

were 1450, 1500 and 1550oF.

steel No. 3 responded much the same in these treatments as it did

at the lower turnaoe temperature of 1550°,. The highest tensile

strengths were observed in samples tempered for 10 minutes and were in

the vioinity of 290 ksi. Elongation ranged between 1 and 2$ exoept

for the sample 8'Usten1tized at 1450°' and. tempered for 1 hour, which

showed 2.!J1, elongation.

With steel No.4, the increased heating rates brought about by

the higher furnaoe temperatures tended to increase strength. Samples

austenitized at 1450 .an;l 15500 F in a furnace at 1650°1 and tempered

10 minutes at 550°F obtained tensile strengths of 308 ksi.Hea.ting

°steel No. 4 in a furnaoe at 1750 F to each of the three austenitizing

temperatures and tampering at 550°F for both 10 and 20 mi..:nu.tes produced

tensile strengths in ElXQElSS of 300 ksi.

Figures 11, 12 and 13 show an upward trend in the tensile strength

of steel No.4 with faster heating rates. Also, as the heating beoomes

44

- - steel No. 4--- steel No. :3

Au.stemti2e, oflC 1450o 1500D 1550

•

••

~"\"\,. 0 .........

, ""::... II __ """"-. ___It ---.:,;__ __

----= ---~-- -...------:::-...-- ------ .:::::::.......-- --.

270

310

300

6020

ClI--------------l!7.,..------

10

_lC

=::;:;;. •.,., .--- ~' -- --=-- ~.:--...----.

() >-::::::::::= i - =--- -:::---- - - Q---"--1t--

Tempering Time, Mlrmtes

Figure 12. Tensile strength And Elongation or SAmples From steels

No.3 .A.1¥l 4 HlU"dened With Rapid. Heating In Fumace At 16500F.

All Samples Were Tempered At 5500 r.

320

310

~ 300..i~

CD 290r-f

~~

280

270

'*- 2..s::0:a 1~0

~

10 20

45

- --steel No. 4--steel No. 3

Austemtize, of)( 14.50o 1500D 1550

60

Tempering T1me, Mlnutes

figure 13. Tensile st.rengtb And Elongation Of Samples From steels

No ~ 3 And 4 Hardened With Rapid Heating In Furnace At 1750°,.

All samples Were Tempered At 550°F.

46

more rapid, the values for tensile strength fall into an inereasingly

more narrow band which indicates a deorease in the effect of austeni..

tizing temperature.

Elongati0l'). was not ~fected as muoh by furnace temperature, or

rate of heating, as W$..S tensile strength. The values were mainly

between 1 and 2~ for samples heatSd, in a :f'urnace at each of the three

temperatures. Some of the samples of both steel No. 3 and 4 heated in

othe furnace a.t 1750 F, hewever, had elongations of approximately 2•.5~

when tempered f0r 1 h0ur.

Elongation did appear to be affected by austenitizing temperature.

Austenitizing samples of both steel No.3 and 4 at the lower tempera

ture for each f'urnace tetllP9rature, tended to produce highest elonga

tion with the 60-mi:tlll:te tempering time while austenitizing at the

higher tem.pera.ture tended to produce highest elongation with the

20-minute tempering time.

steels Ilk>. 3 and 4 did tlQt develop their best oOll1bina:t.ion of pro

perties ldththe same austenitizing treatment. Steel No.3 gave its

best tensile strength and elongation when austen:i.tizad at 14.500 F in

a furnace at 15.50oF wiaile Stee,l No. 4 gave its best properties when

austenitizedat 14500F in a furnaoe at 17500F.

All of the samples u.sed .to st'lldy the effect of austenitizing

trea.tments were tempered at 550°F. In general, tensiJ.e strength

decreased and. elongation increased with increasing t.empering time.

However, for several,aust~tizingtemperatures the' sample tempered

for 20 Dlinuteswas more Q.UQti:J.e than the s~le tempered for 60 minutes.

2. Temperim Treatments

Rapidly heating to the austenitiz.ing temperature was shown in the

previous section to 1?roduoe a signifioant improvement in the strength

of Steels No. :3 and 4. Tensile strengths in exoess of 300 ksi were

obtained. in steel No. It with tell1pering at .5500 F, but elongation was

relatively low. Therefore, the effeot of tempering treatment on duc

tility of the rapidly heated samples was studied. The best hardening

treatments, as given for steels No. J and 4 in the previous section,

were used for these samples.

Table IX gives the tensile strength and elongation of steels

No.1, .3 and 4 hardened by rapidly heating to 14,500F and tempered for

20 minutes at;temperat1;!.1'es. in the range from 400 .to 8000 r. The samples

of steels No. 1 and:3,1fere ;heated in a f'urnaoe at 15500 F, and. the

samples of steeliNG •.4..were heateQ. in a f'u,rnaoe at 17500 F.

Figure 14 shows that steel No. '3 developed a ma.x1mum tensile

ostrength of 300 ksi when tempered 20 minutes at 500 F. steels No. 1

and 4 also shOWed their highest strengths when tempered at 500°F.

They developeet' tensile strengths of approximately 285 ksi.

It was noted that steel No. 4 did not develop as high a strength

in this series as it did in the series shown previously in Figure 13s "1

for the same hardening treatment. Tempering at the 500°F temperature

of this series was expected to give a higher tensile strength than

that developed by temperi.~ at 550°F in the previious series. Although

the tensile strength ourve in iF,tgure 11.1- was drawn through the tensile

°test value of. the sample tempered at 500 F, it is oonsidered possible

that the ten~le itest result on that sample was ~0'W and that the curve

should have been extrapolated to show a strength above 300 ksi. The

tab

leIX

.E

ffec

tor

fem

peri

Dg

Tem

pe1"

8.tu

reO

nst

ren

gth

Pro

pert

.1es

Ot

5am

pJ.e

sR

ap

idly

Hea

ted

.

Fu

rnac

eA

t15

500F

ste

el

No.

1st

eel

No.

3

Har

dem

llR

Tem

peri

ngT

SF

m.'r

SF

El

Au~eni~i:ze

1450

0F4

00

°F2

0m

in1

44

00

20

0o/s

0

500°

F2

84

0 '-0

30

0S

..c0

60rP

F27

5S

1.5

266

S0

.8

7000

F24

9S

2.3

248

S1

.8

800°

'22

2s

2.5

210

s2

.5

Fu

rnac

eA

t1?

,cP

Fste

el

No.

TSF

E1

980

0

282

sjc

0

273

s1

.5

243

s2

.5

217

s2

.0

~

300

280

~..

i 260

CD

i 240G

E-4

220

200

steel No •.4 1 - Fu.rnace At 15500 F)C 3 - PUrMoe At 15500,o 4 - Furnace At 17500F

400 5°0

Tempering Temperature, or

Figure 14. . Et1'~ Of 'l'emper.bg ~I"&ture Oli stre!igth Properties

ot SbM1s No.1, :3 ADd 4. All BaJIlples Were Rapicily Heated To

14,50°, '1'0 Aut!tt.erdt1ze ADim Were Tempered 20 Minutes.

50

reason for this low strength could have been improper hardening,

because the samples of Steel No.4-in this series appeared to reach

temperature sooner than in the previous series, also the low duo

tility in the sample tempered at 500°F may have been responsible for

a bad tensile test~ Not enough da.ta was generated on steel No.1 in

the other studies on hardening and tempering to indicate whether the

strength at the 500°F teMpEn"!ng temperature was low.. It may be noted

that the 300 ksi tens:l:te ~rength obtd.ned in the sample of steel No.3

tempered at 500°' was the highest this particular steel gave in any of

the hardening and temperilllg treatments studied.

Elongation was zero :for the three steels at bo.th the 400 and 500°F

tempering tempePature$~ As temperature increased from 500 to 800°F,

steels No.. 1 ancf 3 showed 8i fairly constant increase in elongation and

reaohed a maximum of 2.5~at 600°F, while steel No.4 inoreased to a

maximum ot 2..5~at 700°F a;,m then dropped otf slightly at 800°F..

Tabla IX shews that the fraoture surfaoes were predominantly

oleavage for the three steels at the 400°F tempering temperature.

Tempering at 500°F produced fracture surfaces whioh were predominantly

oleavage in steel No.1. At higher temperatures, the fraoture surfaoes

were oompletely $hear for each of the three steels. In eaoh of the

three steels, maximum tensile strength ocourred. in the temperature

range where the m.ode of fracture was ohanging from oleavage to shear

and apparently below the telnperature range where any measun.ble elonga

tion ooourred.

Table X gives the strelilgth properties of samples of steels No. :3

and 4 heated to 1l500oF in a f'urna.oe at 1750°,. These samples were

tampered at 350 and 400°F fQr times of 1 and 4 hours.

Tab

leX

.E

ffect

orT

empe

ring

On

stre

llg

thPrope~ies

Of

Sam

ples

Rap

iG1l

yH

eate

dIn

hrn

ace

At

17

50

°,.

ste

el

Ne.

3st

eel

No.

4

Har

den

ing

Tem

per1

.pg

T5

FII

.T

5F

El.

Au.

sten

l.t.i

ze,

1500

°'25

see

35

0°,

1h

r2

00

e0

--

-4

hr

23

0c

0-

--

40

0°'

1h

r2

27

%0

138

e0

4b

r29

1cis

022

8Cfs

0

~

Direot comparison with the properties of the previous serles was

not possible since those samples were a.llstenitized at 14500 F and, in

the case of steel No. ,3, in a furnace at a lower temperature. However,

longer tempering times in this last series gave some improvement in

tensile strength at thQ 400°F temperature. This was most apparent

with steel No. 3 whioh obtained 291 ksi when tempered 4 hours at 400°F.

The 3500 F treatments did not produce enough ductility to permit a valid

test of the ;samples of steel No.4, a.ni they produoed relatively low

tensile strengths in Steel No.3.

None of the sampJies &! this series showed any elongation•

.3 • Pretreatments

steels ,No. ,3, 4 al;)d .5 were given trea,tments prior to the harden

ing treatment. Th. p'l»;'pOse of these treatments was two-fold: (1) to

show what effect candition of the steel before hardenng had on its

strength after harCiening, and (2) to determine whether decarburization

had oocurred in slowly heated samples.

The pretreatment cons:tsted of austenitizing the samples at 14500 F

for times of 10, 20 and ,30 minutes and air cooling. These treatments

were intended to be the same as the austemtizing treatments used on

samples hardene<:l by slow heating. The samples were $Ubsequently hard

ened with rapid heating ta 1.5000 F in a furnaoe at 1.5.50oF and tempered

at 5.50°' fot- 20 minutes.

Table XI gives tensile strength and elongation data. Data from

samples of Steels No• .3 am 4 can be compared directly to data from

samples hardened by rapid heating to 15000 F and not pretreated

(Table VI). A comparison of samples tampered for 20 minutes at 5.500 F

Tab

leX

I.E

Uee

't.O

fP

retr

eatm

eDt.

(Au

steD

itiz

eA

t14

50°F

.And

Ail

'C

Hl)

On

stre

ng

thP

rop

uti

es

Of

Sam

ples

lIa1"

dene

ciIn

Far

nace

At

1.55

00F

.

ste

el

No.

:3ste

el

No.

-.ste

el

No.

5

Hardem~

'1'emtleri~

'1'S

,FE

lTS

FE

l.'1'

8F

El

Bap

i41

yH

eat

To

1,0

00

,50

see

P1'

e-tr

eatm

ent

T

ime

,,.A:t

1450

°11'

:

10m

in

20

min

30m

in

*S

ampl

.ew

ascra

ck

ed

.

5S00

F20

min

285

s1.

718

2cis

0*272~0.5

276

sQ

.8269~

026

28fe

0

265

s0

.8257~

026

68fe

0

~

showed that this pretreatment reduced both tensile strength and elonga

tion and that the properties of' steel No. 4 were affected mora than

were those of steel No.3. Samples of steel No.5 could not be com

pared with sllIIlples whioh were not pretreated, but it is reasonable to

expect a similar reduction in its properties as a result of pretreating..

Increasing the pretreatment time at 14.500 F tended to deorease ten

sile strength and elongation in each of the three steels.. steel No .. 3,

for example, showed very little difference in tensile strength between

the iO-minute pretrea.tmentand no pretreatment, but as pretreatment

time was increased to 20 and 30 minutes, the tensile strength decreased

from 285 ksi to 276 a.nd 265 ksi, respect!vely.. Elongation decreased

from 2~ with no pretreatment to 1.'7% with 10 minutes, and was 0.8~ at

both 20 and 30 minutes pretreatment ..

To determine it decarburlzation was produoed by the pretreatment,

sections £:rom samples of steel No .. 3 were mounted in bakelite and micro

hardness traverses were taken using the Knoop indenter and 100 gram

load. The results on the pretreated samples were oompared with results

on a sample with no pretreatment hardened. with the sarne rapid heating

prooedure and with results on a sample hardened by slowly heating and

austenitizing for 20 minutes in a f'urnace at 1450°,.. All of the samples

had been tempered 20 minutes at .5.50°,..

No definite oorrelation between time at temperature (for pretreat

ing or for hardening) and reduction of hardness at the surface of the

sample was apparent. .All of' the samples showed an average hardness

equivalent to Roakwell C57 - 58 on the oenter region a.bout 0.005 inch

from. the surfaoe. At a depth of 0..001 inch where the first reading of

the traverse was made, the average hardness on the pretreated a.nd slowly

55

heated samples was a.pp1"Gxirnately t-point Rockwell C lower than on the

center region. The hsJ:odness a.t the same depth on the rapidly heated

sample with no pretre&;tmerrt was appro:x:l.ma.tely it points Rockwell C

lower than on the eenterregion.

C. CONP!RISON OF SIX STEELS

Since rapid heating in the hardening operation a.ppeared to improve

strength and duetility apprecia.bly, it was decided to compare the six

steels with each other using this heating procedure. However, as the

data in Ta.bles VI snd VIII ShoW, steels No. :3 and 4 did not develop

their best properties with ElJtB,otly the same hudemngtreat:rnent even

though both gave their best Pt'9perties when they were rapidly heated.

Therefore, sinee tl'J,e hest ha;rdening prooess was not known for each of

the steels!t was decided to adopt a single process fo;r all. The

hardening treatment selected for this work consisted of rapid heating

to 15000 F in a f"urnaoe a.t 15500 F, quenohing in wann oil and tempering

at 550°F for 10 and for 20 :minutes. Duplioate samples were treated

with the results shown in the upper half of Ta.ble XII.

The f'irstcolumn in Table m gives the approximate time elapsed

between the end of the tempering and the tensile tasti)llg. It happened

that the hea.t treating on these sain.ples waS oompleted late one day

and half of them rire tested approximately 15 hours later, early the

next day. The other half were tested late the fol1l0ld.,Xlg day, about

50 hours after the heat treating. An examination «It tb.e results indi

oated thattp.e p1'Opert;i.es of the samples testaGi 15 hours after heat

treating ware appr~ialiJlybelt-tel' t1:I.an those tested 50 Jaours after heat

treating. ItQilirrot!9em reasonable to' believe that the properties

of this material would ohange so rapidly at room temperature.

Tab

1e

XII

.st

ren

gth

Pro

pert

ies

On

sam

pJ.e

so

tS

ixste

els

Un

lto

rmly

Har

dene

d.B

yR

ap

idly

Hea

t.in

gTo

1500

0F

InF

l1rn

aee

At.

1550

0F

.

1'5

FE

lTS

FE

lTS

FE

lTS

FE

l.TS

FE

l

220

e0*

296

s1

.329

9S/e

0•.5

291

s1

.;21

1e

0*30

2CJs

0.7

286

s1

.82~

s1

.328

6s

1.3

291

s1

.7

14

40

0*28

4s

1..0

228

00*

266

C/s0*

215

c0*

270C

js€I

276

s1

.3JO

Osp

1.0

288

s1

.827

6~

0.5

293

s1.

•729

8s

1.3

282

s1.

52

,as

1.8

286

s1

.330

3sp

2.3

28

2s

1.0

298

s1

.5

288

s1

.829

4S/e

0.5

274

s1

.829

'4-s

1.3

10

mi.

n20

min

19

min

~o

min

10m

in2

0lI

dtl

550°

F10

min

305

s1

.72{

)m

in30

0s

1.5

!Om

in26

7sk

0*2

0m

in29

4SJ

i:0.7

40H

ou

rs

20H

ou

rs

5&R

avs

15H

ours

140

Hou

rs

Ela

pse

dT

ime

Bet

wen

liea

tst

eel

No.

1st

eel

No.

2S

teel

No.

Jst

eelh

.4

steel

No.

5st

eel

No

.6lf

Mi't

1·

..Ani

T;9

ns11

.e'e

Bti_

Tem

oel'i

ne1'

5F

El.

*'-

'en

sile

'hat

data

cons

id:e

red.

tob

elo

wan

dn

ot

use

din

det.

er.m

inin

gav

erag

essh

own

inF

igu

re15

.

~

57

Therefore, the samples whose properties are shown in the lower half of

Table XII were treated. These samples showed that the properties were

stable and that for some lU'lknown reason a large percentage of the

samples tested at 50 hours after heat treating gave unusually low ten

sile test dat8.~

Since some of the tensile strengths in Table :xII were oonsidered

to below it was decided to disregard the obviously low data in com

paring the various steels. The hardnesses of the samples were known

and were used to determine the "obv;lously lowtt data. A correlation

between hardness and tensile strength for steel is a.vailable. (13)

This correlation is claimed to be a.ccurate to within 10~. For this

reason, those samples whose tensile strengths were appreoiably lower

than 1~ of the value given in the above hardness-tensile strength

correlation were d:i.sc~ed. On this basis the seven samples indicated

in Table m by an asterisk after their elongation were not used in

detennining the a.verage tensile properties of the six steels shown in

Figure 15.

Figure 15 shows the a.verages 0:£ the tensile properties of the six

steels. steel No. 1 showed the highest tensile strength of 305 ksi

for ~e 10 minute tempering time. Its strength dropped somewhat to

slightly below 300 ksi after tempering for 20 minutes. steel No. 4

gave the second highest tensile strength of almost 300 ksi for both

temper.Lng times. The other steels had strengths in the range of 280

to 290 kEd. Sino'~ theclata fo:ko steels No. 2 and 6 tor the 10 minute

temperi~··tinie Was c1!soard~ acoording to the seleetion prooess des

cribed above, no tensile strength is shown for these steels at the

shorter tempering time.

steel No~A 1

:310 l( 2o :3t1 4

:~d5

'Qp 6

~ :300..D

i..........~

i 290

E-4

280 tf'

i-- 55::::::::::: S

-~:10 20

TeIIlpering Tilne, Minutes

Figure 15. Average Tensile strength And Elongation Of Si.x steels

Hardened By Rapici Heating To 15000 F In A FI1rnace At 15500 F.

All Samples Were Tempered At 550°F.

59

steel No. 1 showed the highest duotility "With 1.~ elongation

after tempering for 10 minutes. Its elongation fell to about 1% after

20 minutes tempering. The other five steels showed an inoreaae in

elongation with inoreased. tempering time. steels No. 2 and 6 had 1%

or less elongation while steels No.3, 4 and 5 had between 1% and 1.5~.

60

V. DISCUSSION OF RESULTS

A. GENERAL

Tensile testing of hardened high carbon steels, which have been

otempered at temperatures below a.bout 700 F to obtain high strength,

presents a. somewhat different problem from the testing of steels at

lower strength levels. High carbon steels at high strength levels

exhibit relatively low ductility and, probably for this t>eason, tend

to be sensitive to both surface oondition and internal discontinuities.

Surfaca notches and dacarbur;ha.tion or internal microoracks and inolu..

sions oan affect the tensile test data obtained on high strength

steels. The extent to whioh it is affected, however, is difficult to

know without employing sophistioated flaw detection equipment and

olosely controlling surfaoe oonditions. SUch sample preparation and

inspeotion was not attempted in this project.

During the experimental work, most instances of' a tensile sample

failing at low strength relative to others of a given series oocurred

when the partioular sample broke in or adjaoent to the grips of the

tensile testingmaohine. This is not to say, however, that all samples

whioh broke in or next to the grips exhibited low tensile values.

Tensile strength aohieved in the test, rather, seemed related to the

mode of .failure as indioated by the fraoture surfaoes -- oleavage or

shear -- whioh in turn was relat.ed to the duotility. Highest tensile

strength most orten ooourred in samples showing sOIne degree of elonga

tion, though not necessarily the highest :relative to other samples,

and usually in samples showing more shear than cleavage on the fracture

surfa.oe. The data. of Table XII obtained 'With the six steels show this

trend. In Figure 16, the t.ensile .strengths of the samples from

Stee11'b.320 .. 1x 2o :3D 4

4 d 5*" p 6300 III '" a "

0

" d Pd

d 00

280p "'5J

,!II *x..*~i 260

e

iE-i 240

*D

220 *It*p*p

61

2001..--.......- ......---1.----110..-.-.......--

o 0• .5 1.0 1.' 2.0 2•.5

Elongation, :Per Cent.

Figure 16. Tens11eStre:ngth-lttLongat1on Relationship Of Six steels.

The Asteri. E!e&d.gnates S8mples Which Failed By A Cl.eavage Or

PreUminarthly CJ.eavage Mode.

62

Table m are plotted against their elongations. The samples with low

est tensile strengths failed predominantly by a cleavage mode and

showed no elongation. The samples with highest tensile strengths

failed predominantly by shear and showed a measurable elongation•

.All samples that failed by a oleaViage or predominantly cleavage

mode are desigllB.ted by an asterisk to the left of the point plotted

in figure 16. All the samples with no measurable elongation had

oleavage or predominantly cleavage type fractures. All the others

failed by shear except the sample of steel No.2 with 302 ksi tensile

strength and 0.% elongation. All samples showing :more than 1~ elonga..

tion had fracture surfaoes whioh showedacorapletely shear type failure.

It seems rea.sorutble to assume that failure at the jaws of the

tensile testing maohine was not responsible, in itself, for lowered

tensile test results. In those steels which were notch sensitive, the

jaws might have provided surface indentations which im.tiated failure.

However, tailure probably could have been initiated almost as easily

at a surface defeot or internal flaw in any other area of the sample.

For this reason tensile tests were not judged "good" or "bad" only

on the basis of the looation of fraoture in the sample. The tensile

strength - elongation. relationship of Figure 16 shows, tor example,

three samples of steel No. 4 that broke at 300 ksi with elongations

ranging trom O.~ to 1.3~. All three failed by a shear or predomi

nantly shear mode, yet two failed in the gripped region and one, with

1~3~ elongation, failed at a position outside of the grips.

Uniform elongation was measured on the seotion of the tensile

sample outside of the fraoture zone in this study. This procedure

should give lower elongation than a. sta.ndard prooedure that would

63

include looal defonnation a.djacent to the fracture. However, this

non-standa.rd method was considered. to give a better indication of the

relative ductility of the steals with rather low ductility. Two

reasons can be given for thinldng this. Local deform.a.tion a.t the

fraoture in some samples prevented fitting the two pieces together

well and would have maQe it impossible to measure their final length.

Secondly, the type tensile test sample used in this 'Work would have

presented a. serious problem with failures outside the gauge length

because no reduoed section was useQ.

In addition to the .relationship between tensile strength and

elongation shown in Figure 16, the observ~;t.i<?ns on the nature of the

fraoture surfaces also indicated a need for ductility in order to

obtain high tensile t~st resuJ,.tswith the testing prooedure being

used. Data on the steels hardened by slow heating and tempered. a.t

various temperatlU'es from 4.50 to ?OOoF (Table V) show that .at the

lower tempering temperatures the steels displayed oleavage type

fractures and low tensile test results. At the higher tempering

temperatures the samples had shear type fraoture surfaces, gave

higher elongation and. showed more reproducible or consistent tensile

strength data (see data on steel No. J in Table V). The highest

tensUe strengths 'Were measured with samples tempered at intermediate

temperatures where the steels were aoquiring sufficient ductility to

permit good tensile testing. At the intermediate tempering temper

ature "Where highest tensile strength was measured, the fracture sur

faces i~cated a mixed failure mechanism with shear tending to be

more prominent. These samples with highest tensile strength did not

give consistent elongation data. It appeared that the appearance of

64

the fraoture surfaoes could be correlated better with high tensile

st.rength values than could the elongation data.

The data for samples hardened. by rapid heating showed the same

tendency to associate highest tensile strength 'With a mixed. roode of

failure (Table IX). Furthermore, the data tend t.o indicate that a

teropering temperature in the vioinity of 5000 F was necessary to give

these steels suffioient ductility to permit meaningful tensile testing.

At lower tempering temperatures the aotual strength of these steels

may have been very high, but it was not possible to load the sa.mples

to their :f'u1l oapaoity with the testing prooedure used in this study.

It is believed that the steels studied. in this investigation

oontained too nch oarbon to show very high strengths and appreciable

du.otility. The high-oarbon martensite tends to be the internally

twinned type in which oarbide precipitation is very effeotive in pre

venting defomation. Perhaps a hardened., lower oarbon steel would oon

tain less twinned martens1te and oould be tempered at lower tempera

tures without losing so much of its ductility, because carbide pre

oipitation is not thought to be so effective in preventing deforma

tion in the lower oarbon :m.artensites with dislocation substruotures. (:3)

It is possible that the improvement in properties of these steels

with rapid heating in the hardening operation was assooiated with their

highoarbon oontent and that the improvement oan be viewed as further

eVidence that their oarbon content was too high to allow them to aohieve

the duotil1ty neoessary to permit measurement of a very high tensile

strength. Austen\.te of more than O.5f, oarbon tends to give roartensite

with a substructure predominantly of the twinned type. (3) In the

slow heating procedure, the steels were held at the austenitizing

65

temperature for at least a short time which could have been long

enough to allow the carbon to diffuse throughout and produce t if' not

homogeneous t at least mostly high-oarbon austenite. The high-oarbon

austenite would the n give a predominantly tw.i..nned type martensite in

whioh oarbide precipitation is very effeotive in preventing deformation

when the tempering temperature is low. High strength is nor:rna.lly

obtained at lower tempering temperatures and this was probably the

oase 'With these steels. However, at those tempering temperatures

where the aotual strength was very high the ductility was apparently

too low to allow acourate determination of the tensile strength. At

higher tempering temperatures (SOOOF or higher) where ductility improved

suffioiently to allow a more nearly accurate test of tensile strength,

the tensile strength had apparently dropped to 300 kai or lower.

The hardening operation employing rapid heating allowed the steel

to spend only a few seoonds in the austenite range, and it is possible

that the austenite at the start of the quench was nonhomogeneo'l9ls 'With

a large portion of the carbon concentrated near the former oementite

sites and with a large percentage of the matenal being lower than

O•.5~ carbon oontent. If' this were the case, this austenite could have

tra.nsformed into a ro.a:rtensite tha.t 'Was predominantly dislooation sub...

structured. Tempering this martensite at low temperatures would have

produced a more ductile material and may have been responsible for the

rapidly heated samples showing a better combinationo:f strength and

ductility.

It would appear possible that a careful examination of the samples

using transmission electron ndorosoopy might be oapable of verifying or

disproving the above ideas. No such study was attempted in this work.

66

Another observation that wight support the idea that the carbon

content was too high to achieve both very high strength and good duc

tility in these steels was the detection of a slightly softer surface

on the samples hardened by rapid hea.ting. Since a small amount of

daoarburization was found. on the steels in the as-received condition,

the low surfaoe hardness could be due to this lower carbonoontent.

As mentioned aoovet lower carbon martensite tends to be more ductile

after low temperature tempering and the sofier surface on the rapidly

heated samples may have made them less sensitive to surface defeats

allowing stress to approach the actual strength of the sample more

olosely during tensile testing. Thus t the higher measured tensile

strengths of the rapidly heated samples might be at least partially

due to a slightly decarburized surface.

The surface on the slowly heated samples may have picked up carbon

by diffusion from the interior which gave the surface slightly higher

hardness than that on the rapidly hee.tad samples. The higher oarbon

surface could have caused these samples to be more notch sensitive and

could have been a oontributing faotor in the obtaining of lower tensile

test data on the slowly heated samples.

If the oarbon content of these steels was indeed too high to give

the best oom.bination of high strength and ductility, a better com.bina

tion of these properties should be realized in lower carbon steels.

It is diffioult to know how much the carbon should be reduced. but

plain oarbon steels in the 0.4 to 0.6,% carbon range should be studied,

if this work is contirmed.

A oomparison of the oompositiona or the six steels given in

Table I shows that steels No.. 3 a.nd. .5 'Were lowest in carbon content..

67

This lower oarbon oontent did not appear to make them more duotile.

steel No. 4 was highest in oarbon content and displayed the most duo..

tility. steel No. 2 was highest in sulfur (0.4~) and phosphorus

(O.2~) which :might have been responsible for its low elongation; yet,

steel No. 6 also showed law elongation and a strong tendency toward

fracture by cleavage and it had sulfur and phosphorus contents appro:xi...

mately equal. to those of the other steels. :l.iJcoept for the high tin

oontent (0.2.0%) in steel No. 1 and the possibly high molybdenum in

steels No. 1 and 3, the conoentrations of the other elements were about

the same in eaoh of the six steels. These limited data do not indicate

any effect of oomposition on properties"

B. HARDENING TREATMENTS

The steels showed different strength properties relative to each

other with different hardening treatments. Rapid heating in the hard

ening operation gave higher tensile strengths than did slow heating

and a soaking time at the austenitirlng temperature. With slow heating

to the austenitizing temperature, the treatment which appeared to give

highest tensile strength on the basis of data developed on steels

No.3, 4 and 5 was to austen1tize at 14,50oF for 20 minutes a.nd to

quenah in warm oil. This treatment produced tensile strengths in the

vicinity of 260 kei and elongations slightly over 3<% after tempering

4 hours at 6000 F (Table IV)" The same hardening treatment produoed a

tensile strength of approxlmately 270 ksi in Steel No. 3 with temper

ing both at 450°F for long times and at 5500 F for a short time

(Table V). Elongation tended to be less than 1.5% at those lower

tempering temperatures"

68

Although rapid heating produced higher tensile strengths than did

slow heating, the various steels gave different tensile strengths when

hardened by exactly the same rapid heating treatment.. steel No .. 4

aohieved highest tensile strength with heating to 14,50oF in a furnaoe

at 17,5ooF. steel No.3, on the other hand, achieved highest tensile

strength with heating to 14500 F in a furnaoe at 1,5,50oF. Hardening

steels No. :3 and 4 by their best treatment and. tempering at 550°F for

10 minutes developed 288 ksi tensile strength and 2~ elongation in

No. :3 and 321 ksi tensile strength and 1~ elongation in No. 4 (Tables

VI and VUI). Tempering steel No. 4 :£'01'60 minutes lowered tensile

strength to 291 kai and. increased elongation to 2t1/J.

steels No. 2 and 6 seemed to show lower ductility than the other

steels at high strength levels and they were not studied thoroughly

enough to know what heat treatment would develop their highest strength

properties.

C. COMPARISON OF STEELS

The experimental workoovered a rather broad area since it was

intended to investigate the properties of the six steels and to deter

mine if any were capable of developing appreciable ductility at tensile

strengths of 300 ksi or higher.. In order to do thi s it was necessary

to limit the number of samples studied but still explore a wide variety

of treatments. Each of the six steels was not given every treatment

stud:led and the number of duplicate samples used to deter.mine proper

ties was very limited. A large number of duplicate sa'11ples would

probably be necessary to evaluate properly the properties of this high

strength, low ductility material. In spite of this deficiency in the

69

da.ta, some discussion of the properties of these steels is possible.

Vllhile .aotua.l values of tensile strength and elongation are mentioned,

it should be remembered that these are usually values obtained on

single samples and the reproduoibility of tensile test results was

probably not high on these samples, especially at the higher strengt.hs

and lower duotilities.

The data generated on the six steels indioated that they oould be

divided into two groups on the basis of their tensile properties.

steels No.1, 3, 4 and 5 showed a tendency toward ductile behavior

while steels Nc!I. 2 and 6 showed a tendenoy t.owa.rd brittle behavior

when heat treated to high st.rengt,h levels. This separation into two

groups is apparent when the tensile data for the steels after harden

ing by slow heating are oompared (Table III). "With this hardening

procedure and. low tem;peringtentperatures~none of the steels gave

suffioient elongation to make it stand out, but after tempering at

600°1 the ductile group (steals No.1, 3, 4 and 5) displayed shear

type failures While the other group had cleavage fraoture surfaoes.

The measured tensile strength was somewhat higher for the ductile

group after tempering at 6000 F and more notioeably higher when the

tempering temperature was lowered to 500°F (Figttre 5).

The steels developed more duotility with the better hardening

treatment whioh used. rapid heating. In this oondition the two groups

of steels separated themse1ves on the basis of' the elongation data

(Table XII and Figure 15). The elongation of' steels No. 2 and 6 was

appreoiably lower than that of steels No.1, 3, 4 and 5.

steels No.1, 2, 3 and 4 developed tensile strengths of 300 ksi

or higher when hardened by the rapid heating procedure and tempered at

70

550°F (Tables VI, VII, VIII and XII). steel No. 4 developed a tensile

strength of' 321 ksi, the highest tensile strength measured dUring the

course of this work. At the 300 ksi strength level, steel No. 4

appeared more ductile than the others, shovdng as much as 2.3% elonga..

tion. steel No. 2 gave low elonga.tion data and tended to give a cleav

age type failure. steel No. 6 behaved very much like steel No. 2 and

it is reasonable to believe that these two steels did not give higher

tensile test results because they lacked sufficient ductility to permit

good tensile testing (Table m). While steel No. 5 did not reach 300

ksi, it gave measureableelongation a.nd appeared to belong in the duc

tile group rather than with steels No. 2 and 6.

71

VI. CONCLUSIONS

1. .All of the steels studied were too high in carbon oontant to

show high tensile strength with appreciable ductility.

2. Tempering below a temperature of about ,OOoF does not suffi...

oiently soften the steels to allow a valid test of their tensile

strengths.

3. A shear or predomi:nantly shear type failure, as indicated by

the fraoture surfaoes of a tensile test sample, was a better indica...

tion of a. good tensile test than was the elongation nleasured on a

sample tempered in the low temperature range.

4. The austenitizing procedure in the hardening operation

appeared to affect the as-quenched oondition of the steel and to

determine the maximum tensile properties that oould be obtained by

subsequent tempering.

,. 'When these steels were tempered to get a. fracture during

tensile testing that was partially oleavage, but predominantly shear,

the steel had the highest tensile properties that could be obtained

by tempering the partioular as-quenched oondition under study.

72

BIRtIOGRAPHY

1.. Chien, Ing Shing (1966) A study of High Strength, Heat Treated

Plain Carbon steels.. Thesis, l>'Jissouri Sohool of Mines And

Metallurgy. 72 p. (With 26 f'igr., 7 tables.)

2. Kisslinger, F.. (1966) Private Communioation.

3. Kelly, P..M.. and J .. Nutting (1961) The Morphology of Martensite ..

JIBI 197, p. 199 - 211.

4.. Tekin, E. and P.M. Kelly (1965) A Study of the Tempering of

steel Using Transmission 1i3.ect1'On Mioroscopy, Precipitation

From It'O»-.Ba.se Alloys. .AD1E Ml!lt. Soc. Cont.. 28, p. 173 - 221.

5. Eguohi, I. et a1 (1961) The Preoipitation of Iron Carbides

During Tempering of Carbon-steel.. Trans. of the Japan Inst .. of

Metals 2, p. 218 - 222.

6. Lement, B.S., B.L. Averback and Morris Cohen (1954) Microstruotural

Changes on Tempering Iron-Carbon Alloys. Trans. ASM 46 \I

p. 851 - 877.

7. Reisdorf \I B.G. (1963) Tempering Characteristios of Some 0.4<;&

Carbon Ultrahigh-strength steels. Trans. AIME 227, p. 1334 - 1341.

8. Baker, A.J., F.J. Lautaand R.P. Wei (1965) Relationship Between

Miorostructureand Toughness in Quenohed and Tempered Ultrahigh

strength steels \I struoture and Properties of Ultrahigh-strength

steels. ASTM Special Teoh. Pub. No. 370, p. 3 - 22.

9. Kelly, P.M. and J. Nutting (1965) strengthening Meohanisms in

Martensite, Physical Properties of Martensite and Bainite.

The Iron and steel Institute (London) Special Report 93,

p. 166 - 170.

10. Bain, E.C. and H.W. Parlon (1961) Alloying Elements in steel.

2nd. ed., Amerioan Sooiety for :Metals, Metals Park, Ohio,

p. 88 .. 96.

11. Osborn, H.B. Jr. (1946) InduotionHeating,. Heat Treatment of

Metals. ASM Leoture Series, p. 113 .. 118.

12. Mima,. G. and S.Hori (1962) struoture Dependence upon the

Austenitizing Prooess of 0.68 Percent Carbon steel. Trans.

of the Japan Inst. of M.etals 3, p. 190 .. 196.

13. Metals &mdbook (1964) Iileat Treating, Cleaning and Finishing.

8th ed.,. Metals Park, Ohio. vol. 2, p. 760.

74

VITA

Robert Lowell Hollenbeck was born on November 4, 1938, at

Mobridge, South Dakota. After gra.duation from Mobridge High Sohool,

he entered the South Dakota School of Mines and Teohnology in 1955

and. graduated in 1959 with the degree of Baohelor ot Science in

Meta.llurgioal Engineering.

He worked as a metallurgist tor the United States Naval Bureau

ot Ships in Washington, D.C. from 1959 until his induction into the

Urdted states Army in 1963. After his disoharge in 1965 he entered

the University o:r Mi.ssoU1"i at Rolla as a graduate student.

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