UDC 669.18-932

Studies of NRIM Continuous Steelmaking Process*

By Ry uichi NAKA GAWA:* S hiro YOS HIMATSU:* Tak lly a UEDA:* Tats llro M ITSUI, ** Akira FUKUZA WA:* A kira SATO:* and TSllyoshi O ZAKI**

Synopsis

The fundamental aspect q! the development of the NRIM multi-stage

trough type continuous steelmaking process and the results of its recent

operations are presented in this jJaper. Though the scale of the plant used

was small (7.8 tlhr in hot metal flow rate), a suitable sejJaration of the

steelmaking reactions to each stage of the continuous steelmaking furnace

and the know-how qf its ojJeration were satiifactorily obtained. As the

result of the separation, that is, silicon and phosphorus were mostly removed

in the first stage so that the final carbon level was controlled mainly in the

second stage, the product with phosphorus as low as 0.005% (dephosjJhori­

z ation rate 96% ) was obtained with comparable amount of lime to that

of the conventional batch type steelmaking processes. The industrializ a­

tion of this process is confirmed to be feasible.

I. Introduct ion

One of the d istinguishing characteristics of the con­tinuous steelmaking process is that the measurement a nd control of steelmaking reactions are more easily made as compared with other processes. Though con­t inuous operation, in general, accompanies some tech­nical difficulties which are not observed in the case of batch operation, it is advantageous in the following points:

(I) Feasibility for mass production (2) Reduction of installation and running cost (3) Uniformity of the quality of product (4) Facility of process control

Any kinds of experimental plant tests which have so far been done for the technical progress and improve­ment in the above-mentioned fields, have more or less aimed to draw these advantages, and eventually related to the continuous operation.

In the iron and steelmaking process, various sorts of continuous operation are adopted: continuous cast­ing, hot and cold strip mill, surface treatment of sheet iron, etc. The blast furnace operation is also con­tinuous in essence.

Due to the complicated reactions at high tempera­ture, steelmaking process is still in batch operation by electric furnace , open-hearth furnace or converter. Especially the basic oxygen steelmaking process has been adopted in many steel plants by virtue of its high productivity. And there is a good chance for the continuation of oxygen steelmaking due to the recent development in both process control and refractories, which would result in full continuous operation of the iron and steel industry. Persevere efforts have been made from earlier times to make steel continuously1- 10) and the reports described the technical feasibi li ty are summarized as follows: 1l- 34)

(1) Spray steelmaking process at BISRA (U.

K.)U - 13)

(2) Tank type continuous steelmaking process at IRSID (France )14- 16)

(3) Single stage trough type continuous steel­making process (WORCRA process) at CRA (Austral­ia)17- 20)

(4) Single stage trough type continuous steel­making process at Bethlehem Steel Co. (U.S.A. )21)

(5) Single stage multi-chamber type continuous steelmaking process at MISiS (U.S.S.R.)22)

(6) Multi-stage trough type continuous steelmak­ing process at NRIM (Japan)23- 34)

In NRIM the research on the continuous steelmak­ing process which takes a part of the integrated con­tinuous iron and steelmaking plant was started in 1964 to obtain fundamental informations. The NRIM three stage trough type continuous steelmaking equip­ment was designed and installed in 1967 from the view point that the multi-stage reactor would be more ad­vantageous for the continuous steelmaking operation . As satisfying results have recently been obtained espe­cially on the dephosphorization, fundamenta l concepts of the NRIM process and its recent results are reported here.

II. Experimental Equip men t of t h e NRIM Con­tinuous Steelmaking Process

1. Fundamental Concepts for the Development of the Ex­perimental Equipment

The experimental equipment was designed with in­tent to realize a continuous steelmaking furnace in which complicated steelmaking reactions can be sep­arated into the specified reactions at the specified stage, where those reactions can be controlled and molten metal can be transported in the simplest way. Through various trials the present unit furnaces and their layout have been adopted.

At first it was considered that the following condi-tions should be fulfilled by every unit furnace:

(1) Steady state to be easily obtainable (2) Bath mixing conditions to be changeable (3) Suitable measuring site to be obtainable (4) Easy slag- metal separation (5) Slag-formation in a short period of time (6) Applicability for countercurrent operation

between metal and slag A special consideration was paid on the m ixing condition, since the controllabilities of these reactions and the stability of the composition of product were

* Originally published in Tetsu-to-Hagane, 59 (1973), 414, in Japanese . English version received March 29, 1973. ** National Research Institute for M etals, Nakameguro, Meguro-ku, Tokyo 153.

Re se arch Article ( 333 )

(334 J Transactions ISIJ, Vol. 13, 1973

markedly affected by the mixing conditions . There­fore, considering the complexity of steelmaking reac­tions, a unit furnace wh ich could provide any level of mixing characteristics is indispensable.

Proposed continuous steelmaking processes can be classified into two types, namely the converter or tank type and the trough type. Tank type reactor belongs to a perfect mixing reactor and seems to be su itable for the promotion of bath mixing and formation of emulsion which play an important role in the steel­making process. In this type of process, however, it is very hard to maintain stable outputs against the variations of inputs, and is not possible to satisfy the conditions(3) and (4) mentioned above. In addition, an extra vessel is necessary for the slag- metal separa­tion. On the contrary, trough type reactor belongs to a plug flow reactor which is attractive to control the reactions occurring inside of the furnace as a factor of position along the reactor. This is advantageous for the m easurement and control of steelmaking reac­tions. But it has also some problems, such as the con­struction of furnace and the heat loss caused by its rectangular shape. Since these two types have re­spectively the merits and demerits, it is difficult to judge which process is more advantageous.

An important item considered for the design of a unit furnace was the mixing characteristics (modified Peclet number or the ratio between perfect mixing and plug flow ), which could easily be selected by the combination of the flow rates of oxygen and hot metal and the lance condition (position, number, height etc.) As the result of this consideration, trough type was adopted in the current work as the most suitable shape for a unit furnace . In the case of trough type the existence of settling flow zone provides the part of slag- metal separation and the site for measurment, respectively. Simultaneous supplying system of oxy­gen and flux (oxy-flux lance method) was adopted for the faster slag-formation. Because of widely variable lance position, slag- metal countercurrent operation is feasible , wh ich would be advantageous for refining of high phosphorus hot metal. The shape of unit furnace was then determined.

In order to make effective continuous steelmaking operation, the following conditions were proposed as the requisites:

(1) To minimize the decrease of reaction efficien­cy which is inherent in continuous operation

(2) To perform a specified reaction at a specified site

(3) Adaptability for the change in product grade (4) Reduction of refractory consumption (5) Easy maintenance

To satisfy these conditions, the furnace should be an ideal plug flow reactor, but it is not so easy to realize these requisites by one furnace vessel.

As it is well known in the field of chemical engineer­ing, a successive arrangement of perfect mixing reac­tors improves whole reaction efficiency, takes the characteristics of the plug flow reactor, and conse­quently provides a specified site (furnace) for a speci­fied reaction . Therefore it becomes easy in the meas-

Relearch Article

urement and control and also offers the optimum application of refractori es depending on the type of reac­tion and temperature. This mea ns, for example, that the use of basic refractories for dephosphorization and the use of cheaper acid refractories for decarburization will be acceptable. From the above reasons, a multi­stage reactor was adopted.

As the consequence of foregoing considerations, steelmaking reactions were supposed to be separated into three groups, that is, desiliconization and dephos­phorization, decarburization, and the final control of steel grade, so that three-stage cascade type continuous steelmaking furnace was adopted.

Concepts for the development of our experimental process have been stated here, and the present plant after several a lterations is called as the NRIM con­tinuous steelmaking furnace- type 16- 2.

2. Constitution of the Experimental Plant

Though the experimental plant must be able to obtain exactly the factors which affect reactions, dis­turbances from some uncertain factors are unavoidable because the present plant is so small as compared with the industrial one. Namely, the scale factor must be taken into account in setting up the equipment. Es­pecially in the case of a small laboratory scale steel­making plant, it is difficult to select the right configura­tion of refractories, and the heat capacity is low in a whole. These facts bring about serious problems for experimental operations. Attention should be paid for the controllable factors as much as possible in order to raise the accuracy of experiments. 1. Hot Pig Iron Feeding Equipment (Holding Furnace)

The capacity of the holding furnace is 15 t because of the restriction of the shop. The size of holding furnace is 1.4 m in inner diameter and 1.6 m in height, and the wall is lined with chamotte and in­sulating bricks . By using a LPG burner, 12 t of hot pig iron at I 400°C can be held in the furnace without any practical temperature drop. The holding fur­nace is equipped with load cells measuring its gross weight and the feeding rate of hot metal is regulated by tilting the furnace oil-hydraulically in accordance with the prescribed time- weight diagram. However, momentary feeding rate by this manual control method deviates considerably, and according to the recorded chart the momentary deviations reach to ± 50 kg/min for the aimed feeding rate, 130 kg/min. From the consideration of the dynamic response of fluid flow, a new tundish was designed , which has a suitable size and 14 mm nozzle to keep the deviation always with­in ± 10% for the aimed value of 130 kg/min. As the result the feeding rate of hot metal is kept within a practical accuracy. 2. Continuous Steelmaking Furnace

As the mean residence time of the continuous steel making furnace , the time required for the completion of reactions in BOF, which is about 20 min, was chosen in the current work. If it is equally dividing into three unit furnaces , the mean residence time for each unit furnace is 7 min, and the hold-up weight of each unit furnace becomes to be about 900 kg when the

flow rate of hot metal is 130 kg /min. Based on the informations obtained from the pre­

liminary experiments,23) the size of a unit furnace having the hold up of 900 kg is decided as 3 m long, 0.30 m wide, and 0.85 m high . Each furnace is lined with tar-dipped magnesia bricks inside and insulating bricks outside as shown in Fig. I. Water-cooled cop­per lances for the injection of oxygen or oxygen with flux are installed at the upper part of each furnace. Their position along the furnace, their blowing angle, and their height are easily changed by lifting the lance assembly with an oi l cylinder. Lances are p laced in a series a long the flowing way of hot metal near to the inlet part of the unit furnace, so that each furnace may have a blowing (reaction ) zone and a non-blowing (settling) zone.

The depth of the molten iron, namely the hold-up weight which is about I 000 kg at present is deter­mined by the height of dum. A tap-hole is installed in the position below the overflow dum, and hot meta l remained is discharged through this hole by tilting the furnace with an oil cylinder when the run is over. A pre-heating burner, a waste gas flue , a chute for solid materials, and a waste gas sampling port are also in­stalled on the furnace.

The vertical view of the arrange men t of the holding furnace, the tundish , the continuous steelmaking fur­nace (each unit furnace has the same size) , and receiv­ing ladles is shown in Fig. 2. 3. O x ygen , Flux, and Coolant Supplying EquiplDent

1. Oxygen Supplying System 33) The system consists of an exclusive line for oxygen

and an exclusive line for oxy-flux line. M easurement of flow rate is made at every unit furnace. Total flow rate of oxygen at one unit is measured with an auto­matic flow meter and it is regulated to a specified value against the fluctuation of pressure and tempera­ture. The aimed error associated is within ± 1.5 % . Tota l flow is divided into two lines ; the one for oxy­flux line regulated with a manual flow indicator and the other for oxygen line supplied the remainder. 2. Flux Supplying System33)

A pneumatic conveyer used for the transportation of a large amount of fine powder like cement is ap­plied for the flux addition by modifying it for the use of a small amount and quantitative transportation. Oxygen distributed to the system is again divided for the use of floating and transportation of flux. The feeding rate of flux is controlled by tracing the tank weight- time line drawn on the chart. Flux carried by oxygen in the transport pipe is ent to lances through a distributing header. The error to the aimed feed­ing rate is within 10% as an average over the entire operating time.

One I m 3 and two 0.5 m 3 tanks are provided for each furnace respectively. 3. Blowing Lance

The lance used for oxygen and flux injection con­sists of an inner tube made of stain less steel with a soldered copper nozzle and water-cooled outer tube made of copper. The straight type nozzle of 5 mm in diameter, on which chromium is plated in the thick-

Transactions ISI1, Vol. 13, 1973 ( 335 )

I cd '::"9!"!2! (9J ij o Hamlll t.'d maJ!Ill' !:>ia o Direc l -ho nde d

tar ' maA'n es ia hr ick o \\Ia ~ n (>s i a !Iri c k

o C ha rn o!\(' hri c k (5) o Ins ulat ing bri ck

o Alum ina cas t a bl e

4000 - 850- -

1. Inlet skimmer 6. Gas samp ling hole

2. Outlet skimmer 7. Burne r

3. Slag-off port 8. Flue 4. Overflow dam 9. Tap hole

5. Lance 10. Coolant feeding chute

Fig. I. Construction of NRIM continuous steelmaking furnace (unit furnace), (mm)

Hecri\'ing ladlp

Fig. 2 . Multi-stage continuous steelmaking equipment

4°°1---;:::=========::::;--] min

10 15 Axial dis tance from nozzle outlet or let pol, em

Fig. 3. Variation of jet velocity along axis

ness of 50 I'" for the protection against wearing, is used in the current work.

Figure 3 shows the relation between the distance from nozzle and the axial velocity of oxygen.

The lance height is adjusted so as to maintain the velocity of oxygen jet on the steel bath surface at 100 to 120 m /sec. 4. Coolant Supplying System

For the improvement of the dephosphorization rate and the bath temperature control, pre-weighed cool­ants, such as iron ore, steel scrap, and reduced pellets, are automatically added into the bath through the chutes installed at the blowing zone or the position just before the slag-off skimmer. 4. Measuring Ins trulDents

In the preceding sections, measurements of the feed­ing rates of hot metal, oxygen, flux , and coolants have .already mentioned, and therefore, the temperature

Research A r ticle

L 336 J Transactions ISIJ, Vol. 13, 1973

measurem en t and the gas a na lysis a re only d escribed here. I . Temperature Measurem ent of Hot M etal

Disposable immersion thermo-couples a re used in­termi ttently for the measurem ent of bath temperature as a standard . A two-color pyromete r a nd immersion thermo-couples are used for con tinuous measurements. The ba th temperature is m easured at the p ool be­tween the slag-off skimmer a nd the outlet d a m. 2. Gas Analysis

Three infra red gas a na lyzers are used for the analyses of CO and CO 2 a nd the errors associated are estima ted to be within ± 2% for the indicated values . The flow ra te of waste gas is not measured yet.

After the experimenta l run , metal and slag samples are taken ou t a nd are subjected for the chemical and spectrographic analyses. Thermal analysis is used for the rapid carbon analysis during the experimental run. 5. Another Equipment

(I ) Cooling water is supplied to la nces, ducts, and parts of furnace bodies with a volute pump by cir­cula tion . For preheating, LPG is mainly used a nd it is supplied a t max imum rate of 200 kg/hr from a va­pori zer . The holding furn ace can be heated up to 1 500°C and each steelmaking furnace up to 1 400°C.

(2) M elting furnace a nd dust collector: An H eroult electri c furnace with the maximum power of 1 500 k VA is used for the melting of pig iron of 3 t.

A dust collecter is a bag-filter. 6. Plant Layout

Present plan t layout is shown in Fig. 4.

III. Experiments

1. Purpose of E xperiments

Purpose of the p resent experiment is no t only to obta in th e know-how of the plant operation, but also to sepera te the complex steelmaking reactions a nd to carry out the specified reactions in a speci fi ed furnace by making effective use of the mul ti-stage reactor . Tha t is, in practice, it a ims to remove all of silicon and to reduce the con ten t of phosphorus as low as possible in the first stage, a nd to rem ove the rest of phosphorus and carbon a nd to control the content of carbon and ba th temperature in the second stage . The third stage is considered as a grading furn ace. However, in the presen t runs, the last two furnaces are respectively used to fill the roles of the first a nd the second stages, and the first furnace is used as a cha nnel for tra nsporting of hot metal. Informations on the steelmaking reactions, which has not yet been fully understood , may be ex­pected from the resul ts obta ined .34 ) For the a na lyses of the results, only the data obta ined in the steady sta te a re used , but not the da ta a t start-up and hut-down, which are practically importa n t in continuous opera­tion, because of the labora tory scale experiments.

2. E xperimental Procedure and Conditions

1. Experimental Procedure

H ot metal of 12 t is melted in an Heroul t electric furnace and i t is then held in the preheated holding

Research Article

6000

El 'r El El I'J

J I 8

) Q

000 ODD I'

JI

6000 - 6000 - - 6000 - - 6000 - -

I . H old ing fu rnace 2. Tundish 3. Co n tinuous stee lma king fu rnace ( 1st stage) 4. Con tinuous steelmaking fu rnace (2 nd stage) 5. Continuous stee lma ki ng furnace (3rd stage) 6 . R eceiving lad le 7. S lag bucket 8. Flue 9.

10. II.

L a nce assembly Oxygen vessel Flux vesse l

12. Contro ller of oxygen a nd fl ux 13. O xygen line

Flux line Coola nt feeder

14·. 15. 16. 17. 18 .

Pl atfo rm (oi l hydrau lic system, reco rde r etc.) T wo-color pyromete r Gas a nalyzer

Fig. 4. Layout o f N RIM expe rimenta l p lant (mm)

furn ace . The preheating of the holding furn aces is very im­

pOl"ta nt to a ttain a stead y sta te in a shor t possible time . As ba th temperatures were occasiona ll y in­fluenced by the insuffic ient preheating in th e earlier run , in the recen t runs the holding furnace has been kept a t I 350°C for 6 hr before the experimen t.

During the opera tion the d ata required for the a na lyses are collec ted continuously or intermittently w ith various kinds of instruments. When the bath temperature exceeds the aimed value, it is regula ted by adding the coola n t. After the completion of speci­fi ed reactions in both stages, the hot meta l, fl ows into rece iving ladles, a nd the slag produced in each stage fl ows into each slag bucket. 2. Experimental Conditions

Experimenta l conditions a re listed in T able 1. In order to keep the same mean residence time, the hot m eta l is fed in the ra te of 125 or 130 kg/min for every experiment.

In the first stage, a ll of the la nces are used for oxy­flux injection, but in the second stage, the lances excep t the second and third ones employed for oxy-flux in­j ec tion are used fo r oxygen blowing . The flux is a mixture of lime a nd fluorspar, a nd silica or iron ore is added partly in p lace of lime for the improvem ent of slag properties .

3. Results and D iscussion

As an example, the varia tions of bath compositions

Transactions ISIJ, Vol. 13, 1973 [ 337 J

Table I. Conditions for operations

Number of operation 48 49 50 51 52 53 56 57

S tage of furnace 2 1_ I 2 2 2 1

1 Total (t) 12 1 12 12 12 I. Pig iron Flow rate 1

125 125 125 130

2 2 2 2

12 12 12 12

130 130 130 130 (kg/min) 1

~~~;!~g ratCN%' /min) 2.2 3. 1 2.2 I 3. 1 1.76 4.4 1 2.2 1 4.4 ~I 4~ ~I~ 2.2 1 3 . 2 2 .2 1 3.6

T Feed~g rate 4 2 5 5 4 6 4 --8 -1 4 8.45 4.51 9 4 --;- 1 4 9 4 I (kg/min) . 1

CaO:CaF2 : 5' 1'0 17-:3-: ' 5: 1 ~ 1 * 5:~1-*-1 5:1:0 1--* -~1 5: 1 :0 5:1:0 5: 1:0 5: 1: 0 4: 1 : 1 1 5: 1:0 1~ 1 Si02 _. _' _1_5 __

(kg/min) - I I -=- ---=-10.; ---=- - 1.-0 1 - - 1.0 -= 1.0 = ~I---=-

Flux

~kg/min) I - 1 1 ~ ---=-1 - 2.0** -=-1 2.0 1 1.0 1 - 1 - .-= -I -~~a~ber of _ _ 5_1 __ 7 I 5 1--7 - -; - 7- 4 7 I 4 1 5 4 5 4 1 5 4 5

Ore

Scrap

Lances Number of oxygen only

Angle CO)

I H eight (mm) I

* Slag from BOF.

* * R educed pellet.

3

5

100

6 3 5 -=--1_5

5

1:0 1

5 5 5

100 100 WOr l30

a nd temperature at the outlet of each furnace with the lapse of time is shown in Fig. 5. From this figure the smooth transitional changes of th e compositions and temperatures at start-up a nd the stabilities of them at the steady state can be recognized as the character­istics of the multi-stage tro ugh type reactor .

R esu lts obtained at the steady state are given in Table 2. Following discussions a re made on the basis of these data .

One of the purposes of this stud y is to know the d ephosphorization behaviour in the first stage. For example, in the 57th run , a hot metal ofO .O I9 % P and the dephosphorization rate of 77.7 % were obtained at the basicity 3.3 in spite of high carbon content 3.07% C. This result clearly indica tes that the NRIM process is very effec tive for the dephosphorization even for the high carbon melt. Furthermore the hot m etal obta ined in the second stage is O.005 % P and O.38% C. From these, it can be concluded that this process IS

very advantageous for the dephosphoriza tion. Photograph I shows the plant in opera tion.

1. D esiliconization

In order to reduce the content of phosphorus in the first stage, it is required to remove all of silicon, a nd a lso, to keep the bath temperature as low as possible (details a re described in the section III. 3. 4 ), because the residual sili con in the metal bath suppresses the ox­idation of phosphorus and the increase of bath temper­ature decreases the dephosphorization ra te. There­fore it is necessary to know the amount of oxygen required for the oxidation of all silicon in hot m etal. Moreover, the es timation of the temperature increase would become possible by knowing the a mount of

5

150 1

5 3 3 3

5 5 5 5 5 2.5 5 5 -;--1--

130 ISO 160 150 130 150 130 150

....... Raw iron - I st stage .- 2nd stage

U 1700 '--:- 1600 111500 ~ 1400

~ 4 *- 3 ~ 2

U 1

'? 0.8 ~ 0.6 . - 0.4 (/) 0.2

* 0.5 ~ 0.4 ~ 0.3

0.2

~ 00.21 c'-.

;:( 0:1 0.0

~ 0.0 *- 0.0 -en 0.0

0.0

0 5 0 5

8 6 4 2

o

•

· · .

.

_ ......... ~~-.~~ ~

I( ~

• • ... . . • • • • • • ~.-.........

· •

\ • •

~:'I.--:--:- Z, • • • ~ ..... .....-~.-............... -~.

• • ~: ....... ..--...-- ........

20 40 60 80

Tim e (min )

100

Fig. 5. R esults of operation (No. 51)

3

2.5

140

Research Article

::0

(I) .. (I) .. ... ()

:>" ;to

::!. o· iD

Nu

mb

er o

f op

erat

ion

Sta

ge o

f fu

rnac

e

---I

I Pig

iron

(0C

) T

emp

. S

teel

(0

C)

·C

(%

)

. Si

(%

) C

ompo

sI-

tion

o

f M

n

(%) I

pig

iron

p

(%)

1 S

(%)

1

C

(%)

Com

posi

-Si

(%

) ti

on

of

ho

t M

n

(%)

met

al a

t -

disc

harg

e p

(%)

S (%

)

CaO

(%

)

SiO

, (%

)

P,O

s (%

)

FeO

(%

) C

ompo

si-

Fe,

O.

(%)

tion

o

f sl

ag a

t T

. F

e (%

) di

scha

rge

Mn

O

(%)

Mg

O

(%)

CaF

, (%

) - C

aO/S

iO,

C

(%)

Si

(%)

Rat

e o

f re

mov

al

Mn

(%

)

P (%

)

__

I-S

-(%

)

Oxy

gen

effi

cien

cy*

(%)

48

49

2 2

1360

1620

16

80

1410

1600

1

1660

3.92

3.

88

---

-0

.55

0.7

0

0.7

4 0.

79

0.15

1

-0.

14

0.06

7 0.

072

3.18

I·

1.12

1.~

8 1.

16

-0.

02

<0.

01

0.03

7 <

0.01

---

_ O.

~~_J

0.4

7 -

0.46

0.

37

0.09

0 0.

060

0.07

9 0.

057

0.04

3 0.

034

0.03

3 0.

033

--

42.3

39

.8

56.5

47

.7

24.0

22

.8

22.5

22

.5

--1

---

3.5

1.

8 2.

5 4.

0 --

-7.

7 4

.3

5.2

6.

3

3.5

1.5

5.0

8

.8

-1

-

8.3

4

.3

6.3

12

.6

--

6.5

I 3

.8

4.0

8

.2

11.2

17

.8

2.5

7.8

---

7.1

7.4

7.5

2.

6 -1

--

1.7

2.0

2

.6

2. I

-18

.9

I 52

.5

15.5

54

.6

--

96.5

1.

8 94

.8

3.9

-I

37.8

5

.4

40.5

12

.7

42.0

19

.3

43.6

15

.7

36.8

1

9.1

15

2.8

------

65.5

86

.0

59.8

81

.7

----

-----

---

--

* --

-.2x~~or C

O _

_ X

100

Oxy

gen

for

CO

an

d C

O,

Tab

le 2

. R

esul

ts o

f ex

peri

men

ts

50

51

52

2 I

2 2

1380

14

20

1520

I

1700

I

143

0 -I

I 55

0 I

650

1 3

.85

15~ 1

1

710

3.8

0

0.7

0

0.4

7

0.61

0.5

0

0.16

0.

17

3.89

0.7

7

0.61

0.1

5

-0-

.080

-1

0.07

0 0

.060

1-3.

49-

0.2

9 I'

3.05

0.

06

3.24

0.

14

_0_

.25_

<~

<0.

01

<0.

01

0.0

9 <

0.01

0.35

I

0.3

5 I

0.33

0.

24

0.38

0.1

3 ,

0.18

0

.080

0.

031

0.08

4

0.03

9 0.

040

0.02

2 0.

030

0.02

3 -1

--

58.5

47

.7

62.5

47

.0

50.7

18.8

_ 29

~J ~O

23.7

18

.4

2.5

1.5

3.7

4.7

2.6

8.3

3

.2

2.6

12.6

3.0

1.

0

~I~'

O 2.

1 4

.3

7~J~5

5.8

1.

8

3T

I 1.

6

8.2

64.3

25.5

-

--I

21.2

51.3

34.

I

84.2

34.2

-1

90.6

1.2

2.3

2.5

8.7

5.8

2.7

20.4

98.4

32.7

52.8

69.0-1

66.0

5.7

12.3

9.1

5.5

2.2

1.9

72

.6

18.4

28.9

87.9

6.1

5.5

8.6

3.5

7.2

6.9

2.7

11 .

7

88.3

37.7

45.8

61.6

62.5

0.30

0.0

54

0.0

27

43.9

22.0

3.2

11.3

2.6

10.7

9.2

_1

7.

9

2.1

2.0

79.7

10.4

13.1

19.4

90.6

53

56

57

2 2

2

1420

1

400

14

10

I 590

I

1 64

0 1

560

1 60

0 1

520

1 1

590

3.84

3

.87

4.02

0. 9

2 0.

52

0.5

1

0.4

3 0.

63

0.63

0.14

0.

16

0.12

0.05

9 ,-

0.06

5

2.96

0.

64

---

<0.

01

<0

.01

--

-0.

25

0.26

0.0

59

' 0

.056

0.02

1 0.

025

50.3

40

.0

18.5

20

.5

1--

2.4

2.2

4.0

7.

6

1.7

2.7

4.1

7

.8

2.3

5

.2

I~I~O

6.2

2.8

2.7

1.

9

22.8

99.0

41.2

59.3

64.5

67.3

60.5

2.8

91.2

3.03

1.

02

1<0.

01_

1

<0.

01

0. 3

5 I

0.2

0

0.03

4 0.

012

0.04

0 0

. 035

51.5

50

.1

---

17.7

20

.4

3.8

1.

9

2.6

7.8

0.8

2

.4

2.6

7.8

5.2

4

.2

3.0

3.

2

9.1

10.0

2.9

2.

4

21.7

98.0

44.4

78.8

38.5

70.4

52.0

23.8

13.7

7.7

81.5

0.05

9

_3'~

1 0.

38

<0.

01

<0

.01

-Q

.32

1 0.

17

0.0

19

1

0.00

5

0.02

5 0.

025

1_

48.

5 19

.1

57.7

17.3

2.7

1_ 0

.8

5.7

1.2

1-4

.3

2.6

6.3

4.2

3.5

1

=3

.8

~I

5.7

6.8

6.2

2.5

65.7

3.3

23.4

92.6

45.6

77.7

59.6

78.0

22.1

10.8

94.7

w

w

00 ~ .., ... '" I:l "' '" ~ o· tl

'" § ::-< <

~ ~

,w

~

(()

'-l

W

I. 5 r--,--r-----y-----,~----y-__,

C

o " Mangan ese

1.0 Si

",:: " ~ 8 Mn

iii:.:: '. '" - ~ 0.5

i.i)0 ~ '" _ u

80

70 1 s t

~ 60

0 0

50 - I X • " ;:;;: 40

"-

" 30 ;:;;:

" 20 ;:;;:

Transactions ISIJ, Vol. 13, 1973 ( 339 )

4.0 ,j

o~ !? ;;r. 7

"re 3.0

' " &6 0

to' O " o " 0

/ ( ,: o I " ,

~ ~ 2.0 u .~

"

U

• 1.0 ~ " - '" , '"

U~ • Firs t s t age (S i2: 0.01 %) ~~~ i' ~st ,,~e l

' . 0. 10 o F ir s t s t age (S i< O.OI %) "

a Seco nd st agt>

" Second s tage o Total 0 - ---'

0 ~:S 0.0 /

1 2~.0~~14~.0~1~6.70~1 8~.0~7.20~.0~2~2~. 0~24.0 1300 1400 1500 1600 1700 0

T empera ture (O C ) 10 20 30 40 50 60 HI O\\11 !l:\y).!en \m : '1' 11\1

Amount of oxygen blown ( Nm 3/ T ll;l )

Fig. 6. R ela tion between the amount of Fig. 7. oxygen blown and the removals of

R elation between the removal o f Fig. 8. R e lat ion between the removal of manganese and the temperature carbon and the amount of oxygen

silicon, carbon, and manganese in hot metal above 0.01 % Si

of molten metal s bl own in each stage furnace and in the aggregate

carbon a nd ma nganese oxidized along with the oxida­tion of silicon. Figure 6 shows the rela tions between the amount of oxygen blown per one ton of hot meta l a nd the amounts of the oxidized silicon, carbon, a nd manga nese under the existence of si li con in the first stage. In F ig. 6 the amount of oxygen required is not corrected for the oxidation o f iron, phosphorus, sulfur, and the secondary oxidation of carbon. Although the experimental condition is limited in a na rrow range shown in Table 1 and the data are not sufficient enough in number, these relations can be expressed by the following experimental equa tions :

Cx; = 0.059Qo, - 0.40 .. . .. ................ (1)

Cc = 0.12Qo, - 1.4 ................. .... ... (2)

CMIl = 0.054Qo, - 0.65 .. . ................ .. (3)

where, Q o, : amount of oxygen blown (Nm 3/T IlM )

CSt, Ce, CMIl : amounts of silicon, carbon and manganese removed by oxidation, respectively (% ).

The proportional constants of these equations may indicate that the amounts of oxygen distributed for the oxidations of silicon, carbon, and manganese are approximately in the ratio of I : 2: I. Constant terms may show mainly the amounts of oxygen required for the oxidation of iron .

The a mounts of carbon and manganese oxidized together with silicon are obtained by eliminating Qo, from Eqs. (I), (2), and (3).

Cc = 2.0Cs;-0.59 .... .. .. ... .. .. ...... (4)

CMn = 0.9 I Cs;-0.28 ... ................ .. (5)

The negative signs in the constant terms of Eqs. (4) and (5) are indicating the selective oxidation of silicon to carbon and manganese, and from these equations it is obvious that the oxidation of carbon and manganese starts after about 0.3% of silicon is oxidized.

In the recent experiments, it becam e possible to

remove a ll of silicon and to keep the bath temperature approximately at I 550°C in the first stage by blowing oxygen 10% more than the a mount required for the si li con removal. By this way, excellent dephosphoriza­tion is a ttained . The amount of oxygen used for the silicon removal in the first stage will be regarded simi­lar to that of BOF, as the oxidation ofO.5 % Si in BOF needs about 15 Nm3 of oxygen per one ton of hot metal. 35 )

2. Removal of Manganese

As apparently seen in Table 2, th is process gives fairly low removal rate of manga nese, which seems to be influenced by low FeO content in slag.

Effect of the bath temperature on the removal rate of manganese is shown in Fig. 7. In the first stage, good correlation is not obtained between them , but in the second stage, the bath temperature has an effect on the remova l of manganese with some correla tion as written in Eq. (6).

D )ln(2) = 530- 0.30 t... .................. (6)

r = - 0.78

where, D~ln (2 ) : demanganization ratio in the second stage (% )

t: temperature (OC).

3. Decarburization

The first stage in the current experiment corre­sponds to silicon blow and the second stage to carbon blow. Figure 8 provides the rela tions between the amount of oxygen supplied and the amount of carbon removed in the whole and respective stages.

In the first stage, the correlation between the de­carburization ratio is not apparent because the rate of oxygen blowing is not varied widely and a lso the oxygen efficiency is lowered by the presence of the simultaneous oxidation of silicon, manganese, and phosphQrus. However, in the second stage and also the entire stage, fairly good correlations are obtained as shown in the following equa tions.

Research Article

( 340 J Transactions lSI], Vol. 13, 1973

Cc(2) = 0.11Qo,- 0.50 ........ . . .. ... ... (7)

r = 0.96

Cc(Z) = 0.096Q0 2- 1.0 ........ .. ........ (8)

r = 0.87

where, C(,(2), Cc(Z ): removals of carbon in the sec­ond and entire stages (%)

Qo, : amount of oxygen blown (Nm3 j TII~r).

Constant terms of these equations mean the amounts of oxygen for the oxidations of the elements except carbon, and the proportional constants seem to be affected by both the oxidations of the rest elements, which occur with the primary oxidation of carbon, and the secondary oxidation of carbon. Since 9.33 Nm3 of oxygen is required for the removal of 1.0%Cjt of hot metal as carbon monoxide, stoichiometrical proportional constant becomes 0.107. The propor­tional constant of the second stage is almost equal to the theoretical value because the decarburization is a dominant reaction in this stage. These constants and proportional constants may depend on the bath tem­perature, compositions and weight of slag, lance con­ditions (number, arrangement, and height of lances, and type, size, and number of nozzles, etc.), mean res­idence time, mixing conditions of bath metal , etc . Among the factors men tioned a bove, only the slag weight and the number and height of lances have so far been examined as the variable factors. However, no effect has been observed in the current work.

Since there is a close relation between the rate of oxy­gen blowing and the amount of carbon removed in the second stage as it is obvious from Fig. 8, it will be possible to control the carbon content accurately in the second stage if the outlet level of carbon in the first stage is known. The amount of oxygen necessary for refining the pig iron of4.2%C to the steel of 0.1 % C is about 53 Nm 3 jt of hot metal as a total, and this value is nearly equal to that of BOF.35)

Continuous waste gas analysis has been examined as one of the carbon control method. However, the quantitative determination of carbon from waste gas is not so easy because the flowing rate of waste gas is not m easured . As for the check of the gas analysis, the amount of carbon removed which was calculated from the result of metal analysis was compared with the value obtained from the total amount of oxygen blown which was required for the oxidation of silicon, manganese, phosphorus, and iron, and from the com­position ratio of CO and CO 2 and is shown in Fig. 9. Choke of sampling probes, breathing-in of air, and fluctuati on in the flow rate of waste gas caused by the dumper of the dust collector are supposed to be the causes of the error of the gas analysis. 4. D ephosphorization

In the first stage, dephosphorization proceeds ef­fectively because of low bath temperature, high fluidity and foaming ability of slag due to high SiOz content caused by the selective oxidation of silicon, and no reversion of phosphorus in the next stage due to the discharge of slag through a slag-off hole in the first stage. On the other hand, this stage has disad-

Research Article

,.-::-;::;-: 1_ 3 0 Fir s t stagel 6

c: o

-~econ~ag.:J 6 - p'" ] ;/ 66

6 I

'" 2 . a 6 •

B~ -;;; ~

U <f)

~ <f)

~ ~ I u "

I '"

u~ ~ ."

o

6 o

O~ ____ ~ ____ ~ ____ ~~ 023

(C",- C"",) from metal analys is (%)

Fig. 9. Comparison between the decarburization rates ca l­culated and observed

100 ~~--~--------------~

90

80

c 0 '

70 6

<=> 60 j 6 <=>

'<

~ 50

40 1° c.: • First stage Si ' 0.01 ",)

cL o First stage (Si< O.O I ',) 6. Second 5 (age

6

10

O~-L __ ~ __ ~~ __ ~ __ ~~ o 7

Basicity of s lag (CaO ' S i02)

Fig. 10. Re lation between the dephosphorization rate and the basicity of slag in each stage furnace

vantages that it is in high level of carbon and low basic ity caused by SiOz formation , and requires a long slag-forming time because of low bath temperature. For the production of high carbon steel by this process, it is necessary to dephosphorize in a high carbon range of the first stage. This seems to be desirable from the view point of the separation of steelmaking reactions. Thus the improvement of the dephosphorization rate in the first stage became one of the major purposes of this study.

Relations between the dephosphorization rate and the basicity of slag are shown in Fig. 10. The de­phosphorization rate in each stage is expressed as fol­lows.

In the first stage, there is a good correlation be­tween the dephosphorization rate and the basici ty of slag and it is expressed as follows :

D p(l) = 21(CaO/SiOz)+8.0 .......... ... .. (9)

r = 0.83

where, Dp(l ): dephosphorization rate in the first stage (%)

CaO jSi02 : basici ty of slag.

This figure clearly shows that the dephosphoriza­tion rate in the first stage exceeds 80 % when the

Transactions ISIJ, Vol. 13, 1973 ( 341 )

100 80 300

0 " 70 o . /

" ~~

" " "

250 t-

o -

/ • First s tage U

I ( 5i 2: 0.01 %)

0 o F irst stage • ( 5i < 0.01 %)

60 e ~ " * 60

200 " " U j I> 5 econd stage

x 0

B- e 50 Cl.. ~ ;:.::

'\ - x 40

Cl.. " " (f) 40

" ----:... " 20 JJ 30 I .-

" (f)

°0 ~ 20

20 40 60 80 )00

ESl im<ll (' d ,·,du e ",,) 10

0 " )50 -B-r-u

0

1 " )00

t;- -. --+-.... . i-

6 6 6

:- 50 i -+

6 • Firs t st age (5 i"> 0.0 )"01 6

o First st age (5i < 0.0) ',,) - 50 ",,,0 t::. Second stage

• f I> I>

• II V • /"'" J AI>

/ 4 I>

~ V "

I>

~/ 0

Fig, II. 5 6 7

Comparison between the de­phosphorization rates obtain­ed by BOF and by continuous steel making: calculated from Eq, ( 10) for BOF

Fig, 12,

Basicity of slag (CaO/ S iO,)

R elation between the desulphuriza­tion rate and the basicity of slag

- 1001L,.0---:1:-::5-----f20o------;2:;:-5---:3;';;0:-----;;;35°----;:40

Bl own oxygen ( Nm3, Tmt )

Fig, 13, R elation between the increment of temperature and the amount of

oxygen blown in each furnace

basicity of slag is more than 3,5, Such a relation is not apparent in the second stage, but the dephosphori­zation rate of 70 % could be a ttained when the basicity of slag is a bout 4,5, In the second stage, less addition of CaO may be required to obtain high basicity of slag, because the fl ow-in silicon from the first stage is almost negligible, As a consequence, for example, steel containing phosphorus less than 0,01 % could easily be produced from the pig iron with 0.165% P by dephosphorizing more than 80% in the first stage and more than 70% in the second,

In Fig, 11 , the dephosphorization rates obtained from the present experiments are compared with the experimental equa tion derived for the BOF process,36)

Z = 149,2 - 0,1 56X**-0,0336Y** "",,( 10)

where, Z: dephosphorization ra te (%) X: final carbon ( x 102%) Y: final temperature COC),

The dephosphorization ra te in the first stage has the tendency to take a higher value than that in BOF when the level of silicon is lower than 0.01 %, while both rates are nearly equal when the silicon content in the melt is more than 0.01 % . The lower dephos­phorization rate in the second stage as compared with BOF results may be due to low basicity of slag. While the basici ty of BOF slag ranges from 4,5 to 5.0, that of this process is lower than 3.0 in many cases, 5. D esuHurization

Figure 12 indicates the relations between the de­su lfurization rate in each stage and the basicity of slag. In the first stage, the desulfuriza tion rate goes up evidently, as the basicity of slag increases, a nd reaches to more than 60% a t the basicity of 3.5, Regarding that the attainable desulfurization rate is 60% at most in BOF,37,38) this process, which can yield the same desulfurization rate with that of BOF in the first stage only, would be acceptable steelmaking process for the removal of sulfur. The relationship between the de­sulfurization rate and the basicity of slag in the second stage is not so close as that in the first stage. As for

th e production of very low sulfur steel, a preliminary desulfurization of pig iron would be indispensable. The apparent relationships are not obtained among the desu lfurization rate, the bath temperature, and the FeO content in slag. 6. Bath T emperature

Figure 13 indicates the increase in the bath tem­perature with the amount of oxygen blown. The correlations are not so close due to the small scale ex­perimental plant, but it could be said that the oxida­tion of silicon in the first stage brings higher tempera­ture increasing rate as compared with that in the second stage. The lower level of temperature in­crease in the second stage than that in the first stage may suggest the greater heat loss due to the higher bath Lemperature in the second stage. 7. R efractories 14, 17,21 , 22 ,3 2)

Selection of refractories has been made in due con­sideration of secure operation in the first p lace. 31,32) The best refractories are used at severe positions like the wall of blowing zone, and the castable and ram­ming mixtures are adopted at the position where re­construction is required after every run . The reliable refractories configuration has been established after trial and error because the furnace has not prevailing shape . The present refractories configuration IS

shown in Fig. I. The existence of a b lowing zone and a settling zone

characterizes this furnace . R efractories in the blow­ing zone are eroded by the physical a ttack by vigorous movement of hot metal and by the chemical attack by emulsified slag. 39 ) R efractories in the settling zone where the slag- metal seperation takes place, are chem­ically attacked only at the slag line .

The skimmers, built in two positions for the slag­meta l seperation under the similar condition to the wall refractories, suffer from the more severe attacks because their both sides are exposed to slag and metal. Few troubles occur with the skimmers by the use of direct-bonded tar- magnesia bricks.

As the over-flow dum is in contact with only the

Research Article

[ 342 J Transactions ISIJ, Vol. 13, 1973

hot metal flowing still , there is no serious problem on eros ion.

Since continuous steelmaking operation is char­acterized by having no variation of temperature and basicity to the refractory used at every site along the furnace, this merit can be realized when the optimal refrac tories configuration is adopted in each stage ac­cording to its specified reactions, and could bring the reduction of refractory consumption.

IV. Conclusion

Basic concepts for the development of the NRIM continuous steelmaking process and the recent experi­mental results were reported here. In spite of a small-scale experimental p lant and a short running time of about 100 min, satisfactory results were ob­ta ined in the separation of reactions in to each stage and the operational technics. We are convinced that th is process would satisfactoril y have practical applica­tion.

The characteristics of this multi-stage continuous steelmaking process have been confirmed , that is, as for the dephosphorization, steel of 0.005% P is pro­duced (dephosphorization rate 96%), and as for the decarburization, carbon level could be controlled main ly in the second stage.

Comparing with other continuous steelmaking pro­cesses, the NRIM multi-stage continuous steelmaking process has the characteristi cs of separating the com­plex steelmaking reactions into several simple ones, a nd it will result in easy control of reaction and mixing, proper selection of refractories, and reduction of capi tal and maintenance cost.

At present the fo llowing works are being carried out steadi ly, i.e., (1 ) preliminary continuous desulfuri­zation, (2) finer control of carbon content, (3) tem­perature control , and (4) stud y in the field of chemical engineering including scale-up and optimization. A cknowledgements

The authors wish to express their grati tude for the valuable d iscussions given by the Continuous Steel­making Research Committee of the Iron a nd Steel Institute of Japan.

The contributions of ass istants of the Melting and Roll ing Section, the First and the Second Laboratory in Development Division to the experiments are also gratefully acknowledged.

REFER ENCES

I ) N. Dobrokchotob: Teorija i Praktika Metallurgii, 10 ( 1939), I.

2) M . W . Thring: J. Inst. Fuel, 22 ( 1950), 178. 3) J. F. E ll io tt : Sobrcmenniee Provlemie Metallurgii, ( 1958),

Izd. An USSR.

4) B. A. Fukle b : Izbestija Buisshich Uchebnuich Zabedenii, (1960), 60.

5) G. B. Alexandrovsky: J. Metals, 15 ( 1963), 585. 6) G . B. A lexandrovsky: J. Metals, 15 ( 1963), 65 1. 7) M . W. Thring : Iron Steel (U.K .), 37 ( 1964), 506. 8) B. A. Fukleb : Teorija i Praktika Intensfikatzii Protzessob

b K onberte rah i Martenobskih Pechah, ( 1965), 198, Izdatel'stbo M etallurgija.

9) M . W. Thring, C. Marsden, and T. W. J enkins: I ron Steel

Research Article

(U. K .), 39 ( 1966), 166. 10) N. K. Leonidob, A. N. Pogbisnob, M. A. Glinkob, and B. A.

Kudrih : Proizbodstbo Chugu na i Sta li , ( 1969), !togi

Nauki i T ehniki.

II ) D. R . G. Davies, M.J. Rhydde rch, and L. J . Shaw: PSI, 205 ( 1967), 8 10.

12) M.J. Rhydderch: J ISJ, 205 ( 1967), 8 14. 13 ) I ron Steel (U.K. ), 40 ( 1967), 374. 14) A. Berthet, J. R ouanet, P. Vayssiere , and B. Trentini: JISI,

207 ( 1969), 790 . 15) A. Be rther, J. C. Krud, J. R ouanet, and P. Vayssiere:

Proceed ings ICSTlS, ( 197 1),272, Suppl. T rans. ISlJ. 16) A. Berthet, J. Blum, M . Girard, and D. M a rtin : Proceed­

ings of the meeting "Alte rnative R outes to Stee l " ( 197 1),

107, I ron Steel lnst., London. 17) H . K. Worner : J. Aus. Inst. M etals, 6 ( 196 1), 167. 18) H . K . Worner, F . H . Baker, 1. H . Lassam, and R . S iddons:

J. Metals, 21 ( 1969),50. 19) H. K . Wo rne r and F. H . Ba ke r : Proceed ings l CSTIS,

( 197 1),277, Suppl. Trans. l S I] . 20) F. H . Baker and H. K . Worne r : Proceedings of the meeting

"Alternative R o utes to Steel ", ( 197 1), 99, I ron Stee l Inst. ,

London . 2 1) E . M. Rudzki , H . L. G ills, B. K . Pease, a nd G. E. Wie la nd :

J. Metals, 21 ( 1969),57. 22) M . A. G linkov: Proceed ings of the meeting "A lte rnative

R outes to Stee l ", ( 197 1), 88, iro n Stee l Inst. , Londo n . 23) R . Nakagawa, T . Ueda, S. Yoshimatsu, T. Mitsui , 1.

Uehara, A. Fukuzawa, and Y. 1 akamura: ReI). Nat. Res.

b lSt. Metals, 10 ( 1967), 557. 24) R . Nakagawa, T . Ueda, S. Yoshim atsu, T. Mitsui, 1. Ue­

hara, A. Fukuzawa, and Y. Nakamura: Tetsu-to-Hagane,

54 ( 1968), S481. 25) R . Nakagawa, S. Yoshimatsu, T. Mitsui , 1. Uehara, A.

Fukuzawa , a nd Y. Nakamura: Tetsu-to-Hagan!, 56 ( 1970),

S65. 26) R. Nakagawa, T. Ueda, S. Watanabe, and H. Saito: T etsu­

to-Hagane, 56 ( 1970), S65. 27) R . Nakagawa, T . Ueda, S. Yoshimatsu , T. Mitsui, A. Sato,

A. Fukuzawa, 1. Uehara, and T. Ozaki: Tetsu-to-Hagan!,

57 ( 197 1), S400. 28) R. Nakagawa, T . Ueda, S. Yoshimats u, T. Mitsui, A. Sato,

1. Uehara, and A. Fukuzawa: Trans. Nat . Res . Inst. Metals, 13 ( 197 1), 54.

29) R. Nakagawa, T. Ueda, S. Yoshimatsu, T. Mitsui, A. Sato, 1. Uehara, and A . Fukuzawa: P roceedings ICSTIS,( 197 1), 290, Suppl. Trans. ISIJ.

30) R. Nakagawa: Japan Patent 6269 13, 653978; French Patent 1576970; British Patent 1207003; U.S. Patent 3617042.

3 1) T. Uehara, T . Mitsu i, Y. Nakamura, R . Nakagawa, and S. Yoshimatsu : ReI). Nat. Res. Inst. Metals, 13 (1970), 363 .

32) 1. Uehara, T. Mitsui, Y. Nakamu ra, R . Nakagawa, and S. Yoshima tsu : Trans. Na t. Res. Inst. Metals, 13 ( 197 1), 254.

33) T. Mitsui , R . akagawa, S. Yoshimatsu, and T . Ueda:

Rep. Nat . Res. Inst . Metals, 16 ( 1973), No.3 . 34) T. Ueda, T. Mitsui, R . Nakagawa, and S. Yoshimatsu:

Trans. Nat. Res. Inst . Metals, 15 (1973), No.4, 170. 35) K . Kato, K . Wakabayashi, T. Zaizen, a nd M . Azuma:

Seitetsu-Kenkyu, 266 ( 1969), 8781. 36) Y. Nagami, K. M a tsunaga, and M. akatani : Tetsu-Io­

Hagane, 50 ( 1964), 2 18. 37) U. Ihama and K . Shiwaku: Tetsu-Io-Hagane, 53 ( 1967),

271. 38) K. Narita, A . Tomita, Y. Hirooka, and Y. Sato: Tetsu­

to-Hagane, 57 ( 1971 ), 1101. 39) J . H. Chesters: Eighth Sir Julius Wernher Memorial L ec­

ture, I nst. Min. M et., ( 1971 ), 1.