Ferrous Alloys

Jeffrey DG VenezuelaDepartment of Mining, Metallurgical and Materials

Metallurgical Board Review

Wrought Iron

Deformable iron

Ductility is due to very low carbon content

used to create gates and furniture w/ intricate designs!

Carbon Steels

Low Carbon - contain up to 0.30% C; typical uses are in automobile body panels, tin plate, and wire products.

Medium Carbon - ranges from 0.30 to 0.60%C; used in tracks, gears and high strength structural components

Carbon Steels

High Carbon- 0.60 to 1.00%C; used in cutting tools, dies, razors, blades, springs and high strength wire

Ultra High

Carbon1.25 to 2.0% C

Microstructures in Steel

AISI-SAE and UNS Designation forVarious Steels

AISI-SAENo.

Composition UNSCounter

part10xx Plain Carbon

SteelsG10xx0

11xx Free cutting, plaincarbon steel whichhave beenresulfurized; lowphosphorus

G11xx0

12xx Plain carbon steelwhich have beenresulfurized; highphosphorus

Steel Nomenclature

ALLOY STEELS13xx Manganese (1 – 2%) G15xx014xx Boron23xx Nickel (3.5%)25xx Nickel (5.0%)31xx Nickel (1.25%), Cr (0.6%)33xx Nickel (3.5%), Cr (1.5%)40xx Molybdenum (0.2 – 0.3%) G40xx041xx Chromium (0.8% - 1.1%), Mo (0.15 – 0.25%) G41xx043xx Nickel (1.65 – 2%), Cr (0.4 – 0.9%), Mo (0.2 – 0.3%) G43xx044xx Molybdenum (0.5%) G44xx046xx Nickel (0.7 – 2%), Mo (0.15 – 0.3%) G46xx048xx Nickel (3.25 – 3.75%), Mo (0.2 – 0.3%) G48xx050xx Chromium (0.4%)51xx Chromium (0.70 – 1.10%) G51xx05xxxx Chromium (1.0-1.5%), C (1.0%)61xx Chromium (0.70 – 1.10%), Vanadium (0.10%) G61xx081xx Nickel (0.2 – 0.40%), Cr (0.3 -0.55%), Mo (0.08 – 0.15%) G81xx086xx Nickel (0.3 – 0.70%), Cr (0.4 -0.85%), Mo (0.15 – 0.25%) G86xx087xx Nickel (0.4 – 0.70%), Cr (0.4 -0.60%), Mo (0.20 – 0.30%) G87xx088xx Nickel (0.55%), Cr (0.5%), Mo (0.35%)92xx Silicon (1.8 – 2.2%) G92xx093xx Nickel (0.25%), Cr (1.2%), Mo (0.12%)98xx Nickel (0.45%), Cr (0.4%), Mo (0.12%)

Low Alloy Steels

Less than 5% total alloy contentprimary function of the

alloying elements is to increase hardenability

HSLA (High Strength Low Alloy steel) has fine grains, low carbon content and alloy additions that strengthen steel by solid-solution strengthening

Designations for Tool Steels:Group Symbol Type

Water-hardening

W

Shock-resisting

S

Cold-work OAD

Oil-hardeningMedium-alloy air-hardeningHigh-carbon highchromium

Hot-work H (H1-H19,incl.,chromium-based;H20-H39, incl.,tungsten-based; H40-H59, incl.,molybdenum-based)

High-speed TM

Tungsten-basedMolybdenum-based

Mold P Mold steels (P1-P19,incl.,low-carbon; P20-P39, incl., other types)

Special-purpose

LF

Low-alloyCarbon-tungsten

High Alloy Steels

Possess strength, wear resistance and dimensional stability

greater than 0.6%C with total alloy contents which range to more than 20%

Tool Steels

High Alloy Steels

Austenitic - obtained by addition of nickel; best known is 18Cr-8Ni used in cooking utensils and tableware

Ferritic- have sufficient Cr such that no austenite forms at any temp; hardened only by coldworking

Martensitic- Cr content is low enough so that austenite can form at high temp and transform to martensite; used for stainless steel cutlery

Stainless Steels (at least 12%Cr)

                                                 

Ferrite formers Austenite formers

Iron Nickel

Chromium Nitrogen

Molybdenum Carbon

Silicon Manganese

  Copper

High Alloy Steels

Nickel Steels - Invar(with 36% Ni) exhibits low expansion; Alnico(20Ni-5Al-12Co-Fe) is used to make powerful magnets

Silicon Steels - contain about 0.5 to 5% Si ; used as core material in magnetic circuits.

Austenitic Manganese Steel “Hadfield Steel” - (1-1.3%C, 11-14% Mn); hardens with cold working during service; for high abrasion applications

Other Specialty Steels

Maraging steels

differ from conventional steels in that they are hardened by a metallurgical reaction that does not involve carbon

strengthened by intermetallic compounds such as Ni3Ti and Ni3Mo (500°C)

have very high Ni, Co, and Mo

TYPES•Gray Cast Iron •Nodular (ductile) Cast Iron •White Cast Iron and •Malleable Cast Iron

Cast IronContain more than 2% Carbon

Carbon Effect = %C + %Si/3

(a) Gray Cast Iron

•weak and brittle in tension

•effective in damping vibrational energy (ex. are engine blocks and equipment base, etc)

•wear resistant and least expensive

Cast Iron

(b) Ductile or Nodular Cast Iron

•addition of magnesium or cerium promotes the formation of nodular graphite

•common applications are valves, pump bodies, gears, etc.

Cast Iron

(c) White Cast Iron

•White fracture surface due to presence of cementite

• very hard but extremely brittle• very limited application;Chilled iron is better and used for heavy duty parts(used as rolls)

Cast Iron

                                                 

(d) Malleable Cast Iron

•Product of annealing white cast (heating at 1700 F: malleableizing)

• temper carbon in ferrite or pearlite matrix

•connecting rods and universal joint yokes, transmission gears, differential cases and certain gears

Cast Iron

Review Questions

1. Wrought iron has carbon content less than:

a) 0.22% c) 2.14%b) 0.022% d) 0.76%

2. HSLA has alloy content less thana) 3% c) 9%b) 5% d) 10%

3. A possible designation for steel with purely pearlitic microstructure is:

a) 4310 c) 4180b) 11120 d) 4340

4. The element which causes formation of nodular graphite:

a) magnesium c) manganeseb) sulphur d) zinc

Review Questions

Review Questions

5. INVAR is an alloy of: a) Fe and Nic) Ni and Cub) Co and Fe d) Fe and Mo

6. Steel known for very good toughness and hardened by the presence of non-carbide-intermetallics: a) tool steels c) maraging steelsb) silicon steels d) HSLA

7. Stainless Steel needs at least this amount of chromium:

a) 5% c) 18%b) 12% d) 15%

8. White cast iron possesses a white fracture surface because ofa) cementite c) graphite flakesb) pearlite d) graphite nodules

Review Questions

9. Which element is not found in plain carbon steel:

a) carbon c) siliconb) magnesium d) phosporus

10. Cast iron used as engine blocks due to its good damping capabilitya) WCI c)malleable CIb) nodular CI d) GCI

Review Questions

Iron and Steel Making

Department of Mining, Metallurgical and Materials Engineering

History of Appearance

Meteoric Iron - came from meteorites!

Wrought Iron - up to 14th century Steel - after 14th century Cast Iron - after 14th century

Source of Iron: Ores

Hematite - Fe2O3 - 70 percent iron

Magnetite - Fe3O4 - 72 percent iron

Limonite - Fe2O3 + H2O - 50 percent to 66 percent iron

Siderite - FeCO3 - 48 percent iron In nature, iron (Fe) is attached to

oxygen (ore) and mixed with silica (SiO2)

Iron Making

IRON MAKING

DIRECT INDIRECT

No melting involved

Solid ore is directly reduced by gaseous reactants

Melting involved

Ore is melted and reduced in this form

DIRECT

Direct Reduction Processes

Bloomery (Old technique) Gas-Based DRP

Midrex (shaft furnace) Circored (fluidized bed)

Coal-Based DRP SL/RN (rotary kiln) Allis-Chalmers Controlled Atmosphere

Reactor (ACCAR)

Bloomery

Ore is burnt together with charcoal with the help of blast air from bellows

Temperature not too high! Product is a porous mass called

‘bloom’product is forged to squeeze out

remaining slag

Direct Reduction Processes

Gas-Based DRP reducing gas

generated externally from the reduction furnace

Coal-Based DRP reducing gas

generated from hydrocarbons in the reduction furnace

Sponge Iron or Direct Reduced Iron (DRI)

virgin iron source uniform in composition, and

virtually free from tramp elements

used increasingly in electric furnace steelmaking to dilute the contaminants present in the scrap used in these processes

Midrex Process (Gas-DRI)

charge is fed from top and hot gas (600 to 900 C) is fed from the bottom of furnace

charge passes thru the preheat, reduction, and cooling zones

reducing gas: 95% H2 + CO

SL/RN Process (Coal-DRI)

The charge (1800°F) usually consists of lump ore (or pellets), coal and flux

Reduction brought about by reducing gases generated from hydrocarbons present in the reduction section

product collected at the bottom

Iron MakingIRON MAKING

DIRECT INDIRECT

No melting involved

Solid ore is directly reduced by gaseous reactants

Melting involved

Ore is melted and reduced in this form

DIRECT INDIRECT

Indirect Reduction Processes

The ore is heated above the melting point of iron

e.g. blast furnace

Blast Furnace

Parts of the Blast Furnace

Blast Furnace Charge

Ore - source of iron Coke - fuel and reducing agent Limestone - flux

Placed in Alternating Layers in the Blast Furnace!

Recipe for Pig Iron

To create a ton of pig iron: 2 tons of ore 1 ton of coke half-ton of limestone 5 tons of air. The temperature reaches 1600

degrees C at the core of the blast furnace!

Blast Furnace Operation

charge descends down the shaft blast of air burns coal and partially

melts ore ore reacts with carbon monoxide (CO)

and is reduced to iron lime combines with silicates to form

slag both molten metal (‘pig iron’) and

slag is tapped at the bottom

HOT METAL

Important reactions in the Blast Furnace

C + O 2 CO 2 exothermic - source of heat

CO 2 + C 2CO Boudouard reaction (source of reducing

agent)

Fe2O3 + 3CO 2Fe+ 3CO 2 indirect reduction of the ore

Fe2O3 + 3C 2Fe+ 3CO direct reduction of the ore

Steel Making Processes

Bessemer ProcessSiemens Open Hearth Oxygen Steelmaking Processes Electric Arc Furnace

Stages of Refining

Primary Refining done in the

converter

Secondary Refining done in a

separate station

Principle of Steel Making Processespig iron is cleaned by

reacting oxygen(from air) with impurities!

Done in Converters

oxides are collected in the slag the heat of oxidation raises the

temperature of the mass and keeps it molten during operation

Bessemer Converter

Bessemer Process

bottom blown (air) capacity: 8 to 30 tons of molten iron main source of heat is the heat of

oxidation of impurities difficult to control

Acid or Basic Process?

Acid Bessemer removes Mn and

C only and retains P and S

used when P content is low

uses silica and fireclay as lining

Basic Bessemer removes Mn, C, P

and S

used when P content is high

uses dolomite as lining

Open Hearth Process aka Siemens Process either AOH(acidic) or BOH(basic)

furnaces have a saucer-like hearth capacity : 200 to 600 tons gas or oil fired oxidation is achieved by addition of iron

ore (although oxygen lancing is favored)! Charge working : 6 to 14 hours

Oxygen Processes

LD process (Linz-Donawitz) first oxygen steelmaking process

Basic Oxygen Furnace American version of LD

Kaldo Process tilted and rotating

Oxygen Processes

oxygen is delivered by a lance lance maybe consumable or

nonconsumable (water cooled) produces large amounts of heat

thus ore and scrap maybe added as heat sink

BOF Steel Converter Exposed

Kaldo Process

BOS Process Sequence

Electric Arc Process heat is generated by electric arcs

struck between carbon electrodes and the metal bath

carbon is removed by oxygen lancing oxidising basic slag to remove the

phosphorus second limey slag is used to remove

sulphur and to deoxidise the metal in the furnace.

Secondary Refining

any post steelmaking process performed at a separate station prior to casting

standard for producing high-grade steel

e.g. deoxidation and desulfurization of steel

Secondary Refining Functions

Desulfurization - CaO, Na2CO3 or CaF2

Denitrification and dehydrogenation - vacuum

Deoxidation - Al and Si Decarburization- pure oxygen gas

Desulfurization

Stringer of MnS

Globular MnS

Killing Steel?

during tapping, a large amount of gas (oxygen) is dissolved in the steel

dissolved O2 reacts with C to form CO which results to bubbling action

bubbling maybe ‘killed’ by adding Al or Ferrosilicon (deoxidizers)

Rimmed, Killed and Semi-Killed

Rimmed Steel no deoxidation, a rim of pure Fe occurs

Killed Steel completely deoxidized

Semi-killed Steel compromise between killed and rimmed some dissolved oxygen

Capped Rimmed

SteelSemikilled Steel Killed Steel

Vacuum Degassing ultimate technique to remove

dissolved gases such as N2, H2 and O2

exposing the melt to very low pressures

based on Sievert’s Law

[Cgas]L = K[Pgas]1/2

Vacuum Degassing and Equipment

RH (Ruhrstahl-Hausen) Type LF (Ladle Furnace) Type AOD (argon oxygen

decarburization) Furnace VOD (vacuum oxygen

decarburization) Furnace

Vacuum Degassing

Steel Products

Steel Products

Review Questions

1. Gas-based DRI uses this as a reducing agent:

a) CO2 c) H2O

b) N2 d) CO

2. The product of the direct reduction process is called:

a) pig iron b) sponge ironb) meteoric iron d) blooming iron

3. The Midrex process is a:a) Gas-based DRI c) Indirect processb) Coal-based DRI d) Oxygen

steelmaker

4. A steel with a cross section of 5”x5” is called a:

a) billet c) slabb) bloom d) ingot

Review Questions

Review Questions

5. Vaccum degassing is done to remove excess:

a) carbon c) oxygenb) manganese d) argon

6. This element is not removed in the Acid Bessemer: a) manganese c) phosphorusb) carbon d) all of the above

7. Stainless Steel is created in this refining chamber:

a) Bessemer c) BOFb) AOD d) EAF

8. The following are used as raw materials used in the blast furnace except:a) limestone c) limoniteb) magnetite d) coal

Review Questions

9. This technique for steelmaking uses an oxygen lance to introduce pure oxygen into molten iron:

a) bessemer c) siemensb) open-hearthd) basic oxygen

10. The problem with the product of the Bessemer process is:a) high oxygen c) high sulfurb) high nitrogen d) high phosphorus

Review Questions

The End