steel making presentation
TRANSCRIPT
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