Materials engineering
Iron and steel
making
Metals: rarely exist in pure state  mostly in ores
Ore: Metallic and other compounds,
mostly oxides
Metallic content:
Iron ores:
Copper ores:
Molybdenum:
30-70% Fe
0.1-0.8 % Cu
0.01-0.1% Mo
4 basic way to gain the metallic parts from ore:
Reduction by carbon
Electrolytic way
Metallotermical process
Dissociation
costs
1) Reduction by carbon
MeO + C  Me + CO
FeO + C  [Fe] + {CO}
molten metals
2) Electrolytic way
gas
Al2O3  Al23+ + 3O2on the cathode: Al3+ + 3e-  Al
3) Metallothermical process
TilCl4 + 2Mg [Ti] + 2MgCl
4) Dissociation
MeX  [Me] + [x]
only at high energy level
Iron and steel
Iron and steel making
Blast furnace
Foundry
Steel making
plant
Foundry
Production of molten steel
Iron producing processes
Purpose:
ore types:
Iron ore  Pig Iron
Fe3O4 magnetite
Fe2O3 hematite
FeCO3 siderite
+ tailings:
~70% Fe
~70% Fe
~50% Fe
silicates, sand, other non ferrous
MnO, Al2O3, P2O5, etc
Concentration of ore
cost
cost of pig iron
cost of concentrating
cost of blast
furnace
30 ~ 70 %
Fe % in ore
magnetite
Blast Furnace Plant
Blast Furnace Plant
Tasks
1) Reduction of the ore
2) Extraction of tailings
3) Melting  separation of the molten iron from the
molten tailings (spec. weight difference)
Charge:
Ore + Coke + Limestone
Dimension of the BF:
Diameter: 4-10 m
Height:
25-30 m
Volume:
300 – 5000 m3
For 1000 t of iron:
2000 t ore +
800 t coke +
500 t limestone +
~ 4000t hot air
Processes in blast furnace
Charge moves down (6-8 hours)
-
Preheating by gas:
coke burns more efficient
Formation of CO
CO reacts with iron ore
Coke reduces CO2 in the gas
C + CO2  2CO
CO reduces the surface of the iron ore.
Indirect reduction
FeO + CO  Fe + CO2
Slag producing by limestone.
CaCO3  CaO + CO2
MgCO3  MgO + CO2
In the bosh the coke burns
C + O2  CO2 + Heat
The coke reduces the molten ore.
Direct reduction
FeO + C  Fe + CO
Molten limestone + other slag components produce eutectic slag
Slag floats over molten iron
Processes in blast furnace – thermodynamics
C+O2CO2
•
Gibbs free energy
•
Reduction of FeO from
690 °C
Processes in blast furnace
Carbon reduces the oxides:
FeO + C  Fe + CO
MnO + C  Mn + CO
SiO2 + 2C  Si + 2CO
alloying elements
P2O5 + 5C  2P + 5CO
SO2 + 2C  S + 2CO
impurities
in molten iron
In BF carbon can reduce
gas
S, P, Cr, Mn, Si
and Ti
70-90%
10-20%
Sulfur and phosphorous are harmful in pig iron, and they must be
removed.
Processes in blast furnace
Desulfurization
FeS + CaO  FeO + CaS
in molten iron
in molten slag
Dephosphorization
P2O5 + 5FeO + 5C + 4 CaO  CaO4P2O5 + 5Fe + 5CO
in molten iron
in molten slag
in molten iron
Result: pig iron
gas
Product of blast furnace
At the bottom of the BF:
Slag on the top
Molten iron on the bottom with~4% C
Near to eutectic composition
Taping at different heights:
different composition different
purpose
C%
Mn%
Si%
S%
P%
for casting
3-4
<1
<4
< 0.1
< 0.1
for steel with Bessemer method
3-4
0.4 – 1
~3
< 0.1
< 0.1
for steel with Thomas method
3-4
0.4 – 1
~2
< 0.1
< 0.1
for steel with Siemens-Martin
method
3-4
0.4 – 1
~1
< 0.1
< 0.1
Product of blast furnace
Taping:
http://www.youtube.com/watch?v=QBLRIEZZEsU
Product of blast furnace
Metallurgy
http://www.youtube.com/watch?v=kPH4dJUVOfc
Steel making
Purpose
Pig iron  steel by fire – refining treatments that
decrease the C content and impurities.
Main steps
1) Charging
2) Oxidation
decreasing C content
3) Increasing temp.
with decreasing C% the Tmelt increases !
4) Deoxidation
decrease FeO and O in molten steel
5) Alloying
6) Casting, solidification
casting of ingots or
continuous casting of bars and billets
Steel making
Processes
 Siemens Martin (open hearth furnace)
 Bessemer converter process
 Thomas converter process
 Oxygen converter process (Linz-Donawitz process - LD)
 Electric arc steel furnace
Siemens Martin process (1864)
Charging
pig iron+scrap
pig iron + ore
Capacity
10-900 t
6-12 h
Too expensive
carbon
0,3 %/hour
burns out
Siemens Martin process (1864)
Bessemer process (1856)
Charging
molten iron
1210-1250ºC
~3% Si
Capacity
5-60 t
15-20 min
First converter method
No external heat
Acidic lining (slag
react.)
Si + O2  SiO2
from the air
Bessemer process (1856)
During the blow C, Si, Mn % decreases.
%
ºC
1700ºC
1250ºC
C
4%
3%
O
Si
Mn
1%
N
blowing time
15 min.
Thomas converter process (1878)
Charging
molten iron
1210-1250ºC
~2% P
No external heat
Similar to Bessemer, but basic lining for slag reaction.
4 P +5 O2  2 P2O5
from the air
Oxygen-converter process (LD)
Charging
molten iron
~3% C
~0.5% Mn
~1% Si
~0.1% P, S
Capacity
15-400 t
No external heat
To avoid overheating when blowing iron ore or scrap are changed.
Limestone is changed for desulfurization & dephosphorization.
Variants of Oxygen-converter process
OLP process
oxygen – limestone – powder
oxygen & CaO powder is blown through the lance
AOD process
argon – oxygen – decarbonizing
oxygen & argon is blown through the lance
Mixed gas system  decreased partial pressure of oxygen
 C% decreases
up to 0.002% C
e.g. for stainless steels
Electric Arc Steel Furnace
Charging
scrap + solid pig iron
~3% C
~0.5% Mn
~1% Si
~0.1% P, S
Capacity
5-200 t
For high grade steels
T > 2500ºC
intensive reaction, N2 dissociation
Electric Arc Steel Furnace
http://www.youtube.com/watch?v=nolpiat6Sk0
Charging scrap
Electric Arc Steel Furnace
http://www.youtube.com/watch?v=G6Uxh-xtU-g
during work
Electric Arc Steel Furnace
http://www.youtube.com/watch?v=3gg9_zTlg4M
Electrode in the furnace
Steel making - oxidization
Purpose
decrease C% and oxidize the impurities (S, P)
In open hearth and electric arc furnace
C + FeO  Fe + CO
from scrap
or iron ore
turbulence in the charge
In air or oxygene blowing converters
2C + O2  2CO
from blowing
air
The dissolved oxygen content
increases
Hamilton’s law
At the given temperature [C][O]=constant
O%
Stainless steels oxidization
requires vacuum
C < 0.02%
O < 0.01%
0.1
0.01
p=1bar
0.001
0.0001
p=1mbar
0.01
0.1
1
C%
The law of distribution and mass action
The law of distribution
At a given temperature the ratio of the amount of a given compound
In the molten iron and in the molten slag is constant.
𝐿(𝑇) =
𝐹𝑒𝑆𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔
𝐹𝑒𝑆𝑖𝑛 𝑡ℎ𝑒 𝑖𝑟𝑜𝑛
The law of mass action
Determines the direction of the reaction
mA + nB
v1=k1(CAB)p
v1
v2
pAB
V2=k2(CA)m(CB)n
At equilibrium v1=v2
Effect of nonmetallic elements S, P, O, N
Effect of sulfur
FeS at grain boundaries
S does not dissolve, forms FeS eutectic with iron.
grain
T
Crystallization at the grain
boundaries.
Cold and hot brittleness
1600
1000
FeS %
0%
To reduce the effect:
1) Alloy with Mn
FeS + Mn  MnS + Fe
MnS is formable at
high temperature
~80%
desulfurization
2) Increase S content
generally S < 0.035%
100%
Effect of nonmetallic elements S, P, O, N
Effect of sulfur - desulfurization
𝐿=
𝐾=
𝐹𝑒𝑂𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔
𝐹𝑒𝑂𝑖𝑛 𝑡ℎ𝑒 𝑖𝑟𝑜𝑛
increases with temperature
𝐶𝑎𝑆𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔 ∙ 𝐹𝑒𝑂𝑖𝑛 𝑡ℎ𝑒 𝑖𝑟𝑜𝑛
𝐶𝑎𝑆𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔 ∙ 𝐹𝑒𝑂𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔
=
𝐹𝑒𝑆𝑖𝑛 𝑡ℎ𝑒 𝑖𝑟𝑜𝑛 ∙ 𝐶𝑎𝑂𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔 𝐹𝑒𝑆𝑖𝑛 𝑡ℎ𝑒 𝑖𝑟𝑜𝑛 ∙ 𝐶𝑎𝑂𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔 ∙ 𝐿
𝐹𝑒𝑆𝑖𝑛 𝑡ℎ𝑒 𝑖𝑟𝑜𝑛 =
𝐶𝑎𝑆𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔 ∙ 𝐹𝑒𝑂𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔
𝐾 ∙ 𝐶𝑎𝑂𝑖𝑛 𝑡ℎ𝑒 𝑠𝑙𝑎𝑔 ∙ 𝐿
To achieve low S%
• increase L : increase the temperature.
• increase CaO content in the slag
• increase CaS content in the slag
• increase FeO content in the slag
The slag must be
changed
Effect of nonmetallic elements S, P, O, N
Effect of nitrogen
nitride compounds precipitation
and/or the solidification of nitrogen in
interstitial solid solution.
 Increases strength decreases
toughness.
 Ageing
Effect of nonmetallic elements S, P, O, N
Effect of phosphorous
T
Keep P content under 0.035%
(0.001%)
γ
α
1000
1.2%
Rm
Rp02
Z
Impact energy
15%
Rm
Rp02
Z
TTKV
TTKV
P% ↑
T
P [%]
Effect of nonmetallic elements S, P, O, N
Effect of phosphorous - dephosphorization
2 P + 5 FeO + 4 CaO  (CaO4 · P2O5) + Fe
in molten iron
in molten slag
in molten iron
Dissolves only in slag
[𝐶𝑎𝑂4 · 𝑃2𝑂5] ∙ [𝐹𝑒] 5
𝐾=
𝑃 2 𝐹𝑒𝑂 5[𝐶𝑎𝑂]4
[𝑃] =
[𝐶𝑎𝑂4 · 𝑃2𝑂5] ∙ [𝐹𝑒]5
𝐾 𝐹𝑒𝑂 5[𝐶𝑎𝑂]4
To achieve low P%
• decrease the temperature.
• increase CaO content in the slag
• increase phosphate content in the slag
• increase FeO content in the slag
The slag must be
changed
Effect of nonmetallic elements S, P, O, N
stress
Effect of oxygen
after long service period
after forming
In form of O or FeO.
Ageing
initial state
strain
Work done till fracture
Impact energy
To reduce the effect:
deoxidation
Methods:
 Settling
TTKV
TTKV
O% ↑
T
Brittel-to-ductile transition temperature
 Diffusional deox.
 Synthetic slag
 Ladle metallurgy
Effect of nonmetallic elements S, P, O, N
Effect of oxigene
Rm
Z
Rm
Z
O [%]
Deoxidation: settling
Deoxidizing elements are loaded into the molten steel.
General reaction:
FeO + Me  MeO + Fe
The amount of deoxidizing elements are limited by their
disadvantageous effect on the properties:
Mn
< 1%
causes grain coarsening & brittleness
Si
< 0.5 % it decreases the toughness.
V
Ti
Al
< 0.1 % they decreases the toughness.
Deoxidation: settling
Effect of deoxidizing element on the dissolved oxygen
O [%]
Mn
0.1
Si
0.01
C
V
0.001
Al
Ti
0.0001
Zr
Me [%]
0.01
0.1
1
Deoxidation: settling
Rimmed steel
Deoxidizing with Mn only
susceptible on ageing
Semi-killed steel
Deoxidizing with Mn + Al
for continuous casting
Killed steel
Deoxidizing with Mn + Si
lower TTKV than rimmed steel
Dead killed steel
Deoxidizing with Mn + Si + Al/V/Ti/Zr
best quality from the point of brittleness
Deoxidation: diffusional and synthetic slag meth.
Diffusional method
Deoxidizing element loaded on the top of the molten
slag. Diffusion of O to slag.
Diffusional synthetic slag method
The molten steel is poured on the top of prepared
FeO-free slag.
molten steel
FeO free slag
Deoxidation: ladle metallurgy
Ladle metallurgy
Powder injection
deoxidizing, desulfurizing, and dephosphorising
powder with Ar gas are blown into the molten
steel.
-
Inclusions are lifting to
the slag.
Almost isotropic
molten steel
This technology with the converter method is the most up-to-date steel
making process
Vacuum handling
A process for deoxidation and degasification
The effect of vacuum on steel
1) Decreasing the partial pressure of the gas above the
molten steel
2) Decrease the content of oxygen.
3) Increase the vaporization rate of low melting point
metals (Zn, Pn, Sn, As)
4) Separates the compounds by dissociation.
~10-6 bar
~10-9 bar
Fe4N
FeO
SiO2
CrN
AlN
Al2O3
TiN
10-12-15 bar
Practically
impossible
Vacuum handling
Two type of process
Vacuum chamber
Steel stream
ladle
Degasificated
steel
Vacuum ladle degassing
Vacuum stream degassing
Vacuum
Molten steel
Effect of dissolved gases on steel
CO
-
in the rimmed steel produces gas bubbles
O2
-
produces gas inclusions and oxide and silicate
inclusions
N2
-
increase the ability for aging and nitride inclusions
H2
-
flocking – H2 bubbles  cracking
Effect of dissolved gases on steel
Tmelting
flocking – H2 bubbles
reason
A4
[H]
[H]
A3
Temp
A3
A4
Tmelting
Effect of dissolved gases on steel
H2 – solution
let the gas atoms depart by diffusion
• slow cooling after casting (several days)
• forging by very soft deformation to make cohesion between
the surfaces of the cracks
+ for N make stable nitrides my mircoalloying elements
Al, V, Ti
 AlN, VN …
Alloying, casting
Alloying
Can only take place after a perfect deoxidation, otherwise
alloying elements would burn.
Casting
Two types:
casting of ingots
continuous casting
Casting of ingots
• simple
• High productivity
• More homogeneous
• slow
Casting of ingots
Solidification process for ingots
- Shrinking effect
- Crystallisation, grain-arrangement, mircostructure
- Segregation
Casting of ingots
Shrinking effect
the top 12-15% of the total weight of killed
steel ingot must be cut off (rimmed steel only
3-5%)
Casting of ingots
Crystallisation, grain-arrangement, mircostructure
R – rate of crystall growing
R
N
N – number of
crystal nuclei
ΔT
Supercooling –
under the
equilibrium
Casting of ingots
Segregation – normal segregation
During the solidification the liquid phase becomes enriched
with alloying elements and impurities.
The difference can be
300% for S
P% 500-600% for P
T
R – rate of crystall growing
S%
C%
Concentration of the
liquid phase
cross section of the ingot
B [%]
Casting of ingots
dendrite
Segregation – inverse segregation
Because shrinkage the alloying elements
and impurities can move inwards between
dendrites.
liquid
phase
The impuritiy concentration is higher
between the dendrites’ arm.
Concentration %
Casting of ingots
Microstricture and segragation in ingot
http://www.substech.com/
Casting of ingots
Continuous casting
Continuous casting
• https://www.youtube.com/watch?v=d72gc6I-_E
Steel refining methods
All of these methods have a remelting and solidification period to:
- Decrease the dissolved gas content and the amount of inclusions
- Produce a homogeneous fine grained crystal structure
- Produce a homogeneous distribution of alloying elements
Used for
- tool steels
- high alloy steels
Steel refining methods
Vacuum arc remelting process
 Removal of dissolved gases, such
as hydrogen, nitrogen and CO;
 Reduction of undesired trace
elements with high vapor pressure;
 Improvement of oxide cleanliness;
 Achievement of directional
solidification of the ingot from
bottom to top, thus avoiding
macro-segregation and reducing
micro-segregation.
Steel refining methods
Vacuum induction remelting process
 Removal of undesired trace elements with high vapor pressures
 Removal of dissolved gases (hydrogen and nitrogen)
Steel refining methods
Electroslag remelting process
Similar technology:
electron beam
remelting process