Steelmaking is composed of “Basic Oxygen Steelmaking” and “Secondary Steelmaking”. What are they?
WHAT IS WHAT BASIC OXYGEN STEELMAKING?
Basic Oxygen Steelmaking
The purpose of the Basic Oxygen Steelmaking (BOS) is to refine the hot metal produced in the blast furnace into raw liquid steel, which may be subsequently refined in the secondary steelmaking shop.
%C
%Mn
%Si
%P
%S
%O
Temp. / oC
Hot metal
4.7
0.2-0.3
0.2-1.5
0.06-0.12
0.02
0.0
13501400
Steel
0.05
0.1
0.0
0.06
16201720
0.01-0.02 0.01-0.02
History of Steelmaking Bottom blow oxygen steelmaking process (1970s): tuyeres were protected by propane or natural gas, or fueloil
Bessemer (1850): air blowing
Thomas (1879): basic (dolomitic) lining and a basic flux
At Linz and Donawitz in Austria (1879): oxygen blowing
Mixed blowing process (late 1970s): Ar or N2 blowing from bottom
Hot metal dephosphorization in Japan (early 1980s): adding CaO and iron ore mixtures
BOF Facilities
BOF Operation
Oxidation Degree in Steelmaking Iron oxide
De-O
WHAT IS SECONDARY STEELMAKING?
Solubility of Oxygen 0.2 wt% O in liquid
Impurities?
Carbon comes from cokes and refractory Sulfur comes from cokes
Phosphorus comes from iron ore Nitrogen comes from atmosphere
Hydrogen comes from water vapor
Oxygen comes from steelmaking
As the quality of resources decreases, the amount of impurities increases!
Tolerable Maximum Inclusion Sizes and Impurity Elements
(Emi,
Efforts to decrease impurities
(After Sasabe)
Typical Facilities for Secondary Refining
Function of Secondary Refining Process
Process Integration for Clean Steel Production
THERMODYNAMICS OF LIQUID STEEL FOR DEOXIDATION
Chemical Potential of Liquids For pure A Gas o
A
RT ln p A*
*
A (l )
For solutions Gas: A(g)+B(g)
At equlim. A
Ao RT ln p A*
A
Ao RT ln p A
*
Liquid
o
A
RT ln p A
A (l )
Liquid: A(l)+B(l)
A
* A
RT ln
p A
A
A* RT ln a A
*
p A
G A G A RT ln a A *
Activity Solutions Two different types of solutions
ai X i Ideal solutions
ai X i Non-ideal solutions Two different types
Raoult’s law
ai i X i i
1
ai X i Positive deviation
ai i X i i
1
ai X i Negative deviation
ai i X i i
1
Henrian Standard
1 wt% Standard
Mole Fraction vs. wt%
Henrian vs. 1 wt% Standards
For further study, see “Chemical Thermodynamics for Metals and Materials” by Prof. Hae-Geon Lee (1999)
Interaction Coefficients In general
a B f B X B
f B f B f B f B B
C
D
A-B solution
ln f B ln f B B ln f BC ln f BD
f B f
B B
Taylor-series
A-B-C solution
ln f B X B X
B C f B f B f B
ln f B X B
B
A-B-C-D solution
ln f C X C X C X 0
C
ln f D X D X D X 0
D 0
j
i
f B f B f B f B B
C
D
ln f i X j
X 0 j
ln f B B B X B BC X C B D X D
Interaction Coeff. for 1 wt% Std. log f B e B B ( wt % B ) e BC ( wt %C ) e BD ( wt % D) B
A
B A
e B A
B e A
M A M B
A
e B
M S
230.3 M B
B
A
where A, B: solutes, S: solvent
For further study, see “Steelmaking Data Sourcebook” by JSPS 19 th committee on Steelmaking (1984) & “Fundamentals of Steelmaking Metallurgy” by Brahma Deo & Rob Boom (1993)
Oxygen in Steel (Case Study) Fe(l) + O = FeO(s) 2Al + 3O = Al2O3(s)
K= K=
aFeO hO aFe aAl2O3 hAl 2 hO 3
At a given temperature and for known slag activity data, the value of hO can be calculated. From the activity of Al2O3, the value of hAl can be calculaed. Log hAl = log[wt%Al] + eAlAl [wt%Al] + eAlC [wt%C] + eAlO [wt%O] Log hO = log[wt%O] + eOAl [wt%Al] + eOC [wt%C] + eOO [wt%O]
For a fixed value of [wt%C], it is possible to solve [wt%Al] and [wt%O].
Deoxidation Equilibrium
THERMODYNAMICS OF SLAG FOR STEEL REFINING
Classification of Oxides
Acid Oxide: Silicate
(Karpoor & Frohberg, 1970)
How to Change the Silicate Structure?
(Waseda, 1980)
Addition of Basic Oxide
Basicity, Activity of Oxygen Ion B = log aO2-
Capacity Concept
Carbonate capacity (Wagner) CO2 O 2 CO32 C CO 2 3
K aO 2 f CO 2
(mass%CO32 ) pCO2
3
BCarbon
C CO 2 3
* C CO 2 3
Carbonate capacity in a reference slag
Sulfide Capacity 1 2
C S 2
S 2 O
K aO 2 f S 2
2
1
S 2 O2 2
pO 2 (mass% S ) pS
BSulfur
2
2
C S 2 C S * 2
1/ 2
INCLUSIONS
Investigation of Inclusions
Origin & Cause of Macro Inclusions
Small spherical inclusion
Octahedral inclusion
Small polyhedral inclusion
Large polyhedral inclusion
a ter Dekkers 2002
Plate like inclusion
Dendrite
Cluster
Aggregate
a ter Dekkers 2002
Formation of dendrite tips during secondary metaluurgy
