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Thermodynamics of SteelmakingAn Introduction

Prof. Joonho Lee, Korea University

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8/13/2019 Lecture 120310 Steel 01 Thermodynamics-Of-Steelmaking JHLEE

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What is Steelmaking? Steelmaking is composed of

“Basic Oxygen Steelmaking” and“Secondary Steelmaking”.

What are they?

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 WHAT IS

BASIC OXYGENSTEELMAKING?

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Basic Oxygen Steelmaking The purpose of the Basic Oxygen Steelmaking

(BOS) is to refine the hot metal produced inthe blast furnace into raw liquid steel, which

may be subsequently refined in the secondary

steelmaking shop.

%C %Mn %Si %P %S %OTemp.

/ oC

Hot

metal4.7 0.2-0.3 0.2-1.5 0.06-0.12 0.02 0.0

1350-

1400

Steel 0.05 0.1 0.0 0.01-0.02 0.01-0.02 0.061620-

1720

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History of Steelmaking

Bessemer (1850):air blowing

Thomas (1879):basic (dolomitic)

lining and a basic

flux

At Linz and Donawitz

in Austria (1879):

oxygen blowing

Bottom blow oxygen

steelmaking process

(1970s): tuyeres wereprotected by propane

or natural gas, or fuel-

oil

Mixed blowing process

(late 1970s): Ar or N2

blowing from bottom

Hot metal

dephosphorization in

 Japan (early 1980s):

adding CaO and iron

ore mixtures

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BOF Facilities

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BOF Operation

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Oxidation Degree in Steelmaking

Iron oxide

De-O

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 WHAT IS

SECONDARYSTEELMAKING?

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Solubility of Oxygen0.2 wt% O in liquid

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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!

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Tolerable Maximum Inclusion Sizes

and Impurity Elements

(Emi,

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Efforts to decrease impurities

(After Sasabe)

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Typical Facilities for Secondary Refining

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Function of Secondary Refining

Process

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Process Integration for Clean Steel

Production

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THERMODYNAMICS OF

LIQUID STEEL FORDEOXIDATION

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Activity

ii   X a     ii   X a  

iii   X a        ii   X a  

1i  

iii   X a     

1i  

iii   X a     

1i  

ii   X a  

Solutions

Two different types of solutions

Ideal solutions Non-ideal solutions

Two different typesRaoult’s law

Positive deviation Negative deviation

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Henrian Standard

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1 wt% Standard

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Mole Fraction vs. wt%

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Henrian vs. 1 wt% Standards

For further study, see “Chemical Thermodynamics for Metals and Materials” by

Prof. Hae-Geon Lee (1999)

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Interaction Coefficients

 B B B

  X  f a  

A-B solution

 B

 B B   f  f   

A-B-C solution

C 

 B

 B

 B B   f  f  f   

A-B-C-D solution

 D

 B

C 

 B

 B

 B B   f  f  f  f   

 D

 B

C 

 B

 B

 B B   f  f  f  f   

In general

  D

 B

C 

 B

 B

 B B   f  f  f  f    lnlnlnln

Taylor-series

 

  

 

 

  

 

 

  

 

  000

lnlnlnln

 DC  B   X  D

 D D

 X C 

C C 

 X  B

 B B B

 X 

 f  X 

 X 

 f  X 

 X 

 f  X  f 

  D

 D

 BC 

C 

 B B

 B

 B B   X  X  X  f       ln

0

ln

 

 

 

 

 j X  j

i j

i X 

 f  

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Interaction Coeff. for 1 wt% Std.

  )%()%()%(log   Dwt eC wt e Bwt e f   D

 B

C 

 B

 B

 B B

 A

 B

 B

 A       

 A

 B

 B

 A B

 A   e M 

 M 

e  

 B

 A

 B

S  B

 A

 M 

 M e    

3.230

where A, B: solutes, S: solvent

For further study, see “Steelmaking Data Sourcebook” by JSPS 19th committee on

Steelmaking (1984) & “Fundamentals of Steelmaking Metallurgy” by Brahma

Deo & Rob Boom (1993)

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Oxygen in Steel (Case Study)Fe(l) + O = FeO(s)

2Al + 3O = Al2O3(s)

K =aFeO

hO aFe

K =a

Al2O3

hAl2 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] + eAl

C [wt%C] + eAlO [wt%O]

Log hO = log[wt%O] + eOAl [wt%Al] + eO

C [wt%C] + eOO [wt%O]

For a fixed value of [wt%C], it is possible to solve [wt%Al] and [wt%O].

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Deoxidation Equilibrium

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THERMODYNAMICS OF

SLAG FOR STEELREFINING

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Classification of Oxides

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Acid Oxide: Silicate

(Karpoor & Frohberg, 1970)

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How to Change the Silicate Structure?

(Waseda, 1980)

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Addition of Basic Oxide

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Basicity, Activity of Oxygen Ion

B = log aO2-

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Capacity Concept Carbonate capacity (Wagner)

  2322   COOCO

223

2

23

)%(   2

3

COCO

O

CO  p

COmass

 f 

aK C 

*23

23

CO

CO

CarbonC 

C  B

Carbonate capacity in a reference slag

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Sulfide Capacity

2

22

2 2

1

2

1

OS OS   

 

2/1

2

2

2

2

2

2   )%(  

 

 

 

 

S 

O

S 

O

S   p

 p

S mass f 

aK 

C 

*2

2

S 

S 

Sulfur 

C 

C  B

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INCLUSIONS

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Investigation of Inclusions

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Origin & Cause of Macro Inclusions

Small spherical inclusion Octahedral inclusion

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Small spherical inclusion Octahedral inclusion

Small polyhedral inclusion Large polyhedral inclusion

a ter Dekkers 2002

Plate like inclusion Dendrite

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Plate like inclusion

Cluster Aggregate

a ter Dekkers 2002

Formation of dendrite tips during secondary metaluurgy Overgrowth during secondary metallurgy

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Formation of dendrite tips during secondary metaluurgy Overgrowth during secondary metallurgy

Cluster from tundish Cluster from clogging materials

a ter Dekkers 2002

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Morphology of Alumina Inclusions

after Dekkers, 2002

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Tundish Configuration

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SEN(Submerged

Entry Nozzle)

      M

    o    u      l      d

Tundish

Mould FluxLiquid Slag

SEN Clogging

(Building up of

Inclusions)

Alumina Inclusions

Nozzle Clogging

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Alumina Inclusions at SEN

after Dekkers, 2002

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Clustering of Alumina Inclusions

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Steel Evolution Never Stop!

Fig. History of the development of cold rolled deep drawing steel sheet (after Emi)

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Concluding Remarks

Crystal growth & Solidification theory

Mechanism of materials at high temp.

Physical Properties (statistical mechanism)

Thermodynamics (statistical thermodynamics)

Reaction kinetics

Heat and mass transferFluid dynamics

Smelting and refining

technology

Phys. & math. Modeling

Computer simulation

Casting & solidification

technology

 JFE 21st Foundation