Stainless steel ?

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?????? ?? ?? 2002. 7 ??? ????? ????? ???? ? ??
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Stainless steel ?
- ??? ??? ?? Cr??? 13?? ??? ??? -
13??Cr ??? ??? ?? Cr2O3? ??? ??(1030Å) ?? -
???, ??? ? ??? ?? Ni, Mo, N, Ti, Cu? ??? ????
?????? ?? ???
- ?? ??? ?? (?? ???? ??) - ??? ??(?, ??, ???) ??? ??? ?? ?? - ??? ??? ?? (?? ???? ??) - ?? ???? ????
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??????? ??
Austenite? Ferrite? Martensite?
?? ? ?? Austenite? Ferrite? Martensite? (??Ferrite?)
??? ??? ???? ???? ??? (??Mar.?? Ms?300? Mf?100150?)
??? ?? ?? ??
?? ???? ?? ???? ?? ?? ?? ??? ??? ?? ??? ?? ???? ??? ????? ??

• Duplex? Austenite? Ferrite? 2?? ??? ??????
  ???
• ? ?? ??

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?????? ?? ??
?? ?? ?? ?? ???? ???? ?? ?? ??
200? Cr-Ni-Mn? Austenite? 201 17Cr-4Ni-6Mn-N ??, ??? ???
300? Cr-Ni? Austenite? 304 18Cr-8Ni ??, ??? ??,??
300? Cr-Ni? Duplex? 329J1 22Cr-5Ni-3Mo ???,??? ??, ??
400? Cr? Ferrite? 430 18Cr ??, ??? ??, ??
400? Cr? Martensite? 410 13Cr ????? Knife
600? Cr-Ni? ????? 630 17Cr-4Ni-4Cu,Nb ???, ??? ??, ??
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?????? ?? ??
?? ?? ( KS ) ?? (JIS) ??(AISI/ASTM) -STS STainless Steel -SUS Special Use for Stainless -304LAISI??? ?? ??? 3?? ?? ? ?? ?? ?? ??
?) STS304L SYS304L 304L -STS STainless Steel -SUS Special Use for Stainless -304LAISI??? ?? ??? 3?? ?? ? ?? ?? ?? ??
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• 1. ???
• ?? ??
• 2. ???
• ?? ??? ?? ??
• ?? ??

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Peculiarities in the production of steel compared
with process metallurgy of non-alloyed and
low-alloyed steels
Stainless steels
Non-alloyed steels
thermodynamic equilibria in the system
thermodynamic equilibria in the system
Fe - C - O
Fe - C - Cr - (Ni) - O
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• Activity
• Chemical strength of elements
• The activity is dependent on the concentration of
  the elements and is influenced by other elements

Effect of Cr on activity coefficients
C O S N
Cr -0.114 -0.16 -0.17 -0.182
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Equilibria in the Fe-C-Cr-O system
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Cr fO
0 0.596
5 0.354
10 0.211
15 0.126
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Activity coefficient and their products for
carbon steel and stainless steel
Alloy fO fC fO x fC
Carbon steel(0.1C) 0.97 1.05 1.02
17Cr steel(0.1) 0.2 0.41 0.08
18Cr-10Ni steel(0.1C) 0.2 0.51 0.1
- Indicates the intensity of decarburization
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Decarburization rates of various refining
processes
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Carbon-Oxygen equilibrium for steels with 18Cr
at 1700 oC
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Oxidation period
Basic reaction C O CO

2Cr 3O (Cr2O3)
p partial pressure a activity
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Reaction for refining Cr alloyed melts
C O CO 2Cr
3O (Cr2O3) (Cr2O3) 3C 2Cr
3CO 1og K - 40,990/T 25.83
Reaction can be moved to the right -
in the case of increased carbon activity -
in the case of low chromium activity -
when the CO - partial pressure is reduced
- and when temperature is increased
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Decarburization Model
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Metallurgical requirements relating to
the process technology of refining Cr
melts derived from the thermodynamics
- decreasing CO partial pressure - increasing
temperature (restricted by the lining life)
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Kinetics
Kinetics are influenced by the transport
procedures - diffusion
- flows - material
transfers
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• The reaction rate is the characteristic value of
  the kinetics
• Reaction rate Changes in the
  concentration of component I with time

• Rates of reactions

- Reaction of 0th order - Reaction of 1st
order
b bulk s surface
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Decarburization of stainless steel may be
distinguished in 3 sections
1) starting phase (1) setting of the transport
flows
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2) linear decline (2) the decarburization
speed is independent
of C-content . Reaction of the
0th order
3) run out phase (3) the decarburization speed
is dependent of
C-content . Reaction of the 1st order
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Critical C concentration - C - content at
the point of transition from linear decline to
run out phase - C - content at the point
of transition from carbon oxidation to Cr
oxidation 1) Linear decline
Decarburization rate determined by oxygen in put
(Vc gt V0) 2)
Run out phase Decarburization rate
determined by oxygen in put
(Vc lt V0)
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De-C rate in AOD and VOD operation as a function
of the carbon content and blowing rate of
refining gas.
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Requirements relating to process technology of
refining Cr-melts derived from the kinetics -
increasing reactions interface - increasing
the distance from the C equilibrium value
(concentration gradient) - high O2 supply
during the linear decline
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Reduction of Cr oxide
Thermodynamics (Si deoxidation)
2(Cr2O3) 3Si 4Cr 3(SiO2)
Requirements
- high Si activity - decreasing SiO2
activity by increasing the slag basicity
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Oxygen equilibrium levels in the production of
an 18Cr stainless steel
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Activity of SiO2 in the CaO-SiO2-CaF2 slag at
1450 oC
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Effect of slag basicity on the oxygen content in
molten steel
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Effect of Si content in steel melt on the
chromium content in molten slag
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Effect of slag basicity on the chromium content
in molten slag.
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Desulphurization
Thermodynamics
S (CaO) (CaS) O
Requirements
- high CaO activity, i.e. higher basicity
degree CaO/SiO2 of the slag - low CaS
activity (large amount of slag or slag
change) - low oxygen activity (controlled
via the reduction agents e.g. silicon)
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Sulfur distribution ratio as a function of Si
content in molten steel
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Desulfurization efficiency as a function of slag
basicity
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• KINETICS
• Reduction Period ? bath slag reactions
• In the case of high slag viscosities, material
  transport can become rate determining in the
  slag.
• For this case, a rate constant is defined for the
  Cr2O3 reduction.

s start f final
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• Requirements
• -Improving the liquidity of the slag
• (with fluor spar)

• Kinetics of desulphurization under reducing
  conditions
• Material transition is controlled by the phase
  boundary reaction
• Si, Mn, Ti and Al increase the speed of
  desulphurization

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?? ??
½ N2 N
Log K - 518/T-1.063 ? ?? ??? ?? ?? ??? ??
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Activity coefficient of nitrogen in liquid binary
iron alloys at 1600 oC.
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Effect of alloying elements on solubility of
nitrogen at 1 atm pressure in liquid binary iron
alloys at 1600 oC
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?????
By J. Chipman D. A. Corrigan
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Effect of Cr on nitrogen solubility in STS304
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?? ??

• AOD??? ??? Purge gas(Ar, Co??)?
• ?? ??
• - ?? ?? ?? ?? ??
• . ???? , ?? ?? ??
• - ??? ?? ?? ??

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Nitrogen changes during refining process
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Effect of initial carbon on nitrogen content in
AOD converter
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Effect of initial carbon on minimum nitrogen
content in AOD converter
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??????? ??? ??
???? ??? (Process Gas Processes) ?? ??? (Vacuum Processes)
??? ?????? ????? ??? ??? ???? ???? CO??? ?? ????? Cr? ?? ?? ? ?? ?? ????? ???? ?? ??? ?? ????? ???? ? ?? ?????? ??? 70 ?? ?? Cr ??? ???? ????? ??? ?? CO??? ??? ????? ??? ??? ?? ?? Ladle?? ??? ????? ?? ?? ??? ?? ?? ??? ????? ?? ?? ?? AOD?? ?? ???? ???? ? ? C, N? ??? ??
AOD (Argon Oxygen Decarburization) ASM (Argon Secondary Metallurgy) MRP (Metal Refining Process) -AOD-L (Argon Oxygen decarburization- Lance) K-BOP (Kawasaki-Basic Oxygen Process) - VOD (Vacuum Oxygen Decarburization) - VOD-K (Vacuum Oxygen Decarburization Converter) - VCR(Vacuum Converter Refining)
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Processing for refining high-Cr melts
AOD
ASM
MRP
AOD-L
K-BOP
VODK
VOD
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Summary
Knowledge of thermodynamics and kinetics are
needed in the Stainless steel refining - Large
interface for reactions by combined-blowing
process . high decarburization speed ?
charge carbon content can vary over wide range
? use of ferrous alloys with high carbon
content - Good adjustment of the required CO
partial pressure by Ar / O2 - process gas
? low Cr - oxidation ? low Si - consumption
for reduction
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- Use of lime-fluorspar slags with high CaO
activity during reduction ? combined
reduction and desulphurization ? lower oxygen
and sulphur contents may be set quickly
and with high accuracy ? high lining life
? high yield of expensive alloy elements
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??????? ????
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???? ? ?? ??
? ? ?? ?? ?? ?? ? ?? ?? ? ?
??? ??? ? ? LD ?? ?? ?? ?, ?? ??? TANDEM?? (????)
STS? SCRAP CHROME NICKEL ALLOYS ? ? ? AOD VOD ?? ?? ? ??? ??? ? ?? Z-MILL?? (REVERSING ??)
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Posco- Pohang works
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NSC-Yawata works
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KSC-Chiba works
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???(Electric Arc Furnace) ??
? ? ? ? ? ?
?? ? ??? ? ???? ??? 3? ??? ?? ???? Arc?? ?? ????
???? ? 1? Scrap??(60)? Melting?2? Scrap??(40)?Melting?Heatng Slag making ? Tapping ? ????? ??? ?????? ???? (C, Si ??? ??) ? ?? ? Fe-Si???? Cr?? ???? ?? .??? ???? .?????? ??,???? .Slag???? ??? ??,Foaming .Cr???? Slag? Cr oxide ??
???? ??(Kwh/T), O2(Nm3/T), ???(Kg/T)
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AOD??
? ? ? ? ? ?
?? ? Ar, N2? ?? ?????? ??? ?? ???? ?? CO?? ??? ??? ??? Cr??? ???? ??
???? ? ??? ? ????? ?? ? ?? ???? ?? ? ??? ???? Cr???? ? ???? ??? ??? ???? ?? CO??? ????? ??? ?? ??? ???? ? ?? ?? ? ??(Si??Al) ? ?? ?? ???? ??? ?? ???
???? Ar, N2, O2, lime, Si (??Nm3,kg/T-S)
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VOD??
? ? ? ? ? ?
?? ? ?????? ??? ???? ??,??? ????? ???? ?? 2?????? AOD?? ??,??? ? ?? ? Cr-????-??C,N? ?? 1 mbar
???? ? VOD(O2 Blowing??)??? ?????, ??? ?? ? VOD??? ????/Lance??/???/Ar?? ?? ???? ?? ?? ??? ? ?? ?? ? ?? ( Si ??Al ) ? ?? ??
CN 409L(11Cr) 436LT(18Cr) 446M(26Cr) 120ppm 150ppm 170ppm KSC 26Cr 100ppm