An idea of thermodynamics for casting hyper-peritectic steel grades for cotinuous casting cotinuous casting Begoña SantillanaDémian Ruvalcaba Jimenez
From raw materials to steel…
Iron ore
Coal Coke
Blast
furnaceBOS
Converters
Hot metal & scrap
Hot metal Hot metal “liquid”“liquid”
Steel “liquid”Steel “liquid”
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Ladle
treatment
Continuous
castersLadle tapping
Continuous caster
Ladles
Turret
3
Tundish
Mould
Secondary cooling
Oxy cutters / pendulum shear
Background
• Steel producers are looking for new products with high added value
• Some of these products have compositions in the hyper peritectic range
• Traditionally, steels with a composition around the peritectic point are difficult to cast ….
• The idea is to cast “alloying out of the peritectic”.
• A medium carbon grade is actually cast in IJmuiden:
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• A medium carbon grade is actually cast in IJmuiden:
• 0.23-0.25%C• 1.5% Mn• 0.3% SI
• But what about the hyper peritectic range? a “new steel” with a mix of the maximum alloying we cast (on different grades):
• 0.2% C• 2 %Mn• 1 % Si (could be more but it will be a so-called electrical steel)
Casting a high alloyed steel
• Peritectic, hyper-peritectic or what??
• Solidification range acceptable for continuous casting?
• Segregation?
• Casting parameters to consider:
• Heat extraction
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• Heat extraction
• superheat
• casting speed
• etc…
Classification
Hypo-peritectic Hyper-peritectic
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Peritectic
Classification for steelmaker’s….
Hypo-peritectic 0.06-0.75
Hyper-peritectic 0.18 up to who
knows…
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Peritectic 0.75-0.18
•This classification is based on sensitivity to formation of depressions and surface cracking in the solidifying shell•Relates to choice of mould fluxes to optimise heat transfer and lubrication in the continuous casting mould•Rule of thumb based on "classical" steel compositions
Binary vs. multi
LIQUID
LIQUID+δ
LIQUID+δ+γ
δ δ+γ
γ
LIQUID+γ
LIQUID
LIQUID+δ
LIQUID+δ+γ
δ
δ+γ LIQUID+γ
0.55 %C
1491ºC
0.16 %C
1491ºC
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γ+(Mn,Fe)S_Q
γ+(Mn,Fe)S_Q+CNb
γ
Peritectic associated defects
1350
1370
1390
1410
1430
1450
1470
1490
1510
1530
1550
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Tem
pera
ture
(ºC
) δδ+γ
δ+L
γ γ+L
LδP
LP
L2γ2
Cδ
δ1
CLCγ
γ1
1350
1370
1390
1410
1430
1450
1470
1490
1510
1530
1550
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Tem
pera
ture
(ºC
) δδ+γ
δ+L
γ γ+L
LδP
LP
L2γ2
Cδ
δ1
CLCγ
γ1
Schematic Fe-C
diagramγ1δ1
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Composition (wt% C)Composition (wt% C)
Shell Structure γ δ γ δ γ δ γ δ L γ δ γ δ γ δ γ δ L γ γ γ γ L
Narrow mushy zone but only a Narrow mushy zone and Extended mushy zone narrow strong austenite layer thick strong austenite layer with narrow fully-solid austenite layer
%C
Type B Sticking
Type A Depressions
Defect susceptibility
Carbon potential-Ferrite potential
• The changes in the Fe–C phase diagram through chemistry can be approximated using an effective carbon content Cp expression of the form [2]:
• Cp = [%C] + XMn[%Mn] + XSi[%Si] + …
• Since the key factor to assess the peritectic reaction is the primary ferrite fraction during solidification, a “ferrite Potential” Fp can be
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ferrite fraction during solidification, a “ferrite Potential” Fp can be defined by the following relationship:
• Fp = 2.5(0.5-%Cp)
Si, Ti, Cr, Mo C, N, Ni, Mn
Lower Cp Higher CpCp
Cp is ‘shifted’ by chemical composition
Carbon potential
gradeA Medium
carbonHyper-
peritecticLCAK
C 0.18-0.22 0.265 0.3 0.045Mn 1.8-2.2 1.3 0 0.22Si 0.8-1.2 0.25 0 0.01
Wolf 1991 0.16 0.19 0.30 0.05
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Wolf 1991 0.16 0.19 0.30 0.05BS STC 0.18 0.22 0.30 0.06
SMS 0.21 0.24 0.30 0.05Howe 0.17 0.21 0.30 0.06NSC 0.16 0.19 0.30 0.05
Kobe 0.33 0.30 0.17 0.17
Cp
QSP
grade High alloyed
steel
C wt% 0.22
Mn wt% 2.1
Si wt% 1
N wt% 0.0007
Ep 0.32 Peritectic equivalent. <1, starts as ferrite. >1, austenite.
A
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Ep 0.32 Peritectic equivalent. <1, starts as ferrite. >1, austenite.
Peri Hit 0.7618 Fraction solid (ferrite) at which the Peritectic is encountered
Delta-P 18.34 Temperature range between loss of ferrite (P-end) and solidus
FF@ sol. 28.5 Fraction ferrite at solidus (i.e. if still on peritectic "plateau")
Liq 1498.8 Liquidus, C
P-start 1461.12 Start of peritectic, C
P-end 1451.57 End of peritectic "plateau", i.e. loss of ferrite, C
Sol 1433.23 Solidus, C
Solidification range
fS
Solidus (fS=1)
ZST (fS=0.8)
ZDT (fS=0.99)LIT (fS=0.90)
RT (0.80≤≤≤≤ fS≤≤≤≤ 0.90) Liquidus (fS=0)
fS
Solidus (fS=1)
ZST (fS=0.8)
ZDT (fS=0.99)LIT (fS=0.90)
RT (0.80≤≤≤≤ fS≤≤≤≤ 0.90) Liquidus (fS=0)
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StrengthDuctility
Temperature
Stage 1Stage 2aStage 2bStage 3
StrengthDuctility
Temperature
Stage 1Stage 2aStage 2bStage 3
Solidification range
Solidification range= Tliq-Tsol
Steel “A” ~63 degrees
LCAK~18 degrees
Thickness mushy zone (CON1D)
A LCAK
Liquidus T(ºC) 1500.3 1532.2Solidus T(ºC) 1435.3 1513.5
Peritectic T(ºC) 1472
Mould exitCastig speed high low high low@ Liquidus (mm) 11.7 10.6 11.8 10.6@ Soliidus (mm) 8.9 7.7 10.7 9.6Thickness "mushy zone" 2.9 2.6 1.1 1
A LCAK
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14
14
0
2
4
6
8
10
0 20 40 60 80 100
Distance from meniscus (% of mould length)
She
ll th
ickn
ess
(mm
)
Liquidus 5m/min
Solidus 5m/min
Liquidus 4m/min
Solidus 4m/min
Liquidus 5m/min LCAK
Solidus 5m/min LCAK
Liquidus 4m/min LCAK
Solidus 4m/min LCAK
Scheil (Thermo-Calc)
“A”
Hyper-peritectic
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Medium Carbon
Phase transition (FactSage)Hyper-peritectic
“A”
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Medium Carbon
Some conclusions
• The “High alloyed steel” is a hyper-peritectic grade, quite early during solidification will pass through the peritectic transformation, how big is that region is unknown.
• “Equilibrium” solidification range is around 60 degrees, thus even if peritectic surface cracking may not occur, the larger the sol-range the more susceptible to other casting defects such as: hot tearing and sticking.
• Non-uniform heat flux in the caster’s could lead to local segregation
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• Non-uniform heat flux in the caster’s could lead to local segregation changing the solidification kinetics.
• The strength of the solid–mush region needs to be checked for this steel.
• Non equilibrium behaviour during actual casting conditions needs to be taken into account: HOW?
Thank you for your Thank you for your attention
Proposal for the Thermo -Proposal for the Thermo -Calc & MICRESS
meeting…
A triple point is characteristic for MICRESS…
• Obvious for this sort of meeting should be a “triple point” …
• IGUAZU… Argentina, Brasil, Paraguay
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Why?
• Is a triple-point… & has tropical weather (sunny the whole year round!!!)
• It has plenty of iron & other elements in a form of precious metals
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Why?
• It has a very inspiring environment …
• the widest waterfall in the world (sorry Zimbabwe but it’s true!)
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Iguazu falls
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Why?
• We could find big topics to discuss… as big as the trees growing there…
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Why?
• We can find a PARROT (not the TC-module!)
• And many “sources of inspiration”
• so maybe “TUCAN” will be the next TC-module???
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