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Processo Q&P (Quenching and Partitioning) Estudo de caso completo. Fernando Rizzo. Projeto de Cooperação Internacional. NSF-CNPq (CIAM) , NSF-EPSRC. J.G. Speer, D.K. Matlock , A. Streicher – Colorado School of Mines, USA. F. Rizzo, A. R. Aguiar – PUC, Rio de Janeiro, Brazil. - PowerPoint PPT Presentation
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1 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Processo Q&P (Quenching and Partitioning)
Estudo de caso completo
Fernando Rizzo
2 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Projeto de Cooperação Internacional
J.G. Speer, D.K. Matlock , A. Streicher
– Colorado School of Mines, USA
F. Rizzo, A. R. Aguiar
– PUC, Rio de Janeiro, Brazil
D.V. Edmonds, Kejian He
– University of Leeds, UK
NSF-CNPq (CIAM) , NSF-EPSRC
3 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Quenching and Partitioning:
- Background
- Fundamental Issues
- Recent Results
•J.G. Speer, D.K. Matlock, B.C. De Cooman and J.G. Schroth, Acta Mater., 51 (2003) 2611-2622. •J.G. Speer, A.M. Streicher, D.K. Matlock, F.C. Rizzo and G. Krauss, Austenite Formation and Decomposition, ed. E.B. Damm and M. Merwin, TMS/ISS, Warrendale, PA, USA, 2003, pp. 505-522. •John G. Speer, David V. Edmonds, Fernando C. Rizzo, David K. Matlock, Current Opinion in Solid-State and Materials Science, 8 (2004) 219-237
4 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
TRIP SteelsMF
Ac3
Time
Te
mp
era
ture
MS
Ac1
B +
C
iC
f
“Conventional”Processing ofSteels with
CC and Isothermal
Transformations
Ac3
Te
mp
era
ture
C = Ci
MF
Time
MS
B +
5 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
The “Q&P” ProcessQuenching and Partitioning
TE
MP
ER
AT
UR
E
TIME
PT,t
AT
QT
Quenchedand Partitioned
Ms
Mf
Provisional US Patent Application: September, 2003
6 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
The “Q&P” Process
Step 1. Austenitize or Intercritically Anneal
- more austenite- lower C
- higher Ms
- less austenite- higher C
- lower Ms
7 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Step 2. Cool (quench?) below Ms
- Ms -TQ controls martensite formation
- intercritical annealing has more stable austeniteand higher carbon martensite
Austenitize + Quench Intercritical Anneal + Quench
8 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Step 3. Diffuse Carbon from Supersaturated Martensite
- Phase compositions change
- Phase boundaries stationary
9 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Q&P Process Schematic
10 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
New Processing Concept (Sheet, Bar,…etc)
Use carbon partitioning intentionally…from partially transformed martensite tountransformed austenite.
Usually precluded because carbide precipitation occurs during tempering of martensite.
Result: carbon-enriched austenite
11 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Thermodynamics of Carbon
Partitioning
12 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Important Questions
How much can we enrich the austenite?
That is…what are the “equilibrium” martensite and austenite compositions?
Or…when does partitioning stop?
13 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
“True” Metastable Equilibrium
Fe3C
% Carbon
Tem
per
atu
re
Fe3C
14 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
“True” Metastable Equilibrium
Fe C
G
xEQ
FeFe
CC
xEQ
15 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
“True” Metastable Equilibrium CANNOT Apply!!
Fe3C
% Carbon
Tem
per
atu
re
Fe3C
XalloyX X
- The equilibrium phase fractions are fixed by the lever rule- The actual phase fractions were fixed by cooling below Ms!
16 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
A New Equilibrium Condition was Hypothesized
“Constrained Carbon Equilibrium” (CCE)
- Iron atoms are completely immobile (the phase boundaries are stationary).- Carbon atoms are completely mobile.- Carbon diffuses until its chemical potential (activity) is equal in ferrite and austenite.- Assume…competing reactions are precluded by
Si/Al
17 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Properties of “Constrained Carbon Equilibrium”
- Not a unique condition at any temperature!- Depends on initial phase fractions/compositions
Fe C
G
II
C
II
C
xI
CPE
x
II
CPE
xI
CPE
x
II
CPE
I
C
I
C
18 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
- Austenite may be more enriched or less enriched than ortho- or para- equilibrium
Fe C
G
II
C
II
C
xI
CPE
x
II
CPE
xI
CPE
x
II
CPE
I
C
I
C
T0
A3
Properties of “Constrained Carbon Equilibrium”
19 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Properties of “Constrained Carbon Equilibrium”
RT
TT
CC
CCEC
CCECCEe
X)4.120105,169(8.43789,76
XX
XXX alloyCCCCECCCE CCECCE
ff
)X1()X1( iCCE CiCCCE ff
Carbon Constrained Equilibrium:
Mass balance:
20 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Key Characteristics of CCE
- Almost all of the carbon should partition to austenite- Enrichment levels are potentially very high
(Fe-0.5C)
21 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Example CCE Calculations - 1.0%C Initial Austenite
M artensite C ontent25%50%75%90%
1x10 - 4 1x10 - 2 1x10 0
Carbon in Ferrite (wt. % )
200
300
400
500
600
Tem
pera
ture
(oC
)
0 2 4 6 8 10
Carbon in Austenite (wt. % )
200
300
400
500
600
1% Carbon
22 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
We have all the pieces to predict microstructure…
Example
Steel Composition: C=0.15 Mn=1.0 Si=1.5
Ms(oC)=539-423(%C)-30.4(%Mn)-12.1(%Cr)-17.7(%Ni)-7.5(%Mo)
Ms=445oC (Steel)
Intercritical Annealing T=810oC
f~ 22% C~ 0.68 wt. % Ms~222oC
f~ 78%
TIA=810oC
23 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Quench T = 150 oC
Fraction of Martensite(Koistinen and Marburger)
Final Microstructure
f~ 10%
fM~ 12%
f~ 78%
Phase Compositions After 450oC Partitioning
C~ 1.5%
CM~ .0019%
Tq=150oC
Tp=450oC
fkm 1 exp 1.1 102 Ms Tq
24 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Q&P Process Design Methodology
Experimental High-Al TRIP Sheet Steel C Al Mn Si P N Cr S
0.19 1.96 1.46 0.022 0.01 0.0018 0.08 0.002
ASSUME:
- Complete partitioning of carbon to austenite
- No competing reactions (carbide formation)
25 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Calculations for Experimental Al-Steel (at QT)
0 100 200 300 400
Q uench Tem perature
0
0.1
0.2
0.3
0.4
0.5
Pha
se F
ract
ion
M in itia l quench in itia l quench
AlSiMnCCo 305.74.30423539)(M s
IA=0.5
26 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Martensite Formation During Final Quench
0 100 200 300 400
Q uench Tem perature
0
0.1
0.2
0.3
0.4
0.5
Pha
se F
ract
ion
M in itia l quench
M fina l quench
in itia l quench
27 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Calculated Final Austenite Fraction in High-Al Steel
final
0 100 200 300 400
Q uench Tem perature
0
0.1
0.2
0.3
0.4
0.5
Pha
se F
ract
ion
M in itia l quench
M fina l quench
in itia l quench
28 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Effect of Intercritical Annealing Step
0 100 200 300 400 500
Q uench Tem perature - oC
0
0.05
0.1
0.15
0.2
0.25
Fin
al A
uste
nite
Fra
ctio
n
IC = 0%
IC = 50%
IC = 75%
29 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Effect of Manganese Content
0 100 200 300 400 500
Q uench Tem perature - oC
0
0.05
0.1
0.15
0.2
0.25
Fin
al A
uste
nite
Fra
ctio
n
0.5% M n1.46% M n
30 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Effect of Carbon Content
31 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Example of DICTRA SimulationSolid-Solid Phase Transformations in Inorganic Materials 2005
Edited by J. HoweTMS (The Minerals, Metals & Materials Society), 2005
CARBON ENRICHMENT OF AUSTENITE AND CARBIDE PRECIPITATION DURING THE QUENCHING AND
PARTITIONING (Q&P) PROCESS
F.C. Rizzo 1, D.V. Edmonds2, K. He 2, J.G. Speer3, D.K. Matlock3and A. Clarke 3
1Department of Materials Science and Metallurgy; Pontifícia Universidade Católica-Rio de Janeiro; RJ 22453-900, Brazil
2School of Process, Environmental and Materials Engineering; University of Leeds; Leeds LS2 9JT, United Kingdom
3Advanced Steel Processing and Products Research Center; Colorado School of Mines; Golden, CO 80401, USA
32 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Simulation Conditions
Steel composition:
•0.19C-1.59Mn-1.63Si wt%
Heat treatment:
•Fully austenitized at 900oC, quenched to 293oC to produce 68% martensite and partitioned at 400oC. The thickness of the ferrite and austenite plates used in the simulation were 0.30 and 0.14 microns, respectively (obtained by TEM).
33 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Carbon Concentration Profiles for ferrite and austenite
0
400
800
1200
1600
2000
2400
2800
3200
AC
R(C
)
0 5 10 1510-8
DISTANCE
DICTRA (2005-07-01:11.46.47) :Ferrite C activityTIME = 1E-04,.001,.01,.1,1,10
CELL #2
2005-07-01 11:46:47.76 output by user Fernando from RIZZO1
0
5
10
15
20
25
30
10-3W
(C)
0 1 2 3 4 5 6 710-8
DISTANCE
DICTRA (2005-07-01:11.59.50) :Austenite C ProfileTIME = 1E-04,.001,.01,.1,1,10
CELL #1
2005-07-01 11:59:50.50 output by user Fernando from RIZZO1
34 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Carbon concentration profiles in and during partitioning under CCE at 400C, for a 0.19C-1.59Mn-1.63Si steel
35 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Average carbon concentration as a function of time for
(0.30m) and (0.14m) plates during partitioning at 400oC
36 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Variation of (a) carbon flux and (b) carbon activity at the interface during partitioning. Time plotted in a log scale
37 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Carbon concentration (wt%) at and interfaces as a function of time during partitioning at 400 oC
38 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Carbon flux and concentration in the center of (a) ferrite and (b) austenite plates as a function of time
39 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
CONCLUSIONS
1. For the scale of microstructure investigated, carbon depletion from the ferrite during partitioning at 400C occurs quite rapidly, around 10-1 seconds, while the austenite takes much longer, around 10 seconds, to achieve a uniform concentration.
2. Due to its rapid depletion, the carbon concentration in the center of the ferrite plate starts to decrease after 10-3 seconds. After this time the driving force for carbide precipitation is gradually reduced.
3. Carbon enrichment of the austenite will promote, initially, a substantial increase in the carbon concentration at the interface and a progressive stabilization of the plate, advancing from the interface to the center. Full stabilization is achieved when the composition of the central region reaches a carbon concentration corresponding to room temperature Ms.
40 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Some Q&P Experimental
Results
41 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
TEM micrographs of the Q&P microstructure produced in a 0.19%C-1.59%Mn-1.63%Si TRIP steel composition
Quenching to 260°C and partitioning at 400°C for 100 s: (a) bright-field image and (b) dark-field image using a (200) austenite reflection.
(a) (b)
42 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012
Total elongation vs. ultimate tensile strength for TRIP, Dual phase (DP), martensitic (M), and Q&P sheet steel products
400 800 1200 1600U ltim ate Tensile S tre ng th , M Pa
0
10
20
30
40T
ota
l Elo
ng
atio
n,
%TRIP (ULSAB)A
TRIP (GM )A
Conventional TRIPB
1-Step Q&PB
2-Step Q&PB
M (ULSAB)A
M (GM)A
M (Ispat-In land)C
DP (ULSAB)A
DP (GM )A
DP (Ispat-Inland)CT R IP
D P
M
Q & P
Note A: 80 mm gauge lengthNote B: 25.4 mm gauge length Note C: Gauge length unspecified