processo q&p (quenching and partitioning) estudo de caso completo

1 Workshop Aplicações da Termodinamica Computacional a Siderurgia 2012

Processo Q&P (Quenching and Partitioning)

Estudo de caso completo

Fernando Rizzo


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


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


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 +


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


The “Q&P” Process

Step 1. Austenitize or Intercritically Anneal

- more austenite- lower C

- higher Ms

- less austenite- higher C

- lower Ms


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


Step 3. Diffuse Carbon from Supersaturated Martensite

- Phase compositions change

- Phase boundaries stationary


Q&P Process Schematic


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


Thermodynamics of Carbon

Partitioning


Important Questions

How much can we enrich the austenite?

That is…what are the “equilibrium” martensite and austenite compositions?

Or…when does partitioning stop?


“True” Metastable Equilibrium

Fe3C

% Carbon

Tem

per

atu

re

Fe3C


“True” Metastable Equilibrium

Fe C

G

xEQ

FeFe

CC

xEQ


“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!


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


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


- 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




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:


Key Characteristics of CCE

- Almost all of the carbon should partition to austenite- Enrichment levels are potentially very high

(Fe-0.5C)


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


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


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


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)


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


Martensite Formation During Final Quench

0 100 200 300 400


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


Calculated Final Austenite Fraction in High-Al Steel

final

0 100 200 300 400


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


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%


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


Effect of Carbon Content


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


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).


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


Carbon concentration profiles in and during partitioning under CCE at 400C, for a 0.19C-1.59Mn-1.63Si steel


Average carbon concentration as a function of time for

(0.30m) and (0.14m) plates during partitioning at 400oC


Variation of (a) carbon flux and (b) carbon activity at the interface during partitioning. Time plotted in a log scale


Carbon concentration (wt%) at and interfaces as a function of time during partitioning at 400 oC


Carbon flux and concentration in the center of (a) ferrite and (b) austenite plates as a function of time


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.


Some Q&P Experimental

Results


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)


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

processo q&p (quenching and partitioning) estudo de caso completo

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