modeling the heat treatment response of p/m components · jominy end quench tests will be performed...

Modeling the Heat Treatment ResponseModeling the Heat Treatment Responseof P/M Componentsof P/M Components

Research Team:• Makhlouf M. Makhlouf, Professor• Richard D. Sisson, Jr., Professor• Virendra S. Warke, Ph.D. Student

Focus Group Members:

• Ian Donaldson GKN Sinter Metals Worcester• John Fulmer Nichols Portland• Chaman Lall Metal Powder Products Co.• Jean Lynn DaimlerChrysler Corporation.• Stephen Mashl (Chair) Bodycote IMT, Inc.• Sim Narasimhan Hoeganaes Corporation• Reinaldo Soave Mahle Metal Leve S.A.• Rocco Petrilli Sinterstahl G.m.b.H.

ObjectivesObjectives

Develop and verify a computer simulation softwareand strategy that enables the prediction of theeffect of heat treatment on P/M components

Simulation predictions will include:

Dimensional changes and distortion

Residual stresses

Type and quantity of metallurgical phases

Hardness

BackgroundBackground

Need

Model provides insight and control of processing conditions to meet - Dimensional tolerances.

- Mechanical properties.

Model can be used to design a process.

Model can be used to optimize an existing process.

1. Develop model and modeling strategy.– Select software– Test predictive ability of software– Develop necessary input for software:

• Heat transfer coefficients during quenching(quenching experiments/measurements)

• Phase transformation kinetics(quench dilatometry – ORNL)

• Phase specific, temperature dependant mechanical properties(high temperature mech. properties measurement)

Project outline

2. Validate model predictions.– Develop/adopt measurement procedures for:

• Residual stresses• Type and quantity of metallurgical phases• Dimensional changes

Project outline (cont.)

Project outline (cont.)

3. Use the model to predict the heat treatmentresponse of select P/M components.

Project outline : DANTE® (cont.)

Schedule: Schedule: Project duration:Project duration: July 2003 July 2003 →→ July 2006 July 2006

1. Develop model and modeling strategy. Select software DANTE Test predictive ability of software Develop necessary input for software: (for FL-4605 PM alloy)

Heat transfer coefficients during quenching(quenching experiments/measurements)

Phase transformation kinetics (quench dilatometry – ORNL) Full density (powder forged) samples 95 % theoretical density samples 90 % theoretical density samples

Transformation induced plasticity measurements (three levels ofapplied stress) Full density (powder forged) samples 95 % theoretical density samples 90 % theoretical density samples

o Phase specific/temperature dependant mechanical properties(high temperature mech. properties measurement)

2. Validate model predictions3. Use model to predict heat treatment response of industrial PM part.

Theta Industries, Inc. 26 Valley Road Port Washington NY 11050 USA

Using a quenchdilatometer

Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry

Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)

1375

1300

1325

1350

2400

2425

1450

2475

2500

Bainite

2550

2575

2600

1625

3650

Ferrite+

Pearlite

2680

1700Ferrite

Number of testsIsothermal holding temperature(°C)

Phases

Matrix for developing the isothermal transformation data sets.


• Full Density samples Isothermal & continuous cooling measurements. Data analysis & fitting for kinetics parameters. Generation of TTT diagram.

• 95% Density samples Isothermal & continuous cooling measurements.• Data analysis & fitting for kinetics parameters.• Generation of TTT diagram.

• 90% Density samples. Isothermal & Continuous cooling measurements.• Data analysis & fitting for kinetics parameters.• Generation of TTT diagram.


Strain vs. time for Bainite transformation in full densityFL-4605 PM steel.


254

116

18

Number of testsCooling rate (°C/s)

14

11

20.5

20.35

10.2

10.1

10.05

Number of testsCooling rate (°C/s)

Test matrix for the Martensitic transformation

Test matrix for generating thecontinuous cooling transformationdatasets

Cooling rate curves for which the dilatation data in continuouscooling tests is acquired



Strain vs. temperature for continuous cooling transformation in fulldensity FL-4605 PM steel

Initial Phase kinetics parameters

CTE, Transformation strain,

Tested time-temperature data

Predicted strain curves

Objective function:Difference between predicted and tested

strain curves

Kinetics checking:

Jominy predictor

TTT diagram predictor

Search optimum kinetics parameters

Satisfied?

Output optimized kinetics parameters

Sensitivity analysis

Yes

Up

da

ted

kin

etic

s p

ara

met

ers

No

Initial Phase kinetics parameters

CTE, Transformation strain,

Tested time-temperature data

Predicted strain curves

Objective function:Difference between predicted and tested

strain curves

Kinetics checking:

Jominy predictor

TTT diagram predictor

Search optimum kinetics parameters

Satisfied?

Output optimized kinetics parameters

Sensitivity analysis

Yes

Up

da

ted

kin

etic

s p

ara

met

ers

No


Pearlite Bainite

MartensiteAustenite


Data fitting to estimate coefficient of thermal expansion as a functionof temperature

Predictive model for Austenite decomposition :Predictive model for Austenite decomposition :

This model is based on kinematics information i.e. data thatrelates to the external shape change is used to predict internalmicrostructure change.

The model is based on the assumption that differential shapechange can be related to differential microstructure changeprovided the base state is known.

The strain vs. time and/or strain vs. temperature data fromdilatometery is fitted into kinetic parameters to predict thechange in phase fraction with time.


State variable approach has been extended to include multiphase decomposition ofaustenite (Фa) to ferrite (Фf), pearlite (Фp), and bainite (Фb)

a,f, & p Subscript for austenite, ferrite, and pearlite, respectively.Фi Phase fraction of a phase.Фf,eq Temperature dependent equilibrium atomic fraction of ferrite.Ki Temperature dependent mobility functions.<.> McCalley bracket; gives the value if argument is positive, else gives zero.φEn,b = γb (Фf+ Фp), reflects influence of existing ferrite and pearlite on the rate of

formation of bainite.

Diffusive Kinetics

1

,

21

,

22

!!•>!<= ffff a

afeqf

a

f

a

eqf

a

ff k """"""

121

,

2)1()1(2

!!•!!= pppp a

ap

a

p

a

eqf

a

pp k """""

bbbb a

a

a

bEnb

a

eqf

a

bb k !!!!! )()1(2 ,

21

,

2+"=

"•



bfecm

n

e

TR

Q

g

f kkATATAeek f

f

f >!<"= +

""

&,)(2 33

)273(41.0#

11

)273(32.0 ,)(2 es

n

e

TR

Q

g

p ATBTAeek p

p

p !<"= +

""#

ss

n

s

TRQ

g

b BTMTBeek b

b

b !<"= +"

",)(2 )273(29.0#

Mobility functions as a function of temperature for diffusive kinetics:

a,f,and p Subscript for austenite, ferrite, and pearlite, respectively.Qi Effective thermal activation energy.ni Critical exponent that relates driving force to the degree of undercooling.

αi Mobility parameters.Bs Bainite start temperature.Ms Martensite start temperature.

Martensitic Kinetics

The martensitic transformation is assumed to be athermal but iswritten and solved in a rate form:

here, U is the heavy-side step function:

where, Tmin is the lowest temperature attained, and αm,βm, andνm are algebraic functions of the carbon level:


)),(()1()( min

1

, TMTMinUdt

dTsammEnmmm

mm !!+=!• """"#" $%

3

3

2

210

10

10

mmmmm

mmm

mmm

CC

C

C

!!!!!

"""

###

+++=

+=

+=


Kinetics data fitting for full density FL-4605 PM steel:

Pearlite Bainite

Martensite

DeteminationDetemination of phase transformation kinetics of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)

TTT diagram for full density FL-4605 PM steel generated using thefitting routine.

Effect of porosity on the phase transformationEffect of porosity on the phase transformationof FL-4605 PM steelof FL-4605 PM steel

Effect of porosity on the phase transformationEffect of porosity on the phase transformationof FL-4605 PM steel of FL-4605 PM steel (cont.)(cont.)

Determination of transformation induced plasticity (TRIP)Determination of transformation induced plasticity (TRIP)

Plastic behavior of steels during metallurgical transformations can beattributed to:

1) Classical plasticity - which is plastic flow arising from variation of theapplied stress or the temperature cycle.

2) Transformation induced plasticity (TRIP) - which is plastic flowarising from variation of phase proportion due to phase transformation.

TRIP has been observed by many researchers during Austenite to Martensiteand Austenite to Bainite transformations.

Low stress dilatometry can be used to determine TRIP by applying anexternal static compressive load just before the transformation begins.

The applied stress must be lower than the flow stress of Austenite at thetesting temperature.

Determination of transformation inducedDetermination of transformation inducedplasticity using low stress plasticity using low stress dilatometrydilatometry

* A negative sign indicates a compressive stress.

Matrix for determining TRIP for the Austenite to Martensite transformation.

Cooling rate : 80°C/s

Temperature for application of stress : 300 °C

2400-12012

1800-9011

1200-6010

0090% of theoretical

density(C)

9

2400-1208

1800-907

1200-606


density(B)

5

2400-1204

1800-903

1200-602

00

Fully dense(A)

1

Load , NStress, MPaSample DensityTestNumber

Determination of transformation inducedDetermination of transformation inducedplasticity using low stress plasticity using low stress dilatometrydilatometry (cont.)(cont.)

* A negative sign indicates a compressive stress.

Matrix for determining TRIP for the Austenite to Bainite transformation.

Isothermal holding temperature : 425°C

1800-9012

1200-6011

600-3010


density(C)

9

1800-908

1200-607

600-306


density(B)

5

1800-904

1200-603

600-302

00

Fully dense(A)

1

Load , N (lbf)Stress (MPa)*Sample DensityTest Number


)()()()( TTTT ethmtp !!!! ""=

εtp TRIP strain

ε Total strain

εthm Thermal strain

εe Elastic strain

Change in diameter vs. time during Austenite to Bainitetransformation under different applied loads for fully densesamples.



90% density 95% density

100% density


0 MPa

60 MPa

30 MPa

90 MPa

Quench dilatometric measurements were performed on FL4605 PM steelsamples of 90% ,95% & 100% theoretical density at ORNL.

Strain vs. time datasets from isothermal dilatational curves and strain vs.temperature datasets from continuous cooling dilatation curves wereobtained from these measurements.

The data for full density samples was fitted into the kinetics equations usinga specialized routine developed by DCT.

TTT diagram for full density FL-4605 powder forged steel has beendeveloped.

The effect of porosity on phase transformation of FL-4605 PM steel has beenanalyzed.

Low stress dilatometric measurements were performed on FL-4605 PM steelfor 3 porosity levels and 4 stress levels at ORNL.

SummarySummary

The data from dilatation curves for samples with 90% and 95% density will befitted into the kinetics equations.

The TTT diagrams for 90% and 95% theoretical density material will beconstructed.

This information will be used to characterize the effect of porosity on the variousaspects of phase transformations in the alloy, including transformation strains,transformation kinetics, and transformation temperatures.

TRIP data will be calculated from the measurements conducted at ORNL.

Effect of porosity on TRIP will be characterized.

Jominy end quench tests will be performed on samples that were pressed andsintered to 90% and 95% of their theoretical density in order to investigate theeffect of porosity on the heat transfer characteristics of the alloy.

Work planned for the next reporting periodWork planned for the next reporting period

modeling the heat treatment response of p/m components · jominy end quench tests will be performed...

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