modeling the heat treatment response of p/m components · jominy end quench tests will be performed...
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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.
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
• 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.
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
Strain vs. time for Bainite transformation in full densityFL-4605 PM steel.
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
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
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
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
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
Pearlite Bainite
MartensiteAustenite
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
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.
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
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
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Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
bfecm
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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:
Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
)),(()1()( min
1
, TMTMinUdt
dTsammEnmmm
mm !!+=!• """"#" $%
3
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Determination of phase transformation kineticsDetermination of phase transformation kineticsparameters using quench parameters using quench dilatometrydilatometry (cont.)(cont.)
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.)
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
0095% of theoretical
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
0090% of theoretical
density(C)
9
1800-908
1200-607
600-306
0095% of theoretical
density(B)
5
1800-904
1200-603
600-302
00
Fully dense(A)
1
Load , N (lbf)Stress (MPa)*Sample DensityTest Number
Determination of transformation inducedDetermination of transformation inducedplasticity using low stress plasticity using low stress dilatometrydilatometry (cont.)(cont.)
)()()()( 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.
Determination of transformation inducedDetermination of transformation inducedplasticity using low stress plasticity using low stress dilatometrydilatometry (cont.)(cont.)
Determination of transformation inducedDetermination of transformation inducedplasticity using low stress plasticity using low stress dilatometrydilatometry (cont.)(cont.)
90% density 95% density
100% density
Determination of transformation inducedDetermination of transformation inducedplasticity using low stress plasticity using low stress dilatometrydilatometry (cont.)(cont.)
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