https://digitalcommons.wpi.edu/etd-dissertations/399/
"Quenching is the rapid cooling process from an elevated temperature. Compared to water and oil quench medium, high pressure and velocity gas is preferred to quench medium and high hardenability steel, with the potential to reduce distortion, stress and cracks. Currently, no standard test exists to characterize the gas quench steel hardenability and measure the performance of industrial gas quench furnaces. In this thesis, the fundamental difference between the liquid and gas quenching, heat transfer coefficient, was emphasized. It has been proven that gas quenching with constant HTC cannot generate the similar cooling curves compared to liquid quenching. Limitations on current gas quench steel hardenability tests were reviewed. Critical HTC, a concept like critical diameter, was successfully proved to describe the gas quench hardenability of steel. An attempt to use critical HTC test bar and measure the HTC distribution of gas quench furnace was made. Gas quenching, usually with slow cooling rate, may reduce hardness and Charpy impact toughness, compared to water and oil quenching. Lattice parameter and c/a ratio of as-quenched martensite in steel was measured using high resolution X-ray diffraction and Rietveld refinement. For AISI 4140, Charpy impact toughness decreases when the cooling rate decreases after quenching and tempering. Austenite percentage and carbon content in austenite is proposed as the dominated mechanism."
Theory of Time 2024 (Universal Theory for Everything)
Heat Transfer, Hardenability and Steel Phase Transformations during Gas Quenching
1. Heat Transfer, Hardenability and Steel Phase
Transformations during Gas Quenching
Yuan Lu
Advisor: Prof. Richard D.Sisson, Jr.
Prof. Yiming Rong
Dec 8th, 2016
2. 2
Crack
Why not water/oil quenching sometimes?
http://www.chileforge.com/Thor.html
http://www.tf.uni-kiel.de/matwis/amat/iss/kap_b/backbone/rb_6_3.html
Distortion
• Distortion and crack are the biggest issues when cooling too fast.
3. 3
Gas quenching
ASM International. Handbook Committee. ASM handbook: Friction, lubrication, and wear technology. Vol. 18. ASM International, 1992.
Heuer, Volker, et al. "Low distortion heat treatment of transmission components." (2010).
ALD gas quench system
• Slow cooling rate compared to water/oil
• Potential to reduce distortion and cracks
• Adjustable: gas pressure and velocity
4. 4
Outline: challenges and solutions
How to develop better steel grade
for gas quenching?
Microstructure and mechanical
properties comparison
challenges solutions
What is the difference between
liquid and gas quenching?
1
2
3
4
5
What steel grade can be used for
gas quenching?
How to evaluate the performance
of gas quench furnace?
Is similar mechanical properties can
be obtained after gas quenching?
HTC comparison between liquid and
gas quenching
Critical HTC method for gas
quenching steel hardenability
HTC distribution evaluation in gas
quench furnace
Model carbon repartitioning
during quench
1
2
3
4
5
5. 5
Outline
How to develop better steel grade
for gas quenching?
Microstructure and mechanical
properties comparison
challenges solutions
What is the difference between
liquid and gas quenching?
1
2
3
4
5
What steel grade can be used for
gas quenching?
How to evaluate the performance
of gas quench furnace?
Is similar mechanical properties can
be obtained after gas quenching?
HTC comparison between liquid and
gas quenching
Critical HTC method for gas
quenching steel hardenability
HTC distribution evaluation in gas
quench furnace
Model carbon repartitioning
during quench
1
2
3
4
5
6. 6
1. Develop quenching model using DANTE
ASM International. Handbook Committee. ASM handbook: Friction, lubrication, and wear technology. Vol. 18. ASM International, 1992.
Ferguson, B. Lynn, Z. Li, and A. M. Freborg. "Modeling heat treatment of steel parts." Computational Materials Science 34.3 (2005): 274-281.
7. 6
1. Develop quenching model using DANTE
ASM International. Handbook Committee. ASM handbook: Friction, lubrication, and wear technology. Vol. 18. ASM International, 1992.
Ferguson, B. Lynn, Z. Li, and A. M. Freborg. "Modeling heat treatment of steel parts." Computational Materials Science 34.3 (2005): 274-281.
• Model is accurate to simulate quenching process.
8. 7
• Gas quench is not equivalent to liquid quench with constant HTC.
1. HTC comparison between liquid and gas quenching
Liscic, Bozidar, et al., eds. Quenching theory and technology. CRC Press, 2010.
9. 8
Outline: challenges and solutions
How to develop better steel grade
for gas quenching?
Microstructure and mechanical
properties comparison
challenges solutions
What is the difference between
liquid and gas quenching?
1
2
3
4
5
What steel grade can be used for
gas quenching?
How to evaluate the performance
of gas quench furnace?
Is similar mechanical properties can
be obtained after gas quenching?
HTC comparison between liquid and
gas quenching
Critical HTC method for gas
quenching steel hardenability
HTC distribution evaluation in gas
quench furnace
Model carbon repartitioning
during quench
1
2
3
4
5
✓
10. 9
2. Limitation: Jominy like end-quench device
Liščić, B. "Hardenability testing of steels when gas quenching is applied." International Heat Treatment and Surface Engineering 8.2 (2014): 86-92.
Liscic
CHTE
• Gas flow is not steady and cooling rate is not low enough.
• Same steel grade, different hardenability curve using different HTC.
Low HTC
High HTC
12. 10
2. Critical HTC method
• Only need one critical HTC for
hardenability
Advantages:
• Back and forth flow design, steady gas
flow
• Get very low cooling rate by increasing
sample diameter
• The critical HTC is defined as the HTC required to form 50% martensite at
the center of a steel alloy rod with an 1 inch (25.4 mm) diameter.
• Lower critical HTC indicates higher gas quench steel hardenability.
ASM International. Handbook Committee. ASM handbook: Friction, lubrication, and wear technology. Vol. 18. ASM International, 1992.
20. 18
2. Critical HTC test
HTC101
HTC206
HTC298
HTC589
• Steel grade gas quench hardenability rank
• Simulation accuracy was verified
21. 19
2. HTC vs. gas pressure and velocity
4140
5.2bar 27.21m/s
502W/m2C
52HRC
4140
13.6bar 10.28m/s
502W/m2C
52HRC
Liscic, Bozidar, et al., eds. Quenching theory and technology. CRC Press, 2010.
22. 20
Outline: challenges and solutions
How to develop better steel grade
for gas quenching?
Microstructure and mechanical
properties comparison
challenges solutions
What is the difference between
liquid and gas quenching?
1
2
3
4
5
What steel grade can be used for
gas quenching?
How to evaluate the performance
of gas quench furnace?
Is similar mechanical properties can
be obtained after gas quenching?
HTC comparison between liquid and
gas quenching
Critical HTC method for gas
quenching steel hardenability
HTC distribution evaluation in gas
quench furnace
Model carbon repartitioning
during quench
1
2
3
4
5
✓
✓
23. 21
3. Fluent analysis: slowest cooling position
• Constant HTC is a good estimation
• Center has the slowest cooling rate
24. 22
3. 2bar nitrogen furnace test
https://www.secowarwick.com/assets/Documents/Brochures/Vacuum-Furnaces/HPGQ-EN5.pdf
25. 22
3. 2bar nitrogen furnace test
https://www.secowarwick.com/assets/Documents/Brochures/Vacuum-Furnaces/HPGQ-EN5.pdf
• 0.5” AISI 4340 is proper to evaluate hardness and HTC distribution
26. 23
Outline: challenges and solutions
How to develop better steel grade
for gas quenching?
Microstructure and mechanical
properties comparison
challenges solutions
What is the difference between
liquid and gas quenching?
1
2
3
4
5
What steel grade can be used for
gas quenching?
How to evaluate the performance
of gas quench furnace?
Is similar mechanical properties can
be obtained after gas quenching?
HTC comparison between liquid and
gas quenching
Critical HTC method for gas
quenching steel hardenability
HTC distribution evaluation in gas
quench furnace
Model carbon repartitioning
during quench
1
2
3
4
5
✓
✓
✓
27. 24
4. Review: martensite lath and austenite film
Morsdorf, Lutz, et al. "3D structural and atomic-scale analysis of lath martensite: Effect of the transformation sequence." Acta Materialia 95 (2015): 366-377.
Galindo-Nava, E. I., and P. E. J. Rivera-Díaz-del-Castillo. "A model for the microstructure behaviour and strength evolution in lath martensite." Acta Materialia 98 (2015): 81-93.
Lerchbacher, Christoph, Silvia Zinner, and Harald Leitner. "Atom probe study of the carbon distribution in a hardened martensitic hot-work tool steel X38CrMoV5-1." Micron 43.7 (2012): 818-826.
Speer, J., et al. "Carbon partitioning into austenite after martensite transformation." Acta materialia 51.9 (2003): 2611-2622.
28. 24
4. Review: martensite lath and austenite film
Morsdorf, Lutz, et al. "3D structural and atomic-scale analysis of lath martensite: Effect of the transformation sequence." Acta Materialia 95 (2015): 366-377.
Galindo-Nava, E. I., and P. E. J. Rivera-Díaz-del-Castillo. "A model for the microstructure behaviour and strength evolution in lath martensite." Acta Materialia 98 (2015): 81-93.
Lerchbacher, Christoph, Silvia Zinner, and Harald Leitner. "Atom probe study of the carbon distribution in a hardened martensitic hot-work tool steel X38CrMoV5-1." Micron 43.7 (2012): 818-826.
Speer, J., et al. "Carbon partitioning into austenite after martensite transformation." Acta materialia 51.9 (2003): 2611-2622.
• Carbon enriched thin austenite film between carbon depleted martensite laths
29. 25
4. AISI 4140: Charpy impact toughness
water quench
Gas quench
30. 25
4. AISI 4140: Charpy impact toughness
water + temper
Gas quench + temper
• Measure carbon distribution in austenite film is difficult.
• Using XRD and modified equation to measure carbon
concentration in martensite lath.
31. 26
4. Carbon content in Martensite
Sherby, Oleg D., et al. "Revisiting the structure of martensite in iron-carbon steels." Materials transactions 49.9 (2008): 2016-2027.
Hardness of as-quenched steel
32. 26
4. Carbon content in Martensite
Sherby, Oleg D., et al. "Revisiting the structure of martensite in iron-carbon steels." Materials transactions 49.9 (2008): 2016-2027.
Hardness of as-quenched steel
34. 27
4. BCC c/a = 1 or BCT c/a > 1 ?
• If BCT, two peaks
Peak should be asymmetric, left hand tail
Residual error <5%
Same to observation
• If BCC, one peak
Residual error > 12%
Peak should be symmetric
Contrary to observation
35. 27
4. BCC c/a = 1 or BCT c/a > 1 ?
• If BCT, two peaks
Peak should be asymmetric, left hand tail
Residual error <5%
Same to observation
c/a = 1 + 0.045 wt%C
c/a = 1 + 0.031 wt%C
Classical equation
Modified equation
36. 28
Outline: challenges and solutions
How to develop better steel grade
for gas quenching?
Microstructure and mechanical
properties comparison
challenges solutions
What is the difference between
liquid and gas quenching?
1
2
3
4
5
What steel grade can be used for
gas quenching?
How to evaluate the performance
of gas quench furnace?
Is similar mechanical properties can
be obtained after gas quenching?
HTC comparison between liquid and
gas quenching
Critical HTC method for gas
quenching steel hardenability
HTC distribution evaluation in gas
quench furnace
Model carbon repartitioning
during quench
1
2
3
4
5
✓
✓
✓
✓
37. 30
C. Lerchbacher, “Atom probe study of the carbon distribution in a hardened martensitic hot-work tool steel X38CrMoV5-1”
Becquart, C. S., et al. "Atomistic modeling of an Fe system with a small concentration of C." Computational materials science 40.1 (2007): 119-129.
Martensite Austenite Martensite
• only carbon, no other alloying elements diffuse
5. Model carbon repartitioning during quench
38. 30
C. Lerchbacher, “Atom probe study of the carbon distribution in a hardened martensitic hot-work tool steel X38CrMoV5-1”
Becquart, C. S., et al. "Atomistic modeling of an Fe system with a small concentration of C." Computational materials science 40.1 (2007): 119-129.
Martensite Austenite Martensite
• only carbon, no other alloying elements diffuse
• varying diffusivity and chemical potential in austenite
• adding Mo or W to decrease carbon diffusivity
5. Model carbon repartitioning during quench
39. 31
• Complete critical HTC test for characterizing gas quenching steel
hardenability.
Conclusions
Future work
• Investigate 1.5” or 2” critical HTC test.
• Finish procedure on HTC distribution evaluation in gas quench furnace.
• Modify c/a ratio and carbon weight percent of as-quenched martensite.
• Find and explain the reason that Charpy impact toughness decreases
with the decreases of cooling rate after quenching and tempering.
• Conduct TEM and ATP analysis.
• Consider potential and diffusivity together during carbon repartitioning.
