Development of Austempering by Gas Quenching Technology

1
Development of Austempering by Gas Quenching
Technology
Smati Chupatanakul chupsma_at_iit.edu T. Calvin
Tszeng tszeng_at_iit.edu Philip Nash nashp_at_iit.ed
u
2
Objectives

• Determine applicability of high pressure gas
  quenching for austempering of low alloy
  carburized gear steels.
• Develop the requirements in steel chemistry
  and/or processing to achieve the targeted
  properties in austempering part.
• Determine the relation between heat transfer
  coefficients and gas pressure/velocity in high
  pressure gas quenching for short processing time.
• Optimize the materials/process for short
  processing time.

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Work Plan Task 1
Determine the transformation kinetics of bainite
and pearlite in carburized AISI 4317

• Cast the specimens of AISI 4317 to a number of
  carbon concentrations.
• Conduct austempering tests of specimens on
  Gleeble 3500.
• Extract kinetics of bainite formation from the
  dilatometric curves.
• Determine the kinetics of pearlite formation
  using dilatometric tests.
• Data analysis.

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Austempering
Austempering is a process in which the heated
steel is quenched from the austenitizing
temperature rapidly enough to avoid formation of
ferrite or pearlite. It is held at a certain
temperature until isothermal transformation from
austenite to bainite is complete and then cooled
to room temperature.
The parts need to be quenched fast enough so that
the transformation to pearlite can be avoided.
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Work Plan Task 1
Determine the transformation kinetics of bainite
and pearlite in carburized AISI 4317

• Cast the specimens of AISI 4317 to a number of
  carbon concentrations.
• Conduct austempering tests of specimens on
  Gleeble 3500.
• Extract kinetics of bainite formation from the
  dilatometric curves.
• Determine the kinetics of pearlite formation
  using dilatometric tests.
• Data analysis.

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TTT Diagram of AISI 4317
Bainite
H.E. Boyer and A.G. Gray, Atlas of Isothermal
Transformation and Cooling Transformation
Diagrams, ASM, Ohio, 1977
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Austempering test on Gleeble 3500

• The part is AISI 1080.
• Austenitzing temperature is 800?C.
• Austempering temperature is 250?C.
• The part dimension is shown below.

Gleeble 3500/3800 Operations Manual
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TTT Diagram of AISI 1080
Bainite
H.E. Boyer and A.G. Gray, Atlas of Isothermal
Transformation and Cooling Transformation
Diagrams, ASM, Ohio, 1977
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Predict the result from the Gleeble test
1
2
3
?
Temperature
Bainite
Time (sec)
fB
1
2
3
1
3
2
?
Time (sec)
Time (sec)
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Bainite

• The non-lamellar aggregate of ferrite and carbide
  which formed in steel by the decomposition of
  austenite above martensite formation but below
  pearlite formation through either isothermal
  transformtion or continuous cooling.
• Two main form
• - Upper bainite
• - Lower bainite

Isothermal transformation diagram for a 0.76C
steel
Callister W.D., Materials Science and
Engineering, 4th edition, John WileySons, New
York, 1997
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Bainite Microstructure
a.)
b.)
c.)
a.) Optical micrograph of a sheaf of upper
bainite in Fe-0.8C wt steel, b) Upper bainite
surrounded by martensite, c.) Lower bainite
surrounded by martensite
Callister W.D., Materials Science and
Engineering, 4th edition, John WileySons, New
York, 1997
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Work Plan Task 2
Microstructure and properties of austempered
bainite

• Characterize the microstructure of austempered
  specimens by optical microscopy and SEM.
• Mechanical tests.
• Conduct mathematical simulation for metallurgical
  process using simple temperature profile.
• Validate calculates results on Gleeble.

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Work Plan Task 3
Determine heat transfer coefficients in high
pressure gas quenching

• Literature survey for existing data.
• Experiment design using instrumented physical
  models.
• Conduct experiments in industrial high pressure
  vacuum furnace.
• Use inverse heat conduction analysis to determine
  heat transfer coefficient.
• Data analysis.

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Cooling Gas in Gas Quenching

• Hydrogen
• Helium
• Argon
• Nitrogen

G. E. Totten and M. A. M. Howes, Streel heat
treatment handbook, Marcel Dekker, New York,1997
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Work Plan Task 3
Determine heat transfer coefficients in high
pressure gas quenching

• Literature survey for existing data.
• Experiment design using instrumented physical
  models.
• Conduct experiments in industrial high pressure
  vacuum furnace.
• Use inverse heat conduction analysis to determine
  heat transfer coefficient.
• Data analysis.

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Work Plan Task 4
Austempering by high pressure gas quenching

• Experiment design for selected axle parts.
• Conduct instrumented experiments in industrial
  high pressure vacuum furnace.
• Carry out full thermal and metallurgical
  simulation.
• Mechanical and metallurgical examination.
• Data analysis.
• Process optimization.