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Project B8: Simulation of phase transformation during hot forming process

Person in Charge: M. Tech. Ankit Kumar

Motivation and goals:
In the sheet metal forming process for steel, cooling rate plays an important role in the final microstructure. Typically, steel is heated above the upper critical temperature to form Austenite (crystal structure changes to face centered cubic) and subsequently cooled:

  • Slow cooling leading to formation of soft phase Pearlite (Ferrite+Cementite)
  • Rapid cooling (Quenching) leading to the formation of hard phase Martensite (Body Centered Tetragonal)

In the project B8, we have the following research objectives: Development of a phase-field model for phase transformation in steel depending on the cooling rate. We aim to consider both (a) Austenite to Pearlite, Bainite and (b) Austenite to Martensite transitions.

Investigation Results
  • Formulation of a multi-phase field model based on the grand potential functional to simulate Austenite to Pearlite diffusive phase transformation and comparison with analytical results.
  • Modification of the free energy model to a “grand elastic potential” to simulate transformations occurring by displacive mechanism, e.g.  Austenite to Martensite phase transformation.
  • Comparison of numerical results with Koistinen-Marburger-Model and Johnson-Mehl-Avrami-Model in co-operation with project A9 and project A14
  • Analytical studies for a stable lamellar growth using a Jackson-Hunt-type calculation and derived expressions for the lamellar velocity and spacing at different undercoolings
  • Phase field simulation of the eutectoid transformation and comparison with analytical results.
   
Martensitic transformation (Displacive mechanism, FCC to BCT) Pearlite growth in 3D (Cementite in red, Ferrite in green)