Combined athermal and isothermal martensite to austenite reversion kinetics, experiment and modelling

Abstract

A novel laser heat treatment setup is presented and used to characterize the reverse transformation of martensite to austenite resulting from highly dynamic laser heat treatments of stainless steel. During laser heat treatments the irradiated spot and its surroundings can experience completely different thermal loads, yet both experience reverse transformation. The experiments are conducted such to reflect these diverse conditions. Next to experiments, a new kinetic model is reported which combines both athermal and isothermal transformation mechanisms to cope with the diversity in conditions in a unified framework. The experimental results show that reverse transformation can proceed extremely fast, yet saturates at intermediate temperatures. Additionally, it is shown that there is good agreement between experiment and model and it is essential to embed both the athermal and isothermal transformation mechanism in the model for achieving this performance. Initial steps towards model validation are performed showing good predictability of a non-isothermal heat treatment with conditions realistic and relevant for industrial laser heat treatments.

Keywords

• Phase reversal
• Athermal transformation
• Thermally activated transformation
• Laser heat treatment
• Austenitic stainless steel
• Kinetic modelling