Modelling of austenite grain growth kinetics in a microalloyed steel (30MSV6) in the presence of carbonitride precipitates

Abstract

Austenite grain growth kinetics in the presence of secondary precipitates of a microalloyed steel (30MSV6) was studied employing quantitative metallographic techniques. Austenitizing experiments were carried out at 1,000, 1,100 and 1,200 °C. According to the experimental data, abnormal grain growth behaviour is observed at 1,100 °C while it is normal at 1,000 and 1,200 °C. TEM observation represents multicomponent carbonitride precipitate, (Ti,V)(C,N), in the as-received steel with a mean radius of 35 nm. A mathematical model is proposed considering austenite grain growth along with dissolution and coarsening kinetics of the multicomponent precipitates. The austenite grain growth model for short-term non-isothermal and subsequent long-term isothermal heating stages was developed using a statistical approach. The model includes an algorithm to estimate the size distribution of austenite grains. Precipitate mean field dissolution and Lifshitz–Slyozov–Wagner coarsening models were integrated in the proposed model to calculate the pinning pressure retarding the grain boundary movement. The mean austenite grain size and the grain size distribution (normal and abnormal) calculated by the model are in good agreement with experimental data.

Keywords:

• modelling
• austenite grain growth
• microalloyed steel
• precipitate
• coarsening

Acknowledgements

The authors acknowledge Dr M. Mazinani and H. Naji for their help with technical details of this work. Further, we would like to thank Nahamin Pardazan Asia Co. for their help to use MIP, image analyzer software.