Effects of alloying elements on the kinetics of austenitization from pearlite in Fe–C–M alloys

Abstract

The effects of alloying elements on the kinetics of austenitization from pearlite structure were studied by computer simulation in Fe–C–M ternary alloys, where M is Mn, Cr, Si or Ni, assuming local equilibrium conditions at all transformation interfaces. A thin austenite film was assumed to nucleate at ferrite/cementite interfaces and grow in one dimension. The existence of a partition to no-partition transition temperature (PNTT) was rationalized. Above the PNTT, the growth rate of austenite is governed by the difference in carbon activity between austenite/cementite and ferrite/austenite interfaces; a substitutional element influences the reaction rate by affecting carbon activity. Below the PNTT, redistribution of M is necessary. The PNTT increases with the concentration of all alloy elements except Ni, which has a large segregation tendency in austenite from both ferrite and cementite, as well as repulsive interaction with carbon. The amount of overheating at PNTT from Ae₁ increases in the order Si (∼Ni), Mn and Cr, essentially in agreement with a recently reported experiment.

Keywords:

• austenitization
• pearlitic steel
• local equilibrium
• growth
• alloy element

Acknowledgements

The authors express their thanks to CISRI-TCS United Open Laboratory, Beijing, for assistance in calculation. The support from the National Natural Science Foundation of China (Grants 51071089 and 51171087) is gratefully acknowledged.