In situ , quantitative analysis of tempering and subsequent austenitization of tempered martensite on continuous heating of a Fe-C-Si-Ni steel using dilatometry

Tempering and austenitization of as-quenched martensite in a Ni-containing medium carbon steel has been studied in situ using dilatometry under continuous heating conditions at a heating rate of 5°C/s. A comprehensive methodology is proposed for the quantitative prediction of the phase fractions from the dilatation measured during tempering and subsequent austenitization. The transient carbide precipitation is weak due to the high heating rate. However, the subsequent cementite precipitation approaches equilibrium fractions towards the end of tempering. The austenitization occurs from a mixture of ferrite and cementite. The predictions are validated through heating and interrupted quenching experiments and microstructural characterization. These results shed light on the complex dynamics of tempering and austenitization during continuous heating.