In-situ determination of carbide dissolution in 52100 bearing steel

Carbide dissolution and phase transformation can be tracked in-situ with dilatometry, via subtle length changes throughout an entire heat treatment cycle. Through combining theoretical calculations of phase fractions with temperature and experimental dilatometry data, kinetic data can be extracted to determine the time required to dissolve carbides at various heating rates and austenitization temperatures. This study aims to develop a dilatometry test method to produce a diagram that predicts carbide dissolution time for steels, which would be particularly useful for heat treaters when designing optimized austenitization schedules. In particular, the carbide dissolution in 52100 bearing steel is investigated at various isothermal temperatures to plot the fraction of carbides as a function of time. The change in length is converted into the fraction of carbides, as determined through various models and thermodynamic data. These results are then compared to phase fractions measured post-heat treatment through optical and electron microscopy. Additionally, XRD is used to characterize the final microstructure directly after quenching.