Retained austenite in SAE 52100 steel post magnetic processing and heat treatment

The application of magnetic fields as a method of reducing retained austenite in steel is based on the thermodynamic argument that paramagnetic austenite is destabilized in the presence of a large magnetic field. The goal of this study was to determine the effect of applying a magnetic field at room temperature after quenching on the amount of retained austenite. After heat treatment and several post-quench delay times, samples of SAE 52100 steel were heat treated then subjected to a magnetic field of varying strength and time. X-ray diffraction was used to collect quantitative data corresponding to the amount of each phase present post processing. Stronger magnetic field strengths resulted in lower amounts of retained austenite for fixed application times. The results for applying a fixed magnetic field strength for varying amounts of time were inconclusive and suggest negligible dependence. When applying a magnetic field after a post-quench delay time, the analyses indicate that decreased delay times result in less retained austenite, which indicates that retained austenite becomes more stable with time after quenching. Established martensite transformation kinetic equations were applied to estimate the effect of the magnetic field on martensite start temperature and the resulting amount of retained austenite. A data fit indicates a 2°C/Tesla shift in martensite transformation kinetics.