Experimental-based computational prediction of the austempered steel reheating results - Laser hardening simulation

Basing on the SYSWELD-driven FEM simulations and dilatometric experiments, we propose a method to predict structural changes in laser hardened austempered 30HGSNA steel containing 18.9 vol% of retained austenite. The ability to predict effects through simulation is very valuable for the design of unconventional hybrid treatments, especially when the initial microstructure is not ferritic-pearlitic. For 2 out of 3 evaluated variants, there was a satisfying prediction of a hardened - transition zone border with the prediction error in the 1.5-8.0 % range. In addition to the methodology adopted in the simulation, the impact of the increased heating rate of the austenitic transformation under continuous heating conditions was also described. The progressive shift of Ac1 and Ac3 temperatures towards higher values occurring at heating rates of tens of degrees C per second and higher was explained by the accumulation of atomic jumps. Mutual influence of the heating rate and retained austenite on Ac1 temperature and hardness decrease of tempered bainite below Ac1 temperature were shown. Austempered steel's hardness after rapid reheating to laser hardening temperatures and microstructural changes were presented.