Influence of heating rate, cooling rate and numbers of pulses on the microstructure of AISI 4140 after short-time-hardening

In recent years, significant progress has been made in application of lasers to surface hardening processes. While there are many investigations on the transformation behaviour during cooling based on initially homogeneous austenite states, there is a lack of data concerning austenite formation at very high heating rates and the impact of the initial austenitic condition on the final microstructure. Moreover the influence of cyclic austenite-martensite-transformation on the microstructure has been studied rarely. Therefore, in this paper the effect of heating rates up to 10000 K/s, cooling rates up to 3000 K/s and the impact of cyclic austenite-martensite-transformations on the microstructure of AISI 4140 (German grade 42CrMo4) are presented.