In situ heat treatment in selective laser melted martensitic AISI 420 stainless steels

The article explores an evolution of a microstructure in AISI 420 martensitic stainless steel during selective laser melting. Several upper layers had hardness of 750 HV and contained 21 ± 12 vol.% austenite phase. The final bulk microstructure consisted of thermally decomposed martensite with hardness of 500–550 HV and unusually high, 57 ± 8 vol.%, amount of austenite. Obtained results indicate that during manufacturing a partitioning and austenite reversion took place, owing to the thermal cycling of the inner regions during manufacturing. Numerical simulation was found plausible to analyze and explain thermally activated processes that occurred in situ. Results of numerical simulation of the thermal cycles in dependence on the processing parameters suggested a possibility to control the thermal processes by variation of the laser energy input.