An effect of the solidification rate on the hardness was investigated in Fe-Cr-Mo-C stainless steel (SUS420J2) produced by rapidly quenched casting process with single-roll at various rolling speeds from 5 to 40m/s. Furthermore the optimizing process to improve hardness after final heat treatment in industrial scale was carried out for the ingot operated with a rolling speed of 10m/s which could exhibit sound state without any materials defaults. A final goal of the higher hardness more than Hv = 800 after final heat treatment could be obtained along the process condition with the tempering (baking) treatment (air cooling after heating at 973K for 120m/s) and the quenching treatment (air cooling after heating at 1323K for 60m/s). The microstructure observation clarified that the origin of the obtained higher hardness in the optimum processed material compared with the as-cast material resulted from the finer grain size of the old austenite phase at 10μm then 20μm of the as-cast one.
