Forgebility evaluation of SNCM 220 steel by warm compression test and microstructure behaviors characteristics

Spheroidizing annealing cycle was applied on the SNCM 220, which is an alloy steel for mechanical structures to improve warm forgeability. Heat treatment was given on the specimen, filled with Ar gas to prevent oxidization. Spheroidizing microstructure was examined in the specimens received the intercritical cycle, measured the largest elongation rate during mechanical properties evaluation. And, carbides cracked more as retaining time at the intercritical annealing was extended. Formability of the SNCM 220 was investigated by changing temperature and compression speed at high temperature under heat treatment condition, set as per the preliminary experiment result. As compression speed was increased, the stress on the specimen was also increased, while the stress was decreased as the temperature was increased. Flow curve by treating the specimen at 600°C - 900°C was also drawn. From the zone at 900°C, pinning appeared due to precipitation hardening. Structure of the specimen was examined, which was changed by deformation speed of flow stress and temperature, confirmed with the compression experiment. The highest hardening value was achieved at 900°C. However, it would be the most beneficial to carry out a forming at 600°C with deformation speed at 0.01 mm/s, at the economic as well as mechanical view point.