Martensitic transformation in the 30CrNi3MoV low-alloy ultra-high strength steel

Martensitic phase transformation characteristics in the 30CrNi3MoV low-alloy ultra-high strength steel were investigated by means of microstructure observation and dilatometric measurements.The results showed that the transformation products in the quenched 30CrNi3MoV steel were two kinds of martensite with different morphologies,lath martensite and acicular martensite,formation of which clearly separate each other in transformation dynamics curves.Lath martensites form in the relatively high temperature range(310℃~260℃) below the Ms,during which diffusion of carbon atoms occurred and resulted into carbon-rich austenite micro regions around martensite lath bunches.Acicular martensites form in the relatively low temperature range(260℃~170℃) below the Ms,which are transformed from the carbon-rich austenite micro regions retained after the formation of lath martensites.Transformation rate of the lath martensite is obviously higher than that of the acicular martensite.