Structure and mechanical properties of steel !Crl2Ni3Mo2VN quenched at 1 010 °C for 1 h

oil cooling and double tempered at 580 ~620 °C for 1 h

air cooling have been studied. Test results show that in tensile specimen tempered at 620 °C 

a large amount of coarsening block M

23

C

6

carbides precipitate at boundary of tempered martensite lath

and the plastic defonnation of specimen goes on by means of twin's motion with lower plasticity ； but the plastic deformation of tensile specimen tempered at 580 °C . goes on by means of slipping motion with better plasticity. The optimum tempering process of the steel is double tempering at 580 °C  for 1 h

air cooling.