Effect of tempering temperature and Mo on microstructure and properties of Ti microalloyed steel

Influences of tempering temperature and Mo element on microstructure and mechanical properties of Ti microalloyed steel were investigated by means of scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results show that the lath-shaped martensite transforms to ferrite gradually with increasing tempering temperature,meanwhile,the hardness of the tested steels increases firstly and then decreases,and the optimum tempering temperature is 600 ℃.It is found that the addition of Mo enhances the transformation from lath-shaped martensite to ferrite during the tempering process of Ti microalloyed steel.The sizes of the precipitates become smaller and the comprehensive mechanical properties of Ti microalloyed steel are improved when(Ti,Mo) C precipitates with size of less than 10 nm.