Abstract: The morphology and substructure of martensites in 7CrSMnMoV steel were observed under optical or electron microscope,and martensitic transformation with its morphology was also analysed.In the normally quenched steel three types of martensites are found,including the wide lath one of dislocation substructure formed preferentially along grain boundaries,the thinner inner laths and the twinning martensite plate in interior of grain.Therefore,an at- tempt was made to substitute lower bainite,formed by short-term isothermal quenching.for intergranular martensite,it is believed that the morphology would be very influential to the stength-toughness of the steel.

Key words: 7CrSiMnMoV steel, martensite, strengthening