Direct observation of martensite phase transformation process in P91 steel

The martensite transformation process of P91 steel was observed directly by the equipments of laser confocal scanning microscope (LCSM), heating stage and digital video. The results show that martensite can nucleate in grain boundary and in grain interior in P91 steel, and can nucleate by stimulation as well. The microstructure of quenched martensite in P91 steel is lath martensite and the substructure is composed of high-density dislocations and twin crystals. The surface of the martensite piece is smooth without strain traces, which indicates that martensite transformation is not a shear process at all. The growth speed of martensite sheet in P91 steel is very fast. The formation time of a martensite piece is less than 4×10-2 s and the average linear growth speed is greater than 0.16 cm /s. ©, 2014, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.