Effect Of Hot Deformation On The Martensite Phase Transformation And Performance Of T92 Steel

To investigate the effects of hot deformation on martensite transformation and microstructure evolution of T92 ferritic steel, the thermal simulation experiments of T92 ferritic steel were conducted on a Gleeble-1500 thermal simulation testing machine. By microstructure examination, phase determination and mechanical performance assessment, the martensite transformation mechanism and MX precipitation behaviour of T92 steels under different strains and deformation temperatures are elevated, providing guidance for the optimization of hot deformation parameters of T92 steel.With the increase in deformation strain, the peak stress will be decreased. As the steel was deformed at the strain range from 15% to 45%, the sizes of martensite laths are not uniform, with a majority of coarse grains, and the boundaries were slightly bent. At the deformation strain of 60%, due to the dynamic recrystallization, the martensite laths were much finer and more homogeneous. The boundaries were evolved into sawtooth or wave shape. With the increase in deformation strain, the martensite start temperature will be increased, and the martensite laths will be refined. The high density of dislocations within martensite laths will facilitate the nucleation of MX carbonitride, contributing to the improvement of high temperature performance of T92 steel. As for the increase in deformation temperature, the peak flow stress will be decreased again. When the deformation temperature changed from 750℃ to 850℃, the martensite laths were fine and homogeneous, and the microstructure consisted of elongated deformed prior austenite grains. With respect to the deformation temperature window ranging from 950℃ to 1050℃, the coarse martensite laths can be observed. At 1150℃, the coarse martensite laths can also be observed. The increase of deformation temperature would lead to the decrease of martensite start temperature, as well as the microhardness of martensite laths. Despite of the coarse prior austenite grains, reduced grain boundaries and severe stress concentration, more MX carbonitrides were precipitated with a finer size and more homogeneous distribution, compared to those attained by standard heat treatment.