Microstructural evolution of high Cr ferrite/martensite steel after deformation in metastable austenite zone

In this paper, the influence of compressive deformation in metastable austenite zone (at 700, 600 and 500 °C, respectively) on microstructural characteristics and martensitic transformation behavior for the high Cr ferrite/martensite steel is investigated by using high-resolution dilatometry and transmission electron microscopy (TEM) observation. The results show that compressive deformation in metastable austenite zone results in decrease of martensite lath width and increase of martensite starting temperature (Ms) due to increase of defection density for martensitic nucleation. The martensitic transformation time is extended by the pre-stress loading above Ms, which is ascribed to decrease of interfacial migration rate during martensitic transformation by means of strain hardening. The results of tempering experiments indicate that decrease of deformation temperature leads to increase of recovery fraction. This is ascribed to that decrease of deformation temperature raises the residual strain energy and thus lowers the apparent activation energy for recovery. Hence, phenomenon of recovery occurs prematurely in the tempering specimen with the low deformation temperature.