Microstructural evolution and mechanical properties of 6Cr13 martensitic stainless steel subjected to cold rolling and heat treatments

Microstructure evolution and mechanical properties of 6Cr13 martensitic stainless steel subjected to cold rolling and subsequent heat treatments were investigated. The microstructure was checked by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The phases were identified by X-ray diffraction (XRD). The results show that the carbides are dissolved and fragmented during the cold rolling process, and the size of the carbides decreases with increasing the rolling reduction. The refinement of the microstructure, including martensite laths, twins and carbides, occurs due to the dislocation activities induced by the cold rolling. A high density of dislocations persists in the steel even after the heat treatments. Furthermore, reversed austenite forms during tempering of the steel with a rolling reduction of 67% at 200 °C and 300 °C. The steel with a reduction of 67% exhibits an ultra-high strength of ∼1913 MPa, an elongation of ∼7% and a microhardness of ∼58 HRC after the heat treatments (i.e., quenched at 1050 °C and tempering at 200 °C), which is attributed to the synergetic effect of microstructure refinement, the formation of reversed austenite and the high retained dislocation density.