Effect of Tempering Process on Mechanical Properties of Cr–Mn–Ni Low‐Alloy Ultrahigh‐Strength Steel

In this study, the relationship between microstructure and mechanical properties of Cr – Mn – Ni low‐alloy ultrahigh‐strength steel subjected to different tempering processes is studied. The results indicate that with increasing tempering temperature, quenched martensite undergoes gradual decomposition. The strength and hardness gradually decrease, while elongation does not exhibit a clear trend. Impact energy initially declines and later increases, with noticeable tempering brittleness observed at 450 °C and 550 °C. The microstructure and properties of two‐step tempering are basically the same as that of conventional tempering. However, extended tempering time leads to a 125% improvement in elongation and superior tensile strength (1760 MPa). The tempering transformation of quenched martensite in the tempering process directly dominates the changes of mechanical properties. The decomposition of supersaturated martensite during tempering is the primary factor affecting grain boundary distribution; however, it has no significant impact on the microstructural orientation relationship or texture evolution. In the tempering brittleness of 550 °C, the distribution of band contrast values, elevated kernel average misorientation at grain boundaries, localized concentration of crystal orientations along <101> and <111>, and the pronounced Brass texture may collectively contribute to the onset of tempering brittleness.