Effect of Rolling and Heat Treatment Process Tempering on the Microstructure and Mechanical Performance of Cr–Ni–Mo High‐Strength Ship Steel

Abstract

The effects of rolling process and tempering temperature on microstructure and mechanical performance of experimental steel are studied. The results show that the yield ratio and elongation of the experimental steel are lower under noncontrolled rolling; under off‐line tempering after controlled rolling, the tensile and yield strength decrease slightly with the increase in quenching temperature, the yield ratio decreases and the elongation increases; under the condition of controlled rolling, ultrafast cooling (UFC), and off‐line tempering, the microstructure is fine martensite lath and a large number of fine precipitates, the steel has the highest strength and elongation. With the increase in tempering temperature, the tensile strength of the experimental steel decreases gradually, the elongation increases monotonously, the yield ratio and impact energy increase first, and then decrease. After comparison and analysis, it is found that the best performance can be obtained by direct online UFC after controlled rolling, and then tempering at 630 °C, that is, tensile strength 908 MPa, yield strength 863 MPa, yield ratio 0.95, elongation 21.41%, and impact energy 94 J at −100 °C.