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 À100 C.

Influence of Heat Input on the Weldability of ASTM A131 DH36 Fillet Joints Welded by SMAW Underwater Wet Welding

“…To achieve uniform microstructures, using a high heat input single weld bed at a slow and constant welding speed is preferable, resulting in a microstructure of PF and LTM, which produces a non-brittle and uniform weld joint. Thus, the use of a high heat input at slow welding rates is preferred because the resulting microstructure increases the ductility of the welding joint, avoiding brittle behavior, which is consistent with the findings of prior studies on similar materials by Gao Wenbin et al [25], Gao Wenbin et al [29], Toumpis Athanasios et al [37], Li Hongliang et al [41], Di Xinjie et al [42], Macias Fernando et al [38], Kozlowska Aleksandra et al [43], Meng Fanxia et al [39], Zhang Hongmei et al [40], and Min-Seok Baek et al [48].…”

“…In contrast, at 1.5 kJ/mm (Figure 7e), the microstructure displays polygonal ferrite (PF) and lath-tempered martensite (LTM), which suggests that the high heat input and multiple welded beads temper the lath martensite (LM). This finding is in line with the results reported by Macias Fernando et al [38], Meng Fanxia et al [39], and Zhang Hongmei et al [40] on similar materials. The microstructures of the RCL HAZ display similar results between low and high heat inputs.…”