The Low-Temperature Toughness Improvement of High-Strength Low-Alloy Steel Due to the Microstructural Changes Caused by the Reheating/Rolling Temperature

Herein, the microstructure, low-temperature toughness, and fracture characteristics of high-strength low-alloy (HSLA) steel prepared by various thermomechanical control processes are systematically studied. Three different reheating/rolling temperatures are designed to obtain microstructures with different prior austenite grain sizes: 20.12 mu m (S810), 27.58 mu m (S910), and 35.19 mu m (S1010). After hot rolling, S810 steel with smaller prior austenite grain size can provide high-density deformed grain boundaries that promote ferrite phase transformation. The S910 and S1010 steels predominantly undergo bainite transformation as the prior austenite grain size and rolling temperature increase. Also, excellent low-temperature toughness is obtained by reducing the reheating/rolling temperature (i.e., S810 steel), reflecting that Charpy impact energy of the core of the steel plate is 118.53 J at -120 degrees C. High performances is mainly attributed to the higher ferrite content, grain refinement, lower dislocation density, and higher proportion of high-angle grain boundaries. Furthermore, fracture morphology analysis demonstrates that the S810 steel exhibits ductile fracture and noticeable plastic deformation at -120 degrees C, while S910 and S1010 steels exhibit brittle fracture and rapid crack propagation. These findings manifest the applicability of the suggested technique in preparing HSLA steel with excellent low-temperature toughness. The prior austenite grain size of high-strength low-alloy steel is refined by reducing the reheating temperature. The fine prior austenite grains offers higher density grain boundary, which promotes the ferrite transformation and is conducive to obtaining excellent low-temperature toughness. The synergistic effect of the tortuous crack path and plastic deformation results in the excellent crack arrestability of S810 steel.image (c) 2024 WILEY-VCH GmbH