Effects of Heat Treatment Process on Microstructure and Mechanical Properties for Extra-Thick High-Strength Steel Plate

To develop thickness>60mm, yield strength>550MPa high-strength steel plate, the effects of heat treatment process on the microstructure and mechanical properties of plate specimens were investigated on the same controlled rolling and cooling process. The research results showed that, a single time-quenching and tempering heat treatment were conducted to obtain the bainite + free ferrite and residual austenite, the grain size was large and the impact toughness was low. Twice-quenching and a tempering heat treatment could refine the microstructure grain size and increase the soft ferrite proportion to obviously improve the mechanical properties and impact toughness. Taking reasonable intercritical quenching after tempering, the mechanical properties of plate are significantly improved.