Effect of Welding Heat Input on the Simulated Heat-Affected-Zone Toughness for Yield Strength 390MPa Class TMCP Steel Plate

In this study, the influence of heat input on the microstructure and toughness of the simulated heat-affected zone (HAZ) of YP390 MPa grade steel with a thickness of 80 mm was investigated. The weld coarse-grained HAZ was simulated using a Gleeble 3500 simulator, with heat input levels ranging from 30 to 650 kJ/cm. Following the HAZ simulation test, the microstructures and Charpy impact properties were examined. For heat inputs ranging from 30 to 50 kJ/cm, the microstructure consisted of bainitic ferrite/acicular ferrite, resulting in an impact toughness exceeding 200 J at -20 ℃. Conversely, in the higher heat input range of 130 to 650 kJ/cm, the simulated HAZ exhibited a lower impact toughness value due to the formation of coarse grain boundary ferrite. A high proportion of acicular ferrite with minimal grain growth was found to be the key metallurgical factor contributing to the improvement of impact toughness.