Fatigue Properties of Quenching and Partitioning 980 Steel Laser Welding Joint Obtained under Rapid Cooling Condition

The laser-welded joints of quenching and partitioning 980 steel were obtained under both air and rapid cooling conditions. The primary focus of this study was to investigate the fatigue properties of these welded joints. The softening induced by the precipitation of carbides in the heat-affected zone, particularly within the tempered martensite, can adversely affect the fatigue properties of the welded joints. The results indicate that the application of rapid cooling serves to reduce the local peak welding temperature and grain size, thereby minimizing carbide precipitation in the tempered martensite within the subcritical heat-affected zone of the welded joints. Consequently, there is an improvement in formability properties and hardness values. Fatigue tests reveal that the fatigue life of the welded joints is significantly extended under rapid cooling conditions. Furthermore, the carbide precipitation of tempered martensite exhibits distinct influences on the strain at the crack tip.