Fatigue properties of laser welded dual-phase steel joints

The aim of this study was to evaluate the effect of laser welding on fatigue properties of DP600 and DP980 steels in relation to the microstructural change and softening in the heat-affected zone. The degree of softening was found to be stronger in the DP980 welded joints than in the the DP600 welded joints. While the severity of the soft zone in the welded DP980 joints led to a significant decrease in the fatigue limit, the mild soft zone present in the DP600 welded joints had little or only a minor effect on the fatigue resistance. Despite the strong effect of the soft zone, the DP980 welded joints showed a similar or even longer fatigue life than that of both the DP600 welded joints and DP600 base metal at higher stress amplitudes. Fatigue crack initiation was observed to occur from the specimen surface, and crack propagation was characterized by the characteristic fatigue striations coupled with secondary cracks.