Abstract
Quenching and partitioning 980 (QP980) steel has been applied to new energy vehicles, but even laser welding joints show poor fatigue performance. In this study, water-cooling assistance is applied to improve fatigue resistance of welded joints. Hardness, tensile and fatigue tests are performed together with microstructure observation (scanning electron microscope, transmission electron microscope and electron back scattered diffraction). It is found that tempering martensite showing low hardness and small average grain boundary angles are responsible for poor fatigue performance. Results show that water-cooling assistance significantly improves welding softening and fatigue crack growth behavior of welded joints.
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