Influence of welding time on performance and failure mode of hot stamping boron high strength steel spot-welded joints

The characteristics of large resistivity,high peak temperature in welding thermal cycle,fast rising rate of temperature and uneven local cooling rate determined the heterogeneity in resistance spot-welded joints of hot stamping boron high strength steel,which resulted in three different failure modes of the joints. The effects of welding time on microhardness, bearing performance,failure modes of the resultant joints were studied,and the failure mechanism was investigated. The results show that the capacities of bearing and energy absorption between 400 ms and 600 ms of welding time were equivalent, and the nugget pull-out could not be the standard for evaluating the quality of joints. The welding defects,stress concentration and local toughness deterioration in HAZ were three main factors that affected the failure of the joints.