Effect of rapid cooling on mechanical properties of welded joint in laser welding of DP1000 dual phase steel

The softening phenomenon in heat affected zone existed in the laser welding processing of DP1000 dual phase high strength steel, which affected the formability and performance of welded structure seriously. In order to improve the formability and performance of welded joint, the way of rapid cooling was used to improve the softening in the heat affected zone of DP1000 dual phase steel laser welding. The microstructure and mechanical properties of welded joint of 1.5 mm thickness DP1000 steel plate with rapid cooling and air cooling were analyzed contrastively through the equipment of tensile tester, micro-hardness tester, scanning electron microscopy and optical microscopy. The results showed that softening zones in heat affected zone of welded joint was narrower under the condition of rapid cooling than under no rapid cooling during laser welding DP1000 dual phase steel. The softening phenomenon improved. The tensile strength and elongation were increased.