Microstructure and Properties of Pulsed Laser Welded Joint of Cold-rolled DP590 Dual Phase Steel Sheet

The cold-rolled DP590 dual phase steel sheets with 1 mm thickness were butt-welded by the pulsed laser welding and the microstructure, mechanical properties and formability of the welded joint were studied. The results show that the microstructure of fusion zone (FZ), heat affected zone (HAZ) and base material (BM) consisted with lath martensite, ferrite and lath martensite, ferrite and martensite respectively. The average micro-hardness of FZ, HAZ and BM was 344, 275, 205 HV respectively. The tensile fracture position of the welded joint was in BM, which showed a ductile fracture. During the Erichsen test, the cracks formed at the center of FZ and then propagated into HAZ and BM perpendicular to FZ. The cracks propagated in FZ by cutting the lath martensite and in HAZ and BM along the ferrite and martensite interface. The formability of welded joint was good and the Erichsen value reached 81.9% that of BM, meeting the requirements for production.