Characteristics of Nd:YAG Laser Welded Joints of Dual Phase Steel

Examination results of microstructure, mechanical properties, fatigue strength and residual stresses of laser welded joints in dual phase HDT580X steel have been presented. The main goal of these studies was to verify whether Nd:YAG laser welding without filler metal can be used for welding of dual phase steel. In the frame of this investigation the microstructure has been studied by optical and scanning microscopy. Mechanical properties have been analysed by tensile, bend and hardness tests. Additionally fatigue tests and residual stress measurements were carried out. The results revealed that the HDT 580X steel is characterized by good laser weldability. The tensile strength of welded joints is at the same level as that of the base metal and the maximum hardness does not exceed 343 HV. The microstructure of welded joints is mainly composed of lath martensite in the weld and a mixture of lath martensite, bainite and ferrite in the heat affected zone (HAZ). The fatigue class FAT was determined, which is equal to 284 MPa and 150 MPa for base material and welded joint, respectively. Residual stresses determined by the hole drilling method and the videoextensometer were: σmax= 573 MPa and σmin= −126 MPa.