Stress Field Numerical Simulation And Mechanical Properties Of X80 Pipeline Steel Joint By Laser Arc Hybrid Welding

Laser arc hybrid welding is a kind of emerging specialty processing technology, which has many advantages such as small groove angle, small deposited amount, high energy density and low heat input when welding thick plate. Therefore, X80 pipeline steel was welded by laser arc hybrid welding. The welding temperature field and stress field are simulated using finite element software ANSYS.Considering the welding process parameters, the interaction of laser and arc and the effect of narrow gap groove on the distribution of heat sources, two laser hybrid welding heat source models are established. One is suitable for flat surfacing welding. And the other is suitable for narrow gap groove welding. Based on the developed source models, welding temperature field under different welding parameters is simulated for the X80 pipeline steel. By comparison, the simulated weld matched the actual weld profiles well, which verified the accuracy of the heat source model.The results of multilayer welding temperature field numerical simulation with narrow gap groove show that the laser arc hybrid welding had fast heating speed, short high-temperature residence time and fast cooling speed.For the analysis of the residual stress distribution of joint, the evolution of the transverse transient stress along the weld length direction during the cooling process and the distribution of transverse transient stress along thickness direction under different welding parameters, welding stress field were calculated by means of thermal structure coupling. The results showed that residual stress is large near the fusion zone and residual deformation is small when using a large laser power and small arc current. The larger laser power is, the greater instantaneous transverse tensile stress produced. Therefore the tendency to crack crystals is greater. Crystal cracks are prone to the beginning and the ending of the weld. Under the same welding parameters, crystal cracks are more likely occurs in narrow gap groove welding than the flat surfacing welding.Microstructure and mechanical properties of the welded joint under different laser arc hybrid welding parameters are studied. The results show that the weld is composed of a large number of acicular ferrite, a certain amount of granular bainite and lath martensite. Coarse grain zone consists of lath martensite and granular bainite. The yield strength and tensile strength of laser hybrid welding arc welding joints is 620 MPa and 710 MPa respectively, which higher than that of the base metal. Impact toughness of weld is high. It can meet the requirements.