Investigation on the microstructure and mechanical properties of autogenous laser welding joint of ITER BTCC case lid

Abstract

Abstract The 316LN stainless steel with a thickness of 21 mm was welded by autogenous laser welding from both sides with an YLS-20000 fiber laser welding system. The microstructure of the welding joint was characterized by optical microscope. The tensile and bending tests were performed at room temperature and impact testing was conducted at 4.2 K. The results show that the thickness of the remelting region decreases with the increase of welding speed. The microstructure of the weld zone was single austenite phase. The tensile strength of the welded joint is 623 MPa at room temperature, equal to that of the base material (624 MPa). The fracture was located in the base metal. The bending test of the welding joint shows that no micro crack could be found on the surface of the samples after bending to 180 degrees, which indicates that the welded joint has good bending strength and plasticity. The average impact absorption energy of the welding area and heat affected zone at 4.2 K is 173 ± 10 J and 241 ± 8 J, respectively. The fracture surface shows a typical ductile fracture mode featured with fine equiaxed dimples and tearing ridges. All the test results meet the ITER design requirement.