Microstructure and properties of 65Mn spring steel by laser welding

To obtain excellent welding joint, 65Mn spring steel was welded by 5 kW CO₂ laser welding equipment.Microstructure, tensile strength, tensile fracture and residual stress of this joint were investigated by means of OM, XRD, SEM, microhardness testing machine, electronic universal testing machine and residual stress test machine.The experimental results indicate that the fine equiaxised crystal, dendrite crystal and cell grain are formed from welding central zone to edge zone, respectively.In the HAZ, the over-heated zone is mainly comprised of coarse acicular martensite.Recrystalline zone mainly consistes of fine acicular martensite.The part transforming zone is comprised of ferrite and pearlite.The welding joint mainly consists of fine α-Fe, Fe₃C and FeSi.The highest hardness value of welding zone and HAZ is 720 HV and 770 HV, respectively.The hardness decreases significantly from HAZ to base metal.The average tensile strength of welding joints is approximately 475 MPa.The average residual stress in welding zone is 105 MPa, and the average residual stress in HAZ is-60 MPa.