.65 Mn Spring Steel Laser Welding

As a kind of machine parts steel, 65Mn spring steel is widely used in machinery, transportation and other fields. As to the traditional welding technology for 65Mn steel, there exists problems such as big heat affected zone and serious thermal brittleness , therefore its application for some fields is limited. The comparision of laser welding with the traditional welding, it has many advantages such as high ratio of depth to widenth, the narrow welding zone , the small heat affected zone and small deformation etc, so laser welding is widely used in many industries.In this paper, 65Mn steel is welded by laser (5kw), and crystallization, microstructure, microhardness, phase structure, tensile strength, fracture, residual stress are investigated with OM, microhardness tester, XRD, SEM. through the experiments we do above, the optimum laser welding parameter on 65Mn Steel is obtained. The above results we achieved provide theoretical guidance for the application of 65Mn Steel by laser welding.The experimental results show that: (1) When P=2.0kW, V=7mm/s, the perfect qualify of laser welding is obtained; (2) The fine equiaxed crystal, dendrite crystal and cell grain are formed from welding central zone to the edge zone, and martensite, bainite and a small amount of ferrite appeared mainly in the heat affected zone; (3) The welding joint mainly consists of fine a-Fe,Fe₃C and FeSi; (4)The average highest hardness in weldind zone is Hv720, and the highest hardness in heat affected zone is Hv770, the hardness obviously decreases from the heat affected zone to substrate.; the average tensile strength is 375 MPa, and the tensile strength can be up to 498MPa under the best welding parameters; and the residual stress is very low, the average residual stress in welding zone is 104MPa ,and the average residual stress in heat affected zone is -76MPa.