Research And Optimization Of Resistance Spot Welding Process Of Hot-stamped Steel B1500HS

With the advantages of high strength and hardness, the hot-stamped steel which is composed of martensite plays a more and more important role to meet the demand of lightweight and safety in automotive industry. Resistance spot welding is typically employed to join structural steel components in the large-scale automatic production of vehicle. Compared with ordinary steel, the weldability of hot-stamped steel is greatly different, and there are many other problems during the welding process, such as softening of heat affected zone, embrittlement of nugget, splashing and so on. So it's significant to research the mechanical and microscopic properties of the resistance welding spots of hot-stamped steel, and obtain the perfect welding parameter.In this paper, resistance spot welding of B1500HS hot-stamped steel with 1.5mm has been researched, using the power-frequency alternating current welding equipment and the mid-frequency inverter one. The tension strength, hardness distribution, microstructure and the cross-tensile fracture appearance have been analyzed. The test results show that the hot-stamped steel has good weldability, and the nugget diameters and tensile shear strength both meet production requirements. The microstructure of spot welded metal is martensite. It's easy to get button fracture mode and shear dimples. The cross-tensile strength has sharply decreased, mainly as a result of the existence of softened zone near heat affected zone.Hot-stamped steel is wildly used in some critical structural components to enhance strength of vehicle, which needs that it must have good resistance spot weldability with different materials. In this paper, resistance spot welding of hot-stamped steel with 2.0mm and H240LAD+Z ordinary low-carbon steel with 0.8mm and 1.5mm have been researched. The tension strength, hardness distribution, and microstructure of welding spots have been analyzed, and obtain the perfect welding parameter. The results show that mechanical and microscopic properties of nugget has been greatly improved under the optimized parameter, and there is no splash during the welding process.