Effect of process parameters on microstructure and properties of spot welded joints of 1000MPa grade high strength steel structure

The effects of electrode pressure,welding current,welding time and pulse tempering on the microstructure and mechanical properties of 1 000 MPa grade high strength steel structure spot welded joint were studied. The results show that with the increase of the electrode pressure and welding current,the nugget diameter of the spot welded joint increases first and then decreases,at the electrode pressure of 2.8 kN and the welding current of 8.0 kN,the spot welded joint has splash. With the increase of the welding time,the diameter of the spot welded nugget is increased gradually,at the electrode pressure of 3.4 kN,welding current of 7.5 A and welding time of 16 cyc,the nugget diameter of spot welding joint is larger,the martensite structure is thin,the hardness is higher,the tensile shear force reaches 13.0 kN,the joint strength is higher. After 1 times pulse tempering and 2 times pulse tempering,the maximum tensile shear strength of the spot welded joint is 13.8 kN and 14.2 kN,respectively,which is 6.15% and 9.23% higher than that of the non-pulse tempered joint.