Finite element simulation of the effect of the second pulse current on temperature distribution and nugget size in resistance spot welding of TRIP1100 steel

In this study, simulation of the effect of the second pulse current on temperature distribution and nugget size of TRIP1100 steel during resistant spot welding was performed by finite element method. Then, the effect of the second pulse current on the weld nugget size, weld nugget microstructure and mechanical properties of the resistant spot welds of the above-mentioned steel was experimentally investigated. Temperature distribution, weld nugget dimensions and heating and cooling cycles during resistant spot welding were predicted by simulation. Based on the simulated thermal cycles and continuous cooling transformation diagram of the TRIP1100 steel, a fully martensitic microstructure was predicted for the weld nugget in all currents. A good agreement was obtained between the simulated and experimental results. It was observed that the nugget diameter logarithmically increases with increasing the second pulse current. Furthermore, the microstructure of weld nugget in all samples was fully martensitic. Assessment of the mechanical properties of the welded samples by shear tension test demonstrated that the maximum load increases with increasing the weld nugget diameter. Nevertheless, the fracture energy decreased with increasing the nugget diameter.