Gas metal arc welding of XPF800 steel for automotive industry: Microstructural evaluation and mechanical properties investigation

In this study, the effect of gas metal arc welding on the mechanical and microstructure properties of hot-rolled XPF800 steel newly produced by TATA Steel has been investigated. This steel finds its role in the automotive industry as chassis and seating applications. The microstructure transformation during gas metal arc welding has been analyzed using scanning electron microscope, optical microscope, and energy dispersive X-ray spectrometry. Tensile, Charpy impact, and microhardness tests have been implemented to determine the mechanical properties of welded samples. Acceptable welded joints have been obtained using heat input in the range of 0.28–0.46 kJ/mm. It has been found that the base metal hardness of the welded sample is 320 HV0.1. On account of the heat-affected zone softening, the intercritical heat-affected zone hardness values have diminished ∼20% compared to base metal.

Effects of welding parameters on tensile properties and fracture modes of resistance spot welded DP1200 steel

In this study, the maximum tensile shear load bearing capacity and fracture modes of resistance spot welded DP1200 steel were investigated, and the tensile shear properties of the joints were evaluated. The effects of different welding parameters on tensile shear properties, fracture modes, microstructure, microhardness, and heat affected zone softening were examined. Weld processes were performed by using 2 to 6 bar electrode pressure as well as 5 and 7 kA weld currents. The microstructure of resistance spot welded materials was evaluated, and the hardness profiles were determined. Experimental results showed that welding current and electrode pressure had a significant effect on the load-displacement characteristics of DP1200 welds. Three different fracture modes were observed in the tensile shear loads. It was also observed that the expulsion had a negative effect on the tensile shear properties.

Modelling of Heat Affected Zone Softening in Laser Welding of M1500

With the implementation of more stringent emissions standards, ultra-high strength steel has been increasingly used in vehicle body to reduce the carbon emissions, but softening in the heat affected zone is one of the most serious issues faced with in welding of this steel. In this paper, a finite element model (FEM) was developed to estimate temperature distribution in laser welding of ultra-high strength steel M1500 and a carbon diffusion model was then developed to estimate the martensite tempering transformation in the softening zone based on the simulated temperature distribution results. Maximum softening degree, minimum hardness point position and boundary of the softening zone were estimated and validated by hardness measurement experiments. This work provides a better understanding of the mechanism for heat affected zone softening in laser welding of ultra-high strength steel.