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Gorti Janardhan,Kaushal Kishore,Goutam Mukhopadhyay,Krishna Dutta 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9
This study aims to investigate the influence of nugget diameter on tensile-shear and fatigue properties of the dissimilar resistancespot-welded joints of interstitial free and high strength niobium microalloyed steel sheets. The spot-weldings are doneat currents of 7 kA and 9 kA at welding time of 300 ms with electrode force of 2.6 kN. Fatigue tests are done at different loadamplitudes, considering the maximum tensile-shear load bearing capacity of the joints. The tests are interrupted before thefinal failure to understand the crack initiation and propagation paths. The study is supplemented by the microstructural anddetailed fractographic analyses. The results indicated that the fatigue strength of the spot-welds increased with a decrease innugget diameter. This could be attributed to the higher microhardness of heat affected zone (HAZ), presence of compressiveresidual stress and lower variation in thickness reduction on the IF steel side, welded at 7 kA. However, the tensile-shearload bearing capacity of the spot-welds increased with increase in the nugget diameter. The failure of the spot-welded jointunder static loading initiates from the HAZ/base metal interface of the IF steel side. Nevertheless, under cyclic loading crackinitiates from the notch root at the interface of two sheets lying in the HAZ of IF steel side. Fractographic investigationsindicate intergranular fracture features in combination with striations, secondary cracks on the IF steel side under cyclicloading. Fracture surfaces of the specimens failed under static loading shows however, shear dimples on the IF steel side.