Experimental studies in weld nugget strength of resistance spot-welded 316L austenitic stainless steel sheet

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Resistance spot welding is one of the oldest and effective joining processes which generates heat by sending an electrical current through the sheets at controlled time and pressure to develop a joint at the interface of the sheets. As the demand for spot welding is drastically increased due to the increase in manufacturing of biomedical and automotive components, a detailed study on the quality of weld generated during the resistance spot welding is required. The quality of spot weld is assessed from the tensile shear strength and weld nugget diameter. An attempt is made through this research work, to study the quality of weld developed by the spot welding process of 1.6-mm-thick 316L-type austenitic stainless steel sheets (1.6 + 1.6 mm). The effect of significant process parameters namely heating time and welding current on ultimate tensile shear strength, weld nugget diameter, and failure modes is studied extensively. The critical weld nugget diameter is predicted by utilizing the proposed analytical model to ensure the tearing-type failure under a tensile shear test. Metallographic and SEM fractograph examinations are carried out to characterize the resistance spot welds. Based on the results, it is inferred that the weld nugget size, i.e., diameter and fusion depth, is the controlling factor of ultimate tensile shear strength and the resulting spot weld failure modes.