Investigation of thin sheet stainless steel resistance spot welds: Effect of weld current on nugget failure and microstructure

Abstract

Thin stainless-steel sheets commonly used in food and beverage industry is resistance spot welded in the process of making leak proof containers. The spot-welding parameters are optimized to obtain maximum nugget size and weld strength. In contrast, least importance is given to the temperature developed at the sheet/electrode interface and subsequent oxidation of the weld. It is well known that the oxidation of the stainless-steel results in the depletion of the chromium in the material affecting its corrosion resistance properties. In this context, this paper is aimed at investigating the effect of resistance spot welding current on the chromium depletion and subsequently on the microstructure of 0.4 mm 304 stainless steel sheet weldments. Comparative study between the microstructures of the heat affected and weld zones were carried using optical microscope and scanning electron microscope. The effect of weld current on the morphology of the delta ferrite formed in the weld zone is presented in the paper with help of pseudo-binary phase diagram. An attempt is made to correlate the local chromium depletion with the microstructure and defect formation.