Resistance spot welding joints of AISI 316L austenitic stainless steel sheets: Phase transformations, mechanical properties and microstructure characterizations

• Published in: Materials in engineering 2014-09, Vol.61, p.251-263
• Main Authors: Kianersi, Danial, Mostafaei, Amir, Amadeh, Ahmad Ali
• Format: Article
• Language: English
• Subjects: AISI 316L austenitic stainless steel; Mechanical properties; Microstructure characterization; Phase transformations; Resistance spot welding; Welding parameters optimization
• ISSN: 0261-3069
• DOI: 10.1016/j.matdes.2014.04.075

•Resistance spot welding of AISI 316L stainless steel sheets.•Microstructure prediction by the use of Schaeffler and Pseudo-binary diagrams.•Non-equilibrium phases including skeletal, acicular and lathy delta ferrite formed.•Mechanical characterization of weld nuggets including peak load and failure energy.•Different failure modes were found at various welding currents. In this paper, we aim to optimize welding parameters namely welding current and time in resistance spot welding (RSW) of the austenitic stainless steel sheets grade AISI 316L. Afterward, effect of optimum welding parameters on the resistance spot welding properties and microstructure of AISI 316L austenitic stainless steel sheets has been investigated. Effect of welding current at constant welding time was considered on the weld properties such as weld nugget size, tensile–shear load bearing capacity of welded materials, failure modes, failure energy, ductility, and microstructure of weld nuggets as well. Phase transformations that took place during weld thermal cycle were analyzed in more details including metallographic studies of welding of the austenitic stainless steels. Metallographic images, mechanical properties, electron microscopy photographs and micro-hardness measurements showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Backscattered electron scanning microscopic images (BE-SEM) showed various types of delta ferrite in weld nuggets. Three delta ferrite morphologies consist of skeletal, acicular and lathy delta ferrite morphologies formed in resistance spot welded regions as a result of non-equilibrium phases which can be attributed to the fast cooling rate in RSW process and consequently, prediction and explanation of the obtained morphologies based on Schaeffler, WRC-1992 and Pseudo-binary phase diagrams would be a difficult task.