Influence of Welding Parameters on 0.4mm Austenitic Stainless-Steel Weld Nuggets

Abstract:

Owing to its superior corrosion resistance properties, thin sheet austenitic stainless-steel grade 304 is widely used in the food and beverage industry. Resistance spot welding (RSW) is a preferred joining method for these sheets because of its speed and efficiency, but RSW can alter the microstructure of the weldments, influencing their strength and corrosion resistance. Parameters such as welding current, time, and electrode force influence weld nugget formation, affecting its shape, size, and strength, while the rapid cooling rate in RSW leads to the formation of skeletal, lathy, and acicular delta ferrite in the weld zone. This study investigates the effect of welding parameters on the microstructure and properties of 0.4 mm AISI 304 stainless steel using peel tests, microstructural analysis, and microhardness testing. Peel test results were used to construct the weld lobe curve for process optimization, and nugget formation under various welding conditions was examined using SEM and EDAX analysis. The pseudo binary phase diagram was used to predict the final weld microstructure, and microhardness measurements confirmed an increase in fusion zone hardness after resistance spot welding. The weld lobe curve revealed that optimal defect free welds without expulsion were obtained at 40 kgf with 3000 to 5000 amperes for 1 to 4 cycles, and at 30 kgf with 5000 to 6000 amperes for 3 to 6 cycles, with electrode force exerting a stronger effect on weld quality than weld time. All welds produced below 4000 amperes at 30 kgf failed through interfacial mode, while weld nuggets above 3 mm diameter within the lobe curve exhibited complete pull out failure. Hardness testing was conducted on samples welded at 40 kgf and revealed that variation in current had a greater influence on fusion zone hardness than changes in weld time from 2 to 5 cycles when current was held constant. Specifically, specimens produced at 2000 amperes showed the highest fusion zone hardness, those at 3000 amperes exhibited intermediate hardness, and samples at 4000 and 5000 amperes had hardness values in the welded zone that closely matched the parent metal. The fusion zone hardness in optimal welds increased to around 200 to 210 HV, while the HAZ in most samples exhibited recrystallization, resulting in hardness values slightly higher than the base metal 195 to 210 HV. In a few samples produced at lower welding current, hardness exceeded 220 HV. Microstructural analysis confirmed the presence of skeletal, lathy, and acicular delta ferrite in both the fusion and heat affected zones, depending on welding current, time, and force. Welds formed with higher current or sufficient heat input favored the development of skeletal delta ferrite, while rapid cooling due to lower heat input resulted in lathy and acicular delta ferrite. All welds exhibited columnar grain growth in the direction of the water cooled electrodes and a distinct heat affected zone surrounding the fusion zone.

• Periodical: Key Engineering Materials (Volume 1044)
• Pages: 29-39
• DOI: https://doi.org/10.4028/p-8EE2Am
• Online since: March 2026
• Authors: Sandhya D. Bhat*, Muralidhara Muralidhara, Vijeesh Vijayan
• Keywords: Acicular Delta Ferrite, Austenite, Lathy, Lobe Curve, Pseudo Binary Phase Diagram

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