Corrosion Fatigue Behavior of Resistance Spot Welded Dissimilar Metal Welds between Carbon Steel and Austenitic Stainless Steel with Different Thickness

Abstract

Abstract Corrosion fatigue behavior of resistance spot-welded dissimilar metals with significant difference in thickness between carbon steel and austenitic stainless steel has been studied. Carbon steel SS400 with thickness of 3.0 mm and 1.0 mm thick- austenitic stainless steel SUS304 were lap joined using resistance spot welding. The welding conditions used including weld current, weld time and electrode force were 4.7 kA, 20 cycles and 6 kN respectively. Corrosion fatigue tests were carried out at a room temperature in seawater environment with the salinity of 34.5 g/L and pH of 8.0. A sinusoidal wave input with a constant stress amplitude was selected whereas the stress ratio and frequency used were 0.1 and 8 Hz respectively. Fatigue tests were also conducted in air as a comparison. Other experiments such as metallographical examination, microhardness measurement, electrochemical tests and nugget area evaluation using neutron radiography were performed for supporting analysis. Results show that corrosion fatigue strength of resistance spot welded in sea water is lower than that performed in the air. The endurance limit of fatigue conducted in air is 32.6 MPa whereas corrosion fatigue samples at this stress fail at about 400,000 cycles. It seems that the hydrogen enhanced plasticity mechanism that tends to ease the generation of dislocations is the cause of corrosion fatigue strength weakening.