Effect of weld metals on fatigue behavior of Nb-added ferritic stainless steel JFE429EX welds in laboratory air and in 3% NaCl solution

Effect of weld metals on the fatigue behavior of Nb-added ferritic stainless steel JFE429EX (15Cr-0.9Si-0.5Nb) welds in laboratory air and in 3% NaCl solution was investigated. Two filler metals with different chemical compositions, Filler I and II, had been used for the MIG butt welding of JFE429EX. Filler II contains Al and Ti to improve microstructure of fusion zone (FZ), resulting in the finer grains than Filler I. Fully reversed axial fatigue tests had been performed using smooth specimens of welds and base-metal specimens at ambient temperature in laboratory air and in 3% NaCl solution. In laboratory air, fatigue strengths of the welds with Filler II were higher than those of the base metal and welds with Filler I. Fatigue fracture occurred at HAZ and FZ in the welds with Filler I, while at base metal in the welds with Filler II. It could be attributed to the finer grains in the FZ of Filler II. In 3% NaCl solution, the fatigue strengths of both welds and base metal became lower than those in laboratory air due to the corrosive environment. However, the welds with Filler II had still the highest fatigue strengths compared with the base metal and welds with Filler I. It indicates that the addition of Al and Ti could suppress sensitization. In both welds, fatigue fracture took place at HAZ, and intergranular crack fractures were observed. It suggested that the heat input of welding led to the sensitization near HAZ.