Metallurgical, Fatigue and Pitting Corrosion Behavior of AISI 316 Joints Welded with Nb-Based Stabilized Steel Filler

A comparative study on 10-mm-thick AISI 316 weld joints fabricated using conventional 316L and Nb based stabilized AISI 347 filler was carried out. Welds were aged at 550 degrees C/50 hours and 750 degrees C/24 hours to induce a varying degree of precipitation. Nb in the case of 347 weld exhibited strong inhibition tendencies against chromium carbide precipitation besides preventing appreciable loss of Ni and Fe in it, unlike the Mo containing 316L weld, which showed significant signs of precipitation. Pitting performance of the welds degraded significantly at 550 degrees C/50 hours condition. Welds with lower pitting potential had relatively higher pit depths. AISI 347 welds under all conditions showed higher pitting resistance and hence resulted in shallower pits than those observed for AISI 316L welds. A higher concentration of O, Cr and Ni in the passive film of AISI 347 weld accounted for its better pitting corrosion resistance. Aging at 750 degrees C/24 hours condition improved the fatigue crack growth resistance of both welds. Due to the fine dispersion of carbides, aged AISI 316L welds showed better fatigue crack growth resistance than AISI 347 welds. Using stabilized filler for welding of AISI 316 stainless steel can significantly improve its pitting performance under harsh pitting corrosion conditions.