Pitting corrosion resistance of as welded and thermally aged nitrogen containing type 316 stainless steel weld metal

Abstract

Type 316 stainless steel weld metal with 0·07%N, prepared using nitrogen bearing 316 stainless steel filler wire by the manual metal arc (MMA) welding process, was evaluated for the microstructural changes and pitting corrosion resistance in as welded and aged (at both 1023 and 1123 K for 0·5, 1, 10, and 100 h) conditions. The initial delta ferrite content was about 5·5 ferrite number, which transformed from 70 to 100% as secondary precipitates depending on the aging conditions. Electrochemical potentiokinetic reactivation studies did not show any reactivation peak indicating the absence of Cr depleted zones. Pitting corrosion studies in a medium of 0·5M NaCl + 0·5M H2 SO4 (acidic chloride) by the potentiodynamic anodic polarisation method showed a significant variation in the pitting resistance which depended on the aging conditions. The pitting corrosion resistance has been correlated to the precipitation kinetics of the secondary phases such as sigma, carbide, and Cr2 N in the weld metal.