Environmentally Assisted Cracking Behavior of 18Ni 250 Maraging Steel Welds Obtained with and Without Flux in Chloride Media

Abstract

Gas tungsten arc welding is extensively used in the fabrication of 18Ni 250 maraging steel motor casings. In this work, the role of flux addition on the environmentally assisted cracking (EAC) and electrochemical corrosion behaviors of these welds in their peak-aged condition is presented. Studies were performed in order to bring out the potential influence of long-term exposure of maraging steel welds to neutral 0.1 M NaCl (mildly corrosive) and acidified 0.1 M NaCl (a relatively more corrosive) environments to understand the EAC behavior of the welds. The study showed that both the fluxed and unfluxed weld metals suffered 21% to 23% loss in ductility in neutral 0.1 M NaCl solution from that of obtained in air. The EAC of the welds in the neutral chloride solution was due to anodic dissolution, while in the acidified chloride solution it was found to be predominantly due to hydrogen embrittlement. The effect of flux in refining the weld microstructure was reflected in: (a) preventing intergranular mode of hydrogen embrittlement of the unfluxed welds and transforming the mode to transgranular cracking, (b) lowering a wide scatter in electrochemical corrosion rate, and (c) reducing the selective attack in the interdendritic regions of the unfluxed welds. Such a transition from intergranular to transgranular cracking might affect long-term service behavior of the welds to corrosion and EAC, though it is not reflected in the short-term tests.