Environmental cracking of welded maraging steel in hydrogen sulphide.

A comprehensive survey of the literature concerning environmental cracking in maraging steels has been carried out, with particular reference to the behaviour of welded joints. The major part of the present experimental work was centred on the performance of submerged-arc welded plate in aqueous hydrogen sulphide. By using pre-craclced specimens, stress-intensity/endurance relationships were determined for weld and parent metals together with mixed structure material from two positions within the heat-affected-zone.From these data, estimated threshold stress-intensities 3/2 of 20-30 MN/m showed little difference between materials from any of the four positions. Endurances themselves, however, were generally lower for weld metal than for parent material. Stage II crack propagation occurred at rates of the order of 10-4 - 10-3 mm/sec, predominantly along prior-austenite grain boundaries. An unusual feature of many tests was an apparent drop in propogation rate after growth was initiated. There followed growth at more or less constant rates before final acceleration just prior to fracture. Fractography showed preferential cracking along specimen edges ahead of the main crack front. This suggested either faster growth under plane stress conditions or a diffusion barrier affecting hydrogen ingress. Scanning electron microscopy confirmed the purely intergranular nature of cracking, and the presence of stretch zones.