Stress corrosion cracking of austenitic stainless steel weld overlays in high temperature water

Investigations were conducted to determine the effects of ferrite content, heat treatment and welding methods on the susceptibility of Fe-Cr-Ni stainless steel weld overlays to stress corrosion cracking in high temperature water. Specimens machined from the stainless steel weld overlays on a carbon steel were tested under the as-welded and the post-weld heat treated condition, respectively. These weld overlays contained about 1 to 13 percent ferrite in an austenite matrix.Tests were conducted in a 3-liter autoclave containing high purity water or chloride-containing water. The stressed U-bends were exposed at 300°C for 300 hr under the undeaerated condition. The results were summarized as follows:(1) No cracking was detected in any specimen of stainless steel weld overlays in high purity water.(2) In contrast with the test in high purity water, cracking was observed for all of the specimens tested in chloride-containing water. The susceptibility to cracking, however, decreased with increasing amount of ferrite in their structure. This tendency was similar to that observed for the wrought alloys.(3) There was no significant difference between the susceptibility to cracking of manual arc welded materials and that of submerged arc welded materials.(4) The susceptibility to cracking of weld overlays was decreased by the post-weld heat treatment at 625°C for 20 hr.(5) The types of cracking observed on the weld overlays were divided into three groups: (a) high austenite-containing alloys were subjected to transgranular cracking, (b) the austeno-ferritic duplex alloys containing about 6 to 9 percent of ferrite exhibited mixed cracks of trans- and inter-dendritic cracking, (c) the duplex alloys containing more than about 10 percent of ferrite were predominantly subjected to interdendritic cracking.(6) These crack paths were discussed with respect to the geometry of the δ phase in their structure.