Abstract
Existing specifications for high alloy austenitic stainless steel castings often require a solution anneal after weld repair to eliminate carbide precipitation in the heat affected zone and thereby prevent intergranular corrosion. The introduction of the argon-oxygen- decarburization (AOD) secondary refining process in many stainless foundries facilitates the production of CN7M and similar alloys with very low carbon levels. Cast test plates in the CN7MS composition having carbon limited to ≤ 0.03% were welded using both GTAW and SMAW processes. Samples were taken, in the as-welded condition, and subjected to a series of tests based on ASTM A262, for the detection of intergranular carbide precipitation. The results indicate that the thermal conditions created by welding are insufficient to induce sensitization in the weld heat affected zone. Based on these encouraging findings, a number of CN7MS castings having minor defects were repair welded and placed in service in the as-welded condition in environments known to induce intergranular attack in susceptible material. After service exposures exceeding two years, in some instances, there was no indication of preferential corrosion at these welds. This confirms the laboratory data and suggests that a postweld solution anneal is unnecessary for these materials if welding parameters are properly controlled.
