Most high nickel chromium bearing alloys can be made susceptible to intergranular corrosion in certain corrosive environments as a result of improper heat treatment or by thermal cycles involved in welding. Tests are available which readily detect susceptibility to intergranular attack, but there is relatively little information on the phases and precipitates which impair resistance to corrosion. Available data indicate that there is a variety of phases, some perhaps submicroscopic, which make these alloys susceptible to intergranular attack. Research is needed on the changes in structure which cause this problem, on the nature of corrosive environments which are capable of intergranularly attacking susceptible material, and on compositional and mill processing changes to reduce susceptibility.
The two tests principally used for detection of susceptibility to intergranular corrosion in these alloys have long been employed as evaluation tests for the austenitic stainless steels. These are the 120 hour boiling ferric sulfate-50% sulfuric...
