Stress-Corrosion Cracking of Cast Iron—Nickel—Chromium Alloys

Abstract

The stress-corrosion behaviour of three chromium—nickel—iron alloys, viz. 25Cr—20Ni—Fe (HK Alloy), 24Cr−24Ni−11/2Nb−Fe (IN—519) and 18Cr—37Ni—Fe (HT Alloy), has been examined in a number of chemical environments known to promote stress-corrosion c:racking in wrought alloys of similar composition. The tests were carried out in sodium and magnesium chloride solutions, sodium and potassium hydroxide solutions and in a number of sulphur acid environments, e.g. sulphur dioxide plus hydrogen sulphide, often described as poly thionic acid.

The alloys generally showed resistance to cracking in chloride environments as good as or better than that which would be expected from wrought alloys of similar composition; when cracking did occur in these environments it was predominantly transgranular. The alloys were susceptible to cracking in the other environments where the attack was exclusively interdendritic; this may have been associated with the large amount of interdendritic chromium carbides present in the cast structures. The niobium containing alloy IN–519 showed better resistance to cracking in these environments.