Effect of Impurities on Stress Corrosion Cracking of 18Cr Ferritic Stainless Steels

The effect of 0∼1.5% nickel in conjunction with other impurities such as phosphorus, carbon, manganese, silicon and nitrogen on stress corrosion cracking of 18Cr ferritic stainless steels was tested in boiling 42% magnesium chloride solution by using U-bend specimens.Susceptibility to cracking depended on the structure of the alloys. Single phase ferritic alloys did not crack regardless of their impurities and nickel content. On the contrary, alloys containing martensite cracked except the cases in which neither phosphorus nor more than 0.5% nickel was contained, and high nickel content resulted high susceptibility to cracking. Since the martensite indicates that γ was present during heating, cracking may be effectively prevented by avoiding γ formation during heat treatment with selection of suitable heat treatment or removal of the austenite forming element such as nickel, carbon, manganese or nitrogen. For this purpose, it may also be effective to avoid the coexistence of phosphorus and more than 0.5% nickel when martensite is contained in structure.Experiments at controlled potential indicate that anodic dissolution was a prerequisite of cracking.