Stress Corrosion of Ferritic Stainless Steels

Ferritic, iron-chromium stainless steels with chromium in the range of 14% to 27% are generally considered resistant to chloride stress-corrosion cracking and are sometimes used for this reason in place of the austenitic 18Cr-8Ni, steels, which readily fail by this form of corrosion. This view was confirmed by Bond, Marshall and Dundas(1), who made laboratory tests on 17%Cr alloys (AISI 430) in which they found that they are immune to cracking in boiling magnesium chloride, calcium nitrate, and sodium hydroxide solutions. However, Renshaw(2) has reported stress corrosion of weldments on Type 430 steel in boiling solutions containing only 50 ppm Cl added as sodium chloride. More recently, Bond and Dundas(3) have published data showing that completely ferritic, 18% to 25%Cr alloys containing some molybdenum become subject to stress corrosion in boiling magnesium chloride solution when the concentration of nickel exceeds 1% and that of copper 0.5%. Thus, ferritic body centered cubic structures in iron-chromium alloys are not generally immune to failure in a chloride stress-corrosion environment which also causes failure of austenitic, face-centered cubic, stainless steels.