The effect of nickel content on the environmental assisted cracking (EAC) behaviour of low alloy steels in sour environments—A review

This particular review attempts to rationalise the effects of nickel level on the susceptibility to environmental assisted cracking (EAC) of low alloy steels. Historically, nickel has been viewed as a detrimental addition; indeed research studies indicated that the use of more than 1% Ni lowers the low alloy steel's resistance to both sulphide and hydrogen stress cracking. However, in view of nickel's beneficial effects on cryogenic tensile, fatigue, and fracture toughness properties there has been renewed interest in rigorously elucidating nickel's true role in environmentally assisted cracking processes. Recent studies tend to show that with the appropriate heat treatment low alloy nickel steels can have equivalent EAC resistance to nickel free steels. Nickel's effect on low alloy steels appears to be in reducing the Ac1 (thus producing untempered martensite when tempered at high temperatures), decreasing the lattice diffusion of hydrogen, enhancing formation of surface trenches, and reducing the overall corrosion rate.