Sulfide Stress Cracking of Nickel Steels

Results of this investigation on the sulfide stress cracking (SSC) of cast and wrought commercial ASTM low-alloy steels containing Ni showed that the apparent “nickel effect” is probably an artifact of the divergence of the proportional limit of a steel from its 0.2% offset yield strength. Higher Ni steels have considerably lower proportional limits than non-nickel steels. Therefore, when stressed just below their yield strength but above the proportional limit, the Ni steels are actually incurring significant plastic strain. When all the steels were normalized to their proportional limit, the low-Ni steels (≤ 2% Ni) failed by SSC under elastic strain, and those steels with high-Ni contents (> 2% Ni) failed under plastic strain. Therefore, the so-called “nickel effect” is a result of the mechanical properties of the steel and not a real nickel effect on SSC resistance.