Relative Effects of S, Sb and P on the Intergranular Fracture of Iron and Nickel Tested at Cathodic Potentials

Abstract

It is generally believed that grain boundary impurities contribute to intergranular fracture in the presence of hydrogen by either; 1) decreasing the intergranular cohesion; 2) enhancing hydrogen absorption along grain boundaries; or 3) a combination of both processes. A comparison of the relative effects of S, Sb and P on the intergranular fracture of iron and nickel has been completed^1,2 and will be summarized in this paper. With sulfur as a bench-mark, the effect of S, Sb and P on the intergranular fracture of iron and nickel at cathodic potentials can be expressed by the following equivalent grain boundary sulfur concentrations, C_s:

$$C_s^{eq}\left( {Fe} \right) = 5 Sb + S + {\gamma _P}P{\gamma _P} > 0$$

((1))

$$C_s^{eq}\left( {Ni} \right) = Sb + S + 0.07P$$

((2))