Stress—corrosion cracking of austenitic stainless steel in hydrochloric acid media at room temperature

Abstract

Stress—corrosion cracking of solution quenched, type 304, stainless steel can occur at room temperature in HCl solutions ranging between 5·10 −1M and 1M HCl. The cracking observed in HCl solutions is similar to that previously observed in H 2SO 4 + NaCl and HClO 4 + NaCl solutions. Cracking occurs at − 0·200 V (NHE), in the active potential region, it is under cathodic control, and it develops in conditions under which the corrosion rate of the external surface area is more or less constant and independent of the HCl concentration, in the range 10 −1 M−1 M HCl. At higher HCl concentrations, corrosion rates increase and uneven, general corrosion occurs instead of cracking. The development of pitting and stress—corrosion cracking under active conditions precludes the conclusion that active—passive cells always play a role in localized corrosion and, in particular, in stress—corrosion cracking. Under these conditions, it has been shown that sensitized and non-sensitized specimens behave similarly (giving rise in both cases to transgranular cracking); active—passive cells, due to chromium depletion at the grain boundaries, are not involved. Active—passive corrosion mechanisms can however arise at more noble potentials (0·100−0·200 V NHE), as in the case of HClH 2O 2 solutions of specific concentration, producing intergranular corrosion of the stainless steel in the sensitized condition.