Stress‐corrosion cracking of austenitic stainless steels with applied E.M.F.

Abstract

AbstractThe stress‐corrosion cracking of chromium‐nickel austenitic stainless steels in 42 wt.‐% aqueous magnesium chloride solution at 150–154°, saturated with air, has been studied under conditions of cathodic or anodic treatment of the metal during the induction period prior to crack initiation and/or during crack propagation.Mild cathodic polarization delays the onset of cracking and fracture, the time to fracture increasing with increasing degree of polarization. With plain 18–8 steel, polarization producing an external current density of 50 μa./cm.2delays for at least 200 h., probably indefinitely, the onset of cracking of material that fractures in about 2 h. in the absence of applied e.m.f. Polarization applied only after crack propagation has begun reduces its rate; propagation ceases immediately if the measured potential of the metal is reduced to ‐ 0.14 v (N‐hydrogen scale), which produces approx. 170 μa./cm.2external current, and after a finite period at slightly less polarization.Anodic polarization producing external current densities of up to 50 μa./cm.2greatly shortens the induction period and, although scarcely increasing the rate of crack propagation, increases the total number of cracks formed.The results are in harmony with the electrochemical mechanism of this type of stress‐corrosion cracking. They indicate that cathodic protection may be a promising practical method for its control in suitable cases.