Index of Susceptibility to Stress Corrosion for Austenitic Steels Based on the Electromechanical Model

Abstract

A model for the stress corrosion of austenitic steels is developed based on the assumption that crack growth occurs purely by preferential anodic dissolution at the yielding crack tip. The process is visualised as one proceeding by steps in which a burst of slip precedes or accompanies anodic dissolution, followed by exponential passivation of the exposed surface. It is postulated that during one such cycle of incremental crack growth, an energy balance equation pnalogous to the one developed by Griffith is satisfied. This involves the concept of an electrochemical work term which varies with the effective anodic dissolution voltage and the crack opening displacement at the tip of the crack during the cycle.

Concepts of plasticity are introduced later in the paper which allow the formulation of equations showing the relationship between susceptibility to stress corrosion cracking and lattice stacking fault energy.

The tunnelling phenomenon observed at crack tips in austenitic steels by Nielsen and by Swann and his co-workers is discussed in terms of a possible energy balance on the atomic scale between the stored elastic strain energy per unit length of dislocation and the equivalent ‘overpotential’ required to dissolve an associated volume of unit length and cross section b_oω, where b_o is unit Bergers vector and ωw is the partial dislocation spacing