The effects of strain rate on the corrosion fatigue behaviour of B.C.C. Fe26Cr1Mo stainless steels

Abstract

The corrosion fatigue damage mechanisms leading to crack initiation were studied in high purity ferritic stainless steels (Fe26Cr1Mo where the composition is given in approximate weight per cent) in a 3.5% NaCl solution at 300 K and at the imposed corrosion potential. Particular attention was paid to the influence of strain rate on both the plastic deformation mechanisms and the dissolution characteristics which govern the crack initiation process. At high strain rates (about 10 −2s −1), pencil glide occurs because of the behaviour of screw dislocations and induces strain localization at grain boundaries; dissolution is then principally localized at grain boundaries, crack initiation is intergranular and lifetimes are reduced in comparison with those in air. The influence of the pH and the strain amplitude is also of great importance. At intermediate strain rates (about 10 −3s −1), dissolution is entirely localized at grain boundaries because of pencil glide; crack initiation is intergranular and fatigue lifetimes are shorter than at high strain rates. At low strain rates (less than 10 −4s −1), the amount of dissolution is lower than the critical value for corrosion fatigue damage. Crack initiation which is induced by the mechanical damage (persistent slip bands due to wavy slip) is transgranular and fatigue lifetimes are similar in air and in the corrosive solution.