Influence of Nitrogen Content on the Stress-Corrosion Susceptibility of Some Austenitic Chromium-Nickel Steels

Abstract

The influences have been examined of nitrogen content, prestrain and ageing on the stress-corrosion susceptibility and chemical reactivity of three experimental 19Cr-11 Ni alloys and a commercial 17Cr-9 Ni steel. The stress-rupture results satisfy an equation of the form: log (t/to) = –A (σ/σY), where t is time to failure, t^o is a function of the nitrogen content, σ is the stress, σΥ is the effective yield stress at the test temperature and A is a strain-dependent constant. Prior ageing has been shown to have no significant effect upon stress-corrosion susceptibility in boiling magnesium chloride solution and stress-ageing cannot contribute to the cracking mechanism at ambient temperatures. A quasi-threshold stress at ∼ 0·7 σΥ is attributed to the onset of subsurface yielding. Slip steps formed in situ possessed chemical activity even in the absence of surface oxide films. A high nitrogen content increased this reactivity and shortened the time to failure by transgranular stress-corrosion cracking.