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Kinetic and fractographic study of the stress corrosion cracking of Austenitic stainless steels Russell, Alan James

Abstract

A variation of the double cantilever beam specimen has been calibrated and used to study the propagation of stress corrosion cracks as a function of stress intensity in 316 and 310 stainless steels, and a TRIP steel exposed to hot aqueous magnesium chloride solutions. The effects of cold work, temperature and applied potential on both the fractography and cracking rates have been examined. The effects of cold work and crack path on crack branching were also investigated. Bpth stress Intensity dependent (Region I) and stress intensity independent (Region II) cracking were observed. Region II having apparent activation energies from 15.1 kcal/g.mole to 18.1 kcal/g.mole. The crack velocities of 25% cold rolled 316 were found to be independent of applied potential over a range of more than 50mV in Region I and 75mV in Region II. In the same material the crack path changed from solely transgranular at low stress intensities and noble potentials to more than 80% intergranular at high stress intensities and active potentials. The topography of the transgranular fracture was similar to that observed by others except in the case of the TRIP steel where nodular features were observed. These observations have been discussed with respect to mechanisms involving the following (i) electrochemical dissolution, (ii) absorption of hydrogen and (iii) adsorption of a damaging species. Of these, an adsorption assisted process is most compatible with the observations. Qualitatively the adsorbed species are envisioned as modifying the behaviour of the surface atoms at the crack tip.

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