Susceptibilite de l’acier 17-4 PH à la corrosion sous contrainte

Etude par essais de traction lente

17-4 PH S17-4 PH steel susceptibility to scc studied using slow strain rate technique

Laboratoire Corrosion-Fragilisalion-Hydrogène Ecole Centrale des Arts et Manufactures, Chatenay-Malabry

Abstract

The susceptibility to SCC of precipitated hardening martensitic stainless steel type 17-4 PH has been studied using slow strain rate technique (SSRT). Two corrosive media were chosen in this study: sulphuric acid (H₂SO₄ IN) at room temperature and 10 % MgCl₂ at room temperature and at boiling temperature (102 °C).

Fracture strain was chosen as a criterion of SCC sensitivity, by calculating the relative ratio levels of the fracture strain S = (ε₁ - ε₁)/ε₁ and εc are fracture deformation respectively in non corrosive and corrosive environments.

Following the results, in the acidic medium, maximum sensibility S_max is observed for the strain rate ε = 2.7 10^-6 s^-1

At this strain rate in boiling 10 % MgCl₂ solution either at the free corrosion potential or at passivating potentials, the steel is not sensitive to SCC. However, cathodic potentials promote SCC. This indicates that hydrogen embrittlement is the main process for SCC on type 17-4 PH steel.