EFFECT OF AUSTENITE PHASE CONTENT ON PITTING POTENTIAL OF A DUPLEX STAINLESS STEEL.

In order to examine the effect of gamma phase content on pitting potential of a duplex stainless steel, pitting potentials for type 329 J1 duplex stainless steel with different alpha / gamma phase ratios prepared by isothermal heat treatment in NaCl and NaCl-H//2SO//4 solutions have been determined by measurements of the anodic polarization curves. The dependence of pitting potentials on gamma phase content is considered on the basis of results for the microscopic observation of pit sites on the surface and EPMA analysis of chemical compositions for alpha and gamma phases. When the structure of type 329 J steel changed from alpha single phase to ( alpha plus gamma ) duplex phase, the pitting potential in NaCl solution decreased. The decrease is attributed to the decrease in chromium content of the transgranular gamma phase on which pits generated with an increase in gamma phase content.