PRECIPITATION OF M23C6 AND sigma -PHASE IN delta / gamma DUPLEX STAINLESS STEELS.

Abstract

Precipitation of M//2//3C//6 and sigma -phase during isothermal aging has been studied by a transmission electron microscope coupled with an energy dispersive X-ray analyser. M//2//3C//6 particles form at both gamma / gamma and gamma / delta boundaries. The particles are crystallographically related to either one of the gamma grains or the gamma grain corresponding to the gamma / gamma or the gamma / delta boundary. The particles nucleating at gamma / delta interphase boundaries grow into untransformed delta -ferrite as an M//2//3C//6/new gamma eutectoid structure dragging the gamma / delta boundaries. Since C atoms are supplied from the gamma behind the eutectoid structure, the reaction will stop after their consumption. Then sigma -phase