Softening by Coarsening of Ni-Al B₂ Phase Particles in Fe-Cr-Ni-Al-Zr Alloy

Abstract

In Fe-Cr-Ni-Al stainless steels, surface alumina layer with good adhesion is formed by heat treatment at a high temperature in oxidizing atmosphere and can prevent burrs from being formed in grinding of cutting edges. On the other hand, as the precipitation velocity of Ni-Al B₂ phase particles dispersed in the matrix of these steels is remarkably high, it is hard to obtain a full solid-solution condition without any fine precipitates by conventional solution treatment. And, the dispersed particles increase the hardness of the material and it is impossible to decrease the hardness sufficiently to form the cutting blade only by the annealing after cold rolling. According to the process developed in this study, most of the B₂ phase particles are dissolved once, cooled slowly and, thus, combined with remaining particles to form coarse particles. As a result, precipitation of fine particles is prevented and softening necessary to form into given shapes is achieved.