Effect of the particle size of starting materials on the degree of homogenization of iron-chromium alloy powders

Abstract

1. Fine iron powders (−0.060 mm) are not suited for the production of iron-chromium alloy powders of various compositions by the method of diffusion impregnation from point sources; their use substantially reduces the gas permeability of the charge bed, creates unfavorable conditions for the free circulation of gaseous chlorides, and decreases the intensity of the process. With a fine iron powder, the mean chromium content of the resultant alloy powder falls. The phenomenon is particularly marked in the case of low-chromium alloys, where iron constitutes the major part of the charge. As a general rule, the particle size of the iron powder should be −0.160+0.060 mm. 2. Use of a fine chromium powder in the preparation of alloy powders of various compositions substantially increases chromium losses with chlorides and makes it impossible to obtain homogeneous powders of high-chromium alloys. For the preparation of alloy powders containing more than 13% chromium, a −0.250+0.160-mm fraction of chromium powder may be recommended. In the production of low-chromium alloy powders, the optimum particle size is −0.100+0.035 mm.