Small Angle X-Ray Scattering from MnS in Silicon Steels

Abstract

In silicon steels, a dispersed MnS impurity phase is believed to pin grain boundaries, inhibit grain growth, and permit the desired secondary recrystallization for optimum orientation, grain size, and magnetic properties of the finished material. However, no experimental evidence has yet been obtained to establish the size distribution of this impurity phase. Therefore, the size distribution of such a precipitate was explored by a small-angle x-ray scattering technique, with a spectrometer using a Johansson-focusing monochromator; spurious surface effects were carefully avoided. Laboratory heats of 3.2% silicon steel compositions with varying sulfur, were prepared by vacuum induction melting of high-purity components; these materials were carefully processed to 0.0005-in. thick foils. Using a sulfur-free sample as reference standard for residual surface scattering, a plot of ln τ (2θ) vs (2θ)2 showed the presumed MnS particles to be 20 A to 150 A in diameter. These results agreed with preliminary observations by transmission-electron microscopy.