Basic Investigation of CVD Method for Manufacturing 6.5% Si Steel Sheet.

Abstract

It has been known for a long time that 6.5% Si steel sheet has excellent soft magnetic properties that make it well suited for use as a magnetic material. However, steel of that composition is brittle and has little ductility; for this reason, the material could not be manufactured on an industrial scale with conventional cold rolling methods. Here, the authors studied and devised a method for continuously producing 6.5% Si steel sheet utilizing the CVD (Chemical Vapor Deposition) method. In this method, 6.5% Si steel sheet is continuously produced with the following procedure: first, low-Si steel, an easy-to-roll material, is rolled beforehand to produce thin strip; then, the CVD treatment using a gas containing SiCl4 is applied to the strip so that silicon is permeated through the surface of the steel strip; and finally, the strip is given a diffusion annealing to uniformly distribute the silicon throughout. While the siliconizing of steel has previously been studied as a way to improve the corrosion resistance of steel, this work marks the first study of this method as a way to produce 6.5% Si steel sheet on an industrial scale. The authors examined the basic conditions required for the process–the process for manufacturing 6.5% Si steel sheet utilizing this type of CVD-based siliconizing treatment technology–by carrying out a theoretical study of related chemical reactions and performing basic research with a simple test apparatus. Based on the results, the authors next conducted an investigation to develop a method for continuously manufacturing the steel in coil form and finally proposed an overall process configuration to realize such a production system.