GB609689A - A process of manufacturing ferrous bodies containing silicon - Google Patents

Abstract

Shaped ferrous bodies more particularly for electrical purposes, are made by intimately admixing ferrous powder with up to 6 per cent silicon powder, compacting the mixture and sintering the compact, at a temperature within the austenitic range of the ferrous component, until silicon is diffused into the ferrous component. This diffusion is effected by either removing from the compact traces of oxygen intially contained therein by the addition of solid deoxidizers such as powdery aluminium, titanium, magnesium, molybdenum and carbon preferably in the form of graphite, or by the use of pure electrolytic iron powder and reduced silicon powder, care being taken to prevent oxidation during handling. The sintering in both methods is carried out in a protective atmosphere, such as dessicated hydrogen, lithium, or the like. In a preferred process according to the former method, a compact of commercial iron powder, up to 3 per cent silicon and the required quantity of solid deoxidizer to bind the oxygen, for example 0.7 per cent graphite, shaped under a pressure of 30-40 tons per sq. in. is sintered at about 1100 DEG C. for 1-2 1/2 hrs. in a protective atmosphere. In a modification carbon or graphite is used as a deoxider in an amount considerably exceeding that required for combining with the oxygen, and excess left after diffusion of the silicon is either removed by a second sintering step in a decarburizing atmosphere such as hydrogen, carbon monoxide or a mixture of both, or retained in the body. In this latter event a similar two-step sintering process may be used and the second sintering step carried out in a protective atmosphere. Silicon in excess of that required to be diffused into the iron may also be used as a deoxidizer. Then if a compact shaped from a mix containing about 4 per cent silicon powder is sintered in a protective atmosphere at about 1000 DEG C. to 1200 DEG C., up to 3 per cent silicon is diffused into the iron. In a further modified process deoxidation may be effected by sintering a compact containing up to 6 per cent silicon in a deoxidizing atmosphere such as dessicated hydrogen for from 6 to 18 hrs. at about 1000 DEG C. to 1200 DEG C. Powder ferro-silicon may be substituted for the silicon powder and a portion of the iron powder, in any of the foregoing processes.