GB722915A - Process for producing a hard and wear-resistant surface on ferrous bodies - Google Patents

Abstract

Ferrous articles having an available carbon content of 0.4 per cent or more, depending on the depth of ferrous material below the surface, are coated with vanadium whilst maintaining the surface at high temperature, the deposited vanadium combining with the carbon of the ferrous material to form an integral surface layer containing vanadium carbide, the carbon content of the ferrous material being initially selected in relation to the depth thereof so that sufficient carbon is available for forming carbide with substantially all the vanadium deposited. The vanadium may be deposited by chemical reduction or reaction at the surface, e.g. by hydrogen reduction of, or exchange reaction with, a vanadium halide, or by thermal decomposition of a halide or carbonyl. Prior to treatment, work-affected surfaces may be removed by anodic treatment or by immersion in 50 per cent hydrochloric acid at 85 DEG C. for 2-10 minutes. A stop coating of copper may be applied to those parts of the surface where vanadium deposition is not desired. Carbon may be added to the article by a carburising process, a similar stop coating being applied to suppress carburisation where desired. In depositing vanadium by decomposition of its chloride, selective induction heating may be employed. The ferrous articles may be packed in (a) 50 per cent ceramic, balance ferro-vanadium; or (b) 20 per cent titanium oxide, balance ferro-vanadium, and placed in V-Ni-Fe alloy baskets which are heated in a retort at 900-1200 DEG C. in a stream of hydrogen and hydrogen chloride, alternating with a stream of hydrogen. Carburisation may be effected in a pack of 20 per cent barium carbonate bound to hardwood charcoal with oil, tar or molasses at 925 DEG C.