GB617849A - Improvements in the manufacture of articles from ferrous metal powders - Google Patents

Abstract

A method of obtaining an article from iron or steel powder which may be mixed with alloying substances such as tungsten, vanadium, copper, cobalt, tantalum, molybdenum, silicon, nickel, chromium, manganese, titanium, aluminium or combinations thereof, comprises forming a compact and heating it in the presence of gaseous chromous chloride so as simultaneously to sinter the compact and to effect diffusion of chromium into the surface layers. In one example of the method the compact is sintered at between 1000 DEG C. and 1200 DEG C. in a chamber through which is passed a mixture of gaseous chromous chloride and an inert or reducing gas preferably hydrogen. If desired, the gaseous chromous chloride may be generated within the chamber by surrounding the compact with pieces of chromium or of a chromium compound and by passing gaseous hydrogen chloride through the chamber, preferably mixed with an inert or reducing gas. A more uniform distribution of the gaseous chromous chloride may be obtained by including among the pieces of chromium or chromium compound, pieces of ceramic material capable of absorbing the gas and subsequently giving it up again. The ceramic material may have been previously impregnated with chromous chloride. In a further modification, the compact may be sintered in an inert or reducing atmosphere in the presence of pieces of chromium or a compound thereof and of the chloride of any metal other than an p alkali metal or an alkaline earth metal.