GB800343A - Method for the powder metallurgical manufacture of chromium alloys - Google Patents

Abstract

In a method of making alloys containing at least 10 per cent Cr, powders are mixed one being ductile metal and containing at least one of the elements of the finished product, and the other being an alloy the structure of which is at least 25 per cent sigma phase; the mixture is compressed into a coherent body and sintered at a temperature below the melting points of the pulverulent components of the mixture so that the sigma phase disappears. The ductile metal powder is preferably a single metal e.g. electrolytic Fe, Ni, forming the base-metal of the alloy, while the rest of the alloying elements are in the alloy powder constituent. The ratio of ductile powder to alloy powder is preferably between 2 and 1/2 ; the grain size should be les than 0.074 mm. (200 mesh) and preferably less than 0.074 mm. (325 mesh), but the powder mix may be agglomerated (before compression) into particles of size below 0.25 mm. Compacting pressures of 7.5 tonnes/cm2 and sintering in hydrogen at 1310 DEG C. for 2 hours are instanced with mixtures of equal parts electrolytic Fe and alloy powder of (a) 50 per cent Cr, 3 per cent Ni and the rest Fe, (b) 45 per cent Cr, 20 per cent Ni, 5 per cent Mo and the rest Fe. Numerous examples of binary, ternary &c. alloys are given which possess the sigma phase in sufficient amount for the carrying out of the process.