GB761369A - Cobalt-base alloy and its manufacturing process - Google Patents

Abstract

A cast alloy for use at high temperatures consists of: Co at least 39 per cent, Cr 20-35 per cent, Mo 5-20 per cent, W 0-10 per cent, Ni 3-15 per cent, C 0.3-1.2 per cent, Ti 0-0.5 per cent, Zr 0.05-0.3 per cent. Si 0.5-2 per cent, Mn 0.5-1.2 per cent (the total less than 3 per cent). Fe less than 6 per cent., the cobalt-base solid solution being present simultaneously in two allotropic forms, viz. the a and b forms, and the relative proportions of the two forms being stable at the temperature of use. The proportions of the a -promoting elements Ni, Fe and C and the b -promoting elements Cr and Mo are preferably such that the a and b forms are present in the alloy in substantially equal amounts, i.e. the atomic proportions of Co, the a -promoters and the b -promoters are preferably 9:1.5-2:7 respectively. The relative proportion of the allotropic forms is rendered constant at the temperature of use by casting the alloy into preheated moulds and maintaining the alloy in the moulds at a temperature in the region of the future working temperature for at least 24 hours. The alloy may be subsequently subjected to a mechanical strain at a temperature equal to or greater than the working temperature.