Powder metallurgy workpieces prodn. system - in which carbon is added as necessary between annealing and compression stages before sintering

摘要

The process produces metal items by heating a metal powder consisting mainly of tool, alloy or stainless steel or a high-tensile metal alloy. The powder is produced by pulverising and water-quenching of a melt to give irregularly-shaped particles, in a vacuum of 1.0 Torr at 900 degrees C to reduce the oxygen content, followed by controlled cooling to anneal the powder. The powder is compressed into blanks of >=60% relative density, and heated in a first stage in a vacuum below the setting temp. of the powder for at least half an hour to reduce the oxygen content to 0.7%. In a second stage their temp. is increased to a sintering temp., while a vacuum or partic. atmosphere is maintained round them. Sintering continues for 0.5-4 hrs. to increase the relative density to >=93%. The items are produced to standard dimensions, giving a charge weight of >=20 kg for the blanks heated in the first two stages. Between annealing and compression the powder is analysed for C and O content, C being added as necessary. Sintering temp. is selected to suit the C content, being maintained constant within +10 deg. C during sintering.