LIQUID-PHASE SINTERING OF HIGH-SPEED STEELS

Attempts were made to reduce the sintering temperature required to density two different grades of high-speed steel by the introduction of copper-phosphorus to promote liquid-phase sintering and by adding carbon to lower the solidus temperature. The use of nitrogen-atmosphere sintering in an effort to lower the sintering temperature through absorption of interstitial nitrogen into the steel did not succeed. Copper-phosphorus combined with carbon additions was successful in reducing sintering temperatures by approximately 100-degrees-C but was more effective in the M3/2 (molybdenum) than in the BT6 (tungsten grade) steels. Densification via a liquid-phase sintering mechanism occurs in a number of stages as different liquid phases are produced by interaction between the copper-phosphorus and the steel. Growth of carbides by solution and reprecipitation due to the transport of alloying elements through these liquid phases is suggested as a major densification process.