Atmospheric Pressure Sintering

Although vacuum is the preferred mode of sintering, wear parts made of tool steels and high-speed steels can be sintered to conventional P/M densities or to full density at atmospheric pressure and in atmospheres with dew points below -40 °C (-40 °F). Atmosphere-sintered parts have higher oxygen and nitrogen levels than vacuum-sintered parts.

Nitrogen-based, dissociated ammonia, and hydrogen atmospheres are viable alternatives to vacuum. Atmosphere composition has little effect, however, on sintered density. Parts sintered in pure nitrogen or nitrogen-base atmospheres are nitrided. Increasing the nitrogen content decreases the sintered transverse rupture strength. Consequently, as-sintered transverse rupture strength is lowest for parts sintered in nitrogen and highest for parts sintered in hydrogen. Sintered high-speed steels and tool steels should be double tempered to maximize transverse rupture strength.

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