Bt Magnet-technologie Gmbh

Robert Boschgmbh

Mannesmann Aktiengesellschaft

Rudolf Schneider

Karl-Heinz Lindner

Bernhard Schelb

Method for the case-hardening of higher-molybdenum-alloy sintered steels

A process for producing sintered parts with high wear resistance and good dynamic strength properties from formed bodies, which have been pressed as green parts from a completely-alloyed air-hardened heat-treatment steel powder with a carbon content of at least 0.3% added in the form of graphite. The process includes sintering the parts under protective gas at a sintering temperature of at least 1000.degree. C. and subsequent cooling. The sintered parts are cooled immediately after sintering from the sintering temperature to a first holding temperature in the range of Ar.sub.3 to a maximum of 150.degree. C. above Ar.sub.3 and are held for a first holding period of 5 to 25 minutes at this temperature (austenitizing phase). Immediately after this, the sintered parts are cooled in accelerated fashion to a second holding temperature by convective gas cooling and are held at this temperature for a second holding period. The second holding temperature lies in a temperature range in which a bainitic structure forms and is of such a length that a bainitic structure portion of at least 50% is established. The sintered parts are then cooled to room temperature.

Process and device for producing sintered parts

In a process for producing a workpiece from sintered metal, especially from sintered iron, the latter is subjected, after sintering, to a steam treatment at temperatures below 500.degree. C., especially at 430.degree.-480.degree. C., at a steam partial pressure of from 20 to 80 mbar, especially from 30 to 50 mbar, to form an oxide layer on the surface, and to subsequent surface-hardening. Workpieces, especially internally geared wheels for starters, having a wear-resistant surface and, in the core, properties unchanged by the hardening are obtained.

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Froendenberg, Germany

Rudolf Schneider