Patent ID: 7559995

Claim:
Process for heat treating metal workpieces, the method comprising: heating the workpieces to a first temperature under a vacuum or a neutral or reducing gas atmosphere during a heating phase; carburizing the workpieces at the first temperature and at a first pressure reached at the end of the heating phase and for a first period of time in a gas atmosphere containing a hydrocarbon during an enrichment phase following directly upon the heating up phase; transitioning the workpieces from the first temperature to a second temperature below or greater the first temperature under a vacuum or a gas atmosphere containing chiefly nitrogen during a first temperature transition phase following immediately upon the enrichment phase; boriding the workpieces at the second temperature and at a second pressure reached at the end of the first temperature transition phase for a second period of time in a gas atmosphere containing boron during a boriding phase following directly upon the first temperature transition phase, wherein the gas atmosphere during the boriding phase contains at least one of boron trichloride and boron trifluoride and diborane; transitioning the workpieces from the second temperature to a third temperature below or greater the second temperature under a vacuum or in a gas atmosphere containing mainly nitrogen during a second temperature transition phase following directly upon the boriding phase; and quenching the workpieces from the third temperature to a temperature below 150° C. during a quenching phase following upon the second temperature transition phase; such that the process creates an edge layer on the workpiece comprising an outer iron boride layer and a case hardening layer beneath the iron boride layer.