Method and device for heat treatment of metal workpieces as well as a heat-treated workpiece

Process for heat treating metal workpieces, especially for the combined carburizing, boriding and hardening of ferrous products, with the following steps:

• a) Heating the workpieces to a first temperature (φ1) under a vacuum or a neutral or reducing gas atmosphere during a heating phase (A);
• b) Carburizing the workpieces at the first temperature (φ1) and a first pressure (p1) reached at the end of the heating phase (A) and for a first period of time (Δt1) in a gas atmosphere containing a hydrocarbon during an enrichment phase (B) following directly upon the heating up phase (A);
• c) Cooling the workpieces from the first temperature (φ1) to a second temperature (φ2) under a vacuum or a gas atmosphere containing chiefly nitrogen during a first cooling phase (C) following immediately upon the enrichment phase (B);
• d) Boriding the workpieces at the second temperature (φ2) and at a second pressure (p2) reached at the end of the first cooling phase (C) for a second period of time (Δt2) in a gas atmosphere containing boron during a boriding phase (D) following directly upon the first cooling phase (C);
• e) Cooling the workpieces from the second temperature (φ2) to a third temperature (φ3) under a vacuum or in a gas atmosphere containing mainly nitrogen during a second cooling phase (E) following directly upon the boriding phase (D) and
• f) Quenching the workpieces from the third temperature (φ3) to a temperature below 150° C. during a quenching phase (F) following upon the second cooling phase (E).