1. Annealing:
Annealing temperature: 710 ~ 740 °C, holding time is decided by the thickness of the DIN 1.2738 die steel, one hour per 25mm. Colding in furnace after thermal insulation.
2. Destressing:
Heating temperature: 600 °C (annealed condition), 550 °C (quenching and tempering state), holding time is decided by the thickness of the 1.2738 steel, one hour per 50mm. Colding in furnace after thermal insulation.
3. Quenching and tempering:
Preheating temperature 500 ~ 600 °C, quenching temperature 840 ~ 880 °C, holding 30min (the mold have to quenching in the protective gas to prevent oxidation and decarbonization). Oil cooling, cooling to 50 ~ 70 °C, immediately tempered.
Tempering holding time is decided by the thickness of the 1.2738 steel mould, one hour per 25mm, at least 2h. Tempering temperature: 180 °C / 200 °C / 300 °C / 400 °C / 500 °C / 600 °C, the hardness: 52HRC / 51HRC / 48 HRC / 46HRC / 42HRC / 34HRC.
4. Induction hardening:
The DIN 1.2738 die steel may be treated by flame or induction hardening to increase the surface hardness to 50HRC. Colding in air after hardening. Small mould can use common quenching medium, immediately tempered after hardened, tempering temperature 180 ~ 200 °C.
5. Nitriding:
Nitriding temperature + nitriding time: 525 ° C + 20h, the nitride layer thickness 0.30mm; 525 °C + 30h, the nitride layer thickness 0.35mm; 525 °C + 50h, the nitride layer thickness 0.50mm.
6. Nitrocarburizing:
570 °C to maintain nitrocarburizing 2h, the mold surface hardness is about 700HV, nitrided layer depth is about 0.1mm.
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