Designation
DIN: | 21 MnCr 5 |
AFNOR: | 20 MC 5 |
UNI: | - |
AISI: | 5120
|
Chemical composition:
Strength:
max. 210 HB
(≈ max. 710 N/mm²)
Thermal conductivity at 100 °C:
38.5 W/m K
Character:
standard steel for case-hardening with good machinability; high surface hardness with tough core
Application:
machine parts and moulding plates with a high surface hardness;
synthetic resin press moulds for the processing of thermoplastics and thermosetting plastics.
Treatment by
possible:
Polishing, etching, EDM
Nitriding:
Usually, hardened parts are not nitrided → loss of hardness.
Hard chroming:
recommended, results in increased wear and corrosion resistance
Heat treatment:
Soft annealing:
670 to 710 °C for about 2 to 5 hours
slow controlled cooling, further cooling in air, max. 205 HB
Carburising:
900 to 950 °C. The choice of the carburising means and carburising temperature depends on the desired surface carbon content, the carburising graph and the required case depth.
Application:
870 to 930 °C in powder/salt bath, cooling in oil/warm bath at 160 to 250 °C
Intermediate stress-relieving heat treatment:
630 to 650 °C, about 2 to 4 hours with slow furnace cooling
Preheating:
350 °C depending on dimensions
Hardening:
curing temperature 810 to 840 °C in oil of ~ 60 °C warmth
Cooling:
down to about 100 °C in oil, then in air to about 50 °C
Tempering:
1 hour per 20 mm part thickness, at least 2 hours
Annealing graph:
Technical tip:
- For mirror polishing we recommend the steel for through hardening 1.2767.
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