Low Pressure Carburising

Low Pressure Carburising

Low Pressure Carburising

LPC is a case hardening process carried out in a vacuum furnace using hydrocarbon gases at very low pressure and elevated temperatures to obtain a hardened surface layer of tempered martensite and a tough core. The treatment is used to increase the wear resistance and fatigue life of components.


  • The pitch to root ratio of the carburised layer (case depths) in gears is almost 1:1 (uniform).
  • High hardness below the surface compared to conventionally carburised parts.
  • Faster cycle times.
  • Parts can be carburised between 930°C and 1000°C (1700° and 1830°F).
  • Penetration of carbon in deep blind holes resulting in uniform hardness on the entire profile.
  • Carburising of small holes and blind holes.
  • Avoidance of part cleaning after the heat treatment due to high pressure gas quenching (dry quench).
  • Reduction of dimensional alterations by temperature-independent heat transfer during high pressure gas quenching.
  • Enhanced mechanical properties – elimination of inter-granular oxidation layer, improved fatigue properties.
    • Dimensional control – low distortion, predictable and repeatable
    • Environmentally friendly
    • Reduced manufacturing steps such as post grinding, cleaning and inspection
    • Enhanced cleanliness of products
    • Precise control of case depth, microstructure and hardness
    • Better case depth uniformity for complex shapes. Case depth uniformity can be maintained within ±0.002” in most cases.

Application & materials

Typical applications of LPC include gears, shafts, axles, nozzles, injectors, spindles etc.

20CrNiMo2-2 / 1.6523 / AISI 8620
20MnCr5 / 1.7147 / AISI 5120
14NiCrMo13-4 / 1.6657 / AISI 9310
14NiCr14 / 1.5752 / AISI 3310

Process details

Low pressure carburising with high pressure gas quench is primarily used for transmission gears and diesel fuel injectors that require a uniform carburised layer on every surface of the part, with minimal dimensional movement. The process produces a very clean surface, thus eliminating further post cleaning of the part after heat treatment.