Low pressure carburising (LPC)

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.

Benefits of low pressure carburising

• 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

Low pressure carburising 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.