Gas Carburising

Gas Carburising

Carburizing is a thermochemical diffusion process that introduces carbon into a solid ferrous alloy, typically low carbon alloy steels. This is accomplished by heating the metal in a carbon rich atmosphere above transformation temperature for a pre-determined time allowing carbon atoms to diffuse into the surface layers. The carbon diffusion depth is time and temperature dependent, and the related effective case depth (ECD) can vary from shallow, 0.2-1mm, to medium 1-3mm, to deeper depths of 4 to 6mm.After this diffusion process has taken place, the carburized parts are then quenched to harden the surface carburizing layer. The core will harden in accordance with the alloy and carbon content of the material.

process

The total process is applied in three phases:

  • A thermochemical process in a chamber furnace with integrated quench to enrich the surface in a carbon rich environment in a temperature range of 880 to 980°C.
  • Hardening is achieved after quenching either in oil, polymer/water solution or salt.
  • A tempering operation follows in which the parts are isothermally heated for a period of time in a furnace. Tempering temperature and time in the furnace depend on product requirement and application. The tempering process minimizes peak stresses and reduces crack initiation.

Carburizing is a widely used surface hardening process for low carbon steels. The industrial importance of carburizing is expressed in its market share, as one third of all hardening heat treatments are covered by carburizing and hardening.

Benefits

Carburizing and quenching produces extremely hard surfaces which are highly resistant to wear. Moreover, failure from impact loading is avoided due to a softer core. Unlike other case hardening processes, this process is suitable for deep case depths. The process is easily controlled and case depth as well as carbon potential can be controlled to within strict parameters. Because the parts are treated within a protective atmosphere, carburized parts are usually aesthetically pleasing to the eye.

Application

Typical applications include transmission gears and shafts for automotive, wind turbine and pump components and all applications where components are required to operate for long periods and under high impact loads. A wide variety of steels can be carburized. The unique combination of a hard wear-resistant surface and a tough core can be controlled by the choice of alloy elements and process parameters.