Strength, toughness, hardness, accurate carbon adjustment controls, reduction of oxidation on the edges. Inert gas hardening offers an exceptional range of possible applications. Computer-operated (bell-type furnace) systems, a precise combination of parameters – all processes are documented and are 100% reproducible.


Areas of application

Automotive industry | Medical technology | Aerospace industry
Electrical industry | Textile industry | Mechanical engineering | Tool making


Material groups

Unalloyed to medium-alloyed steels and thermochemical processes

Inert gas hardening heat treatments

Vertical and suspended batches up to 850mm in length (depending upon shape)

  • Stress-relief annealing

    Stress-relief annealing takes place at temperatures below the Ac1 transition temperature; it is followed by slow cooling to reduce the inner tension (residual stress).


    Hardening serves to achieve a high hardness in the component, preferably by martensite accumulation. It consists of the following two stages: austenitizing and cooling at an adequate speed.

    Quenching and tempering

    Hardening with subsequent tempering, mostly above 550°C, to reach a desired combination of mechanical properties, in particular to increase the toughness compared to the hardened condition.


    A thermo-chemical treatment of a workpiece in an austenitized condition; the carbon content of the surface layer is increased. The carbon content, when austenitized, is in a solid solution.

    Case hardening

    Case hardening consists of carburization, or carbonitriding with subsequent hardening – either directly afterwards or after an interim cooling and re-heating to achieve an adequate hardening temperature. Before hardening, the outer layer is enriched with carbon (carburization) or with carbon and nitrogen (carbonitriding). Compared to carburization, the additional nitrogen accumulation results in a higher temperability by changing the conversion behavior of the outer layer, and thus also resulting in a higher tempering stability after hardening. Depending upon the required characteristics or the requirements of the following process (e.g. grinding), after the hardening process the component is tempered or deep-frozen and then tempered. Case-hardening the outer layer of workpieces and steel tools (with C contents of 0.2 %) achieves a significant increase in the hardness of the outer layer and an enhancement of the mechanical properties of the workpiece/tool.

    Carbon nitriding

    This process is similar to case hardening. In addition to carbon, the surface is also enriched with nitrogen in the carbon nitriding process.

    Artificial ageing through subzero cooling

    A process to achieve dimensional stability of heat-treated parts by means of subzero cooling directly following the heat treatment. Its purpose is the conversion of the remaining austenite and the creation of a stable structure.

Advantages of inert gas hardening using the bell-type furnace

  • Vertical and suspended batches up to 750mm in length
  • Accurate carbon potential adjustment controls
  • Reduction of oxidation on the edges
  • Computer-operated processes
  • Complete documentation of processes

All heat treatments at H-O-T are tailored to the application in question and to the contours of the workpiece.

Talk to us.
We’ll be happy to advise you.

T: +49 (0)911 36014-1042

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