Vacuum heat treatment


The following heat treatment techniques are carried out under vacuum:

  • Stress relieving (Info)
  • Quenching and tempering (Info)
  • Hardening (Info)
  • Tempering (Info)
  • Soft annealing (Info)
  • Normalizing (Info)
  • Structural heat treatment (Info)
  • Steam tempering (Info)
  • Sub-zero cooling (Info)

The results of H-O-T vacuum heat treatment are:

Minimum distortion of the component and maximum efficiency in use.

A comprehensive quality control ensures stringent compliance with the stated results and provides helpful suggestions for the continuous further development of our process flow.

Having worked in steel treatment for decades and by consistently cooperating with well-known steel producers, H-O-T is able to guarantee maximum customer satisfaction at the very highest level.

Stress relieving

Stress relieving is necessary when existing residual stresses have a detrimental influence on distortion behaviour. Correction of the resulting changes in shape and size are taken into consideration by adding a certain allowance. The temperature must be below the Ac1 transition temperature but should nevertheless be as close as possible to this temperature so that it is not necessary to maintain the temperature after heating. Heating and cooling must be carried out in such a way that no additional or new residual stresses can develop.
In the case of cold work steels, the normalizing process is preferred if coarse grain formation might occur as a result of re-crystallisation when stress relieving.

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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.

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

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A single or repeated heating of a hardened component to a pre-determined temperature (<ac1), maintenance of the given temperature and subsequent adequate cooling rate.

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Soft annealing

Heat treatment to reduce the hardness of a component to a predetermined value.

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Consists of heat treatment to austenise the steel, together with subsequent cooling in calm/inactive air.

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Structural heat treatment

Like stress-relief annealing, the purpose of structural heat treatment is to disperse stresses caused by machining the material; the process is normally carried out after rough machining. The treatment consists of hardening followed by annealing. As a result of the change in structure, reduced changes in shape and dimensions can be anticipated during subsequent heat treatment.

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Steam tempering

A dark blue-grey oxide layer (magnetite) is deposited on the surface of the tools during steam tempering. As well as changing the optical appearance, steam tempering improves corrosion-resistance and minimises the coefficient of friction.

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Sub-zero cooling

Treatment after hardening to convert a large amount of the residual austenite to martensite. The treatment consists of a cooling process and the maintenance of a given temperature below room temperature.

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  • Forming dies
  • Aluminium mould inserts
  • Batch assembly
  • Injection moulding die
  • Injection moulding die
  • Heat treatment furnace
  • Heat treatment furnace
  • Heat treatment furnace
  • Heat treatment furnace  with helium quenching
  • HRC hardness testing
  • Vickers hardness testing
  • Nozzles
  • Moulds
  • Moulds
  • Various tools
  • Cutters
  • Stamping die
  • Countersink
  • Tools with black oxide finish

We update and optimise precision machine tools and high-grade components.