High Pressure Gas Quenching

For many years now, gas quenching has been the preferred process in the heat treatment of high-speed steels and hot and cold working tool steels.

With the development of separate gas quenching chambers, it is often possible to replace oil quenching with high-pressure gas quenching using nitrogen or helium for heat treating case hardening steels or other low alloyed materials.

The success of this dry quenching technology is based on its environmental and commercial efficiency. Quenching gases such as nitrogen or helium are absolutely inert and without any ecological risk. They leave no residues on the workpieces or in the hardening furnaces. Therefore, investments in equipment such as washing machines or fire monitoring systems are redundant. This, in turn, reduces operating costs for hardening. When helium is used as a quenching gas, appropriate recycling systems for unlimited repeated use of the helium are available.

There is a difference in the quenching pattern, using gas quenching vs. oil quenching, because of the laws of physics. The following diagram shows the different phases which occur during quenching in liquid media: film boiling, bubble boiling as well as the convection phase. The individual phases are characterized by very different heat transfer coefficients, which lead to big temperature gradients in the part, causing distortion of the part. Gases don’t show phase changes during quenching. Heat transfer all over the part is more homogeneous and the risk of distortion is reduced. Excellent process control for the entire quenching process is guaranteed by the control of gas pressure and gas velocity. With these parameters, the quenching speed can be adjusted to the parts requirements.

2. Heat transfer and temperature distribution during immersion cooling, 3. Heat transfer and temperature distribution during high-pressure gas quenching

Process Advantages
The main advantages of high pressure gas quenching are reduced distortion which mostly helps to avoid hard machining steps and dry and clean parts afterwards. After gas quenching the parts surface is free from quenching media, dust or other residuals, which is the required condition for further process steps like coating.

Advantages of Gas Quenching

  • Reduction of hardening distortion and/or variation of distortion
  • Quenching intensity adjustable by control of gas pressure and gas velocity
  • Process flexibility
  • Clean, non-toxic working conditions
  • Integration into manufacturing lines
  • Reproducible quenching result
  • Clean and dry parts, no washing
  • Simple process control

1. Typical load of gear shafts for gas quenching, 2. Gas Quenching Pressure, 3. Distortion after heat treatment