Hydrogen in high-pressure gas quenching: creating opportunities

Kraus Dominic - Aichelin Holding GmbH (Austria)

Reducing energy consumption, greenhouse gas emissions, environmental impact, and the availability and sustainable use of raw materials have become top priorities for large energy-consuming industrial sectors such as industrial furnaces and kilns. However, this opens up opportunities for new innovations and changes the payback period for already existing alternative technologies.

Vacuum heat treatment with high-pressure gas quenching is a proven process for heat treating primarily high-alloy tool steels. By increasing the quenching pressure up to 20 bar and using either helium or hydrogen as the quenching medium, this process can also be applied to the heat treatment of case hardening steels and lower alloy steels. However, primarily for economic reasons, its use was largely limited to nitrogen, and the use of hydrogen was often not pursued. Nevertheless, changes in the environmental policy framework now offer new opportunities, which will be discussed in more detail in this contribution. In addition, the aspect of gas mixtures should also be mentioned. Only a few papers discuss the effects of a modified quenching rate – with slow cooling in the MS temperature region – on the fatigue strength of carburized and gas-hardened low-pressure steels and its effect on the fatigue strength. This aspect should also be addressed here as there may be additional potential.

However, the limitations of high-pressure gas quenching are also demonstrated by the example of austempering. Compared to martensite, the main advantages of bainitic structures are increased toughness and compressive stresses at the surface of the heat treated parts. In addition, the distortion is usually lower due to lower thermal and phase transformation stresses. Initial work has been done in the area of high-pressure gas quenching for this application, but standard salt bath quenching dominates due to its significant advantages.