Quenching steel parts in 20-bar helium

Hardening of steel by quenching is a metallurgical process that has been used for at least 1,000 years. Even so, optimization of the quenching process based on metallurgical and economical principles is today more important than ever. In this context, gas quenching offers a potentially useful alternative to traditional media. A qualitative comparison of oil and gas quenchants highlights the advantages of gas in terms of total performance, total cost, and health, safety, and the environment. This explains why applications for gas quenching and vacuum heat treating in combination with gas quenching are growing at the expense of other media (molten salt, aqueous polymers, oil, and water). The major advantages of high-pressure gas quenching in 20-bar helium over quenching in oil are: Ability to control quench intensity via selection of gas type, pressure, and velocity; uniform quenching provided by single-phase heat transfer; reduced distortion; parts are clean and dry after hardening, eliminating washing; no disposal problems. Compared with other gas-quench candidates, helium has a low density, is safe to use, and is readily available, easily stored, and economical when recycled.