Helium gas is more expensive than other vacuum-furnace cooling gases, but its benefits can offset its higher cost.
Helium gas has been evaluated for use as a quench gas in vacuum heat treating in several studies over the years. For example, in the 1970s, Abar Corp. studied the effects of different cooling gases including helium at a specific pressure and flow rate on the cooling rate in a vacuum furnace in work that also studied the effects of varying nitrogen-gas quenching parameters (i.e., gas flow rate and gas pressure) on cooling rate. Results showed that the cooling rate for helium, as well as those for nitrogen and hydrogen gases are better than that of argon, and that the cooling rate of nitrogen increases with increasing gas flow rate and increasing gas pressure. Studies by Air Products in the early 1990s using its patented rapid gas quenching arrangement showed improvement in cooling rate using gas mixtures of helium and argon. Other studies showed that cooling rate improves incrementally with increasing gas-cooling pressure. Recent studies by Solar Atmospheres shows helium gas quenching provides significant improvements in performance with respect to cooling rate and energy costs, which can offset the higher cost of the gas.