On 2018-08-08 14:48:54
Gas selection for quench hardening of alloy steel
Gas quenching (alloy steel) is hardened by inert gas pressure quenching at a pressure of 2 to 20 bar. Commonly used in vacuum furnaces, nitrogen and argon are common quenching gases.
Cooling in argon produces a slow heat transfer rate, followed by nitrogen, then helium and finally hydrogen. All of these gas mixtures are used, but nitrogen is more attractive, especially from a cost perspective, but some alloys (such as titanium) have limitations.
Theoretically, there can be no limitation and pressure to improve the cooling rate by increasing the gas velocity. However, in fact, very high-pressure and very high-speed system construction is complicated and expensive. In general, the power required for gas recirculation increases faster than the benefits produced.
Recent changes in material chemistry and pressure hardening designs (eg, alternating air flow, directionally adjustable blades, and variable speed drives) have become possible, and gas hardening is now used to produce full hardness in many traditional oil-hardened materials.