Vacuum atmospheres are slightly reducing at heat-treating temperatures (over 1800°F); thereby keeping clean parts clean and cleaning up the surface of those with minor oxidation.

Inert gas quenching in vacuum furnaces has several advantages over conventional liquid quenching systems:

• Flexibility to change cooling rates easily, even within a single cycle. Gas quenching can produce full hardness in steels that were formerly oil quenched. In liquid quenching, where the cooling rate is fixed, multiple baths may be required.
   
• Ability to more precisely control heat-up and quench rates helps minimize distortion.
   
• Gas quenched parts are clean and scale-free.
   
• M series steels are relatively sensitive to atmosphere, thus vacuum heat treating is advantageous.
   
• Processing in vacuum furnaces produces no toxic or combustible waste gases, which makes it safer and more environmentally friendly than many liquid-quenching processes.
  
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