Selection of atmosphere:

The surrounding in the thermal enclosure (furnace) is termed atmosphere. The atmosphere consists of gases and is usually air. However, in some heat treatment, thermo-mechanical processing, sintering etc special type of atmosphere is required to  

• Prevent oxide formation, if the heating material is prone to oxidation.
  
  
• Decarburize steel.

• Control the surface chemistry of steel which means the elements must not be oxidized or reduced during heating.

• Produce “blueing” effect in steel. The blueing effect imparts a wear-resistant and oxidation- resistant surface finish.

• reduce oxides formed on the surface.

• Make the surface hard by allowing carburizing or nitriding.