Furnace atmospheres play a vital role in the success of the heat-treating process. It is important for the heat treater to understand why we use them and what the best atmosphere is for a specific application. Many different types of atmospheres are used. It is critical to understand how a particular atmosphere is chosen as well as its advantages and disadvantages and to learn how to control them safely.
In simplest terms, the purpose of a furnace atmosphere varies with the desired end result of the heat-treating process. The atmospheres used in the heat-treating industry have one of two common purposes:
• To protect the material being processed from surface reactions, i.e., to be chemically inert (or protective)
• To allow the surface of the material being processed to change, i.e., to be chemically active (or reactive)
The proper selection of a furnace atmosphere is highly dependent on both the desired purpose of the atmosphere and/or the type of heat treatment being performed.
Additional examples of the uses of furnace atmospheres include:
• Purging air (oxygen) from a furnace
• Controlling the surface chemistry to prevent oxidation and/or reduction reactions from occurring
• Controlling the surface chemistry to allow oxidation and/or reduction reactions to take place
• Avoiding decarburization of the surface
• Allowing surface-chemistry reactions for the purpose of introducing a chemical species such as carbon (carburizing) or nitrogen (nitriding)
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