Page "Blacksmith" Paragraph 94

During the 20th century various gases ( natural gas, acetylene, etc.

) have also come to be used as fuels for blacksmithing.

While these are fine for blacksmithing iron, special care must be taken when using them to blacksmith steel.

Each time a piece of steel is heated, there is a tendency for the carbon content to leave the steel ( decarburization ).

This can leave a piece of steel with an effective layer of unhardenable iron on its surface.

In a traditional charcoal or coal forge, the fuel is really just carbon.

In a properly regulated charcoal / coal fire, the air in and immediately around the fire should be a reducing atmosphere.

In this case, and at elevated temperatures, there is a tendency for vaporized carbon to soak into steel and iron, counteracting or negating the decarburizing tendency.

This is similar to the process by which a case of steel is developed on a piece of iron in preparation for case hardening.