Mild heat treating of steel components describes a process in which steel is subjected to a combination of heating and cooling operations in order to increase its strength and durability. Heat treating refines the grain of the steel as the carbon molecules react with the iron content. This traditional process works for medium- and high-carbon steel, but not for mild steel, which has a low carbon content. Mild steel must be case hardened. This involves changing the chemical composition of the surface layer of the metal by allowing it to react with a source of carbon. This process creates a hardened steel “case” around the softer, low-carbon mild steel.
Heat a piece of newly milled, mild solid steel by placing it in a heating chamber or heating it with a brazing torch. Heat the item until it glows red hot.
Quickly immerse the item in a high-carbon compound such as Kasenite. The carbon granules will melt onto the surface of the mild steel. Allow the steel to cool slightly.
Return the steel to the heat source. Reheat the tool to a red-hot temperature. During this process, the carbon material will melt onto the surface of the tool and create a high carbon “case” on the mild steel piece.
Immerse the steel piece suddenly in a cooling chamber or container of cool water. Allow the tool to return to room temperature and then remove it from the water. This process will forge a hardened surface onto the tool or mild steel piece.
Repeat this process as necessary to create a hardened shell. The casing process will not create a harder tool than what is obtained in the first process. However, the thickness of the hardening shell can be increased up to .02-.03 inch.
If you perform this task in a classroom, place insulated firebrick in a semicircle around the tool during the heating process. The firebrick will reflect the heat back onto the mild steel, and make the heating process simpler.