This is the most common heating process of all, toughening is used to increase the hardness of the metal. The workpiece is subjected to heat, at a specific temperature, and then is allowed to cool rapidly. This results in increased hardness and strength
Cases hardening, also known as surface hardening, is a type of hardening where the surface of the metal object is subjected to hardening, whereas the metal deeper inside remains soft. Thus, this process helps in forming a thin layer of hard metal at the surface.
In this heat treatment process, the workpiece is subjected to heat in presence of another material that releases carbon on decomposition. So, when heated the released carbon is absorbed into the surface of the metal. The carbon content on the surface will result in a harder surface compared to the inner core.
During the process, workpieces are heated in a sealed chamber, before nitrogen and carbon are added. The part is heated into the austenitic range, a phase change occurs and carbon and nitrogen atoms diffuse into the part. Low-carbon, low-alloy steels with low hardenability are good for this process.
Induction heat treatment is a process used for the surface hardening of steel and other alloy components. The workpiece is heat-treated with a copper coil and is heated above the transformation temperature. The alternating current in the coil induces an alternating magnetic field within the workpiece which causes the outer surface of the part to heat to a temperature above the transformation range.