|Techniques Of Heat Treating||Tempering|
|Types Of Heat Treating||Differential Hardening|
|Usage/Application||Pre- and post-welding treatment for control of properties, stresses and distortion.|
Pre-welding heat treatment involves heating the joints to be welded to specified temperatures before welding can be carried out. Likewise, post-welding heat treatment involves heating the weldment to specified temperatures to allow for gradual cooling and minimization of stresses. Stress relieving is based on the same principle, to relieve any external and internal inherent stresses before a component is put into service
Heat treatment and stress relieving can be carried out in a variety of ways. Electrical Resistance Treatment makes use of the principle that as current is passed through a metal, the resistance of the metal to the current flow causes an increase in its temperature. This increase further causes an increase in resistance, thereby requiring more current for penetration. Various temperatures can be achieved by gradually increasing the currents and based on the material being treated. Electrical Resistance Treatment can be done by using 80V, which is safer but more expensive, or 220V, which is comparatively cheaper. It consists of electrical coils that are wound around the parts to be treated. Current is passed through the coils, which causes the corresponding increase in temperature.
Another type of treatment is the Induction Treatment. This is based upon mutual induction, where electric currents are induced in metals via induction coils. These induced currents cause an increase in temperature.
A third type of heat treatment makes use of high velocity, oil-fired burners. These burners can be placed on the outside or inside the components, and fired at high velocities. The flame and resultant exhaust gases cause heating of the component, thereby enabling heat treatment. Damper and flow control can be used to ensure even and proper heating of the entire components.