Annealing Heat Treatment

Annealing involves heating to a predetermined temperature, houlding at this temperature, and finally cooling at a very slow rate. The temperature at which steel is heated and holded for duration varies with chemical composition, size, shape of component. Annealing can be the final or preparatory step for further treatment.

Purpose of Annealing

• Relieve internal stresses developed during solidification, machining, forging, rolling or welding.
• Improve or restore ductility and toughness.
• Enhance machinability.
• Eliminate chemical non uniformity.
• Refine grain size.

Normalising Heat Treatment

Limited to some, but not all, steels, normalising can soften, harden or stress relieve a material, depending on its initial state. The objective of the treatment is to counter the effects of prior processes, such as casting, forging or rolling, by refining the existing non-uniform structure into one which enhances machinability/formability, in certain forms, meets final mechanical property requirements.

A primary purpose is to condition the steel so that, after subsequent shaping, a component responds satisfactorily to a hardening operation (e.g. aiding dimensional stability). Normalising consists of heating the suitable steel to a temperature typically in the range 830-950°C (at or above the hardening temperature of hardening steels, or above the carburising temperature for carburising steels) and then cooling in air. Heating is usually carried out in air, so subsequent machining or surface finishing is required to remove scale or decarburised layers.