Annealing of Steel^[1]

Steels may be annealed to facilitate cold working or machining, to improve mechanical or electrical properties, or to promote dimensional stability. This article, using iron-carbon phase diagram, describes the types of annealing processes, namely, subcritical annealing, intercritical annealing, supercritical or full annealing, and process annealing. Spheroidizing is performed for improving the cold formability of steels. The article provides guidelines for annealing and tabulates the critical temperature values for selected carbon and low-alloy steels and recommended temperatures and time cycles for annealing of alloy steels and carbon steel forgings. Different combinations of annealed microstructure and hardness are significant in terms of machinability. Furnaces for annealing are of two basic types, batch furnaces and continuous furnaces. The article concludes with a description of the annealing processes for steel sheets and strips, forgings, bars, rods, wires, and plates.