Heat treatment is a term used by metallurgists to describe a range of thermal processes designed to manipulate properties of engineering and decorative alloys to meet requirements. Many treatments involve heating of the alloys to specific temperatures for specified periods of time and then cooling at a defined rate that may be rapid or slow. In jewelry, annealing of precious metal alloys is often undertaken to soften cold-worked material to enable further working without cracking or fracture. But other types of annealing are also carried out, for example, to stress relieve alloy items to prevent stress corrosion cracking or to age-harden them.While annealing and age-hardening of jewelry metals have been discussed in previous "Basic Metallurgy" presentations, the "whys" and "wherefores" of such treatments have not been fully explained. There are several types of annealing treatments in use, each with different objectives. This presentation focuses on heat treatments used in the jewelry industry and attempts to explain the underlying principles involved.

Author: Dr. Christopher W. Corti