Hardened & Tempered For Higher Quality
Metals need to be hardened for an improvement in their mechanical properties, as well as an increase in the level of hardness, producing a tougher, sturdier item. Alloys are heated above the critical transformation temperature for the material, then cooled rapidly enough to cause the soft initial material to transform to a much harder, stronger structure. Alloys may be air cooled, or cooled by quenching in oil, water, or another liquid, depending upon the number of alloying elements in the material. Hardened materials are usually tempered or stress relieved to improve their dimensional stability and toughness.
Steel parts usually require heat treatment to obtain improved mechanical properties, such as increasing hardness or strength. The hardening process consists of heating the components above critical temperature, holding at this temperature at a rate fast enough to allow the material to transform to a much harder, stronger and then tempering. Steel is essentially an alloy of iron and carbon and the other elements to go into solid solution. Quenching ‘freezes’ the micro-structure, inducing stresses. Parts are subsequently tempered to transform the micro-structure, achieve the appropriate hardness and eliminate the stresses.
Metal tempering is done to develop the required combination of hardness, strength and toughness or to relieve the brittleness of fully hardened steels. The combination of quenching and tempering is critical to make tough parts.
This treatment follows a quenching or air cooling operation. Tempering is generally considered effective in relieving stresses induced by quenching in addition to lowering hardness to within a specified range, or meeting certain mechanical property requirements.
Tempering is the process of reheating the steel at a relatively low temperature leading to precipitation and spheroidization of the carbides present in the micro-structure. The tempering temperature and times are generally controlled to produce the final properties required of the steel. The result is a component with the appropriate combination of hardness, strength and toughness for the intended application. Tempering is also effective in relieving the stresses induced by quenching.