The purpose of preliminary heat treatment is to improve the processing performance, eliminate internal stress and prepare a good metallographic structure for the final heat treatment. The heat treatment processes include annealing, normalizing, aging, and quenching and tempering.
(1) Annealing and normalizing of cutting machine Annealing and normalizing are used for blanks that have been thermally processed. For carbon and alloy steels with a carbon content of more than 0.5%, in order to reduce their hardness and ease of cutting, annealing is often used; for carbon and alloy steels with a carbon content of less than 0.5%, in order to avoid sticking the knife during cutting, Instead, it is normalized. Annealing and normalizing can still refine the grains and uniform the structure, in preparation for the subsequent heat treatment. Annealing and normalizing are usually arranged after rough manufacturing and before roughing.
(2) Aging treatment The aging treatment is mainly used to eliminate the internal stress generated in the blank manufacturing and mechanical processing. In order to avoid excessive transportation workload, it is sufficient to arrange an aging treatment for parts with general accuracy before finishing. However, parts with high accuracy requirements (such as the box body of a coordinate boring machine, etc.) should be arranged for two or more aging treatment procedures. Simple parts are generally not subject to aging treatment. In addition to castings, for some precision parts with poor rigidity (such as precision screws), in order to eliminate the internal stress generated during processing and stabilize the part processing accuracy, multiple aging treatments are often arranged between roughing and semi-finishing. For some shaft parts, aging treatment should be arranged after the straightening process.
(3) Quenching and tempering is to carry out high temperature tempering treatment after quenching, it can obtain a uniform and fine tempered sorbite structure, and prepare for reducing deformation during subsequent surface quenching and nitriding treatment, so the tempering Can be used as preliminary heat treatment.
Because the comprehensive mechanical properties of the quenched and tempered parts are better, some parts that do not require high hardness and wear resistance can also be used as the final heat treatment process.