Heat treatment characteristics of metal cutting machine tool parts

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Metal cutting machines are devices that use cutting methods to process metal blanks into parts; we commonly refer to them as machine tools. In our country’s machine tool industry, the volume of production varies depending on the size of the machine tools; medium and small-sized machine tools are generally produced in batches, while large and heavy-duty machine tools are manufactured individually or in small batches. The working condition of components in conventional machine tools, such as load-bearing, impact resistance, and lubrication conditions, are significantly better than those in automobiles, tractors, and heavy machinery. 　　Parts serve as the support for the entire machine tool, and high precision retention is required of them. The heat treatment characteristics of machine tool parts can be summarized as follows: (1) Simple types of steel are used; generally, non-alloyed (carbon) structural steel and alloy structural steel are employed. A few components, such as steel-lined guides and hardened lead screws, are made from low-alloy tool steel and bearing steel. 　　(2) Many parts require local or surface hardening. Many machine tool components only need high wear resistance in their surface areas; aside from a few parts that are hardened using salt bath furnaces, most are hardened through local surface hardening methods such as induction heating, laser heating, and ultrasonic heating. 　　(3) Use of periodic operation furnaces Oxidation-free heating of most parts is carried out using salt bath furnaces. It is carried out in a vacuum furnace or by pouring kerosene into a gas carburizing furnace to create a protective atmosphere. 　　(4) Precision parts require high dimensional stability. Typically, one or more stabilization treatments are carried out during the manufacturing process, such as stress-relief annealing, low-temperature aging treatment, and cold treatment, in order to minimize residual internal stresses and ensure high dimensional stability. 　　(5) Most steel parts must undergo pre-heat treatment. Cast steel parts, forgings, and rolled products, among others, need to go through pre-heat treatments such as annealing, normalizing, or quenching and tempering in order to increase their strength, eliminate structural defects, and improve their machinability. These treatments also prepare the structure of the parts for subsequent heat treatment, thereby reducing deformation during heat treatment. 　　(6) Widespread use of low-temperature chemical heat treatment: The design of machine tool components generally takes rigidity into account, resulting in lower requirements for heat treatment; such components exhibit high wear resistance and good dimensional stability. Therefore, low-temperature chemical heat treatment processes such as nitriding and nitrocarburizing have been widely used.