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Vacuum heat treatment process of 40Cr steel

Heat treatment plays a very important role in mechanical manufacturing. Generally, it does not change the shape of the tool, and rarely changes its chemical composition. Instead, it changes the fine structure inside the tool, or the chemical composition on the surface of the tool, so as to improve its basic use performance and process performance.

In order to obtain the required physical and mechanical properties of metal tools, in addition to the selection and use of materials and molding processes, it is indispensable to select appropriate heat treatment processes. Steel is the most widely used material in the machinery industry, is an important object and main content of heat treatment, and can be properly controlled through heat treatment to achieve the desired purpose.

40Cr steel is a medium carbon modulated steel with moderate price and easy processing. It can achieve certain wear resistance, toughness and plasticity through heat treatment. When the steel is between 550-570 ℃, it has the best comprehensive mechanical properties and is suitable for high-frequency quenching and other surface hardening treatments. It is widely used in life and is very popular.

Overview of Traditional Heat Treatment Process for 40Cr Steel

The heat treatment process can be generally divided into three types: overall, surface and chemical heat treatment. According to the different heating medium, temperature and cooling method of 40Cr steel, different heat treatment processes can be used to obtain different properties and obtain the required metallographic structure to obtain the required mechanical properties.

In the overall heat treatment process, there are roughly “annealing, normalizing, quenching and tempering” and other basic processes, such as the annealing process of 40Cr steel, which is heated to an appropriate temperature and cooled slowly to obtain good service performance, or to prepare for quenching. In addition, the normalizing treatment of 40Cr steel heats the workpiece to a suitable temperature and then cools it. Its effect is similar to that of annealing, except that the internal metal structure obtained is more refined, which can improve the cutting performance of 40Cr steel, or serve as its final heat treatment.

In the quenching treatment of 40Cr steel, after heating and holding, it is rapidly cooled in water, oil or other solutions with water and inorganic salts to make it hard and brittle. In order to reduce the brittleness of 40Cr steel and conduct appropriate tempering, the “four torches” make 40Cr steel workpieces or workpieces have certain strength and toughness through different heat treatment processes. After modulation, this traditional heat treatment process becomes aging treatment.

The process technology of heat treatment has been continuously developed and updated, and the heating and cooling technologies have been reformed. Up to now, vacuum heat treatment, controlled atmosphere heat treatment and thermomechanical treatment have emerged, as well as the creation of new surface heat treatment processes.

In view of the development direction of the new process, the main efforts are to “improve the strength and toughness of the workpiece, enhance the anti fatigue and wear resistance, further reduce the oxidation and decarburization during heating, reduce deformation, further save energy, reduce costs, improve efficiency and reduce pollution”.

1.Controlled atmosphere heat treatment

It refers to the heat treatment conducted in a furnace with controllable furnace gas composition, and the controllable atmosphere to prevent chemical reaction on the workpiece surface is called protective atmosphere. It has the advantages of avoiding oxidation and decarburization of steel parts, saving steel, improving quality and ensuring dimensional accuracy. For example, some workpieces with complex shapes and requiring high elasticity can be formed by stamping low carbon steel and penetrated carburizing to replace high carbon steel. It includes endothermic atmosphere, exothermic atmosphere, exothermic endothermic atmosphere, drip type atmosphere, etc.

2.Vacuum heat treatment

Vacuum heat treatment can reduce deformation, reduce and prevent oxidation, purify the surface, decompose the oxides on the surface, and obtain a bright surface for the workpiece. The degassing effect of vacuum heat treatment can improve the toughness of steel and increase the service life of the workpiece. Reduce or omit cleaning and grinding processes, improve working conditions, and realize automatic control. Vacuum annealing, vacuum quenching and vacuum carburizing.

Vacuum heat treatment has the advantages of high quality, low energy consumption, no pollution (or less pollution), which can effectively prevent 40Cr steel from producing defects, improve surface roughness and reduce friction coefficient. The vacuum heating is carried out in the form of radiation. The heating is slow, the furnace temperature is uniform, the product deformation is small, and the dehydrogenation effect is also available. All these are conducive to improving the cutting life of the mold tool. The service life of vacuum quenching can be increased by 3 to 4 times than that of salt furnace quenching (average number of rolled pieces). The cutting contrast tests of the tools quenched by vacuum furnace, box furnace and salt bath furnace were carried out. The service life of the tools from high to low was vacuum furnace, box furnace and salt bath furnace. This shows the advantages of vacuum heat treatment.

Heat treatment equipment selection: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for vacuum heat treatment of 40Cr steel tools and dies. Good temperature control accuracy and uniformity ensure the effective implementation of the vacuum heat treatment process. SIMUWU focuses on the manufacturing of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum gas quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.