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Vacuum Heat Treatment Furnace

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Why vacuum heat treatment is necessary

In modern life, we come into contact with a variety of metal products, such as steel bridges, car casings, kitchen knives, stainless steel guardrails, iron pots, cans, iron hammers, etc.
In order for metal workpieces to have these properties that meet our different needs, in addition to selecting the appropriate alloy, almost all others rely on different metal heat treatment methods.
So what is heat treatment?
Metal heat treatment is to heat metal or alloy workpieces in a certain medium to a suitable temperature, maintain it at this temperature for a certain period of time, and then cool it in different media at different speeds, thereby changing the surface or internal texture of the metal material. A process to control the performance of microstructure.

Why vacuum heat treatment is necessary

Heat treatment performed in a negative pressure atmosphere or vacuum is called vacuum heat treatment. It can not only prevent the workpiece from oxidation and decarburization, but also keep the surface of the treated workpiece smooth and clean, and improve the performance of the workpiece. After vacuum heat treatment, the parts have small distortion and high quality, and the process itself is flexible and pollution-free. Therefore, vacuum heat treatment is not only a necessary means for vacuum heat treatment of some special alloys, but is also used in the heat treatment of general engineering steel, especially tools, molds and precision couplings. The service life after vacuum heat treatment is longer than that of general vacuum heat treatment. Big improvement.
Metal vacuum heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing processes, vacuum heat treatment generally does not change the shape and overall chemical composition of the workpiece, but changes the microstructure inside the workpiece or changes the surface texture of the workpiece. Chemical composition, which gives or improves the performance of the workpiece. Its characteristic is to improve the intrinsic quality of the workpiece. Therefore, it is a special process in machinery manufacturing and one of the important processes in the manufacturing of mechanical parts and tools and molds. It can ensure and improve various properties of the workpiece, such as wear resistance, corrosion resistance, etc. It can also improve the structure and stress state of the blank to facilitate various cold and hot processing.

For example, after long-term vacuum annealing treatment of white cast iron, malleable cast iron can be obtained to improve the plasticity; gears adopt the correct vacuum heat treatment process, and the service life can be doubled or dozens of times longer than that of gears without vacuum heat treatment; in addition, cheap carbon By infiltrating certain alloy elements, steel has certain properties of expensive alloy steel and can replace certain heat-resistant steels and stainless steels; almost all tools and molds require vacuum heat treatment before they can be used.
The microstructure of metals is complex, and the metallographic phases will be different under different conditions. Different metallographic phases will lead to different performance. Moreover, the metallographic structure can be changed and controlled through vacuum heat treatment. Steel is the most widely used material in the machinery industry, and vacuum heat treatment of steel is also the main content of metal vacuum heat treatment. In addition, the mechanical, physical and chemical properties of aluminum, copper, magnesium, titanium, etc. and their alloys can also be changed through vacuum heat treatment to obtain different performance properties. The picture below shows the main metallographic structures of steel (the steel is sampled, ground, polished, and finally corroded with a specific corrosive, and the structure is observed under a metallographic microscope).

Vacuum annealing

Vacuum annealing is to heat the workpiece to an appropriate temperature, adopt different holding times according to the material and workpiece size, and then slowly cool it. The purpose is to make the internal structure of the metal reach or approach an equilibrium state, or to release the internal stress generated in the previous process. , to obtain good process performance and service performance, or to prepare the structure for further quenching. Taking No. 45 steel as an example, the metallographic phase after annealing is austenite and becomes too soft after annealing. Generally, 45 steel is not annealed.
Professional explanation: Heat the hypoeutectoid steel workpiece to 20-40 degrees above AC3 (the final temperature at which ferrite transforms into austenite during heating). After keeping it warm for a period of time, slowly cool it with the furnace (or bury it in sand or lime). Medium cooling) to a vacuum heat treatment process of cooling in air below 500 degrees.

Vacuum hardening
Vacuum hardening is to heat and preserve the workpiece and then quickly cool it in a quenching medium such as water, oil or other inorganic salt solutions, organic aqueous solutions. The rear steel becomes harder but at the same time becomes brittle. Taking No. 45 steel as an example, it is rarely quenched alone because it is difficult to obtain the desired hardness.
Professional explanation: A vacuum heat treatment process that cools austenitized steel parts at an appropriate cooling rate so that the workpiece undergoes unstable organizational structure transformation such as martensite in all or within a certain range of the cross section.

Vacuum tempering
Vacuum tempering is to reduce the brittleness of steel parts. The quenched steel parts are kept at an appropriate temperature above room temperature and below 650°C for a long time, and then cooled. This process is called tempering.
Professional explanation: The vacuum quenched workpiece is heated to an appropriate temperature below the critical point AC1 (the starting temperature of the transformation of pearlite to austenite during heating) for a certain period of time, and then cooled using a method that meets the requirements to obtain the required structure. and performance of the vacuum heat treatment process.