vacuum heat treatment technology

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Vacuum quenching advantages

Vacuum heat treatment technology was used earlier in foreign countries. In 1968, Hayes company of the United States and vacuum Research Institute of Japan successively developed vacuum quenching oil and water quenching agent. As a result, vacuum quenching technology has developed rapidly in the heat treatment industry, from single chamber furnace to multi-component machine group, from general vacuum quenching to high pressure gas quenching, vacuum water quenching, vacuum carburizing, vacuum heat treatment Vacuum carbonitriding and multicomponent carbonitriding. After decades of efforts, the design, manufacturing level and quality of domestic vacuum furnace manufacturers have been greatly improved. The use of domestic vacuum equipment to replace imported vacuum equipment has gradually increased, thus reducing the production cost of users and rapidly expanding the application scope of vacuum heat treatment. At present, it has been widely used in the vacuum heat treatment and vacuum chemical heat treatment of important parts such as various tool steel, stainless steel, bearing steel, carbon steel, cemented carbide, alloy steel and high alloy steel

(1) Bright quenching can be realized

When the vacuum degree in the furnace reaches 1-10-1pa, the surface of the workpiece will not be decarburized and carburized, so as to realize the purpose of bright quenching. The machinery factory purchased a double chamber vacuum quenching furnace for bright quenching of the spindle bottom of the textile machine parts made of GCr15 bearing steel. The technical requirements of the spindle bottom are very high. The inner top of the spindle bottom is no longer machined after cold stamping R. no decarburization and other defects are allowed on the surface after quenching. Previously, it was heated with salt bath containing sodium cyanide, and then it was heated with 50% NaCl + 50% Na2CO3 The medium temperature salt heating, quenching medium is 20% concentration of NaOH aqueous solution, the operation condition is poor. After quenching with vacuum furnace, the quality is guaranteed and improved, and the operating conditions are greatly improved. The triangle of knitting machine made of Cr12MoV steel after vacuum quenching has stable quality and wear resistance, which improves the service life of the product. Since then, in the textile machinery industry, according to the product specifications, the relevant enterprises have purchased various specifications of domestic vacuum furnaces. According to incomplete statistics, about 30 domestic vacuum furnaces are in use.

In addition, it is widely used in precision small and micro (bearing inner diameter < 9mm) bearings. The quality of bearing rings made of stainless steel and bearing steel after vacuum quenching is very good, because there is no decarburization and Carburization on the surface of the rings after vacuum quenching, and the ring material can be degassed, and the impurities can be reduced to less than 1.5ppm, so that the hardness distribution is uniform and the deformation is abnormal Therefore, the wear resistance of the bearing is improved, the elastic limit and contact fatigue strength are high, the service life of the bearing is prolonged, and the market competitiveness is improved.

(2) It has the function of degassing

When the vacuum degree is lower than the corresponding decomposition pressure of metal or alloy, the oxide will decompose, and the free oxygen will be discharged out of the vacuum room immediately, so that the internal quality of the workpiece will be improved. The billet of iron and steel parts will inhale a very small amount of hydrogen, nitrogen, carbon monoxide and other gases in the atmosphere during smelting, resulting in micro pores, which are easy to cause hydrogen embrittlement and other defects. Cemented carbide, when pressed, air will enter. Therefore, for the tool steel, the residual gas in the workpiece can be removed by vacuum technology, so that the structure can be pure. For cemented carbide, the residual gas in the workpiece can also be removed by vacuum treatment.

Due to the application of vacuum technology, for Cr12MoV, Cr12, Cr4W2MoV, 6cr4w3mo2vnb (65Nb), 9CrSi, 7crmo3v2si (LD), W6Mo5Cr4V2 cold working die steels and 3Cr2W8V, 4Cr5MoSiV1, 5cr4w5mo2v hot working die steels which need to bear large load and strength and toughness, the drawing die, extrusion die, hot rolling die, etc. made of them are degassed when heated in vacuum furnace After vacuum quenching, the strength and wear resistance of the die are greatly improved. The service life of the die can be generally increased by 30% ~ 120%, and the service life of individual die will be even higher. For W6Mo5Cr4V2, w18cr4v1, w18cr4vco5, W4Mo3Cr4VSi, w2mo8cr4co8 (M42) and other high speed steel cutting tools, vacuum quenching can not only improve product quality, but also replace the high-temperature salt bath quenching production line with high energy consumption, which can save a lot of energy and reduce environmental pollution, and improve operating conditions. Vacuum furnace is widely used in small and medium-sized enterprises and professional mould factories. In particular, the proportion of private enterprises using vacuum furnace in the quenching of cutting tools, dies and electric tools is gradually increasing.

(3) It can reduce the machining allowance after heat treatment

Vacuum heat treatment is widely used in vacuum quenching and carburizing of GCr15, W6Mo5Cr4V2 and 27simnmova oil pump fittings because it has no oxidation decarburization, little distortion and clean brightness. In this way, it can avoid the phenomenon of black structure (decarburization) on the surface of inner hole of fittings due to residual salt cleaning or protective atmosphere caused by salt bath furnace For the needle valve body of carbon steel, the carburizing layer of 0.5-0.9mm can be guaranteed by vacuum carburizing, but it is difficult to be guaranteed by controlled atmosphere furnace carburizing. For piston pump and other precision hydraulic parts, vacuum quenching can reduce distortion, improve wear resistance and ensure stable quality of the workpiece. It has been several decades since vacuum quenching technology was applied to oil pump nozzle and plunger pump hydraulic parts, which has been widely recognized in improving product quality.

(4) Clean process

Vacuum heat treatment is a clean heat treatment process, which plays an important role in the whole heat treatment process. It can improve the product quality, change the appearance of heat treatment workshop and improve the operating environment. It is a technology worthy of popularization and application.

(5) Advantages of vacuum carburizing

The product quality of vacuum carburizing is better than that of controlled atmosphere furnace carburizing. After carburizing with controlled atmosphere furnace, it is necessary to use quenching press to correct while quenching. Sometimes, its quality can not meet the technical requirements. Moreover, it is difficult to guarantee the carburizing layer and carbon concentration distribution uniformity, which often leads to internal oxidation, resulting in non Ma black group With the emergence of weaving, productivity is sometimes affected. Therefore, carburizing of small and medium-sized gears and gear shafts in motorcycles, automobile reducers, automobile engines and other parts with high quality requirements has gradually changed from controlled atmosphere carburizing to true air carburizing in qualified enterprises. Low pressure vacuum carburizing and high pressure gas quenching technology can be used to carburize gears and gear shafts with higher quality requirements. It has been gradually applied in China.

Vacuum quenching medium

The auxiliary materials of vacuum quenching include loading frame (basket), loading plate, nitrogen and quenching medium. The loading frame (basket) and loading tray need to be made of 40cr25ni20 and other heat-resistant steel materials. It is better to use liquid nitrogen with content > 99.995% for nitrogen, because liquid nitrogen can ensure the purity of nitrogen and is convenient for operation and maintenance. Quenching medium needs special vacuum quenching oil, which is suitable for use under atmospheric pressure. It has short distillation range, low saturated vapor pressure, strong oxidation resistance, not easy to volatilize and easy to vacuum. Good brightness, easy to clean, less oil consumption. It has the advantages of good thermal oxidation stability, stable cooling performance and long service life. Therefore, the hardness uniformity of the quenched workpiece is good, the distortion is less, and the workpiece is clean and bright.

Industry usage

At present, according to incomplete statistics, there are more than 1000 sets of vacuum equipment in use at home and abroad, which are respectively used in tooling, bearing, oil pump nozzle, hydraulic parts, gear, cemented carbide and other industries.

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