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Vacuum Heat Treatment Furnace

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Effects of Vacuum Heat Treatments on Steels for Bearing Applications

In recent years, with the improvement of metallurgical technology, the smelting equipment and technology of bearing steel in important steelmaking plants have fully reached the international advanced level, and the preparation of chemical components and the control of non-metallic inclusions have reached the technological level. The high-quality, high-grade high-quality, and special-grade high-quality bearing steels currently supplied have met the market demand. For some special-supplied bearing steels, they have fully reached the international advanced level. The bearing steel products have been used in aviation, aerospace, Automotive, construction machinery, precision machine tools and other industries.

Vacuum heat treatment equipment for bearing steel parts

The vacuum heat treatment of bearing steel is generally classified into inner ring, outer ring, roller, steel ball, needle roller, etc. according to the product classification. Among them, the vacuum heat treatment process of the inner and outer rings is relatively complicated, and the technical requirements are very high. Their materials are generally: GCr15SiMn, GCr15, GCr18Mo, GCr15SiMo, GCr4, etc., select the corresponding material according to the technical requirements, size and effective thickness of the product. Their vacuum heat treatment equipment is generally a vacuum quenching furnace, which is more suitable for vacuum heat treatment of small and medium-sized bearings.

For the heating and quenching of the inner and outer rings of bearing steel with an effective thickness ≥ 10mm, it is difficult to meet the technical requirements for the core structure of the quenching with fast bright or overspeed quenching oil, especially some companies require that the core structure of the product must be ≤ level 1, For this reason, it is necessary to carry out martensitic quenching or lower bainite austempering with nitrate salt, and only in this way can quenching meet the technical requirements. The sealing of the furnace door of the heating equipment must be reliable, and the fire sealing device of the furnace door must be good.

Vacuum heating quenching furnace

For precision parts such as small stainless steel bearings and high-carbon chromium bearings with high product technical requirements, vacuum quenching technology can be used. Two Chamber Vacuum Oil Gas Quenching Furnace is a better choice, and its operating environment is friendly. According to the number of layers of the basket Or different charging methods, choose vacuum quenching oils with different cooling rates, vacuum quenched parts have the advantages of uniform hardness, good fatigue resistance, high wear resistance, long service life, less distortion after quenching, and clean and bright. During vacuum quenching, under the condition that the alloy elements do not volatilize, the vacuum degree is higher, the residual oxygen and water vapor in the furnace will be reduced a lot, and the quenched bearing ring has good brightness and maintains the original color of the metal, but the vacuum degree is not high. The selection is too high, otherwise it will cause defects such as dechrome on the surface of the ferrule.

Adjustment of Vacuum Heat Treatment Process for Bearing Steel Parts

The vacuum heat treatment of the whole set of solid bearings is more complicated than the quenching of the ring, and the quenching distortion of the outer ring is the most prominent. Under the premise of improving product quality, many companies have tightened the vacuum heat treatment requirements for hardness, roundness and taper. It requires good vacuum heat treatment equipment and advanced and reasonable vacuum heat treatment process.

For conveyor belt furnaces, lower heating temperature and appropriate heating and holding time should be adopted, and different heating temperatures (820-850°C) should be used according to different product specifications, and sufficient preheating time should be left. Ferrules with an outer diameter of <50mm can be stacked in bulk. Ferrules with an outer diameter of ≥50mm need to be stacked manually or automatically. Ferrules with an outer diameter of>100mm must be stacked manually. A certain gap should be left between them to prevent extrusion deformation of the outer ring due to thermal expansion during heating. The choice of quenching oil should be graded quenching oil with long service life and high temperature resistance. The oil curtain in the quenching oil tank should use a submerged pump. The frequency (0-5) and feeding speed of the stepless speed regulator.

It is a good choice to quench the small miniature bearing rings with high precision requirements in a vacuum furnace. Vacuum quenching can remove harmful impurities in the steel, thereby improving the wear resistance and contact fatigue of the bearing rings by more than 2 times. However, the degree of vacuum should not be too high, generally 1-10-1Pa, otherwise it will be dechromed, causing local sticking of bearing parts during vacuum quenching, and reducing wear resistance.

For the vacuum heat treatment process of high-precision bearings, it is recommended to add a cold treatment lower than the end point of Mf martensite transformation at -78°C, which can improve the dimensional stability of the bearing. Austenite is about 8% (GCr15SiMn), and there is no need for cryogenic treatment at -180°C, otherwise, because the amount of residual volume (2.6%) is too small, it will cause too much stress in the structure and cause superfiber cracks, which will reduce the Contact fatigue life and impact toughness, so cryogenic treatment at -180°C is not recommended. In particular, it should be reminded that there are two tanks for cold cleaning and hot cleaning on the conveyor belt production line. The cold cleaning tank equipped with a (4-7°C) refrigerator should be directly connected to the back of the quenching oil tank, and finally connected to the hot cleaning tank, otherwise It cannot stabilize the size, and the effect of applying cold water is much worse than that of cold treatment.