Common quality defects of bearing parts after heat treatment

Common quality defects of bearing parts after heat treatment include: quenching microstructure overheating, underheating, quenching cracks, insufficient hardness, heat treatment deformation, surface decarburization, soft spots, etc.

    Overheat

    The microstructure after quenching can be observed from the rough mouth of the bearing part, but the microstructure must be observed to determine the degree of overheating. If coarse needle-shaped martensite appears in the quenched structure of gcr15 steel, it is quenched and superheated. The formation may be caused by excessive overheating of the quenching heating temperature or excessive heating and holding time; or it may be due to the serious banding of the original structure, forming a local martensite needle-like coarseness in the low carbon zone between the two zones. Local overheating caused. The retained austenite increases in the superheated structure, and the dimensional stability decreases. Due to the overheating of the quenched structure, the coarse crystal of the steel causes the toughness of the part to decrease, the impact resistance is lowered, and the life of the bearing is also lowered. Excessive heat can even cause quenching cracks.

    2. Underheat

    If the quenching temperature is low or the cooling is poor, the tortite structure exceeding the standard is formed in the microstructure, which is called the underheated structure, which lowers the hardness and sharply reduces the wear resistance, which affects the bearing life.

    3. Quenching crack

    The crack formed by the internal stress of the bearing part during the quenching and cooling process is called quenching crack. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel; the original defects of the working surface (such as surface micro cracks or scratches) Trace) or steel internal defects (such as slag inclusions, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation; insufficient tempering after quenching of parts Or not tempered in time; the cold punching stress caused by the previous process is too large, forging and folding, deep turning tool marks, sharp edges and corners of the oil groove. In short, the cause of quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured surface has no oxidation color. It tends to be a longitudinal straight crack or annular crack on the bearing ring; the shape on the bearing steel ball is s-shaped, t-shaped or ring-shaped. The microstructure of the quenching crack is that there is no decarburization on both sides of the crack, and the difference is obvious with forging cracks and material cracks.

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Detailed explanation: maintenance, cleaning and overhaul of bearings

Bearing maintenance

Rolling bearings are a wide range of important mechanical basic components that are widely used in various fields of the national economy and national defense. The mechanical and working environment in which rolling bearings are used varies widely, so special attention should be paid to the maintenance of the bearings and the service life of the bearings. Bearing Installation Rolling bearings are precision parts that are of high precision and, if not properly installed, will lose their precision and performance and, in severe cases, cause bearing failure. Therefore, the site where the bearings are mounted and the installation tools must be cleaned to prevent various particulates from being carried inside the bearings. When installing and disassembling the bearing, it should not be directly hammered. Uniform pressure should be applied. When the shaft and the bearing are engaged with a large interference, the bearing should be installed immediately after heating.

Anti-rust of bearing products

The bearing is a precision mechanical part. From the factory to the long-term circulation. In order to prevent the bearing from rusting during transportation or storage under various environmental conditions, it must be rust-proofed. According to the national GB/TS597 standard. The rust prevention period of the bearing is half a year. Generally, the anti-rust period of the bearing is one year, and the anti-rust period of the bushing with higher requirements for use is two years. Bearings cannot be used during rust prevention for a variety of reasons. When the bearing rust prevention period is reached, the original rust inhibitor should be removed.

Bearing packaging

Since the bearings are precision parts and there are many circulation links, the products are easily damaged by environmental conditions such as snow, dust, temperature, corrosive substances during these circulation processes. Therefore, the bearing packaging is required to have multiple performances, such as shockproof, moisture-proof, anti-collision, anti-corrosion, and pressure resistance.

Bearing storage

No leakage of rain should be allowed in the warehouse. The bearing storage position should be protected from direct sunlight. The indoor air should be circulated, but there should be no dust. Ventilation and temperature control equipment should be installed in the warehouse. The warehouse should be kept dry, the relative temperature should be controlled below 80%, the indoor temperature should be controlled at 25 degrees, and there should be no large temperature changes during the day and night. When the temperature is too low, the rusting agent is easy to crystallize and crack, resulting in rusting of some metal exposed. The temperature is too high, the rusting agent is easily lost (evaporated) or deteriorated, and the temperature difference between day and night is likely to cause moisture to condense on the bearing surface to cause rust. For winter seasons, the bearing storage location should not be close to the heating. The ground in the warehouse should be hard and not easy to get dust on the ground. Bearings must not be stored in a warehouse with corrosive materials such as acids, alkalis, and salts, chemical raw materials, and large materials. It is not easy to invade harmful gases around the warehouse where the bearings are stored.

Bushing transport

Improper transportation of the eclipse is the most likely to cause loss to the bearing, such as fretting wear, rust, smashing, indentation, etc., the most unloading can even lead to cracks in the bearing and directly fail. Therefore, special attention should be paid to the transportation quality of the transportation link to avoid unnecessary damage to the bushing. The bearing transporter should be placed horizontally and the pressure should not be applied to the outer diameter of the bearing to prevent deformation of the bushing. When the transport tools are placed on the pallet, the distance between the boxes should be as close as possible to reduce the impact and vibration caused by the shaking during transportation.

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