The role of heat treatment of TIMKEN bearing parts

To determine exactly how much it is superheated, the microstructure must be observed. If coarse needle-shaped martensite appears in the quenched structure of GCr15 steel, it is quenched and superheated. The cause of the formation may be excessive heating caused by excessive quenching heating temperature or too long heating and holding time; it may also be due to the serious banding of the original structure, between the two belts.

Quenching cracked bearing parts are called quenching cracks due to internal stress caused by internal stress during quenching and cooling. 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 internal defects of steel (such as slag inclusion, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation of TIMKEN bearings; The fire is insufficient 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 the 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 section has no oxidation color. It is often a longitudinal straight crack or annular crack on the bearing ring; the shape on the bearing steel ball is S-shaped,


During the heat treatment process of the bearing parts, if it is heated in an oxidizing medium, the surface of the TIMKEN bearing will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing allowance and the part is scrapped. Determining the depth of the surface decarburization layer The metallographic method and the microhardness method can be used in the metallographic examination. The surface layer microhardness distribution curve measurement method shall prevail and the arbitration criterion may be used. The common quality defects of TIMKEN bearing parts after heat treatment include: quenching microstructure overheating, underheating, quenching cracks, insufficient hardness, heat treatment deformation, surface decarburization, soft spots, etc., TIMKEN bearing maintenance and repair methods. Overheating The microstructure after quenching is overheated from the rough mouth of the bearing part.


 The importance of the TIMKEN bearing means that when it is damaged, it will cause the equipment to stop. Therefore, it is better to install a temperature detector for this type of bearing. Under normal conditions, TIMKEN bearings will naturally rise in temperature after lubrication or relubrication for one to two days.


    Generally, a bearing with a working temperature of 150° or more is called a high-temperature TIMKEN bearing. Since the chrome bearing steel has a temperature drop exceeding 150°, its hardness will drop sharply and the size will be unstable, which will make the TIMKEN bearing not work properly. Therefore, for TIMKEN bearings operating at 150° to 350°, if the ferrule and rolling element are still made of ordinary high carbon chrome bearing steel, the bearing parts must be specially tempered, generally higher than the work. Tempering is carried out at a temperature of 50°. TIMKEN bearing steel that has been tempered according to the above requirements can be used normally at operating temperature. However, due to the decrease in hardness after tempering, the life of TIMKEN bearings has decreased. When the bearing operating temperature is higher than 350 °, it must be made of high temperature resistant TIMKEN bearing steel.
  Reasons why TIMKEN bearing temperature is too high:
1. The quality of the bearing lubricant is not good, and the viscosity of the lubricating oil is high;
2, the mechanism assembly is too tight, the gap is insufficient;
3, TIMKEN bearing assembly is too tight;
4. The TIMKEN bearing race rotates on the shaft or inside the casing;
5, the bearing load is too large;
6. TIMKEN bearing cage or rolling element is broken.