1. Heat treatment deformation

During heat treatment, there are thermal and structural stresses in the components of self-aligning roller bearings. These internal stresses can overlap or partially cancel each other, making them complex and variable. They can change with changes in heating temperature, heating speed, cooling method, cooling speed, part shape and size, so heat treatment deformation is inevitable. Understanding and mastering its changing patterns can keep the deformation of self-aligning roller bearing parts (such as the ellipticity of the ring, size increase, etc.) within a controllable range, which is beneficial for production. Of course, mechanical collisions during heat treatment can also cause deformation of parts, but this deformation can be reduced and avoided through improved operations.

2. Over

Overheating of the microstructure after quenching can be observed on the rough surface of the self-aligning roller bearing parts. But to accurately determine the degree of overheating, it is necessary to observe the microstructure. If coarse needle like martensite appears in the quenched microstructure of GCr15 steel, it is a quenched and overheated microstructure. The possible cause of formation may be comprehensive overheating caused by excessive quenching heating temperature or prolonged heating and insulation time; It may also be due to the severe banded carbides in the original tissue, which form local martensite needle like coarseness in the low-carbon area between the two bands, causing local overheating. The residual austenite in the overheated tissue increases and the dimensional stability decreases. Due to the overheating of the quenched structure and the coarsening of the steel crystals, the toughness and impact resistance of the parts will decrease, and the service life of the self-aligning roller bearings will also be reduced.

3. Underheating

If the quenching temperature is too low or the cooling is poor, it will produce a martensitic structure in the microstructure that exceeds the standard specifications, known as undercooled structure. It reduces hardness, sharply reduces wear resistance, and affects the service life of self-aligning roller bearings.

4. Soft dots

The phenomenon of insufficient local hardness on the surface of self-aligning roller bearing parts caused by insufficient heating, poor cooling, and improper quenching operation is called quenching soft spots. It can cause a serious decrease in surface wear resistance and fatigue strength, just like surface decarburization.

5. Surface decarburization

During the heat treatment process of self-aligning roller bearing parts, if heated in an oxidizing medium, the surface will undergo oxidation, reducing the mass fraction of carbon on the surface of the parts and causing surface decarburization. If the depth of the surface decarburization layer exceeds the final machining allowance, the part will be scrapped. The determination of the depth of surface decarburization layer can be done using metallographic and microhardness methods in metallographic examination.

6. Quenching cracks

The cracks formed by internal stress during the quenching and cooling process of self-aligning roller bearing parts are called quenching cracks. The reasons for this type of crack are: due to high quenching heating temperature or rapid cooling, the thermal stress and tissue stress caused by changes in metal mass volume are greater than the fracture strength of the steel; The original defects on the working surface (such as surface micro cracks or scratches) or internal defects in the steel (such as slag inclusion, severe non-metallic inclusions, white spots, shrinkage residue, etc.) form stress concentration during quenching; Severe surface decarburization and carbide segregation; Insufficient or delayed tempering of parts after quenching; Excessive cold stamping stress caused by the previous process, forging folding, deep turning tool marks, sharp edges and corners of oil grooves, etc.