Zhengzhou Gou's tells you about the quenching defects of bearing parts and how to prevent them

In order to transform the supercooled austenite of the workpiece into martensite or bainite to obtain a martensite or bainite structure, it is then combined with tempering at different temperatures to greatly improve the strength, hardness and wear resistance of the steel. , fatigue strength and toughness, so as to meet the different use requirements of various mechanical parts and tools, a high-frequency quenching machine needs to be used to quench the workpiece to varying degrees. Bearings play a very important role in the mechanical transmission process, and have high requirements on their wear resistance and service life. Therefore, it is essential to use a high-frequency quenching machine to quench the bearings. However, what quenching defects will occur during the quenching process? How should we solve it?

1. Overheating fracture. This is mainly because the quenching temperature is too high. We can lower the quenching temperature to solve the problem.

2. The diameter of residual coarse carbides exceeds the specified value. This is mainly caused by repeated annealing and serious uneven carbide in raw materials. We should strengthen the control of raw materials and try to avoid repeated quenching.

3. Underheated fracture, this is mainly due to the low quenching temperature. We should increase the quenching temperature.

4. Soft spots on the surface. This is mainly because the sodium carbonate aqueous solution is improperly prepared, the temperature is high, and there is oil on the sodium carbonate aqueous solution. We can use hot preparation of the sodium carbonate aqueous solution at a temperature <35°C, or increase the concentration of the sodium carbonate aqueous solution by 15% to 20% (mass fraction). Solve the problem.

5. The carbide network is larger than level 2.5

Cause:

The mesh shape of raw materials exceeds the regulations

During forging, the stop forging temperature is too high and the annealing temperature is too high, and the cooling is slow to form a network.

Prevention method: Heat to 930-950 degrees for normalizing in a salt furnace or protective atmosphere furnace, anneal at low temperature after normalizing, and then quench and temper.

6. The amount of distortion exceeds the regulations

Cause:

Uneven cutting stress distribution and high quenching heating temperature

Uneven annealing structure

Large furnace loading capacity, uneven heating, too fast and uneven cooling, and mechanical collision during heating and cooling.

Prevention methods:

Add stress relief annealing process to reduce quenching heating temperature

Improve the uniformity of annealed structure

Improve the uniformity of heating and cooling

7. Quenching cracks

Cause:

Stress concentration, surface decarburization.

The organization is overheated, the quenching temperature is too high or the holding time at the upper limit of the quenching temperature is too long.

Cooling too fast, the oil temperature is low, and the moisture content in the quenching oil exceeds 0.25%

Preventive methods:

Reduce the surface roughness of turning, increase the stress relief process to reduce surface decarburization and carbon depletion, and avoid stress concentration in parts during design and processing.

Increase the oil outlet temperature of parts or increase the temperature of quenching oil

Reduce quenching temperature

8. Superheated acicular martensite structure

Cause:

Quenching temperature is too high or holding time at higher temperature is too long

The raw material carbide is seriously banded

The size distribution of carbides in the annealed structure is uneven or some fine flake pearlite exists

Prevention methods:

Reduce the quenching temperature

Control carbide unevenness according to material standards

Improve the annealing quality and make the annealed structure into uniform fine-grained pearlite

9. The hardness is low and the microstructure is qualified.

Cause:

Quenching and holding time is too short

Severe surface decarburization

Quenching temperature value is low

The oil cools slowly and the oil output temperature is high

Prevention methods:

Extend the holding time

Properly increase the quenching temperature

Heating in a protective gas furnace or applying 3%-5% boric acid alcohol (mass fraction) solution