Common defects and countermeasures during annealing of chromium steel rolling bearing parts

Chromium bearing steel is the main steel type used in manufacturing rolling bearing parts. Annealing of bearing steel is mainly to meet the quality requirements of the workpiece. The purpose of annealing is to reduce the hardness and improve the machinability; eliminate residual stress, stabilize the size, reduce the tendency of deformation and cracks; refine the grains, adjust the structure, and eliminate structural defects. However, the workpiece will encounter some defects during annealing, how should we solve them?

Annealing defects and their countermeasures.

1. The decarburization layer exceeds the specified depth

Cause:

1. The raw materials are severely decarburized by forging or normalizing.

2. The sealing of the furnace is poor, or it is heated in an oxidizing atmosphere, the annealing temperature is high, the holding time is long, or it is normalized and repeatedly annealed.

Remedy:

Change to other models

Preventive measures:

1) Strengthen decarbonization control of raw materials and forgings

2) Improve the sealing of the furnace and heat it in a neutral flame furnace.

3) Execute the process correctly to prevent out-of-control over-temperature.

4) Do not perform normalizing and repeated annealing as much as possible

2. The network carbide exceeds the specified level

Cause:

1. The forging structure has serious carbide network, which cannot be eliminated during annealing.

2. The annealing temperature is too high and the cooling is too slow.

Remedy:

Normalize first and then perform the first annealing

Preventive measures:

1) Strictly control the forging organization

2) Prevent out-of-control annealing, excessive temperature, and too slow cooling

3. Too soft

Cause:

1. Multiple annealing or cooling rate is too slow

2. Tissue overheating

Remedy:

Normalizing first and then annealing

Preventive measures:

Sufficient heating, but not too hot, appropriate cooling speed.

4. Too hard

Cause:

1. The cooling rate is too fast, resulting in dense point-like pearlite.

2. Not hot enough, with flaky pearlite remaining.

Remedy:

Adjust the process and perform secondary annealing

Preventive measures:

Sufficient heating, but not too hot, appropriate cooling speed.

5. Coarse particle carbides

Cause:

1. Raw material carbide is uneven (mesh, strip)

2. The forging structure has thick flakes of pearlite.

3. Repeat annealing

4. The annealing temperature is too high and the cooling rate is slow.

Remedy:

Normalize first and then perform the first annealing

Preventive measures:

1) Strictly control the quality of raw materials and forgings

2) Try not to perform repeated annealing, let alone multiple annealings.

6. Carbide particles vary in size and are unevenly distributed. The heated part of granular pearlite becomes coarse flaky pearlite.

Cause:

1. The heating temperature is too high, or the holding time at the upper limit temperature is too long.

2. There is a large amount of furnace installed, and the uniformity of the furnace temperature is poor, or under normal processes, some workpieces are still heated to too high a temperature and the heat preservation time is too long.

3 The raw material structure is uneven

Remedy:

Normalize first and then adjust the process, perform rapid annealing or normal annealing.

Preventive measures:

1) Strictly control the quality of raw materials and forgings

2) Reasonably formulate processes and strictly implement them

3) The amount of furnace installed is reasonable and evenly placed.

4) Improve furnace temperature uniformity

7. Point-like pearlite plus some fine flake pearlite

Cause:

1 The raw material structure is uneven

2. The heating temperature is low or the holding time is insufficient.

3. The heating temperature is too high and the cooling speed is too fast.

4. There is a large amount of furnace installed, the temperature uniformity of the furnace is poor, or under normal processes, some (local locations) workpieces are not heated enough, or the heat preservation time is not enough.

Remedy:

Adjust the process according to different defects and perform secondary annealing

Preventive measures:

1) Reasonably formulate processes and strictly implement them

2) Control the cooling speed not too fast

3) Improve furnace temperature uniformity

4) Strictly control the quality of raw materials and forgings

5) The amount of furnace charging should be reasonable and the placement should be even.

This article briefly introduces some common defects and countermeasures of chrome steel roller bearing parts during annealing. I hope it will be helpful to you. If you would like to know more about workpiece annealing or induction heating equipment please feel free to contact us.