How to Control the Formation of Quenching Cracks?

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After the product is quenched and heat-treated, cracks usually form, mainly longitudinal cracks, transverse cracks (arc cracks), network cracks, and peeling cracks. The following describes how to control the formation of quenching cracks.

After the product is quenched and heat-treated, cracks usually form, mainly longitudinal cracks, transverse cracks (arc cracks), network cracks, and peeling cracks. The following describes how to control the formation of quenching cracks.

Longitudinal Crack:

1. Check the raw material for non-metallic inclusions, band structure, grain size, forging or rolling streamline folding, it is not advisable to continue quenching when raw material defects exceed the standard, quenching cracks are observed in the metallographic structure, and there should be no decarburization on both sides of the cracks.

2. The graded isothermal quenching is used to make the workpiece incompletely hardened to reduce the tangential fracture stress. It can also be quenched with water and oil.

3. The size range of the sensitive area to avoid quenching cracks is generally 8~15mm for carbon steel and 25~40mm for oil quenching of low alloy steel.

Lateral cracks:

1. After the parts are preheated, they are then heated to the quenching temperature for quenching. Pre-cooling before quenching can reduce cracking.

2. Properly increase the quenching temperature and increase the hardenability, which can reduce the formation of quenching cracks (applicable to high-carbon steel parts).

3. For sharp corners, grooves and uneven cooling of parts, measures should be taken to reduce thermal stress and tissue stress.

4. There must be no oxide skin soft spots on the parts. Even heating can prevent transverse cracks.

5. Holes on induction hardened parts should be blocked to prevent overheating and cracking around the holes.

Reticulated Cracks:

1. High-carbon steel and carburized parts use non-oxidizing heating, try not to decarburize, so that the difference between the surface and the inside volume should not be too large.

2. The salt bath furnace fully deoxidizes and removes slag to avoid oxidation, decarburization or corrosion on the surface of the workpiece.

3. Avoid air cooling after carburizing.

4. To prevent overheating and burning, the heating speed should not be too fast.

Peeling Crack:

1. Ensure that the carburized layer and the carbonitriding layer have a certain transition zone, that is, uniform diffusion, and no steep slopes in the hardness gradient or carbon concentration gradient. If this crack is found, it can be resolved by diffusion treatment.

2. For induction heating hardened parts, there should also be a transition zone.