What is reason for cracking of 40Cr screw after heat treatment?

Quenching temperature is too high, cooling speed is too fast, cooling time is too long, improper use of coolant and other reasons will lead to cracking of quenched parts.

What is the reason for the cracking of 40Cr screw after heat treatment

If 40Cr heat treatment is not normalized or annealed, will it crack during quenching? If 40Cr is normalized or annealed, it may also crack during quenching, so there is no causal relationship between normalizing and annealing process and quenching cracking. There are many reasons for quenching cracking, such as raw material defects, quenching process design, quenching medium problems, etc., which may cause cracking. 40Cr is widely used as quenched and tempered steel, Generally, the quenching and tempering process is regarded as an intermediate process, without the need for additional pre heat treatment (the steel will be annealed before leaving the factory, and the forgings will also be annealed after forging)

After quenching and tempering of 40Cr, do you want to temper immediately? Quenching and tempering is quenching + high temperature tempering. 40Cr has good hardenability, but it also has a large tendency of cracking. Therefore, tempering must be carried out immediately after quenching. If it is placed for a period of time, it may have cracked before it has cooled to room temperature! Generally, it will be separated from the quenching agent at 100 ℃ after quenching to prevent cracking

Can 40Cr U-bolt be bent after heat treatment? Hardness hrc20 μ 24: This hardness can be folded, but there should be a process of 200 degree stress relief after folding, otherwise the fatigue strength of the material is not good

The adjusted hardness of ball pin forged by 40Cr material is hrc34, and the cracking after rolling: the cracking of the material may be caused by the cracks produced during forging, or by the cracks caused by improper temperature control during heat treatment. During heat treatment, the temperature is too high, resulting in the overburning phenomenon, so that the martensite of the heat treated material is coarse, the fracture is coarse-grained, the toughness and the plasticity are low

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