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How to choose the quenching method and quenching agent for square tubes?

How to choose the quenching method and quenching agent for square tubes?

Jun 20,2023
How to choose the quenching method and quenching agent for square tubes?
At present, water is often used as the quenching agent in the heat treatment of square rectangular pipes. This is because in the quenching medium, due to the fast cooling speed of water, square rectangular pipes are prone to deformation during quenching. When the deformation of steel pipes is severe, they are scrapped due to the inability to proceed to the next process. Therefore, when selecting the quenching method, it is necessary to not only meet the quenching requirements of the steel pipe, but also control the deformation within the allowable range.
black square tube
Based on the above analysis, it is ideal for the steel pipe to be quenched in a rotating manner, while also undergoing internal and external cooling. The internal cooling uses a nozzle to spray water into the pipe, with a flow rate of no less than 10m/s. External cooling can be achieved by spraying or immersion in a quenching tank, but there must also be a stirring nozzle inside the quenching tank. In short, the quenching of steel pipes should achieve the required cooling capacity and achieve uniform cooling as much as possible, which is the guiding ideology for selecting the quenching method.

The ideal quenching agent is to cool faster in the high-temperature zone to avoid the disintegration of austenite and improve the hardenability of steel; The cooling rate is slower in the low temperature zone to reduce the structural stress during Martensite transformation and reduce deformation or cracking. There is no ideal quenching agent, but these two factors should be considered when selecting quenching agents.

The selection of quenching agent should be considered based on various factors such as the variety of steel pipes, technical requirements, and steel composition. Taking petroleum pipes as an example, high grade (strength) steel pipes undergo heat treatment using a quenching and tempering process, which involves quenching and high-temperature tempering. Most steel types choose medium carbon alloy structural steel with low carbon content. The thickness (wall thickness) of the steel pipe is basically the same, and the difference in stress distribution at various locations during quenching is relatively small, resulting in a relatively low risk of cracking. Therefore, water can be preferred as the quenching agent.
The advantage of water is its fast cooling speed, which can improve the hardenability of steel, reduce alloy content in steel, and reduce production costs. In addition, using water as a quenching agent is stable and economical in production. Due to the fast cooling rate of water, the steel pipe undergoes significant deformation, and in the case of certain defects on the surface of the steel tube, it will expand into defects during quenching and be scrapped.

If the carbon content in steel is high, in order to reduce deformation or cracking during quenching, fast quenching oil or water-based quenching liquid with a slower cooling rate should be selected as the quenching agent.