In order to improve the surface hardness and abrasion resistance of rectangular tubes, some surface treatments can be performed on them, namely flame surface fire, high and medium frequency surface quenching, and some chemical heat treatment. Generally speaking, most high and medium frequency surfaces are quenched, and the heating temperature is 850-950°C. Considering its poor thermal conductivity, the heating rate should not be too fast, otherwise it will cause defects such as
melting and some quenching cracks. High-frequency quenching requires that the matrix of the rectangular tube after normalizing is mainly pearlite. Cooling adopts water spray or aqueous solution of polyvinyl alcohol. The tempering temperature is in the range of 200-400 ℃, and the hardness is 40-50HRC, which can ensure the hardness and wear resistance of the surface of the rectangular tube.
In addition, rectangular tube heat treatment also has the following three advantages:
For rectangular tubes with high accuracy, the required accuracy is high. Therefore, dimensional stability must be maintained. Because of straightening in the air and slow cooling rate, it has a stabilizing effect on austenite. Will increase the number of residual austenite rectangular tubes in the organization, so it must be cold treated.
2.Reduce quenching deformation
Due to the slender rectangular tube, it is easy to deform during the hardening process, so the deformation must be strictly controlled. Heat treatment is a very critical process. In the quenching and cooling process, the plasticity of supercooled austenite is used for timely alignment. The key step to ensure the improvement of its qualification rate is to perform heat bath quenching or cooling in oil for a certain period of time for thermal alignment.
At the same time, hanging heating should be performed during heating to reduce the deformation of quenching.For high-precision guide rails, gas nitriding or ion nitriding is used to reduce deformation;
The rectangular tube is mainly subjected to contact fatigue load, so it must have high hardness, so it should be quenched, or surface quenched or chemically heat treated, followed by low temperature tempering.
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