The majority of a500 square tubes are steel pipes, which are unpacked, flattened, crimped, welded to form round tubes (maybe seamless pipe or welded pipe), and then rolled into square tubes from round tubes and then cut into required lengths. Square tubes are divided into structural square tubes, decorative square tubes, architectural square tubes, mechanical square tubes, etc. according to their uses.
In order to better improve the surface strength and wear resistance of the rectangular tube, the rectangular tube is subjected to surface heat treatment, such as flame surface, high-frequency induction hardening, organic chemical heat treatment, etc. Generally speaking, the common heat treatment is high-frequency quenching, and the heating temperature is 850-950°C. Due to poor heat transfer, the heating rate cannot be too fast, otherwise defects such as melting cracks and heat treatment cracks will occur. Induction quenching stipulates that the base material is dominated by ferrite after quenching, and spray paint water or spray paint acrylic emulsion aqueous solution for refrigeration. The quenching temperature is between 200-400°C, and the strength is 40-50HRC, which can ensure the strength and wear resistance of the surface of the rectangular tube.
In addition, the heat treatment of a500 square tube has the following three advantages:
1. Dimensional stability For the high-precision a500 square tube, the precision required is high, so the dimensional stability must be maintained. Due to the straightening in the air, the cooling speed is slow. Therefore, it has a stabilizing effect and will increase the number of residual rectangular tubes in the tissue, so cold treatment must be carried out;
2. Reduce quenching deformation. Since the a500 square tube is slender, it is easy to deform during quenching. To strictly control its deformation, heat treatment is a very critical process. In the process of quenching and cooling, the use of cold plasticity for timely correction is a key step to ensure an increase in the pass rate. For this reason, hot bath quenching or oil quenching should be carried out; after cooling for a certain period of time, thermal correction is recommended. At the same time, suspension heating should be carried out during the heating process to reduce quenching deformation. For high-precision guide rails, gas nitriding or plasma nitriding should be carried out to reduce deformation.
3. The high-hardness rectangular tube mainly bears the contact fatigue load, so it must have high hardness. Therefore, heat treatment, induction hardening or organic chemical heat treatment should be carried out, and then low temperature tempering treatment should be carried out.