What is high-strength square tube?

The performance characteristics of high-strength square tube are high strength, good toughness and impact resistance.
Strength: yield point（ σ s）≥390mpa；
Tensile strength（ б b）≥635mpa；
elongation δ 5（%）≥25；
Hardness hb ≤ 187hv,
Heat treatment specification: normalizing 850 ° C; Quenching 880 ° C; Temper 600 ° C.
Material: made of high-quality carbon structural steel by hot rolling or cold drawing.
Usage: used for manufacturing water-cooled wall pipe, boiling water pipe, locomotive water tank steam pipe and arch brick pipe, etc.
Specification and appearance quality:
Each batch of steel pipes shall be inspected one by one, and the surface shall be free of cracks, folds and double skin defects; Ultrasonic flaw detection shall be conducted for each steel pipe to inspect the mechanical properties of the weld. Generally, the longitudinal reinforcement diameter of the weld is 0.2-0.25mm, the longitudinal reinforcement diameter of the circumferential weld is 0.75-1mm, and the longitudinal stress reinforcement at the socket shall not be less than 0.25mm
Chemical composition The chemical composition of the finished product conforms to the provisions of GB 222-84.
Physical and mechanical properties:
1) The stress-strain curve of tensile test shall be flat without abrupt change
2) Impact test The low-temperature impact toughness of the sample is tested by the cold bending test method at the specified temperature
3) Cracks are not allowed on the pipes flared by hydraulic or pneumatic devices
4) The stress non-uniformity of bending test shall not exceed the specified value.
Process flow: After the steel strip is automatically threaded into a thin disc shape and continuously produced, it is leveled by a multi-pass straightener, and then enters the high-frequency welding unit. The two ends are butted by a high-frequency lap welder to form a circular corrugated welding. After the welding, the steel pipe is sized and cut by the sizing and cutting unit. Finally, the steel pipe is quenched and tempered by the finishing unit, and then sprayed with primer to complete the production process.
(6) Product standard gbt8163-2008 Galvanized Welded Square Section Steel for Fluid Transmission gbt9711.1-1997 Hydrogen-resistant Alloy Steel Plates for Petroleum and Natural Gas Industry Part 1: Development of Thick-walled Seamless Steel Tubes gbt3094-1986 Seamless Steel Tubes for Low-pressure and Medium-pressure Boilers gb5310-95 Large Diameter Welding Electrodes for Low-pressure Boilers syt5038-2000 (ministerial standard).