Carbon steel square tubes: The cornerstone of industrial structures

Carbon steel square tube has become an indispensable structural material in modern construction, mechanical manufacturing and decoration projects due to its regular cross-sectional shape, excellent strength-to-weight ratio and high processing flexibility. It not only meets various force requirements such as load-bearing, bending resistance and torsional resistance, but also brings significant economic benefits to engineering projects with its low cost and mature production technology.

Manufacturing process and classification

1. Welded square tubes: By rolling carbon steel plates or steel strips into shape and then welding them into shape through processes such as resistance welding (ERW), submerged arc welding (SAW), or electron beam welding (EFW). This type of pipe has high production efficiency and low cost, and is widely used in medium and low pressure structures and decorative occasions.
2. Seamless steel pipe: It is made by drilling and piercing steel ingots through hot rolling or hot extrusion technology, and then processed by drawing. It has no welds, uniform wall thickness, and more stable and reliable mechanical properties. It is suitable for engineering projects that require high strength, high precision, and operation in harsh environments.

Standards and Specifications

International standard

ASTM A500: A common standard for structural square tubes in the United States, it is divided into four grades: Grade A/B/C/D and is widely used in cold-bending or slightly forming applications.
EN 10219: The EU standard for welded hollow sections for structural use, which has a certain correspondence with ASTM A500 in terms of size and performance grades.

National standards and Japanese standards

GB/T 6728, GB/T 3094: Commonly used standards for cold-formed welded and seamless square tubes in China.
JIS G3466 (STKR 400/490) : A Japanese standard for cold-rolled and welded square tubes. The tensile strength corresponding to STKR 400 is ≥ 400 MPa, and the tensile strength corresponding to STKR 490 is ≥ 490 MPa.

Common dimensions and wall thicknesses

The side length of the square ranges from 10×10 mm to 600×600 mm, and the selectable wall thickness ranges from 0.5 mm to 20 mm. Usually, it can be processed to a fixed length according to the engineering requirements.

Chemical composition and mechanical properties

Chemical composition: The carbon content is usually less than 0.25%, the manganese content is between 0.3% and 1.5%, and the content of phosphorus and sulfur does not exceed 0.04%. These ensure that the material has excellent weldability and good plasticity.

Mechanical performance index

The tensile strength ranges from 350 to 550 MPa. The yield strength ranges from 205 to 345 MPa, with the specific value depending on the material and the standard level followed.
Seamless square tubes have better load-bearing capacity and fatigue resistance due to the absence of weld defects. Welded square tubes, on the other hand, demonstrate a relatively high cost-performance ratio in medium and low pressure applications.

Typical application scenarios

Construction and municipal structures: scaffolding, guardrails, support frames, bridge components, etc., in situations where light weight, high strength and good torsional stability are required.

Mechanical equipment and brackets: machine tool frames, conveyor equipment brackets, storage shelves, etc. When high dimensional accuracy and load-bearing uniformity are required, seamless square tubes are preferred.

Decoration and furniture: Industrial-style railings and furniture frames, with surfaces that can be sprayed or electroplated, balancing aesthetics and structural performance.

Light-duty pipeline systems: For non-potable water, gas transportation and low-pressure oil pipelines, attention should be paid to pipeline sealing and anti-corrosion treatment.

Summary

Carbon steel square tubes, with their comprehensive advantages of "square cross-section, high strength, light weight, easy processing and low cost", play a fundamental and crucial role in the fields of building structures, mechanical supports, industrial decoration and lightweight pipelines.