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Help CenterSquare Steel & Square Tube，Q195、Q215、Q235B、20#、45#
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1. Product Introduction
Square tube, fully named square steel tube, is a hollow cold-formed section steel with a square cross-section. It is mainly manufactured from ordinary carbon steel strips and steel plates through high-frequency welding or seamless extrusion processes to form a closed square hollow structure. Featuring stable structure, complete specifications and strong processing adaptability, the product is widely used in building steel structures, municipal engineering, mechanical equipment, agricultural facilities, transportation, decoration engineering and other fields. The industry mainly divides it into two categories: ERW welded square tubes and seamless square tubes. Welded square tubes are cost-effective and serve as the mainstream general product in the market, while seamless square tubes are mostly applied in heavy-load, high-pressure and precision working conditions.
2. Production Process Classification
2.1 ERW Welded Square Tube
Manufactured from hot-rolled and cold-rolled carbon steel strips through a full set of automated processes including uncoiling, flattening, continuous roll forming, high-frequency resistance welding, internal and external weld bead removal, fixed-length cutting and straightening. This production process features high efficiency, high dimensional accuracy, smooth surface and no obvious deformation, ensuring stable finished product quality. Adaptable to most general engineering scenarios, it is the most widely used and versatile square tube product at present.
2.2 Seamless Square Tube
Processed from carbon steel seamless round tubes through cold drawing, extrusion and shaping to form a square cross-section. The tube has no welding seams and uniform tube wall structure, with far superior compression, torsion and tensile properties compared with welded square tubes and stable mechanical performance. It is applicable to harsh working conditions such as high-pressure bearing, heavy machinery, precision equipment and high-strength steel structures, with higher added value and selling price.
3. Common Material Grades
3.1 General Ordinary Carbon Steel Grades
Q195, Q215 and Q235B. Among them, Q235B is the most commonly used grade on the market, featuring good toughness, excellent plasticity and weldability, and no risk of brittle fracture. It is widely used in conventional scenarios such as building frames, guardrail supports, ordinary steel structures and decorative frames.
Q355B is a low-alloy high-strength material with greatly improved strength, hardness and bearing capacity compared with ordinary carbon steel. It boasts strong load-bearing and impact resistance, and is mostly used in heavy-load scenarios including heavy-duty steel structures, engineering machinery bases, vehicle girders and large equipment supports.
3.2 Custom Special Carbon Steel Grades
20# and 45# high-quality carbon steels feature high material density and excellent mechanical processing performance. Their strength and wear resistance are greatly improved after heat treatment, mainly used for customized processing scenarios such as mechanical processing parts, precision equipment components and high-strength transmission supports.
3.3 General Foreign Trade Standard Grades
SS400 (Japanese standard), S235JR and S355JR (European EN standards) have stable material properties and meet international export testing standards, suitable for overseas projects, foreign trade orders and cross-border infrastructure projects.
4. Specification Parameters
Industry general marking format: Side Length × Wall Thickness × Length (mm), standard example: 50×50×3.0×6000mm
Side Length: Outer side length is marked by default as the industry general standard. Customization for inner side length needs to be noted in advance, and dimensional tolerances strictly comply with national and industry standards.
Wall Thickness: Actual thickness of the tube wall. Customization of standard national tolerances and negative tolerances is available to meet different load-bearing and cost requirements.
Standard Length: Conventional stock lengths are 6m, 9m and 12m. Custom cutting of any size and non-standard customization are supported, with a small processing fee charged for fixed-length products.
Conventional Size Range: Small specifications: 10×10mm~50×50mm; medium specifications: 60×60mm~150×150mm; large specifications: 160×160mm~400×400mm; conventional wall thickness: 1.2mm~16mm, and special wall thicknesses can be customized on demand.
5. Surface Treatment Methods
5.1 Black Tube (Mill Finish / Hot-Rolled Black Tube)
It is the original finished product state with hot-rolled oxide skin on the surface and no subsequent treatment, featuring the lowest cost and high cost performance. Suitable for indoor concealed projects and scenarios requiring subsequent self-spraying, brushing and anti-corrosion treatment, it is not recommended for direct use in outdoor humid and corrosive environments.
5.2 Pickling and Shot Blasting Treatment
Pickling and shot blasting processes completely remove oxide skin, rust and impurities on the tube surface, leaving the tube smooth, oil-free and rust-free. It can greatly improve the adhesion of subsequent paint spraying and baking coatings, serving as the preferred pre-process for deep processed painted products.
5.3 Hot-Dip Galvanizing Treatment
It is the mainstream long-term anti-corrosion process in the industry. Finished square tubes are immersed in high-temperature molten zinc liquid to form a thick and evenly attached zinc layer inside and outside the tube wall. The zinc layer features strong adhesion, excellent anti-rust and anti-corrosion performance, wind and rain resistance, and acid and alkali resistance, with a service life of more than 10 years. Widely used in outdoor guardrails, photovoltaic supports, municipal engineering, outdoor steel structures, greenhouse frames and other open-air scenarios.
5.4 Electro-Galvanizing (Cold Galvanizing) Treatment
Adopting electrochemical galvanizing process, the tube surface is smooth and beautiful with a thin zinc layer and medium anti-rust performance. It is only applicable to indoor dry environments, decorative components, indoor supports and other non-corrosive and rain-free scenarios, and not suitable for long-term outdoor use.
5.5 Anti-Rust Paint / Epoxy Primer Coating
Spraying black or gray epoxy anti-rust primer on the tube surface achieves short-term anti-rust protection with high cost performance. It meets the anti-rust needs of indoor short-term storage and temporary components, and can be used as a semi-finished product pretreatment process.
6. Executive Standards
GB/T 6728: National standard for cold-formed thin-wall steel sections, applicable to all kinds of welded square and rectangular tubes
GB/T 3094: National standard for cold-drawn special-shaped steel tubes, applicable to seamless square tubes
EN 10219: European standard for cold-formed hollow profiles, commonly used for foreign trade export
ASTM A500: American standard for hollow section steel, applicable to North American foreign trade orders
7. Core Product Performance Characteristics
Excellent structural performance: High bending, torsion and compression strength, good overall rigidity and stable load-bearing capacity. It is lighter than solid steel, effectively saving raw material costs.
Strong processing adaptability: Regular tube cross-section and uniform wall thickness allow secondary processing such as cutting, welding, drilling, bending and polishing, adapting to the production of various customized components.
Convenient installation and transportation: Standardized product specifications and strong modular adaptability simplify stacking, transportation and on-site installation, greatly shortening the construction cycle.
Clear working condition adaptation: Conventional thin-wall welded square tubes are suitable for ordinary load-bearing, decoration and support scenarios; thick-wall seamless square tubes meet the strict usage requirements of heavy-load, high-pressure and precision machinery.
Warm Prompt: Thin-wall square tubes are not suitable for ultra-high pressure medium conveying scenarios. Seamless thick-wall square tubes are recommended for high-pressure and heavy-load working conditions.
8. Main Application Fields
Construction Industry: Factory steel structures, curtain wall keels, building frame supports, scaffolding, floor support structures
Municipal Engineering: Road protective guardrails, fence railings, traffic signal poles, municipal landscape frames, urban enclosure frames
Mechanical Equipment: Large equipment racks, equipment bases, conveyor supports, industrial equipment support frames
Agricultural Facilities: Greenhouse frames, breeding shed frames, agricultural equipment support frames
Transportation: Truck girders, container auxiliary frames, logistics equipment supports, vehicle structural parts
Decoration Engineering: Iron art modeling, indoor and outdoor decorative frames, landscape modeling supports, engineering decorative frames
9. Packaging and Delivery Instructions
9.1 Product Packaging
Conventional products are bundled and packaged with steel strips firmly to prevent collision and deformation during transportation. For foreign trade export products, overall woven bag wrapping and plastic end caps at both pipe ends are optional to protect the pipe orifice from deformation and collision damage.
9.2 Delivery Cycle
Conventional in-stock specifications and black square tubes: Fast delivery within 3-7 days; Hot-dip galvanized, non-standard fixed-length, special material and large-size customized products: Delivery within 7-15 days. The specific cycle can be adjusted through negotiation according to order quantity.
9.3 Quality Inspection Guarantee
All products can be delivered with official material certificates and mechanical property test reports. On-site sampling inspection by customers and third-party flaw detection and dimensional accuracy verification are supported. All products comply with corresponding national and foreign trade standards.
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