Black Annealed Welded Square Steel Tube

Black annealed welded square steel tube is a carbon steel hollow section that manufacturers produce through electric resistance welding followed by a controlled annealing heat treatment. This annealing process softens the material, improves ductility, and reduces internal stresses, making it easier to form and fabricate compared to standard welded tube .

Product Parameters

Square size range: 20mm x 20mm to 400mm x 400mm .

Regular sizes include 20×20, 25×25, 30×30, 40×40, 50×50, 60×60, 80×80, 100×100, 120×120, 150×150, and 200×200 mm.

Wall thickness: 1.0mm to 15mm .

Common thicknesses: 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0 mm.

Length: 6 meters standard, with custom lengths from 3m to 12m available.

Processing technique: ERW (Electric Resistance Welded) followed by annealing in a controlled atmosphere furnace .

The annealing process slowly heats and cools the tube to achieve the desired mechanical properties .

Execution standards: ASTM A500, EN 10219, EN 10305-5, GB/T 6728 . Packaging: Seaworthy bundles with steel strips, waterproof paper wrapping, and end protectors.

Surface treatment: Black annealed finish (black oxide layer), we also offer oiled, painted, or galvanized as requested.

Chemical Composition (Typical for Q195/Q235 Grade)

Carbon (C): 0.06-0.22%
Manganese (Mn): 0.25-0.80%
Phosphorus (P): ≤0.040%
Sulfur (S): ≤0.040%
Silicon (Si): ≤0.35%

Physical Properties

Tensile Strength: 330-450 MPa
Yield Strength: 195-235 MPa
Elongation: 23-30%
Hardness: Reduced compared to non-annealed material, improving machinability
Ductility: Enhanced through annealing, allowing bending and forming without cracking

Product Applications

Furniture frames for chairs, tables, beds, and shelving units . Construction frameworks and structural supports for buildings. Automotive components such as chassis parts and roll cages. Machinery guards and equipment frames. Fencing, railings, and handrails requiring clean appearance. Decorative and architectural metalwork.