Q235B square steel tube is a widely used carbon structural steel product known for its excellent weldability, good toughness, and reliable strength. It is commonly manufactured in square, rectangular, round, and customized shapes according to project requirements.
As one of the most frequently used structural steels in China, Q235B is suitable for general engineering, building structures, mechanical fabrication, and industrial applications.
Grades & Types
Material Grade: Q235B (Carbon Structural Steel)
Types Available:
Q235B Square Tubing
Q235B Rectangular Tubing
Q235B Round/Customized Hollow Sections
Available Sizes
Section Size: 20×20 mm to 600×600 mm
Wall Thickness: 1.0 mm – 30 mm
Lengths: 6 m, 12 m, or custom lengths (up to 24 m for projects)
Applications
Q355 square hollow sections are widely used in demanding structural, industrial, and mechanical applications due to their high yield strength (≥355 MPa), tensile strength (470–630 MPa), and excellent toughness.
They are commonly applied in:
Construction & Infrastructure
Used for support frames, scaffolding, bridges, airport terminals, and MRT structures.
Q355 SHS/RHS is capable of withstanding 2.5–3.5 times its own weight in static structural loads.
Typical usage in high-rise projects often exceeds 1,200–3,000 tons per project.
Impact test values (KV2 ≥27 J at –20°C) ensure reliability in cold climates.
Shipbuilding & Offshore Platforms
Applied in decks, support frames, bulkheads, and marine structures.
The corrosion allowance can reach 1.5–2.5 mm depending on the environment.
Meets toughness requirements for low-temperature marine service.
Cranes & Heavy Machinery
Used in boom structures, crane arms, hydraulic lifting frames, and heavy machine supports.
The high yield strength allows Q355 sections to carry 15–30% more load than Q235.
Fatigue resistance performance improves equipment service life by 20–40%.
Mechanical & General Engineering
Used for automotive frames, agricultural machinery, machine body structures, and conveyor systems.
Dimensional accuracy allows tolerance control within ±0.5–1.0 mm, ensuring machine alignment.
Mechanical Properties (GB/T700 Q235B)
| Item | Requirement |
|---|---|
| Yield Strength (min) | 235 MPa |
| Tensile Strength | 375–500 MPa |
| Elongation | ≥ 26% (depending on thickness) |
Q235B provides a balance between strength and ductility, making it ideal for general structural applications.
Chemical Composition (Max, %)
| C | Mn | Si | P | S |
|---|---|---|---|---|
| ≤ 0.22 | ≤ 1.40 | ≤ 0.35 | ≤ 0.045 | ≤ 0.045 |
Low carbon content ensures excellent weldability and formability.
Performance Characteristics
Excellent Weldability:
Q235B can be welded easily using MIG, TIG, arc welding, and resistance welding without preheating for most sizes.
High Ductility & Formability:
Suitable for bending, cutting, punching, flattening, stamping, and general fabrication.
Reliable Strength for General Structures:
Offers balanced strength for load-bearing components in construction projects.
Wide Size Range & Custom Production:
Supports special sizes, customized wall thicknesses, and tailored lengths.
Production Process
Q235B square tubes can be produced in seamless or ERW welded types:
ERW (Electric Resistance Welded):
Most commonly used; stable quality and cost-effective
Seamless:
Used for pressure piping, heavy-duty structural components
All welded tubes are inspected and the weld seam can be leveled or removed upon request.
