CARBON STEEL · SQUARE & RECTANGULAR TUBE

Q235B Carbon Steel Square Tube
GB/T 6728 Cold-Formed Welded Hollow Section

Strong, straight and easy to weld — the workhorse square and rectangular hollow section for steel structures, racks, frames and machinery.

STANDARD: GB/T 6728 GRADE: Q235B CUSTOM SIZE AVAILABLE

YIELD STRENGTH

≥235 MPa

TENSILE STRENGTH

370–500 MPa

SIZE RANGE

20×20–200×200

01 · PRODUCT OVERVIEW

Q235B square and rectangular hollow sections are cold-formed from hot-rolled strip and longitudinally welded to GB/T 6728. The section is square to tight corners, straight and torsion-resistant, delivering predictable strength for structural and mechanical use at a very competitive cost.

WHY CHOOSE Q235B TUBE

One material, one grade — Q235B only, no mixed chemistries in the batch. Uniform wall thickness, clean weld seam, precise outer dimensions and cut-to-length service for every order.

02 · KEY FEATURES

Square Precision

Sharp, even corners and straight sidewalls improve joint fit-up and speed up frame assembly.

High Strength-to-Weight

Closed hollow section gives excellent bending and torsional stiffness per kilogram — lighter structures than open profiles.

Easy Welding

Low carbon Q235B welds cleanly in all positions — joints are strong and free of hard spots.

Consistent Wall Thickness

Roll-formed from controlled strip, wall and corner thickness stay uniform along the full length.

Seaworthy Packing

Bundles steel-banded and weather-protected, safe for long sea freight to any destination.

Cut-to-Length Service

Any length from 1 m to 12 m, precise mitre or square cutting available for ready-to-use parts.

03 · CHEMICAL COMPOSITION (Cast Analysis, %) — Q235B

Elemento	C	Y	Minnesota	PAG	S
Max Content	0.20	0.35	1.40	0.045	0.045

Note: Values are maximum cast analysis in percent. Mill test certificates accompany each batch.

04 · MECHANICAL PROPERTIES (Base Metal)

Propiedad	Valor	Test Method
Fuerza de producción (ReH)	≥ 235 MPa	GB/T 228.1
Resistencia a la tracción (Rm)	370 – 500 MPa	GB/T 228.1
Alargamiento (A)	≥ 26 %	GB/T 228.1
Charpy Impact (20 °C)	≥ 27 J	GB/T 229
Weld Seam	Flattening test — no crack	GB/T 246

TENSILE STRENGTH — COMMON GRADES COMPARISON

Q235B Tube (370–500 MPa)RANGE

Q355B (470–630 MPa)HIGHER

05 · PHYSICAL PROPERTIES

DENSITY

7.85 gramos/cm³

MELTING POINT

≈ 1490 °C

MODULUS OF ELASTICITY

200 – 210 GPa

THERMAL EXPANSION

≈ 12×10⁻⁶ /K

06 · COMMON SPECIFICATIONS

Section	Tamaño (milímetros)	Espesor de pared (milímetros)	Longitud (m)
Square Tube	20×20 – 100×100	1.5 / 2.0 / 2.5 / 3.0 / 4.0	6 / 12
Square Tube (Large)	120×120 – 200×200	4.0 / 5.0 / 6.0 / 8.0 / 10.0	6 / 12
Rectangular Tube	20×30 – 150×200	1.5 – 10.0	6 / 12
Superficie	Acabado de la fábrica; galvanized, painted or oiled on request