Q355B Carbon Steel Square Bar | GB/T 702 Hot Rolled & Cold Drawn Square Steel Bar

High yield strength for heavy load bearing
Good low-temperature impact resistance
Excellent weldability and machinability
Strict dimensional tolerance control
Wide size range for engineering customization

Product Overview

Q355B Carbon Steel Square Bar is manufactured in accordance with GB/T 702 standard. It is available in hot rolled and cold drawn production processes. Hot rolled Q355B square bar features black oxide surface, while cold drawn type has smooth bright surface. This grade replaces the old Q345B grade, delivering higher mechanical performance, outstanding impact toughness and reliable welding performance. Widely used for heavy-load supports, engineering structures, lifting parts, machinery frames and construction projects. We can supply customized cutting lengths to meet different project requirements.

Carbon Steel Square Bar

Chemical & Mechanical Property Snapshot

Item	Q355B Carbon Steel Square Bar (GB/T 702)
Carbon (C)	≤0.20%
Silicon (Si)	≤0.50%
Manganese (Mn)	≤1.60%
Phosphorus (P)	≤0.035%
Sulfur (S)	≤0.035%
Yield Strength (Min)	355 MPa
Tensile Strength	470–630 MPa
Elongation (Min)	≥21%
Impact Test	B grade, +20℃ impact energy

Detailed Technical Specifications

Specification Item	Parameter
Product Name	Q355B Carbon Steel Square Bar
Standard	GB/T 702
Production Process	Hot-Rolled / Cold-Drawn
Size Range	Hot Roll:10×10–200×200 mm; Cold Drawn:5×5–50×50 mm
Surface Condition	Hot-rolled black surface / Bright cold-drawn surface
Dimensional Tolerance	Hot Roll: ±0.5–2 mm; Cold Drawn: ±0.1–0.3 mm
Length	3m–12m or customized cut length
MOQ	5 Ton
Lead Time	7–15 working days
Package	Steel bundle with metal strapping, waterproof wrapping

Size Specification Table

Type	Size Range	Available Side Dimensions (mm)	Tolerance
Hot Rolled Carbon Steel Square Bar	10×10 mm–200×200 mm	10, 12, 16, 20, 25, 30, 40, 50, 60, 80, 100, 120, 150, 200	±0.5–±2 mm
Cold Drawn Carbon Steel Square Bar	5×5 mm–50×50 mm	5, 6, 8, 10, 12, 14, 16, 20, 25, 30, 40, 50	±0.1–±0.3 mm

Product Comparison Table

Comparison Item	Q235B Carbon Steel Square Bar	Q355B Carbon Steel Square Bar	S235JR Carbon Steel Square Bar	S355JR Carbon Steel Square Bar	A36 Carbon Steel Square Bar
Equivalent Standard	GB/T 702	GB/T 702	EN 10059	EN 10059	ASTM A675
Manufacturing Process	Hot-Rolled / Cold-Drawn	Hot-Rolled / Cold-Drawn	Hot-Rolled / Cold-Drawn	Hot-Rolled / Cold-Drawn	Hot-Rolled / Cold-Drawn
Size Range	Hot Roll: 10×10–200×200 mm; Cold Drawn: 5×5–50×50 mm	Hot Roll: 10×10–200×200 mm; Cold Drawn: 5×5–50×50 mm	Hot Roll: 10×10–200×200 mm; Cold Drawn: 5×5–50×50 mm	Hot Roll: 10×10–200×200 mm; Cold Drawn: 5×5–50×50 mm	Hot Roll: 10×10–200×200 mm; Cold Drawn: 5×5–50×50 mm
Surface Condition	Hot-rolled black surface / Bright cold-drawn surface	Hot-rolled black surface / Bright cold-drawn surface	Hot-rolled black surface / Bright cold-drawn surface	Hot-rolled black surface / Bright cold-drawn surface	Hot-rolled black surface / Bright cold-drawn surface
Dimensional Tolerance	Hot Roll: ±0.5–2 mm; Cold Drawn: ±0.1–0.3 mm	Hot Roll: ±0.5–2 mm; Cold Drawn: ±0.1–0.3 mm	Hot Roll: ±0.5–2 mm; Cold Drawn: ±0.1–0.3 mm	Hot Roll: ±0.5–2 mm; Cold Drawn: ±0.1–0.3 mm	Hot Roll: ±0.5–2 mm; Cold Drawn: ±0.1–0.3 mm
Yield Strength (Min)	235 MPa	355 MPa	235 MPa	355 MPa	250 MPa
Main Application	General steel structures, mechanical frames, mold blanks	Heavy-load supports, engineering structures, lifting parts	European-standard structural fabrication, mechanical bases	High-strength European engineering structures	American-standard machinery, structural components
Cost Level	Medium	Medium-High	Medium	Medium-High	Medium
Feature	Good weldability & machinability	High strength, good impact resistance	Excellent weldability, CE compliance	High strength, CE certified	Stable performance, ASTM standard

App Market

Reliable Steel Coil Solutions For Diverse Industrial Applications

Hardware Stamping Blanking

Steel Structure Support

Machine Frame

Product Packaging

Secure Export Packaging For Safe Handling And Delivery

FAQs

What is Q355B square bar standard?

Q355B carbon steel square bar follows GB/T 702 standard for hot rolled and cold drawn solid square steel bars.

What is the difference between Q355B and Q235B square bar?

Q355B has much higher yield strength and better impact resistance, suitable for heavy load applications, while Q235B is for general light structural use.

Can Q355B square bar be welded?

Yes, Q355B has good weldability. Common welding methods can be adopted following proper welding procedures.

What surface options do you supply?

Two types: hot rolled black surface, and bright cold drawn surface with tighter tolerance.

Is custom cutting available for Q355B square bar?

Yes, we can cut to your required length, MOQ 5 tons, lead time 7–15 working days.

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Q355B Carbon Steel Square Bar | GB/T 702 Hot Rolled & Cold Drawn Square Steel Bar