Q345B is a low-alloy high-strength structural steel grade widely used in Chinese construction, bridge building, machinery manufacturing, and offshore engineering. With a minimum yield strength of 345 MPa, it offers 40% higher strength than Q235B while maintaining good weldability and formability. Huaxia-Steel supplies Q345B carbon steel plate direct from factory with full certification and competitive export pricing.
Product Overview
Our Q345B steel plates are produced to GB/T 1591-2018 (replacing the older GB/T 1591-2008, where Q345B was redesignated as Q355B). They are hot-rolled from continuously cast slabs, controlled-cooled for uniform microstructure, and supplied in as-rolled or normalized condition.
Key features of Q345B steel plate:
- High yield strength (≥345 MPa for t≤16mm) — enables lighter, more efficient structures
- Excellent weldability with low carbon equivalent (CEV ≤ 0.44%)
- Good impact toughness at 20°C (≥27J Charpy V-notch)
- Available in thicknesses from 3mm to 200mm
- Cost-effective alternative to ASTM A572 Gr 50 or S355JR
Specification Table
| Parameter | Specification |
|---|---|
| Standard | GB/T 1591-2018 (Q355B equivalent) |
| Thickness | 3.0 – 200.0 mm |
| Width | 1,000 – 3,200 mm |
| Length | 3,000 – 12,000 mm (custom cutting available) |
| Thickness Tolerance | ±0.15mm (t≤8mm), ±0.30mm (8 |
| Width Tolerance | +5/-0 mm |
| Flatness | ≤ 4mm/m (t≤25mm), ≤ 3mm/m (t>25mm) |
| Surface Finish | Hot-rolled (default), shot-blasted (optional) |
Mechanical Properties by Thickness
| Thickness (mm) | Yield (MPa) | Tensile (MPa) | Elongation (%) | Impact (J, 20°C) |
|---|---|---|---|---|
| ≤ 16 | ≥ 345 | 470–630 | ≥ 20 | ≥ 27 |
| 16 – 35 | ≥ 325 | 470–630 | ≥ 19 | ≥ 27 |
| 35 – 50 | ≥ 295 | 470–630 | ≥ 18 | ≥ 27 |
| 50 – 100 | ≥ 275 | 470–630 | ≥ 17 | ≥ 27 |
Chemical Composition
| Element | C | Si | Mn | P | S | Nb | V | Ti |
|---|---|---|---|---|---|---|---|---|
| Max (%) | 0.20 | 0.50 | 1.70 | 0.035 | 0.035 | 0.07 | 0.15 | 0.20 |
Available Grades & Equivalents
| Grade | Standard | Equivalent | Yield (MPa) |
|---|---|---|---|
| Q345B | GB/T 1591 | — | ≥ 345 |
| Q355B | GB/T 1591-2018 | Direct upgrade | ≥ 355 |
| A572 Gr 50 | ASTM A572 | US equivalent | ≥ 345 |
| S355JR | EN 10025-2 | European equivalent | ≥ 355 |
| SM490B | JIS G 3106 | Japanese equivalent | ≥ 325 |
Manufacturing Standards
Our Q345B plates are manufactured under the following standards:
- GB/T 1591-2018: High-strength low-alloy structural steels (current Chinese standard)
- GB/T 709: Dimensional and shape tolerances for hot-rolled steel plates
- GB/T 2975: Sampling standards for mechanical testing of steel products
- ASTM A6/A6M: General requirements for rolled structural steel (for export dual-certification)
Applications
- Construction: High-rise building columns, beams, and bracing members
- Bridges: Box girders, orthotropic decks, and support structures
- Machinery: Excavator booms, crane jibs, and heavy equipment frames
- Shipbuilding: Hull structures (with Z35 through-thickness certification)
- Pressure vessels: Low-temperature service tanks and silos
- Offshore: Platform decks and jacket structures (with supplementary requirements)
Quality Assurance
- Mill test certificate: EN 10204 3.1 MTC with full chemistry, mechanical properties, and heat number
- Ultrasonic testing: Available per EN 10160 (S0–S3 levels) or GB/T 2970
- Z-direction testing: Through-thickness properties (Z25/Z35) available for welded structures
- Surface inspection: Visual and magnetic particle inspection for surface defects
- Dimensional verification: Thickness measured at 25mm from edges; flatness checked on inspection table
- Third-party inspection: SGS, BV, TÜV, or CCS inspection available on request
Packaging & Shipping
- Plates bundled with steel straps on wooden skids or steel pallets
- Anti-rust oil application for sea freight (optional)
- VCI (volatile corrosion inhibitor) paper for long-term storage protection
- Loading: 20–28 tons per 20ft container; 25–30 tons per 40ft container (depending on thickness)
- Custom cutting to size available before packaging
- Full export documentation: Commercial invoice, packing list, MTC, Bill of Lading
Request a Quote
Get factory-direct pricing on Q345B carbon steel plate with guaranteed mechanical properties and full certification. Contact Huaxia-Steel today with your thickness, width, length, and quantity requirements. Explore our complete carbon steel product catalog for additional grades and products.
