Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591: Properties & Equivalents
Comprehensive data sheet for Q345B carbon and low-alloy high-strength steel coil according to Chinese standard GB/T 1591. Includes chemical composition, mechanical and thermal properties, international equivalent grades, and application guidance.
Hot rolling, controlled rolling, normalizing, cold forming, welding, machining
- Phone : +8618037372205
- Email : [email protected]
- WhatsApp: Contact via Whtsapp
- WeChat: +8618037372205
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 Introduction
Q345B is a Chinese standard low-alloy high-strength structural steel defined in GB/T 1591-2008 (superseded by GB/T 1591-2018 with grade Q355B). It offers a minimum yield strength of 345 MPa and is widely used in welded structures, bridges, vehicles, and pressure vessels. The steel exhibits good weldability, toughness, and formability. Its composition includes controlled amounts of carbon, manganese, silicon, and microalloying elements to achieve desired strength and ductility. Delivery condition is typically hot-rolled or controlled rolled. Equivalent international grades include ASTM A572 Gr. 50 and EN 10025-2 S355JR.
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 Chemical Composition
The following chemical composition is based on ladle analysis as specified in GB/T 1591-2008 for grade Q345B with thickness ≤100 mm. Values are maximum unless a range is indicated. Microalloying elements (Nb, V, Ti) may be added singly or in combination to refine grain structure and improve strength.
| Element | Standard Value (%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.20 | |
| Silicon (Si) | ≤ 0.50 | |
| Manganese (Mn) | ≤ 1.70 | |
| Phosphorus (P) | ≤ 0.035 | |
| Sulfur (S) | ≤ 0.035 | |
| Niobium (Nb) | ≤ 0.07 | Optional microalloying |
| Vanadium (V) | ≤ 0.15 | Optional microalloying |
| Titanium (Ti) | ≤ 0.20 | Optional microalloying |
| Nitrogen (N) | ≤ 0.012 | If sufficient Al or other N-binding elements present |
| Aluminum (Al) | ≥ 0.015 (total Al) | Or as agreed, for grain refinement |
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 Thermal and Electrical Physical Properties
Physical properties are typical for low-alloy carbon steels and are influenced by the exact composition and heat treatment. These values are derived from general engineering data for comparable steel grades and are not specified in GB/T 1591-2008. They serve as a guideline for design calculations.
| Property | Typical Value | Unit | Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | Room temperature |
| Elastic Modulus (E) | 200 – 210 | GPa | Room temperature |
| Shear Modulus (G) | 80 – 81 | GPa | Room temperature |
| Poisson's Ratio (ν) | 0.27 – 0.30 | — | Room temperature |
| Thermal Expansion Coefficient (α) | 11.5 – 12.5 | 10⁻⁶/K | 20 – 100°C |
| Thermal Conductivity (λ) | 45 – 52 | W/(m·K) | Room temperature |
| Specific Heat Capacity | 460 – 500 | J/(kg·K) | Room temperature |
| Electrical Resistivity (ρ_e) | 0.20 – 0.25 | 10⁻⁶ Ω·m | Room temperature |
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 Mechanical Properties
Mechanical properties according to GB/T 1591-2008 for flat products (coil/plate). Values depend on the nominal thickness (t) of the product. The table shows the minimum required values. Impact test energy (KV) applies for Charpy V-notch at +20°C for quality level B. Typical values at room temperature are provided for reference.
| Property | Value (Specified / Typical) | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 345 | MPa | t ≤ 16 mm |
| Yield Strength (ReH) | ≥ 335 | MPa | 16 < t ≤ 40 mm |
| Tensile Strength (Rm) | 470 – 630 | MPa | t ≤ 100 mm |
| Elongation (A) | ≥ 20 | % | t ≤ 40 mm, L0=5.65√S0 |
| Elongation (A) | ≥ 19 | % | 40 < t ≤ 100 mm |
| Impact Energy (KV2) | ≥ 34 (longitudinal) | J | +20°C, Charpy V-notch |
| Bending Test (Mandrel Diameter) | D = 1.5a (t ≤ 16 mm) | 180° bend; a = thickness | |
| Bending Test (Mandrel Diameter) | D = 2a (16 < t ≤ 100 mm) | 180° bend |
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 International Equivalent Standards and Direct Substitute Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2018 | Q355B | Successor grade to Q345B; slightly higher min. yield strength (355 MPa) |
| USA / International | ASTM A572 / A572M | Grade 50 | Closest equivalent; min. yield 345 MPa (50 ksi) |
| European Union | EN 10025-2 | S355JR | Min. yield 355 MPa, impact 27J at +20°C |
| European Union | EN 10025-2 | S355J0 | Min. yield 355 MPa, impact 27J at 0°C |
| Japan | JIS G 3106 | SM490A | Min. yield 325-365 MPa depending on thickness; weldable structural steel |
| Japan | JIS G 3135 | SPFC 590 | High-strength cold-rolled steel; approximate for formability |
| International | ISO 630-2 | S355B | Corresponds to EN S355JR; min. yield 355 MPa |
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 Application Introduction
Q345B steel coil is extensively used in structural applications requiring high strength and good weldability. It is suitable for both indoor and outdoor environments, with protective coatings recommended for corrosive conditions. The steel can be processed by cutting, bending, welding, and machining to produce finished components.
Product Applications: Structural frameworks and columns, Bridge beams and decking, Chassis and frames for heavy vehicles, Storage tanks and silos, Crane booms and lifting beams, Transmission towers and poles, Corrugated steel sheets, Welded pipes and hollow sections
Processed into products: Welded H-beams and I-beams, Gusset plates and stiffeners, Brackets and support brackets, Machinery bases and platforms, Flanges for piping connections, Structural angles and channels, Cold-formed sections (C, Z purlins), Dozer blades and wear parts (after hardening)
Application industries: Building and construction, Bridge engineering, Automotive and transportation, Pressure vessel and boiler manufacturing, Lifting and hoisting machinery, Marine and offshore structures (non-critical), General mechanical engineering, Agricultural equipment
Q345B Low-Alloy High-Strength Steel Coil per GB/T 1591 Similar / Comparable Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2008 | Q345C | Lower temperature impact toughness (0°C) |
| China | GB/T 1591-2008 | Q345D | Low temperature toughness (-20°C) |
| China | GB/T 1591-2018 | Q355B | New standard replacement with 355 MPa min. yield |
| USA | ASTM A572 | Grade 55 | Higher yield strength (380 MPa) option |
| EU | EN 10025-2 | S355J2 | Impact at -20°C, better toughness |
| India | IS 2062 | E350B | Min. yield 350 MPa, for structural use |
Notes:
Important: Q345B was superseded by Q355B in GB/T 1591-2018, but the grade is still widely referenced in legacy designs and existing stock. When ordering, confirm the applicable standard. For welded structures, low-hydrogen welding procedures are recommended to avoid cold cracking. Normalizing may improve toughness. For thicknesses above 40 mm, check with the supplier for guaranteed mechanical properties.
- Share
