Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 - Properties & Equivalent Grades
Explore the detailed material data of Q420D carbon and low-alloy high-strength steel coil under the Chinese standard GB/T 1591. Includes chemical composition, mechanical and physical properties, international equivalents, and application guidance.
Welding, bending, cutting, forming, machining, hot rolling, cold rolling, normalization
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Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Introduction
Q420D is a high-strength low-alloy structural steel grade defined in GB/T 1591. It offers a minimum yield strength of 420 MPa and excellent low-temperature toughness (Impact energy ≥ 47 J at -20 °C), making it suitable for demanding structural applications. The steel exhibits good weldability, cold formability, and strength-to-weight ratio. It is primarily used in heavy-duty structures such as bridges, buildings, offshore platforms, and machinery where weight reduction and high load-bearing capacity are critical. Delivery condition is typically as-rolled, normalized, or thermo-mechanically controlled processed (TMCP), depending on thickness and customer requirements.
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Chemical Composition
The table below lists the chemical composition requirements for Q420D steel according to GB/T 1591-2018. Values are maximum unless a range is specified. Microalloying elements such as Nb, V, and Ti may be added singly or in combination to achieve the required strength and toughness. The steel is fully killed and contains fine grain practices.
| Element | Standard Value | Remarks |
|---|---|---|
| C | ≤ 0.20 | Carbon |
| Si | ≤ 0.50 | Silicon |
| Mn | ≤ 1.70 | Manganese |
| P | ≤ 0.030 | Phosphorus |
| S | ≤ 0.030 | Sulfur |
| Nb | ≤ 0.07 | Niobium |
| V | ≤ 0.20 | Vanadium |
| Ti | ≤ 0.20 | Titanium |
| Cr | ≤ 0.30 | Chromium |
| Ni | ≤ 0.80 | Nickel |
| Cu | ≤ 0.30 | Copper |
| Mo | ≤ 0.20 | Molybdenum |
| N | ≤ 0.015 | Nitrogen |
| Als | ≥ 0.015 | Total aluminum, acid-soluble method |
| Ceq | ≤ 0.50* | Carbon equivalent; *for thickness ≤ 50 mm (typical requirement) |
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Thermo-physical & Electrical Properties
The following physical properties are typical for low-alloy high-strength structural steels similar to Q420D at room temperature unless specified. These values are for general engineering guidance and are not specifically mandated by GB/T 1591.
| Property | Typical Value | Unit | Test Condition / Note |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | Ambient temperature |
| Modulus of Elasticity (E) | 206 | GPa | Ambient temperature |
| Shear Modulus (G) | 79 | GPa | Ambient temperature |
| Poisson's Ratio (ν) | 0.30 | — | Ambient temperature |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20 – 100 °C |
| Thermal Conductivity (λ) | 53 | W/(m·K) | At 20 °C |
| Specific Heat Capacity | 460 | J/(kg·K) | Ambient temperature |
| Electrical Resistivity (ρₑ) | 0.15 – 0.25 | μΩ·m | Ambient temperature |
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Mechanical Properties
Mechanical properties for Q420D steel coil are dependent on thickness. The values below are based on GB/T 1591-2018 requirements for longitudinal test pieces. Impact tests are performed on V-notch Charpy specimens at -20 °C. Bend test mandates no cracks on the outer surface when bent to the specified diameter.
| Property | Required Value | Unit | Test Condition / Thickness |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 420 | MPa | Thickness ≤ 16 mm |
| Yield Strength (ReH) | ≥ 400 | MPa | Thickness 16 < t ≤ 35 mm |
| Yield Strength (ReH) | ≥ 380 | MPa | Thickness 35 < t ≤ 50 mm |
| Yield Strength (ReH) | ≥ 360 | MPa | Thickness 50 < t ≤ 100 mm |
| Tensile Strength (Rm) | 520 – 680 | MPa | Thickness ≤ 100 mm |
| Elongation (A) | ≥ 18 | % | Thickness ≤ 40 mm, gauge 50 mm or 80 mm |
| Elongation (A) | ≥ 17 | % | Thickness 40 < t ≤ 100 mm |
| Impact Energy (KV₂) | ≥ 47 | J | Longitudinal, -20 °C |
| Bend Test (d = bend dia., a = specimen thickness) | d = 2a | — | Thickness ≤ 16 mm, 180° bend |
| Bend Test | d = 3a | — | Thickness 16 < t ≤ 100 mm, 180° bend |
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Completely Equivalent Material Standards & Replaceable Grades
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-3 | S420N | Normalized/normalized rolled weldable fine grain steel; min. yield 420 MPa, -20°C impact 47J |
| Europe | EN 10025-3 | S420NL | Similar to S420N with lower temperature toughness (-50°C) |
| Europe | EN 10025-2 | S420M | Thermo-mechanically rolled; min. yield 420 MPa, tensile 500-660 MPa |
| International | ISO 4951-2 | FeE420 | Equivalent high yield strength steel |
| USA | ASTM A572 | Grade 60 | Min. yield 415 MPa (60 ksi); impact test must be specified separately |
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Application Introduction
Q420D steel coil offers an excellent combination of high strength, good ductility and reliable low-temperature impact toughness. It is widely used in welded, bolted and riveted structures. Typical processing includes hot/cold forming, cutting, and welding with appropriate preheat and interpass temperature control to avoid cold cracking. Application industries and products:
Product Applications: High-rise building steel framework, Long-span bridges (girders, box sections), Offshore platform deck beams and legs, Pressure vessel shells (where permitted), Heavy-duty crane booms and chassis, Mining machinery structural parts, Welded pipes and hollow structural sections
Processed into products: H-beams, I-beams and welded plate girders, Steel columns and truss members, Welded box columns and built-up sections, Flanges and webs for plate girders, Boom and arm segments for excavators, Tower tube sections and cross arms, Chassis frames for heavy trucks and trailers
Application industries: Construction and infrastructure, Bridge engineering, Offshore and marine structures, Heavy machinery and equipment, Shipbuilding (limited use in secondary structures), Power transmission and telecom towers, Railway vehicles and automotive frames
Q420D High-Strength Low-Alloy Steel Coil per GB/T 1591 Similar / Alternative Material Recommendations
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591 | Q390D | Min. yield 390 MPa; slightly lower strength but similar toughness requirements |
| China | GB/T 1591 | Q460D | Higher strength grade, min. yield 460 MPa, for weight-critical applications |
| Europe | EN 10025-2 | S355J2 | Lower strength (min. yield 355 MPa) but widely available; -20°C impact |
| Japan | JIS G 3106 | SM520B/C | Min. yield 355-365 MPa; suitable for welded structures, toughness depends on grade |
| USA | ASTM A709 | Grade 50W | High-strength low-alloy structural steel, comparable to S355, with atmospheric corrosion resistance |
Notes:
Material should be supplied fully deoxidized and fine-grain treated. For thicknesses over 100 mm, mechanical properties may be agreed upon. Welding procedures must be qualified; low hydrogen processes are recommended. For dynamic and fatigue-loaded structures, additional testing may be required per project specifications.
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