Q420E High-Strength Low-Alloy Steel
Q420E High-Strength Low-Alloy Steel: GB/T 1591 Structural Grade with -40°C Toughness
Complete material data for Q420E carbon and low-alloy high-strength steel coil including chemical composition, mechanical properties, thermal and electrical physical properties, international equivalents, and typical applications.
Hot rolling, controlled rolling, normalizing rolling, thermomechanical controlled processing (TMCP), welding, bending, cutting, machining, cold forming
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Q420E High-Strength Low-Alloy Steel Introduction
Q420E is a low-alloy high-strength structural steel defined in Chinese standard GB/T 1591-2018. It belongs to the Q420 strength class with a minimum yield strength of 420 MPa and quality level E, which guarantees Charpy impact energy of at least 34 J at -40°C. The steel is microalloyed with elements such as Nb, V, and Ti to achieve fine grain strengthening and excellent weldability.
- Typical characteristics: high strength, good low-temperature toughness, excellent weldability, and cold formability.
- Main delivery conditions: as-rolled, controlled rolling, normalizing rolling, or thermomechanical controlled processing (TMCP).
- Supplied as coils, plates, sections, bars, and other shapes.
Q420E High-Strength Low-Alloy Steel Chemical Composition
The chemical composition of Q420E according to GB/T 1591-2018 is characterized by low carbon content for weldability, controlled manganese, and the addition of microalloying elements such as niobium, vanadium, and titanium. Phosphorus and sulfur are strictly limited for higher grade E (impact at -40°C). Key aspects:
- Carbon equivalent (CEV) is typically limited to ensure weldability; maximum values depend on thickness.
- Fine-grained practice is required, achieved by the addition of grain-refining elements (total Nb+V+Ti ≤ 0.22%).
- Aluminum is used as a deoxidizer and for grain refinement (Al≥0.015% total or acid-soluble).
| Element | Standard Value (max) | Remarks |
|---|---|---|
| C (Carbon) | 0.20 | Unless otherwise agreed, carbon equivalent limit applies |
| Si (Silicon) | 0.50 | Higher silicon may be permitted for improved corrosion resistance |
| Mn (Manganese) | 1.70 | Maximum for improved strength and hardenability |
| P (Phosphorus) | 0.020 | Lower limit for E-grade (low-temperature toughness) |
| S (Sulfur) | 0.010 | Lower limit for E-grade |
| Nb (Niobium) | 0.07 | Grain refiner; may be added individually or in combination |
| V (Vanadium) | 0.20 | Grain refiner and precipitation strengthener |
| Ti (Titanium) | 0.20 | Grain refiner; total Nb+V+Ti ≤ 0.22% |
| Cr (Chromium) | 0.30 | Residual element; may be intentionally added up to 0.30% |
| Ni (Nickel) | 0.80 | Residual; may improve toughness |
| Cu (Copper) | 0.30 | Residual; if specified, Cu can be up to 0.50% |
| Mo (Molybdenum) | 0.20 | May be present as residual or microalloy addition |
| N (Nitrogen) | 0.015 | For products with sufficient aluminum, nitrogen is bound as AlN |
| Als (Aluminum, total) | ≥0.015 | Total aluminum or acid-soluble aluminum, sufficient for grain refinement |
Q420E High-Strength Low-Alloy Steel Thermal and Electrical Physical Properties
Typical physical properties for Q420E low-alloy steel at room temperature and moderately elevated temperatures. These values are not specified in GB/T 1591 but are representative of similar carbon-manganese microalloyed steels. Variations may occur depending on exact composition and processing history.
- Density is close to pure iron due to low alloy content.
- Thermal expansion and conductivity are similar to other constructional steels.
- Electrical resistivity is typical for ferritic steels.
| Property | Typical Value | Unit | Temperature / Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | 20°C |
| Elastic Modulus (E) | 210 | GPa | 20°C |
| Shear Modulus (G) | 81 | GPa | 20°C |
| Poisson's ratio (ν) | 0.29 | — | 20°C |
| Thermal expansion coefficient (α) | 11.7 | 10⁻⁶/K | 20–100°C |
| Thermal conductivity (λ) | 48 | W/(m·K) | 20°C |
| Specific heat capacity (c) | 470 | J/(kg·K) | 20°C |
| Electrical resistivity (ρₑ) | 0.19 | Ω·mm²/m | 20°C |
Q420E High-Strength Low-Alloy Steel Mechanical Properties
Mechanical properties for Q420E are specified in GB/T 1591-2018. The values depend on product thickness. Tensile tests are performed on transverse specimens. Impact tests use longitudinal V-notch specimens. Bending is a cold forming test with specified bend diameters.
- Yield strength is reported as upper yield (ReH) for steel exhibiting yield phenomenon; otherwise as 0.2% proof strength (Rp0.2).
- Elongation is measured on a proportional gauge length (5.65√S₀), except for thickness <3 mm where a fixed gauge length may be used.
- Impact energy is guaranteed at -40°C for grade E.
| Property | Standard Requirement | Unit | Test Condition / Thickness Range |
|---|---|---|---|
| Yield Strength (ReH) | ≥420 | MPa | Thickness ≤ 16 mm |
| Yield Strength (ReH) | ≥400 | MPa | Thickness 16 < t ≤ 40 mm |
| Yield Strength (ReH) | ≥380 | MPa | Thickness 40 < t ≤ 63 mm |
| Yield Strength (ReH) | ≥360 | MPa | Thickness 63 < t ≤ 80 mm |
| Yield Strength (ReH) | ≥340 | MPa | Thickness 80 < t ≤ 100 mm |
| Yield Strength (ReH) | ≥320 | MPa | Thickness 100 < t ≤ 150 mm |
| Tensile Strength (Rm) | 470 – 630 | MPa | Thickness ≤ 100 mm |
| Tensile Strength (Rm) | 450 – 600 | MPa | Thickness 100 < t ≤ 150 mm |
| Elongation after fracture (A) | ≥19 | % | Thickness ≤ 40 mm, gauge length 5.65√S₀ |
| Elongation after fracture (A) | ≥18 | % | Thickness 40 < t ≤ 63 mm |
| Elongation after fracture (A) | ≥18 | % | Thickness 63 < t ≤ 100 mm |
| Elongation after fracture (A) | ≥17 | % | Thickness 100 < t ≤ 150 mm |
| Impact energy (KV₂, longitudinal) | ≥34 | J | At -40°C, all thicknesses |
| Bend test (180°) | D = 2a | — | Thickness ≤ 16 mm, width of test piece b = 2t |
| Bend test (180°) | D = 3a | — | Thickness 16 < t ≤ 100 mm |
| Bend test (180°) | To be agreed | — | Thickness > 100 mm |
Q420E High-Strength Low-Alloy Steel Direct Equivalent Material Standards and Substitution Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2018 | Q420E | Base material; minimum yield 420 MPa, impact -40°C ≥34 J |
| European Union | EN 10025-4 | S420ML | Thermomechanical rolled; yield 420 MPa, impact -50°C ≥27 J; closest EU equivalent but impact test temperature differs |
| European Union | EN 10025-3 | S420NL | Normalized/normalized rolled; yield 420 MPa, impact -50°C ≥27 J; requires different delivery condition |
| International | ISO 4950-2 | E420DD | Quenched and tempered; yield 420 MPa, impact -20°C; requires heat treatment, only partially equivalent |
| Japan | JIS G 3106 | SM490YB (modified) | Yield 365–460 MPa depending on thickness; may need supplementary impact testing to match -40°C |
Q420E High-Strength Low-Alloy Steel Application Introduction
Q420E combines high strength with excellent low-temperature toughness, making it ideal for heavy welded structures exposed to harsh environments. Its fine-grain structure and good weldability allow for efficient fabrication.
- Welding: Preheating is rarely required for moderate thicknesses, but attention to heat input and interpass temperature is recommended. Consumables matching the base metal strength (e.g., E55 type) are used.
- Forming: Cold forming is possible for thin gauges; hot forming should be controlled to avoid grain coarsening.
- Corrosion protection: As an unalloyed/low-alloy steel, painting or galvanizing is required for atmospheric exposure.
Product Applications: Welded H-beams and built-up sections for high-rise columns, Fabricated bridge girders and box sections, Offshore jacket legs and nodes, Wind turbine tower sections (tubular), High-strength spiral-welded pipes for long-distance gas transmission, Versatile steel plates for machinery manufacturing
Processed into products: Flange and web plates in plate girders, Stiffened panels for ship decks and bulkheads, Boom and arm plates in hydraulic excavators, Transition pieces and flanges in wind towers, Weld neck flanges and tank shells for pressure vessels, Chassis members and subframes for heavy-duty vehicles, Cut-to-shape brackets and gusset plates
Application industries: Bridge construction (steel box girders, trusses, arch bridges), Building and civil engineering (high-rise frames, stadiums, airport terminals), Offshore and marine structures (platforms, wind turbine towers, ship hulls), Heavy machinery (excavator booms, crane structures, dump truck bodies), Pressure vessels and storage tanks (LPG, ammonia, low-temperature applications), Transportation (railway wagons, vehicle chassis, truck frames)
Q420E High-Strength Low-Alloy Steel Similar and Alternative Materials with Comparable Performance
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591 | Q390E | Slightly lower yield (390 MPa), same -40°C toughness; good replacement where strength reduction acceptable |
| China | GB/T 1591 | Q460E | Higher strength (460 MPa yield), same toughness; may require thickness reduction or design adjustments |
| USA | ASTM A572/A572M | Grade 65 (Type 3 with toughness) | Yield 450 MPa (≥450); Charpy impact can be specified at -40°C; higher strength but chemical variations |
| European Union | EN 10025-4 | S460ML | Higher yield (460 MPa), impact -50°C; often used when weight savings justify strength upgrade |
| European Union | EN 10025-3 | S420N | Normalized, yield 420 MPa, impact only -20°C; suitable when lower toughness requirements acceptable |
| Russia/GOST | GOST 27772 | S390-1 / S440-1 | Not fully equivalent; strength classes overlap; toughness grades must be selected carefully |
Notes:
Additional considerations for Q420E:
- The steel is generally supplied with a quality certificate per EN 10204 type 3.1 or as agreed.
- For thicknesses above 100 mm, special agreement on mechanical properties and heat treatment may be required, as standard values are less defined.
- A carbon equivalent (CEV) control option can be specified to ensure good weldability. Typical CEV maximum values: ≤0.45% for thickness ≤100 mm, and ≤0.47% for larger thicknesses (using the IIW formula).
- Ultrasonic testing to GB/T 2970 or equivalent can be specified for critical welded joints.
- When ordering steel coil from service centers, the material is often supplied with a limited test report indicating typical properties. Always confirm that the coil carries a melt number traceable to the original steelmaker's certificate.
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