EN10025-4 S420ML Steel
S420ML Steel: EN 10025-4 Thermo-Mechanically Rolled Weldable Fine-Grain Structural Steel
Detailed material data for S420ML according to EN 10025-4: chemical composition, mechanical properties, thermal and electrical properties, equivalent grades, applications.
Thermo-mechanical rolling, cold forming, welding, machining
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EN10025-4 S420ML Steel Introduction
S420ML is a thermo-mechanically rolled weldable fine-grain structural steel grade specified in EN 10025-4. The designation 'S' stands for structural steel, '420' indicates the minimum yield strength of 420 MPa for thicknesses ≤16 mm, 'M' denotes thermo-mechanical rolling (TMCP), and 'L' specifies impact toughness at a test temperature of -50 °C with a minimum energy of 27 J. This steel offers an excellent combination of high strength, good weldability, and superior low-temperature toughness. Its fine grain size is achieved through controlled rolling and cooling, eliminating the need for subsequent normalizing heat treatment. Typical applications include heavily loaded welded structures in bridge building, crane construction, offshore engineering, and heavy machinery, where weight savings combined with high safety standards are crucial. The material is supplied in the as-rolled condition (TMCP) and complies with strict limits on carbon equivalent (CEV) to ensure weldability without preheating under appropriate conditions.
EN10025-4 S420ML Steel Chemical Composition
The chemical composition of S420ML is defined by EN 10025-4. The steel is fully killed and fine-grain treated, with minimum aluminium or other grain-refining elements. The maximum carbon equivalent (CEV) values depend on the product thickness and are specified to guarantee weldability. The table lists the maximum limits unless a range or minimum is indicated.
| Element | Value (max, %) | Notes |
|---|---|---|
| Carbon (C) | 0.16 | CEV limits apply additionally |
| Silicon (Si) | 0.50 | - |
| Manganese (Mn) | 1.70 | - |
| Phosphorus (P) | 0.025 | - |
| Sulfur (S) | 0.020 | - |
| Nitrogen (N) | 0.015 | Total Al/N ratio ensures minimum Al content for fine-grain practice |
| Aluminium (Al) | ≥0.015 (total) | Minimum total aluminium required; alternatively other grain-refining elements may be used |
| Niobium (Nb) | 0.05 | - |
| Vanadium (V) | 0.12 | - |
| Titanium (Ti) | 0.05 | - |
| Molybdenum (Mo) | 0.20 | - |
| Nickel (Ni) | 0.30 | - |
| Chromium (Cr) | 0.30 | - |
| Copper (Cu) | 0.55 | - |
| Carbon equivalent (CEV) | Formula-based | CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Maximum CEV values depend on thickness: e.g., ≤0.39% for ≤63 mm, ≤0.41% for >63≤100 mm, etc. |
EN10025-4 S420ML Steel Thermal and Electrical Physical Properties
The following physical properties are typical for low-alloy structural steels of this grade. They are not mandatory requirements of EN 10025-4 but are provided as engineering reference. Density, thermal expansion, thermal conductivity, specific heat capacity, and electrical resistivity are measured at room temperature unless otherwise noted.
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Modulus of elasticity (E) | 210 | GPa | At 20 °C |
| Shear modulus (G) | ≈81 | GPa | At 20 °C |
| Poisson's ratio (ν) | 0.3 | - | At 20 °C |
| Thermal expansion coefficient (α) | 12.0 × 10⁻⁶ | K⁻¹ | From 20 °C to 100 °C |
| Thermal expansion coefficient (α) | 12.8 × 10⁻⁶ | K⁻¹ | From 20 °C to 200 °C |
| Thermal expansion coefficient (α) | 13.5 × 10⁻⁶ | K⁻¹ | From 20 °C to 400 °C |
| Thermal conductivity (λ) | 53 | W/(m·K) | At 20 °C |
| Thermal conductivity (λ) | 50 | W/(m·K) | At 200 °C |
| Specific heat capacity (cₚ) | 460 | J/(kg·K) | At 20 °C |
| Specific heat capacity (cₚ) | 500 | J/(kg·K) | At 200 °C |
| Electrical resistivity (ρₑ) | 0.22 × 10⁻⁶ | Ω·m | At 20 °C, typical for low-alloy steel |
EN10025-4 S420ML Steel Mechanical Properties
The mechanical properties of S420ML are guaranteed for transverse test pieces (unless otherwise agreed). The minimum yield strength, tensile strength, and elongation are thickness-dependent. Impact toughness is verified at -50 °C (designation L). Bending tests are mandatory with specified mandrel diameters depending on thickness. All test results must comply with the values given in EN 10025-4.
| Property | Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield strength (ReH) | ≥420 | MPa | Nominal thickness ≤16 mm |
| Yield strength (ReH) | ≥400 | MPa | Nominal thickness >16 mm ≤40 mm |
| Yield strength (ReH) | ≥390 | MPa | Nominal thickness >40 mm ≤63 mm |
| Yield strength (ReH) | ≥370 | MPa | Nominal thickness >63 mm ≤80 mm |
| Yield strength (ReH) | ≥360 | MPa | Nominal thickness >80 mm ≤100 mm |
| Yield strength (ReH) | ≥340 | MPa | Nominal thickness >100 mm ≤120 mm |
| Tensile strength (Rm) | 520 – 680 | MPa | Nominal thickness ≤40 mm |
| Tensile strength (Rm) | 500 – 660 | MPa | Nominal thickness >40 mm ≤100 mm |
| Tensile strength (Rm) | 480 – 640 | MPa | Nominal thickness >100 mm ≤120 mm |
| Elongation after fracture (A) | ≥19 | % | Gauge length L₀=5.65√S₀ (L₀=80 mm for thickness >3 mm); transverse, thickness ≤40 mm |
| Elongation after fracture (A) | ≥18 | % | Transverse, thickness >40 mm ≤63 mm |
| Elongation after fracture (A) | ≥17 | % | Transverse, thickness >63 mm ≤100 mm |
| Elongation after fracture (A) | ≥17 | % | Transverse, thickness >100 mm ≤120 mm |
| Impact energy (KV) | ≥27 | J | Longitudinal or transverse, -50 °C, 10×10 mm specimen |
| Bending test (mandrel diameter) | 2t (t ≤16 mm) | - | Bend angle 180°; t = specimen thickness |
| Bending test (mandrel diameter) | 3t (16 < t ≤40 mm) | - | Bend angle 180° |
| Bending test (mandrel diameter) | 3.5t (40 < t ≤63 mm) | - | Bend angle 180° |
| Bending test (mandrel diameter) | 4t (63 < t ≤100 mm) | - | Bend angle 180° |
| Bending test (mandrel diameter) | 5t (100 < t ≤120 mm) | - | Bend angle 180° |
EN10025-4 S420ML Steel Fully Equivalent Material Standards and Substitute Grades
| Country/Region | Standard | Grade | Notes |
|---|---|---|---|
| European Union | EN 10025-4 | S420ML | Original grade; M = TMCP, L = -50 °C impact |
| International | ISO 24314 | S420ML | Structurally identical; adopts the same designation |
| Germany | DIN EN 10025-4 | S420ML | National adoption of EN standard |
| France | NF EN 10025-4 | S420ML | National adoption of EN standard |
| United Kingdom | BS EN 10025-4 | S420ML | National adoption of EN standard |
| Italy | UNI EN 10025-4 | S420ML | National adoption of EN standard |
| Spain | UNE EN 10025-4 | S420ML | National adoption of EN standard |
| Sweden | SS-EN 10025-4 | S420ML | National adoption of EN standard |
| Poland | PN-EN 10025-4 | S420ML | National adoption of EN standard |
| Japan | JIS G 3106 | SM490B? (not fully equivalent) | SM490B has yield 325 MPa, only similar if considering S420ML. No direct TMCP equivalent with L-impact. |
| China | GB/T 19879 | Q420GJ? (not direct) | No exact match; Q420GJ has C ≤0.20 and impact at -20 °C or -40 °C. |
EN10025-4 S420ML Steel Application Introduction
S420ML is specifically designed for welded steel structures that require high strength, good toughness at low temperatures, and excellent weldability. Thanks to the thermo-mechanical rolling process, the steel achieves fine grain refinement without the need for heat treatment after rolling. This makes it cost-effective for large welded components where preheating should be minimized. The guaranteed impact energy at -50 °C ensures safe application in cold climates and offshore environments.
Product Applications: Welded bridge girders and box sections, Offshore platform legs and decks, Heavy crane booms and lifting equipment, Wind turbine towers and foundations, Heavy-duty vehicle chassis, Pressure vessels (when additional HIC/SSC requirements are met), Steel pipes for structural applications, Shipbuilding components (if certified by classification societies)
Processed into products: Plate girders, Column and beam assemblies, Crane runway beams, Boom segments for mobile cranes, Submerged arc welded main frames, Welded tubular joints, Flanges and web plates, Earthmoving bucket parts, Offshore module structural elements
Application industries: Bridge construction, Heavy machinery and crane manufacturing, Offshore and marine engineering (platforms, wind turbine foundations), Civil engineering and building construction (high-rise, stadiums), Transport and vehicle manufacturing (heavy trucks, trailers, rail cars), Mining and earthmoving equipment, Pressure vessel and boiler fabrication (if supplementary certifications apply)
EN10025-4 S420ML Steel Similar and Closely Related Material Grades
| Country/Region | Standard | Grade | Notes |
|---|---|---|---|
| European Union | EN 10025-4 | S420M | Same strength, M = TMCP, but impact at -20 °C instead of -50 °C |
| European Union | EN 10025-3 | S420N | Normalized rolled fine-grain steel, impact at -20 °C |
| European Union | EN 10025-3 | S420NL | Normalized rolled, impact at -50 °C; chemical composition and toughness differ from TMCP grade |
| European Union | EN 10025-4 | S460ML | Higher strength (460 MPa yield), same TMCP delivery and -50 °C impact |
| European Union | EN 10025-6 | S420QL | Quenched and tempered steel, higher carbon content, impact at -50 °C, different weldability |
| International | ISO 4951-2 | S420M, S420ML | Similar high-strength fine-grain steels for structural use |
| USA | ASTM A572/A572M | Grade 60 [415 MPa] | Only strength matches, no L-class impact guarantee, different production route |
| USA | ASTM A709/A709M | Grade 60 | Bridge steel with higher toughness zones, but not identical to TMCP S420ML |
| China | GB/T 1591 | Q420D, Q420E | Similar yield strength, Q420E has -40 °C impact, not quite -50 °C; non-TMCP delivery possible |
| Japan | JIS G 3106 | SM520C | Higher strength 520 MPa class, but not the same impact temperature combination |
Notes:
- S420ML is typically delivered with a mill test certificate according to EN 10204 Type 3.1 or 3.2 as agreed.
- The steel can be cold formed within limits; for severe forming, hot forming or stress-relief annealing may be considered, but the TMCP condition may be affected by reheating above 580 °C.
- Welding procedures should be qualified; low hydrogen welding consumables are recommended to avoid cold cracking. Preheating is generally not required for moderate thicknesses due to low CEV.
- The steel is fully killed and grain-refined; additional requirements for through-thickness properties (Z-quality) can be specified per EN 10164.
- For atmospheric corrosion resistance, grades with improved weathering properties (e.g., S420W) are available under EN 10025-5, but not covered in the -4 standard.
- All data is based on EN 10025-4:2019 edition. Earlier editions (2004) may have slightly different limits; always verify with the actual product standard.
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