S460ML
1.8838
Thermomechanically rolled weldable fine-grain structural steel · EN 10025-4:2019+A1:2022 · EN 10025-1 for Construction Products Regulation applications
S460ML is a 460 MPa-class, thermomechanically rolled fine-grain structural steel for heavily loaded welded structures requiring specified low-temperature toughness. Its principal advantages are high strength, a controlled carbon equivalent and longitudinal Charpy requirements extending to −50 °C. The strength depends on product thickness, and the TMCP delivery condition imposes important restrictions on hot forming and subsequent thermal treatment.
- 460 MPa at nominal thickness ≤16 mmMinimum yield strength · The specified minimum falls progressively to 385 MPa for thicknesses over 100 mm up to 150 mm.
- Longitudinal KV2 ≥27 J at −50 °CLow-temperature toughness · This is the defining ML quality requirement; transverse impact properties require a separate ordering option.
- Thermomechanically rolledDelivery condition · The property combination cannot be reproduced by heat treatment alone.
- Nominal thickness ≤150 mmThickness scope · Applies to covered flat and long products; actual mill availability may be narrower.
- 0.45–0.48%Maximum CEV · IIW carbon-equivalent limit increases with nominal thickness.
- Hot forming prohibited by the product standardThermal-processing restriction · Stress relieving above 580 °C or longer than one hour can also impair properties.
Overview
- Designation system
- Steel name to EN 10027-1; steel number to EN 10027-2
- Product forms
- Hot-rolled plate, sheet, strip and wide flats, Hot-rolled structural sections, Hot-rolled bars and rod
- Condition
- Thermomechanically rolled condition (M/TMCP), ML low-temperature impact quality
- Density
- 7850 kg/m³ (Volumetric mass specified by EN 10025-4 for calculating nominal product mass; it is not a heat-specific measured property.)
What the designation means
The designation is property-based. “S” identifies structural steel; “460” is the minimum specified upper yield strength in MPa for nominal thickness up to 16 mm; “M” identifies the thermomechanically rolled delivery condition; and “L” identifies the quality having specified impact-energy values down to −50 °C. The corresponding numerical designation is 1.8838.
EN 10025-4 covers hot-rolled flat and long products in nominal thicknesses up to 150 mm. S460ML is classified as an alloy special steel under EN 10020, although its useful combination of strength and weldability is obtained mainly through fine-grain metallurgy and controlled thermomechanical rolling rather than heavy alloying. The steel is fully killed, has a fine-grain structure and contains sufficient nitrogen-binding elements.
Chemical composition and carbon equivalent
| Element | Requirement, mass % |
|---|---|
| C | ≤0.18 |
| Si | ≤0.60 |
| Mn | ≤1.70 |
| P | ≤0.030 |
| S | ≤0.025 |
| Al total | ≥0.020, unless sufficient other nitrogen-binding elements are present |
| Nb | ≤0.05 |
| V | ≤0.12 |
| Ti | ≤0.05 |
| Cr | ≤0.30 |
| Ni | ≤0.80 |
| Mo | ≤0.20 |
| Cu | ≤0.55 |
| N | ≤0.025 |
For long products, the permitted P and S limits may each be 0.005 percentage point higher. Product-analysis limits are separate and apply only when product analysis is ordered.
| Nominal product thickness (%) | ≤16 mm | >16 to 40 mm | >40 to 63 mm | >63 to 150 mm |
|---|---|---|---|---|
| Maximum CEV by nominal thickness | 0.45 | 0.46 | 0.47 | 0.48 |
For compositions specially controlled for hot-dip galvanizing under Option 5, the permitted CEV can be increased by 0.01 or 0.02 percentage point, depending on the specified silicon range.
The composition table defines permitted limits, not a target recipe. Actual heats are normally optimized by the producer for strength, toughness, rolling route and weldability. Welding assessments should therefore use the certified heat analysis and actual product thickness rather than assuming that every S460ML heat has the maximum permitted CEV.
Room-temperature tensile properties
| Nominal thickness t | Minimum ReH or Rp0.2 | Tensile strength Rm | Minimum elongation A |
|---|---|---|---|
| t ≤16 mm | 460 MPa | 540–720 MPa | 17% |
| >16 to 40 mm | 440 MPa | 540–720 MPa | 17% |
| >40 to 63 mm | 430 MPa | 530–710 MPa | 17% |
| >63 to 80 mm | 410 MPa | 510–690 MPa | 17% |
| >80 to 100 mm | 400 MPa | 500–680 MPa | 17% |
| >100 to 150 mm | 385 MPa | 490–660 MPa | 17% |
A is based on proportional test pieces with L0 = 5.65√S0. For products thinner than 3 mm using L0 = 80 mm, elongation values are agreed when ordering.
For plate, strip and wide flats at least 600 mm wide, the tensile-test direction is transverse to rolling. For other products, the tabulated values apply to longitudinal test pieces. For irregular long-product sections, the controlling thickness is that of the part from which the sample is taken.
The number 460 in the grade name must not be applied indiscriminately to thick material. Structural calculations, purchase specifications and material substitutions must use the yield strength associated with the actual nominal thickness and relevant product location.
Impact toughness and test orientation
| Test temperature (J) | +20 °C | 0 °C | −10 °C | −20 °C | −30 °C | −40 °C | −50 °C |
|---|---|---|---|---|---|---|---|
| Minimum longitudinal Charpy V-notch energy | 63 | 55 | 51 | 47 | 40 | 31 | 27 |
The normal verification temperature for ML quality is −50 °C. Another tabulated temperature can be agreed at the time of order.
| Test temperature (J) | +20 °C | 0 °C | −10 °C | −20 °C | −30 °C | −40 °C | −50 °C |
|---|---|---|---|---|---|---|---|
| Minimum transverse Charpy V-notch energy — Option 30 | 40 | 34 | 30 | 27 | 23 | 20 | 16 |
Transverse verification is not the basic requirement. It must be specified at the time of order and is performed instead of the normal longitudinal verification.
The impact requirement is an average for a set of three specimens. One individual result may be below the specified average provided it is at least 70% of that value. Subsize-specimen requirements are reduced in direct proportion to specimen cross-sectional area. Impact testing is not required for flat products and sections below 6 mm thickness, or for bars and rod below the dimensional thresholds stated in the standard.
ML is a material-quality designation, not a complete brittle-fracture assessment. Permissible service temperature still depends on design stress, detail category, thickness, strain rate, fabrication history and the applicable structural design standard.
Welding and thermal processing
S460ML is specified as suitable for welding, with general arc-welding recommendations taken from EN 1011-2. Thermomechanical processing generally permits a more favorable composition than normalized steel at the same strength level, but it does not remove the risk of hydrogen-assisted cold cracking. Welding procedure qualification should address actual CEV, thickness, restraint, diffusible hydrogen, consumable strength and toughness, heat input, preheat or interpass requirements, and the required properties of the weld and heat-affected zone.
| Operation | Standard-related implication |
|---|---|
| Hot forming | Shall not be undertaken; the delivered TMCP condition is not suitable for hot forming. |
| Stress relieving | Treatment above 580 °C or longer than 1 hour may deteriorate mechanical properties. Required post-treatment properties should be agreed when ordering. |
| Cold forming | Reduces ductility and requires appropriate bend design and procedure control. |
| Optional flangeability | For specified flat products up to 12 mm, Option 11 provides minimum bend radii of 4t with the bend axis transverse to rolling and 5t with the axis longitudinal to rolling. |
| Optional roll forming | Option 12 applies to plate, sheet and strip up to 8 mm, using the specified flangeability radii. |
| Flame straightening | Use controlled procedures consistent with CEN/TR 10347 and producer guidance; uncontrolled heating can impair the TMCP property balance. |
Optional forming guarantees apply only when explicitly specified in the order.
If hot-dip galvanizing is intended, Option 5 allows agreement of silicon and phosphorus ranges suited to coating formation. Galvanizing requirements, prior cold work, local stress concentration and the risk of brittle behavior should be considered together rather than treating coating compatibility as a chemical-composition issue alone.
Product control, testing and ordering
An order should state the quantity, product form, dimensional and tolerance standard, nominal dimensions, full designation EN 10025-4 — S460ML or EN 10025-4 — 1.8838, required inspection and testing options, and the EN 10204 inspection-document type. The required document type should be taken from the project or fabrication standard rather than assumed from the grade alone.
| Requirement | Ordering implication |
|---|---|
| Product analysis | Option 2; specify sampling frequency if other than once per cast. |
| Through-thickness ductility | Option 4; specify the required EN 10164 Z-quality where lamellar-tearing resistance is needed. |
| Galvanizing composition | Option 5; agree the applicable Si/P category. |
| Ultrasonic examination | Options 6, 7 or 8, depending on flat product, relevant section type or bar; state the required acceptance class. |
| Per-parent plate or coil testing | Option 13 for impact testing, or Option 14 for impact and tensile testing. |
| Transverse impact testing | Option 30; state test orientation and temperature clearly. |
| Alternative impact temperature | Option 24; state the required test temperature. |
| Surface quality | Specify any class different from the standard default for plate, wide flat, section, bar or rod. |
| Plate tolerances | Hot-rolled plate defaults to EN 10029 thickness tolerance class A unless another class is agreed. |
| Special sulfur limit | Option 32 permits agreement of S ≤0.010% by heat analysis for applications requiring enhanced sulfur control. |
Acceptance classes and options should be selected from the design, fatigue, fabrication and inspection requirements of the specific structure.
Basic mechanical verification is normally by test units within each cast: 60 tonnes or part thereof, with specified 80-tonne provisions for certain heavy sections. A test unit contains products of the same form, grade, quality and yield-strength thickness range. This is not the same as testing every individual plate or section; use the per-parent plate or coil options where that level of traceability is required.
Check commercial availability before finalizing the design. EN 10025-4 permits both flat and long products to 150 mm, but individual mills may offer S460ML only in selected forms, dimensions and thickness ranges.
Substitution boundaries
A matching nominal yield-strength number does not establish equivalence. Substitution must consider the product standard, delivery condition, thickness-dependent strength, impact quality and orientation, product form, dimensional tolerances, composition and CEV, inspection documents, test frequency and any project options. In particular, normalized, quenched-and-tempered, cold-forming and hollow-section grades carrying “S460” are materially and contractually different products.
Sources
- BS EN 10025-4:2019+A1:2022 — Hot rolled products of structural steels, Part 4British Standards Institution
- DIN EN 10025-4:2023-02DIN Media
- SIST EN 10025-4:2019+A1:2023 previewSlovenian Institute for Standardization
- S460ML Declaration of PerformanceArcelorMittal
- S460M/ML technical informationArcelorMittal Europe – Flat Products
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