S355NL
1.0546
Normalized or normalized-rolled weldable fine-grain structural steel; alloy quality steel under EN 10020 · EN 10025-3:2019 · EN 10025-1:2004 when supplied as a CE-marked construction product
S355NL is the low-temperature-toughness quality of the EN 10025-3 S355 fine-grain structural steel family. It combines a minimum yield strength of 355 MPa at thicknesses up to 16 mm with normalized or normalized-rolled delivery and a specified longitudinal Charpy V-notch minimum of 27 J at −50 °C. It is intended principally for heavily loaded welded structures operating at ambient or low temperatures, but strength, test orientation and some chemistry limits depend on product form and thickness.
- EN 10025-3:2019; steel number 1.0546Standard and identifier · The 2019 edition supersedes EN 10025-3:2004.
- Normalized or normalized rolledDelivery condition · The letter N identifies the delivery condition; normalizing rolling is intended to produce a condition equivalent to normalizing.
- Minimum 27 J longitudinal KV2 at −50 °CLow-temperature toughness · The L suffix distinguishes this quality from S355N, whose routine impact verification is at −20 °C.
- 355 MPa for nominal thickness ≤16 mmMinimum yield strength · The specified minimum decreases progressively with thickness, reaching 275 MPa above 200 mm through 250 mm.
- 0.43% through 63 mm; 0.45% above 63 mm through 250 mmMaximum CEV · Based on heat analysis using the IIW carbon-equivalent formula; this is a weldability control, not a complete welding procedure.
- Hot-rolled flat and long products through 250 mmProduct scope · EN 10025-3 does not define structural hollow sections or fabricated components as product forms.
Overview
- Designation system
- EN 10027-1 steel name and EN 10027-2 steel number
- Product forms
- Hot-rolled plate, sheet, strip and wide flat, Hot-rolled sections, Bars and rod, Other flat and long products within EN 10025-3
- Condition
- Normalized, Normalized rolled
- Density
- 7850 kg/m³ (Volumetric mass specified by EN 10025-3 for calculating nominal mass; it is not a heat-specific measured density.)
What the designation means
| Element | Meaning | Practical significance |
|---|---|---|
| S | Structural steel | Identifies the intended structural application class. |
| 355 | Minimum specified yield strength of 355 MPa for nominal thickness ≤16 mm | It is not a universal yield value; lower minima apply to thicker material. |
| N | Normalized or normalized-rolled delivery condition | The required properties apply in this controlled metallurgical condition. |
| L | Low-temperature toughness quality | Routine impact verification is longitudinal Charpy V-notch testing at −50 °C. |
EN 10025-3 covers hot-rolled weldable fine-grain structural steels for heavily loaded welded structures at ambient and low temperatures. S355NL is fully killed, has a fine-grain structure and contains sufficient nitrogen-binding elements. The standard classifies S355 as an alloy quality steel under EN 10020, although in engineering practice it is commonly described as a low-alloy or microalloyed structural steel.
Specified chemical composition and weldability control
| Element | Flat products, mass % | Long products, mass % | Qualification |
|---|---|---|---|
| C | ≤0.18 | ≤0.18 | Maximum |
| Si | ≤0.50 | ≤0.50 | Maximum |
| Mn | 0.90–1.65 | 0.90–1.65 | Range |
| P | ≤0.025 | ≤0.030 | Long products are permitted 0.005 percentage point more. |
| S | ≤0.020 | ≤0.025 | Long products are permitted 0.005 percentage point more. |
| Nb | ≤0.05 | ≤0.05 | Maximum |
| V | ≤0.12 | ≤0.12 | Maximum |
| Al total | ≥0.020 | ≥0.020 | Minimum does not apply if sufficient other nitrogen-binding elements are present. |
| Ti | ≤0.05 | ≤0.05 | Maximum |
| Cr | ≤0.30 | ≤0.30 | Maximum |
| Ni | ≤0.50 | ≤0.50 | Maximum |
| Mo | ≤0.10 | ≤0.10 | Maximum |
| Cu | ≤0.55 | ≤0.55 | Maximum |
| N | ≤0.015 | ≤0.015 | Maximum |
Additional combined limits apply: V + Nb + Ti ≤0.22% and Mo + Cr ≤0.30%. Values are standard heat-analysis requirements, not a typical mill aim.
| Nominal thickness t | Maximum CEV |
|---|---|
| t ≤ 63 mm | 0.43% |
| 63 < t ≤ 100 mm | 0.45% |
| 100 < t ≤ 250 mm | 0.45% |
Special chemistry agreed for hot-dip galvanizing can increase the permitted CEV by 0.01 or 0.02 percentage point under the conditions specified in EN 10025-3.
Product analysis is not the default basis for acceptance. It must be ordered as an option, and the product-analysis tolerances differ from the heat-analysis limits. A product check should therefore be assessed against the applicable product-analysis table rather than directly against the heat limits.
Thickness-dependent tensile properties
| Nominal thickness t | Minimum ReH or Rp0.2 | Rm | Minimum elongation A |
|---|---|---|---|
| t ≤ 16 mm | 355 MPa | 470–630 MPa for t ≤100 mm | 22% |
| 16 < t ≤ 40 mm | 345 MPa | 470–630 MPa | 22% |
| 40 < t ≤ 63 mm | 335 MPa | 470–630 MPa | 22% |
| 63 < t ≤ 80 mm | 325 MPa | 470–630 MPa | 21% |
| 80 < t ≤ 100 mm | 315 MPa | 470–630 MPa | 21% |
| 100 < t ≤ 150 mm | 295 MPa | 450–600 MPa | 21% |
| 150 < t ≤ 200 mm | 285 MPa | 450–600 MPa | 21% |
| 200 < t ≤ 250 mm | 275 MPa | 450–600 MPa | 21% |
Elongation values shown use a proportional specimen with L0 = 5.65√S0. Thin flat products tested with a non-proportional specimen require attention to the applicable test-piece requirements.
For plate, strip and wide flats at least 600 mm wide, the tensile values apply to test pieces transverse to the rolling direction. For other products they apply parallel to the rolling direction. For irregular long-product sections, the controlling thickness is the thickness of the part from which the specimen is taken. These distinctions matter when reviewing certificates or comparing plate with sections and bars.
Impact toughness and low-temperature qualification
| Test temperature | Minimum absorbed energy |
|---|---|
| +20 °C | 63 J |
| 0 °C | 55 J |
| −10 °C | 51 J |
| −20 °C | 47 J |
| −30 °C | 40 J |
| −40 °C | 31 J |
| −50 °C | 27 J |
Routine verification for the NL quality is at −50 °C. Testing at another listed temperature can be agreed at the time of order.
The standard requirement is based on longitudinal specimens. Transverse Charpy testing is a separate ordering option and has lower specified energy values; for S355NL the corresponding transverse minimum at −50 °C is 16 J. A project requiring transverse toughness must state this explicitly rather than assuming that the NL suffix provides it.
Impact testing is subject to product-size limitations. For flat products and sections below 6 mm, no impact test is required. Reduced-width specimens may be used where full-size specimens cannot be machined, with minimum energy reduced in proportion to specimen cross-sectional area. Bars and rod have separate dimensional thresholds. Consequently, an S355NL certificate does not necessarily contain a measured −50 °C result for every thin product.
Fabrication implications
S355NL is specified as weldable, with general arc-welding practice governed by EN 1011-2. The CEV limits support weldability but do not eliminate hydrogen-assisted cold-cracking risk. Procedure qualification, consumable hydrogen level, heat input, preheat or interpass temperature and post-weld control should be based on actual certificate chemistry, combined thickness, restraint, joint design and required heat-affected-zone toughness. Increasing thickness and restraint generally increase the level of control required.
Flat and bar products can retain the specified mechanical properties after normalizing following delivery, or after controlled hot forming satisfying the relevant guidance. Uncontrolled heating can alter the normalized fine-grain condition. Stress relief above 580 °C or for more than one hour may impair mechanical properties; for flat products EN 10025-3 recommends a maximum stress-relief temperature of 560 °C. Higher temperatures or longer holding times require agreed post-treatment properties.
Cold forming reduces ductility and can affect brittle-fracture resistance. Flangeability of S355 flat products through 16 mm and roll-forming suitability through 8 mm are optional requirements rather than automatic characteristics of every order. If hot-dip galvanizing is intended, the coating process and steel chemistry should be coordinated at enquiry stage; EN 10025-3 provides a specific option for controlling silicon and phosphorus.
Inspection, testing and certification
S355NL is supplied with specific inspection and testing. The purchaser must specify the required EN 10204 inspection document. Heat analysis, tensile testing and impact testing—subject to product-size limitations—form the basic verification. Mechanical testing is performed by test units within each cast, normally 60 tonnes or part thereof, with larger test units permitted for specified heavy-section cases.
| Certificate item | Why it matters |
|---|---|
| Complete designation | Confirm EN 10025-3, S355NL or 1.0546 and the applicable edition. |
| Product form and dimensions | Strength minima, sampling and P/S limits can depend on thickness and product form. |
| Delivery condition | Confirm normalized or normalized rolled, rather than assuming any hot-rolled S355 condition is acceptable. |
| Heat chemistry and CEV | Check both individual limits and the applicable thickness-dependent CEV maximum. |
| Tensile orientation and results | Confirm that the specimen orientation and controlling thickness are appropriate to the product. |
| Charpy orientation, temperature and specimen size | Verify longitudinal or specified transverse testing, −50 °C where required, and whether full-size or reduced specimens were used. |
| Traceability | Heat and product identification must remain linked to the material after cutting and fabrication. |
| Additional options | Check ultrasonic testing, through-thickness properties, parent-plate testing, surface class or forming requirements where ordered. |
Specifying and purchasing S355NL
A complete order should identify quantity, product form, dimensional standard, dimensions and tolerances, EN 10025-3 S355NL or 1.0546, the required EN 10204 inspection document and every project-specific option. Plate orders should also address the required EN 10029 tolerance class; the basic EN 10025-3 requirement is thickness tolerance class A unless another class is agreed.
| Requirement | How it is addressed |
|---|---|
| Through-thickness ductility | Specify an EN 10164 quality such as Z15, Z25 or Z35 where lamellar-tearing resistance is required. |
| Internal soundness | Specify ultrasonic testing and the applicable acceptance class for plate, sections or bars. |
| Transverse impact toughness | Invoke the EN 10025-3 transverse-impact option and state the required test temperature. |
| Per-parent-plate or per-coil testing | Order the relevant option if routine test-unit verification is insufficient. |
| Product analysis | Specify the option and required sampling frequency. |
| Cold-forming suitability | Order flangeability or roll-forming suitability where required. |
| Galvanizing response | Agree the silicon/phosphorus chemistry option and coating specification. |
| Enhanced surface condition | State the required EN 10163 class and subclass rather than relying on the basic class. |
| Low sulfur for special applications | Where justified, agree the optional tighter sulfur limit at enquiry and order. |
Availability of particular combinations of thickness, product form and options should be established with the producer before finalizing the design or purchase specification.
Do not accept a certificate stating only “S355” or substitute another S355 quality solely because its room-temperature yield strength is similar. The product standard, delivery condition, low-temperature impact requirement, test orientation, thickness range and certification must all match the application.
Sources
- BS EN 10025-3:2019 — Hot rolled products of structural steels: Technical delivery conditions for normalized/normalized rolled weldable fine grain structural steelsBritish Standards Institution
- DIN EN 10025-3:2019-10 — Hot rolled products of structural steels, Part 3DIN Media
- SIST EN 10025-3:2019 — Standard overview and previewSlovenian Institute for Standardization / iTeh Standards
- BS EN 10025-1:2004 — General technical delivery conditionsBritish Standards Institution
- Declaration of Performance 1.0546 S355NL to EN 10025-3:2019Marcegaglia Plates
- S355NL / 1.0546 hexagonal bar Declaration of PerformanceSaarstahl AG
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