S355K2
1.0596
Hot-rolled non-alloy quality structural steel with specified notch toughness · EN 10025-2:2019 · EN 10025-1:2004
S355K2 is the high-toughness K2 quality of the S355 non-alloy structural-steel family in EN 10025-2. It combines a minimum yield strength of 355 MPa at thicknesses up to 16 mm with longitudinal Charpy V-notch energy of 40 J at −20 °C up to 150 mm. Strength, ductility, toughness and carbon-equivalent limits depend on product thickness, while delivery condition, product form, inspection document and optional testing must be stated or agreed when ordering.
- 1.0596Steel number · Assigned under EN 10027-2.
- S = structural steel; 355 = minimum yield strength at t ≤ 16 mm; K2 = 40 J at −20 °CDesignation meaning · The 355 MPa value does not apply at all thicknesses.
- 40 J at −20 °C for t ≤ 150 mmSpecified toughness · Longitudinal KV2 specimens; 33 J applies to flat products above 150 mm.
- Flat products: 400 mm; long products: 250 mmMaximum product thickness · Impact values for sections above 100 mm must be agreed at order.
- Fully killed steel, designation FFMetallurgical quality · Nitrogen-binding elements are required.
- 0.45–0.49% depending on thicknessMaximum CEV · IIW carbon equivalent based on heat analysis; special galvanizing or copper options can increase the permitted value.
Overview
- Designation system
- EN 10027-1 steel name; EN 10027-2 steel number
- Product forms
- Hot-rolled plate and sheet, Hot-rolled strip and plate cut from strip, Wide flats and flats, Hot-rolled sections, Bars and rod, Semi-finished products intended for further rolling, subject to agreement
- Condition
- +AR — as rolled, +N — normalized or normalized rolled, +M — thermomechanically rolled; available for long products and hot-rolled strip, not quarto plate under EN 10025-2
- Density
- 7850 kg/m³ (Volumetric mass used by EN 10025-2 for calculating nominal product mass; not a heat-specific measured density.)
Designation, scope and product-form limits
S355K2 is defined by EN 10025-2, which covers hot-rolled flat and long products of non-alloy structural steels. The designation is not a chemistry-only grade: conformity requires the applicable chemical composition, thickness-dependent tensile properties, K2 impact performance, manufacturing condition, inspection and dimensional requirements of the ordered product.
| Element | Meaning | Practical significance |
|---|---|---|
| S | Structural steel | Distinguishes it from the E-series engineering steels also covered by EN 10025-2. |
| 355 | Minimum specified yield strength of 355 MPa for nominal thickness ≤ 16 mm | Minimum yield strength decreases progressively as thickness increases. |
| K2 | Specified longitudinal Charpy V-notch toughness of 40 J at −20 °C for the principal thickness range | A higher toughness requirement than S355J2, which specifies 27 J at −20 °C. |
The EN 10025-2 scope extends to 400 mm for flat products of K2 quality and to 250 mm for S355K2 long products. Tubes and structural hollow sections are not supplied as EN 10025-2 S355K2; they require the appropriate hollow-section or tube standard, even where a similar-looking grade designation exists.
Chemical composition and weldability controls
| Element | Nominal thickness | Maximum mass fraction |
|---|---|---|
| C | ≤ 16 mm | 0.20% |
| C | > 16 to 30 mm | 0.20% |
| C | > 30 mm | 0.22% |
| Si | All applicable thicknesses | 0.55% |
| Mn | All applicable thicknesses | 1.60% |
| P | All applicable thicknesses | 0.025% |
| S | All applicable thicknesses | 0.025% |
| Cu | All applicable thicknesses | 0.55% |
S355K2 is fully killed. Nitrogen is not assigned a simple maximum because sufficient nitrogen-binding elements must be present. For long products, particular footnote allowances can apply to P and S.
| Element | Nominal thickness | Maximum mass fraction |
|---|---|---|
| C | ≤ 16 mm | 0.23% |
| C | > 16 to 30 mm | 0.23% |
| C | > 30 mm | 0.24% |
| Si | All applicable thicknesses | 0.60% |
| Mn | All applicable thicknesses | 1.70% |
| P | All applicable thicknesses | 0.035% |
| S | All applicable thicknesses | 0.035% |
| Cu | All applicable thicknesses | 0.60% |
These are product-analysis limits, not target compositions. Product analysis is an order option rather than an automatic requirement.
| Nominal product thickness (%) | ≤ 30 mm | > 30 to 40 mm | > 40 to 150 mm | > 150 to 250 mm | > 250 to 400 mm |
|---|---|---|---|---|---|
| Maximum CEV by nominal thickness | 0.45% | 0.47% | 0.47% | 0.49% | 0.49% |
For long products above 150 mm, the standard includes a higher special limit in the relevant table note. Copper-alloyed or controlled-silicon galvanizing options can also increase the permitted CEV.
S355K2 is generally weldable by conventional structural-steel processes, but the grade name does not determine preheat or consumable practice. Welding procedure development should consider the actual inspection-certificate chemistry, CEV, combined thickness, heat input, diffusible hydrogen, restraint and ambient temperature. EN 10025-2 refers arc-welding practice to EN 1011-2. Increasing thickness and restraint increases the risk of hydrogen-assisted cold cracking.
Thickness-dependent tensile properties
| Nominal thickness | Minimum ReH or Rp0.2 | Tensile strength Rm |
|---|---|---|
| < 3 mm | 355 MPa for the ≤ 16 mm yield band | 510–680 MPa |
| 3 to 16 mm | 355 MPa | 470–630 MPa |
| > 16 to 40 mm | 345 MPa | 470–630 MPa |
| > 40 to 63 mm | 335 MPa | 470–630 MPa |
| > 63 to 80 mm | 325 MPa | 470–630 MPa |
| > 80 to 100 mm | 315 MPa | 470–630 MPa |
| > 100 to 150 mm | 295 MPa | 450–600 MPa |
| > 150 to 200 mm | 285 MPa | 450–600 MPa |
| > 200 to 250 mm | 275 MPa | 450–600 MPa |
| > 250 to 400 mm | 265 MPa | 450–600 MPa |
The >250 to 400 mm band applies to flat products. ReH is determined where a yield phenomenon is present; otherwise Rp0.2 is used.
| Nominal thickness | Longitudinal A min. | Transverse A min. |
|---|---|---|
| 3 to 40 mm | 22% | 20% |
| > 40 to 63 mm | 21% | 19% |
| > 63 to 100 mm | 20% | 18% |
| > 100 to 150 mm | 18% | 18% |
| > 150 to 250 mm | 17% | 17% |
| > 250 to 400 mm | 17% | 17% |
For plate, strip and wide flats at least 600 mm wide, tensile specimens are normally transverse to the rolling direction. For other products the longitudinal direction applies.
The designation S355 must not be interpreted as guaranteeing 355 MPa yield strength in thick plate or heavy sections. Design and purchasing documents should use the property band corresponding to the actual nominal thickness.
K2 toughness and Charpy testing
| Nominal thickness | Minimum average KV2 energy | Applicability |
|---|---|---|
| ≤ 150 mm | 40 J | Flat and long products, subject to specimen-size limitations; values for sections above 100 mm must be agreed. |
| > 150 to 250 mm | 33 J | Flat products only. |
| > 250 to 400 mm | 33 J | Flat products only. |
The requirement is the average of three tests. One result may be below the specified average provided it is not below 70% of that value; the standard contains retest rules where initial results do not comply.
The K2 suffix describes a standardized Charpy performance, not a complete brittle-fracture assessment or a general minimum service temperature. Permissible thickness at a given design temperature also depends on stress level, detail category, strain rate, fabrication, residual stress and the applicable structural design code.
No impact test is required where a usable specimen cannot be obtained under the standard's dimensional rules: generally below 6 mm for flat products and sections, below 16 mm diameter for round bars, or below 12 mm thickness for rectangular bars. Where reduced-width specimens are used, the specified energy is reduced in direct proportion to specimen cross-sectional area.
S355K2 provides a higher specified energy at −20 °C than S355J2, but it does not introduce a lower test temperature. Selection between J2, K2 and fine-grain grades should therefore follow the governing fracture-toughness rules rather than designation shorthand alone.
Delivery condition and subsequent thermal processing
| Condition | Description | Product-form considerations |
|---|---|---|
| +AR | Conventional as-rolled condition | Permitted for long products, strip and quarto plate. |
| +N | Normalized or normalized rolled condition | Permitted for long products, strip and quarto plate; most appropriate where later normalizing or hot forming is intended. |
| +M | Thermomechanically rolled condition | Permitted for long products and hot-rolled strip; not a delivery condition for quarto plate under this specification. |
Unless a condition is ordered, the manufacturer may select among the conditions permitted for the product form. EN 10025-2 applies the same mechanical-property tables to each permitted condition.
Products in +AR or +M condition should not be assumed suitable for subsequent normalizing or hot forming without manufacturer confirmation. Only products supplied in +N are required to retain the tabulated properties after normalizing or properly controlled hot forming. Thermomechanically rolled properties cannot necessarily be recreated by later heat treatment.
Stress relieving is accepted, but exposure above 580 °C or for more than one hour can degrade mechanical properties. For normalized or normalized-rolled flat products, the standard recommends a maximum stress-relief temperature of 560 °C unless properties after the proposed treatment are agreed at order. Flame straightening, rerolling and uncontrolled heat treatment can likewise alter strength or toughness.
Forming, galvanizing and through-thickness performance
Ordinary S355K2 should not be confused with S355K2C. The C suffix identifies a separately numbered variant for which suitability for specified cold-forming applications can be ordered. If guaranteed flanging, roll forming or cold drawing is required, the appropriate C grade and applicable EN 10025-2 option should be specified rather than relying on the general ductility of S355K2.
For hot-dip galvanizing, coating requirements are specified using EN ISO 1461, while the steel composition can be ordered under the EN 10025-2 galvanizing option. Silicon and phosphorus affect coating growth and appearance. Composition controls selected for galvanizing may permit a small increase in maximum CEV, so the agreed chemistry should be recorded in the purchase specification.
Standard tensile and Charpy requirements do not guarantee resistance to lamellar tearing. Where welded details impose significant strain through the plate thickness, improved deformation properties should be ordered to EN 10164, for example an appropriate Z-quality, using the relevant EN 10025-2 option.
Ordering, inspection and acceptance
| Item | What to specify or verify |
|---|---|
| Product and dimensions | Plate, strip, section, bar or other form; nominal dimensions; dimensional and shape tolerance standard. |
| Full grade designation | EN 10025-2 — S355K2 or 1.0596, including +AR, +N or +M when a particular condition is required. |
| Inspection document | Required EN 10204 document type, commonly 3.1 where product-specific certified results and traceability are needed. |
| Impact testing | Confirm test temperature, orientation, thickness applicability and whether verification from each parent plate or coil is required. |
| Optional testing | Product analysis, ultrasonic testing, through-thickness properties, special surface class or additional inspection as applicable. |
| Fabrication requirements | Cold-forming variant, galvanizing-compatible chemistry, weldability restrictions or post-delivery thermal treatment. |
| Certification and marking | Heat identity, grade, quality, delivery condition and manufacturer identification. |
| Project requirements | Any stricter toughness, chemistry, traceability or testing provisions imposed by the design or execution specification. |
Under specific inspection, EN 10025-2 requires heat analysis, tensile testing and—subject to dimensional limitations—impact testing for K2 products. Mechanical-property testing is normally performed by test unit rather than on every individual plate or section. For flat K2 products, testing from each parent plate or coil is available only when the corresponding order option is invoked.
Dimensional tolerances are governed by the standard appropriate to the product form, not by the grade designation alone. Examples include EN 10029 for hot-rolled plate, EN 10051 for continuously rolled strip and cut lengths, and EN 10365 for common channels and I/H sections. Internal soundness is not universally guaranteed: ultrasonic acceptance must be specified using the applicable option and test standard where required.
Sources
- BS EN 10025-2:2019 — Hot rolled products of structural steels: Technical delivery conditions for non-alloy structural steelsBSI
- SIST EN 10025-2:2019 — EN 10025-2:2019 previewSlovenian Institute for Standardization
- EN 10025-2:2019 — Scope and technical delivery conditionsUNI — Ente Italiano di Normazione
- Declaration of Performance No. 1.0596 — S355K2 to EN 10025-2:2019Marcegaglia
- Guidance Note 3.01 — Structural steel grades and subgradesSteel Construction Institute
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