Grade A
Weldable ordinary-strength carbon-manganese hull structural steel · IACS UR W11 Rev.9, Normal and higher strength hull structural steels · Applicable classification-society rules implementing IACS UR W11 · IACS UR W2 for mechanical testing · IACS UR W17 for approved welding consumables
Grade A is the baseline 235 MPa minimum-yield hull structural steel in the IACS ordinary-strength series. Its distinguishing feature is not higher strength but its relatively limited specified notch-toughness assurance: Charpy testing is generally absent at 50 mm thickness and below, while thicker products are subject to delivery-condition-dependent requirements. Correct specification therefore requires the classification society, product form, thickness, delivery condition and certification basis—not merely the words “Grade A.”
- 235 MPaMinimum yield strength · Upper yield strength ReH, or 0.2% proof strength where ReH cannot be determined.
- 400–520 MPaTensile strength · The classification society may permit Grade A sections to exceed the upper limit.
- 22% minimumSpecified elongation · For proportional specimens with gauge length 5.65√S₀; different minima apply to specified 200 mm full-thickness specimens.
- No routine CVN requirement at t ≤ 50 mmToughness distinction · Grade A should not be assumed to possess a guaranteed Charpy energy at or below this thickness.
- Plate/wide flat ≤100 mm; sections/bars ≤50 mmStandard product range · Greater thickness requires case-specific consideration by the classification society.
- UR W11 Rev.9Current IACS edition · Current on October 1, 2026. Rev.10 is published but does not enter into force until January 1, 2027.
Overview
- Designation system
- IACS/classification-society hull structural steel designation
- Product forms
- Hot-rolled plate, Wide flat, Rolled section, Bar
- Condition
- As rolled, where permitted, Normalized, Controlled rolled/normalizing rolled, Thermo-mechanically rolled (TM/TMCP)
- Density
- 7850 kg/m³ (Representative engineering density for carbon steel; not a Grade A acceptance requirement.)
What the designation means
IACS UR W11 divides ordinary-strength hull structural steels into Grades A, B, D and E. All have the same nominal tensile-property level—235 MPa minimum yield strength and 400–520 MPa tensile strength—but differ principally in deoxidation, delivery-condition and notch-toughness requirements. Grade A is the least toughness-controlled member of this series.
UR W11 is a unified minimum requirement implemented through individual classification-society rules. The class rules, approved mill scope and project specification remain the controlling purchasing documents.
Grade selection for an actual ship structure is governed by the applicable hull rules and may depend on structural category, plate thickness, design temperature and location. The existence of an approved Grade A product does not establish that Grade A is acceptable for every hull member.
Chemistry and steelmaking requirements
| Element or relationship | Requirement | Applicability or qualification |
|---|---|---|
| Carbon, C | ≤0.21% | For sections, C may be as high as 0.23%. |
| Manganese, Mn | ≥2.5 × C | The numerical minimum depends on the actual carbon content. |
| Silicon, Si | ≤0.50% | Maximum. |
| Phosphorus, P | ≤0.035% | Maximum. |
| Sulfur, S | ≤0.035% | Maximum. |
| Aluminium | Not specified | Grade A does not have a general fine-grain aluminium minimum. |
| Other intentional additions | To be reported | The society may restrict residual elements detrimental to processing or service. |
These are grade requirements, not representative mill chemistry.
| Product/thickness | Requirement |
|---|---|
| Grade A products, t ≤50 mm | Any deoxidation method except rimmed steel. |
| Grade A products, t >50 mm | Killed steel. |
| Sections, t ≤12.5 mm | Rimmed steel may be accepted only with special classification-society approval. |
If specially approved rimmed Grade A sections are supplied, that fact is required to be stated in the documentation.
Delivery condition and thickness
| Product and thickness | Normal requirement | Important qualification |
|---|---|---|
| Plate or wide flat, t ≤50 mm | Any permitted condition | Commonly as rolled, normalized, controlled rolled or TM, subject to mill approval. |
| Plate or wide flat, 50 < t ≤100 mm | Normalized, controlled rolled or thermo-mechanically rolled | As-rolled supply requires special society approval and additional impact testing. |
| Sections and bars, t ≤50 mm | Any permitted condition | UR W11's normal scope for these product forms ends at 50 mm. |
| Products above the normal scope | Case-specific approval | Requirements may be varied or supplemented after review of the technical circumstances. |
“Any” does not mean that condition is commercially interchangeable without review. The approved manufacturing route and condition shown on the certificate must match the order.
TM/TMCP properties result from controlled deformation and temperature history and cannot necessarily be reproduced by subsequent normalizing or other heat treatment. Before hot forming, stress relieving or high-heat-input welding of TM material, the effect on mechanical properties must be assessed against the mill and classification-society approval.
Mechanical properties and testing
| Property | Requirement | Test qualification |
|---|---|---|
| Yield strength | ≥235 MPa | ReH, or Rp0.2 where an upper yield point cannot be determined. |
| Tensile strength | 400–520 MPa | The upper limit may be exceeded for Grade A sections at society discretion. |
| Elongation | ≥22% | Proportional specimen, L₀ = 5.65√S₀. |
These requirements apply throughout the normal UR W11 thickness range.
| Product thickness | Minimum elongation |
|---|---|
| t ≤5 mm | 14% |
| 5 < t ≤10 mm | 16% |
| 10 < t ≤15 mm | 17% |
| 15 < t ≤20 mm | 18% |
| 20 < t ≤25 mm | 19% |
| 25 < t ≤30 mm | 20% |
| 30 < t ≤40 mm | 21% |
| 40 < t ≤50 mm | 22% |
These values must not be confused with the 22% requirement for proportional specimens.
| Thickness | Test temperature | Minimum average energy, longitudinal | Minimum average energy, transverse | Key qualification |
|---|---|---|---|---|
| t ≤50 mm | — | Not routinely required | Not routinely required | Grade A at this thickness has no general guaranteed CVN energy. |
| 50 < t ≤70 mm | +20°C | 34 J | 24 J | Testing may be waived for fine-grain normalized material; TM waiver is at society discretion. |
| 70 < t ≤100 mm | +20°C | 41 J | 27 J | Same waiver provisions apply. |
| Nominal plate t <6 mm | — | Generally not required | Generally not required | General UR W11 exemption. |
| Product t <10 mm when testing is required | Specified grade temperature | Sub-size rules apply | Sub-size rules apply | Testing may instead be waived at society discretion. |
Values are based on standard 10 × 10 mm specimens. A set comprises three specimens; the average must comply and only one individual result may be below the average requirement, provided it is at least 70% of that requirement.
Longitudinal Charpy specimens are normally used. Transverse testing may be required by the purchaser or society, and the supplier must guarantee the transverse values. For products over 40 mm thick, impact specimens are taken at the quarter-thickness position rather than immediately below the rolled surface.
Surface quality and dimensional control
UR W11 requires freedom from defects prejudicial to the intended use and references recognized surface-quality standards such as EN 10163. Cracks, laminations, shells, sharp seams and similar injurious defects require repair or rejection regardless of their apparent size. Plate and wide-flat thickness tolerances are controlled separately by IACS UR W13.
Grinding repair is limited: nominal thickness may not be reduced by more than 7% or 3 mm, whichever is less, and the remaining thickness must still satisfy the applicable tolerance. Repair extent and verification are also controlled. Welding repair requires classification-society acceptance and must not be treated as an ordinary shop correction.
Welding and fabrication implications
Grade A is intended to be weldable, but the grade designation alone does not define preheat, heat input, consumable hydrogen level or allowable welding procedure. These depend on actual ladle chemistry, product thickness, joint restraint, welding process, ambient conditions and the approved fabrication rules. The WPS and consumables must be approved for the applicable classification society and structural application.
IACS UR W17 correlates approved consumable grades with hull structural-steel grades; Grade A is within the ordinary-strength consumable system. Higher toughness consumables may generally satisfy lower toughness categories, but strength matching, mixed-grade joints and any society-specific restrictions must still be checked. Do not select consumables solely from a commercial AWS or EN classification without confirming the corresponding class approval.
Cold forming and thermal straightening should follow the shipyard's approved procedures. Particular care is required where the supplied condition is TM/TMCP because uncontrolled reheating can remove the microstructural benefit created during rolling. Grade A's absence of routine CVN testing at common thicknesses should also be considered before severe forming, operation at low temperature or use in fracture-critical details.
Ordering, traceability and acceptance
| Item | Why it matters |
|---|---|
| Classification society and rule edition | Defines the controlling acceptance, survey and certification requirements. |
| Grade designation | State Grade A explicitly; avoid an unqualified order for “marine plate.” |
| Product form and dimensions | Requirements and normal scope differ between plate, wide flat, section and bar. |
| Delivery condition | Especially important above 50 mm and for any subsequent heat treatment or high-heat-input welding. |
| Approved manufacturer and thickness range | Class approval is specific to the mill, grade, product, condition and maximum approved thickness. |
| Impact testing | State any purchaser-required CVN testing, orientation, temperature and energy above the grade minimum. |
| Through-thickness quality | Order a suitable Z-quality separately where lamellar-tearing resistance is required. |
| Surface and dimensional quality | State any enhanced surface class, ultrasonic examination or tighter tolerance requirement. |
| Certification and survey | Require class-endorsed certification and traceability where the material forms part of a classed structure. |
Extra requirements must be stated in the purchase order; they do not arise automatically from the Grade A designation.
UR W11 certification includes the purchaser's order identification, cast and piece identification, steelworks, grade, specified ladle analysis, delivery condition when other than as rolled, applicable test results and the classification-society identity. Each finished piece is normally marked with the society brand, Grade A identification, steelworks identity and cast or piece number.
Limitations and substitution
Grade A should not be substituted merely on the basis of its 235 MPa yield strength. A building steel such as S235, ASTM A36 or another general structural steel may have different chemistry, toughness, product-condition, dimensional, survey and traceability requirements. Conversely, higher-strength ship steel is not automatically a drop-in replacement because scantlings, fatigue details, welding procedure, consumables and class approval may change.
ASTM A131/A131M Grade A is a closely related shipbuilding designation with the same ordinary-strength yield level, but it is a separate procurement specification. For example, ASTM A131/A131M-19 imposes delivery-condition provisions that are not identical to the IACS Rev.9 options. Material should be ordered and certified to the specification named by the design and classification documents rather than treated as automatically interchangeable.
Grade A is not a corrosion-resistant grade. Marine durability depends on coating, cathodic protection, corrosion additions, detailing, inspection and maintenance. Special corrosion-resistant hull-steel designations require separate qualification and marking.
Sources
- IACS UR W11 Rev.9 — Normal and higher strength hull structural steelsInternational Association of Classification Societies
- IACS UR W11 current and future versionsInternational Association of Classification Societies
- IACS UR W17 Rev.6 — Approval of consumables for welding normal and higher strength hull structural steelsInternational Association of Classification Societies
- ABS Rules for Materials and Welding, Part 2American Bureau of Shipping
- ASTM A131/A131M-19 — Standard Specification for Structural Steel for ShipsASTM International
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