NK Grade A36 Shipbuilding Steel Plate
NK Grade A36 Shipbuilding Steel Plate - High Strength Hull Structural Steel Data
Comprehensive material data for NK Grade A36 shipbuilding steel plate (equivalent to AH36 high-strength hull structural steel per ClassNK), including chemical composition, mechanical and physical properties, international equivalents, and application guidelines.
Hot rolling, Normalizing, Thermomechanical Controlled Processing (TMCP)
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NK Grade A36 Shipbuilding Steel Plate Introduction
NK Grade A36 is a high-strength hull structural steel plate standardized by Nippon Kaiji Kyokai (ClassNK). It conforms to the AH36 grade in the IACS unified requirements and is identified as NK KA36 in the ClassNK rules. This steel offers a minimum yield strength of 355 MPa for thicknesses up to 50 mm, combined with good weldability and impact toughness guaranteed at 0 °C.
- Yield strength ≥ 355 MPa (t ≤ 50 mm)
- Tensile strength 490–620 MPa
- Charpy V‑notch energy ≥ 34 J at 0 °C (longitudinal)
The steel is typically supplied in normalized or thermomechanical controlled rolled (TMCP) condition. Its strength-to-weight ratio and marine environment suitability make it a primary choice for critical ship structures and offshore components.
NK Grade A36 Shipbuilding Steel Plate Chemical Composition
Composition limits for NK Grade A36 conform to ClassNK Rules Table K3.2 for high-strength hull structural steels. Grain-refining elements such as Al, Nb, V, and Ti may be added individually or in combination. Residual copper, nickel, chromium, and molybdenum are controlled to ensure good weldability and mechanical properties.
| Element | Specified Value (max unless range) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.18 | Ladle analysis |
| Manganese (Mn) | 0.90 – 1.60 | |
| Silicon (Si) | 0.10 – 0.50 | |
| Phosphorus (P) | ≤ 0.035 | |
| Sulfur (S) | ≤ 0.035 | |
| Aluminum (Al) | ≥ 0.020 (total) or ≥ 0.015 (acid soluble) | When used for grain refining |
| Niobium (Nb) | 0.02 – 0.05 | When added |
| Vanadium (V) | 0.05 – 0.10 | When added |
| Titanium (Ti) | 0.007 – 0.02 | When added |
| Copper (Cu) | ≤ 0.35 | Residual element |
| Nickel (Ni) | ≤ 0.40 | Residual element |
| Chromium (Cr) | ≤ 0.20 | Residual element |
| Molybdenum (Mo) | ≤ 0.08 | Residual element |
| Carbon Equivalent (Ceq) | ≤ 0.40 | Required for cold-formed plates over 25 mm thickness (per ClassNK rules) |
NK Grade A36 Shipbuilding Steel Plate Physical Properties
The following physical properties are typical for carbon‑manganese structural steels comparable to NK A36. Actual values may vary slightly depending on the specific manufacturing process and microstructure. These data are suitable for engineering calculations and design.
| Property | Typical Value | Unit | Condition/Reference |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | Ambient temperature |
| Modulus of Elasticity (E) | 205 | GPa | Ambient temperature |
| Shear Modulus (G) | 80 | GPa | Calculated from E and ν |
| Poissonʼs Ratio (ν) | 0.30 | — | Ambient temperature |
| Coefficient of Thermal Expansion (α) | 11.7 | 10⁻⁶/K | 20–100 °C |
| Thermal Conductivity (λ) | 50 | W/(m·K) | At 20 °C |
| Specific Heat Capacity (Cp) | 460 | J/(kg·K) | At 20 °C |
| Electrical Resistivity (ρe) | 0.23 | 10⁻⁶ Ω·m | At 20 °C |
NK Grade A36 Shipbuilding Steel Plate Mechanical Properties
Mechanical properties of NK KA36 plates as required by ClassNK Rules. Tensile testing is performed on longitudinal specimens with a gauge length of 5.65√S₀. Impact toughness is verified at 0 °C for A-grade steels. Bending tests are carried out at ambient temperature without cracking.
| Property | Specified Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 355 | MPa | Thickness ≤ 50 mm, longitudinal |
| Yield Strength (ReH) | ≥ 345 | MPa | Thickness > 50 ≤ 70 mm, longitudinal |
| Tensile Strength (Rm) | 490 – 620 | MPa | Thickness ≤ 70 mm, longitudinal |
| Elongation (A) | ≥ 21 | % | Gauge length 5.65√S₀, thickness ≤ 50 mm, longitudinal |
| Elongation (A) | ≥ 20 | % | Thickness > 50 ≤ 70 mm, longitudinal |
| Impact Energy (KV, 0 °C) | ≥ 34 | J | Longitudinal, Charpy V‑notch, average of 3 tests |
| Impact Energy (KV, 0 °C) | ≥ 24 | J | Transverse, Charpy V‑notch, average of 3 tests |
| Bend Test | d = 3a | – | 180° bending, thickness ≤ 25 mm |
| Bend Test | d = 4a | – | 180° bending, thickness > 25 ≤ 50 mm |
NK Grade A36 Shipbuilding Steel Plate Internationally Fully Equivalent Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| International (IACS) | IACS UR W11 | AH36 | Fully equivalent to NK KA36 |
| USA | ABS Rules | AH36 | American Bureau of Shipping |
| UK | LR Rules | AH36 | Lloyd's Register |
| Norway/Germany | DNV Rules | AH36 (VL A36) | DNV |
| France | BV Rules | AH36 | Bureau Veritas |
| China | CCS Rules | AH36 | China Classification Society |
| South Korea | KR Rules | AH36 | Korean Register |
| Italy | RINA Rules | AH36 | RINA |
NK Grade A36 Shipbuilding Steel Plate Application Introduction
NK Grade A36 plates are primarily used in ship hull and offshore structures, where high strength and adequate low-temperature toughness are essential. The A-grade guarantees impact properties at 0 °C, making it suitable for ambient marine applications. The steel is readily weldable and formable with standard shipyard practices.
- Preheating is generally unnecessary for thicknesses below 30 mm under normal conditions.
- Common welding methods: SMAW, SAW, FCAW, GMAW.
- Post-weld heat treatment is not mandatory but can be applied if required by design codes.
- Excellent cold forming and edge bending characteristics.
Product Applications: Container ships, Bulk carriers, Oil tankers, Offshore platform decks, Jack-up rig legs, Ship hull plates (bottom, side, deck), Stiffeners and girders
Processed into products: Hull shell plates, Deck plates, Longitudinal and transverse stiffeners, Bulkhead panels, Structural beams, Keel and bilge components, Hatch coaming
Application industries: Shipbuilding, Offshore Oil & Gas, Marine Engineering, Port and Harbor Construction
NK Grade A36 Shipbuilding Steel Plate Similar Grades with Comparable Properties
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A131/A131M | Grade AH36 | Similar yield and tensile strength; used for marine applications; minor differences in chemical composition and deoxidation practice |
| Europe | EN 10225 | S355G7+M | Weldable structural steel for fixed offshore structures; min. yield 355 MPa; more stringent chemical limits; often used for offshore platforms |
| Japan | JIS G 3106 | SM490A/B/C | General structural steel with min. yield strength 325–365 MPa; not specifically for shipbuilding but can substitute in less critical structural parts |
Notes:
The data above are based on publicly available ClassNK Rules. For actual deliveries, the specific mill certificate should be consulted. Additional supplementary requirements, such as through-thickness tensile properties (Z-grade), ultrasonic testing, and higher toughness grades (D, E), can be agreed upon at the time of ordering.
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