NK A70 Shipbuilding Steel Coil
NK A70 Shipbuilding Steel Coil: High-Strength Hull Structural Plate & Strip
Comprehensive data sheet for NK A70 shipbuilding steel coil: chemical composition, mechanical properties, physical performance, international equivalents, and application guidance in accordance with ClassNK Rules and IACS UR W11.
Welding, bending, flame cutting, forming, and machining; suitable for thermomechanical controlled processing (TMCP) and quenching & tempering (QT)
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NK A70 Shipbuilding Steel Coil Introduction
NK A70 is a high-strength shipbuilding structural steel grade certified by Nippon Kaiji Kyokai (ClassNK) and designed in accordance with IACS UR W11. It corresponds to the KA70 designation under the NK Rules, where 'A' indicates an impact test temperature of 0°C. With a minimum yield strength of 700 MPa and excellent toughness, this grade is intended for critical hull and offshore structures where weight reduction and high load-bearing capacity are essential. The steel is supplied as coils, plates, or strips in normalized, thermomechanically rolled, or quenched and tempered condition, offering good weldability and formability for heavy fabrication.
NK A70 Shipbuilding Steel Coil Chemical Composition
Chemical requirements based on IACS UR W11 for high-strength hull structural steels with a specified minimum yield strength of 700 MPa (grade A70). All values are maximum limits unless a range is indicated. Additional microalloying elements may be added to achieve the required mechanical properties, subject to agreement.
| Element | Standard Value (wt%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.20 | Ladle analysis |
| Silicon (Si) | ≤ 0.55 | Ladle analysis |
| Manganese (Mn) | 0.50 – 1.70 | Ladle analysis |
| Phosphorus (P) | ≤ 0.025 | Ladle analysis |
| Sulfur (S) | ≤ 0.025 | Ladle analysis |
| Nitrogen (N) | ≤ 0.020 | Ladle analysis |
| Copper (Cu) | ≤ 0.35 | If required |
| Chromium (Cr) | ≤ 0.20 | If required |
| Nickel (Ni) | ≤ 0.40 | If required |
| Molybdenum (Mo) | ≤ 0.08 | If required |
| Niobium (Nb) | ≤ 0.05 | Microalloying |
| Vanadium (V) | ≤ 0.10 | Microalloying |
| Titanium (Ti) | ≤ 0.020 | Microalloying |
| Aluminum (Al) total | ≥ 0.020 (if added) | Grain refining |
NK A70 Shipbuilding Steel Coil Thermal and Electrical Physical Properties
Representative physical data for quenched and tempered / TMCP structural steels with 700 MPa yield strength class. Actual values may vary slightly with specific chemical composition and heat treatment. These values assist in design calculations and thermal processing.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | Room temperature |
| Modulus of Elasticity (E) | 205 | GPa | Room temperature |
| Shear Modulus (G) | 80 | GPa | Room temperature |
| Poisson's Ratio (ν) | 0.3 | — | Room temperature |
| Thermal Expansion Coefficient (α) | 11.5 | 10⁻⁶/K | 20 – 100°C |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20 – 200°C |
| Thermal Expansion Coefficient (α) | 12.8 | 10⁻⁶/K | 20 – 300°C |
| Thermal Conductivity (λ) | 45 | W/(m·K) | 20°C |
| Thermal Conductivity (λ) | 42 | W/(m·K) | 100°C |
| Specific Heat Capacity (c) | 460 | J/(kg·K) | Room temperature |
| Electrical Resistivity (ρ_e) | 0.20 | Ω·mm²/m | 20°C |
NK A70 Shipbuilding Steel Coil Mechanical Properties
Tensile and impact requirements according to IACS UR W11 for NK A70 (KA70). Transverse or longitudinal testing orientation as specified by the purchaser. Impact tests for Grade A are performed at 0°C. Values apply to product thickness up to 100 mm unless another limit is agreed.
| Property | Standard Required Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) min. | 700 | MPa | All thicknesses (as rolled or conditioned) |
| Tensile Strength (Rm) | 760 – 940 | MPa | Thickness t ≤ 100 mm |
| Elongation (A5) min. | 14 | % | Gauge length 5.65√S₀; longitudinal; t ≤ 50 mm |
| Elongation (A5) min. | 12 | % | Gauge length 5.65√S₀; longitudinal; 50 < t ≤ 100 mm |
| Bend Test (180°) | No cracks or flaws | — | Mandrel diameter 4t (t ≤ 25 mm) |
| Bend Test (180°) | No cracks or flaws | — | Mandrel diameter 5t (25 < t ≤ 50 mm) |
| Bend Test (180°) | No cracks or flaws | — | Mandrel diameter 6t (50 < t ≤ 100 mm) |
| Charpy Impact Energy (KV) min. | 34 | J | Longitudinal, 0°C |
| Charpy Impact Energy (KV) min. | 24 | J | Transverse, 0°C |
NK A70 Shipbuilding Steel Coil Fully Equivalent Standards and Replacement Grades
| Country / Region | Standard / Classification Society | Grade | Remarks |
|---|---|---|---|
| International | IACS UR W11 | A70 | Base specification for all IACS members |
| Japan | NK (ClassNK) | KA70 (NK A70 equivalent) | Original enquiry grade |
| USA | ABS | ABS A70 | Identical requirements |
| France | BV | BV A70 | Identical requirements |
| Norway / Germany | DNV | DNV A70 | Identical requirements |
| United Kingdom | LR | LR A70 | Identical requirements |
| China | CCS | CCS A70 | Identical requirements |
| South Korea | KR | KR A70 | Identical requirements |
| Italy | RINA | RINA A70 | Identical requirements |
| Russia | RS | RS A70 | Identical requirements |
NK A70 Shipbuilding Steel Coil Application Introduction
NK A70 steel coil is developed for weight-critical, highly stressed marine and offshore structures. Its combination of ultra-high strength, good low-temperature toughness, and weldability makes it suitable for severe service conditions. Typical applications:
- Container ship deck and side shells
- Bottom girders and stringers in large bulk carriers
- Legs and jack-up components of mobile offshore units
- Heavy-lift crane pedestals and booms
- Blast-resistant walls and modules on offshore platforms
Product Applications: Ship hull plates and stiffeners, Fatigue-critical deck and bottom panels, Offshore substructures and deck modules, Crane booms and lifting frames, Wind turbine installation vessel hulls
Processed into products: Shell strakes and keel plates, Longitudinal and transverse frames, Web frames and brackets, Deck stringer plates, Bulkhead plating, Pile-guide and spudcan elements
Application industries: Shipbuilding (commercial and naval vessels), Offshore oil & gas (fixed platforms, FPSOs, jack-up rigs), Marine engineering structures, Heavy lifting and transport equipment
NK A70 Shipbuilding Steel Coil Comparable / Analogous Alternative Materials
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-6 | S690Q / S690QL | Quenched & tempered structural steel; min. yield 690 MPa, but lacks mandatory ship classification certification. |
| Europe | EN 10149-2 | S700MC | Thermomechanically rolled high-strength low-alloy steel for cold forming; different delivery condition and not certified for marine use. |
| USA | ASTM A514/A514M | Grade Q / modified | High-yield-strength quenched & tempered alloy steel plate; similar strength but different impact test requirements. |
| Germany | DIN EN 10025-6 | S690QL1 | Structural steel with improved low-temperature toughness; may be used in offshore if agreed, but not a direct ship classification substitute. |
| China | GB/T 16270 | Q690D | High-strength structural steel plate; similar tensile properties but needs additional assessment for marine application. |
Notes:
Important considerations:
- Maximum product thickness under IACS UR W11 is generally 100 mm; for greater thicknesses, supplementary agreement and testing are required.
- Welding procedures must be qualified with appropriate preheat, interpass temperature, and low-hydrogen consumables to avoid cold cracking.
- When specified as 'KA70' under NK Rules, Charpy tests at 0°C are mandatory; other temperature classes (KD70, KE70) are available for lower service temperatures.
- The stock availability of NK A70 in coil form depends on the rolling mill capabilities; plate is the most common form.
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