NK Grade F36 Shipbuilding Steel Plate
NK Grade F36 Shipbuilding Steel Plate - Low-Temperature High-Strength Hull Structural Steel
Comprehensive material data for NK Grade F36 shipbuilding steel plate, including chemical composition, mechanical properties, thermal properties, international equivalents, and application guide for marine structures.
Hot rolling, thermo-mechanical controlled processing (TMCP), normalizing (if required), welding, bending, cutting
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NK Grade F36 Shipbuilding Steel Plate Introduction
NK Grade F36 is a high-strength shipbuilding structural steel plate certified by ClassNK (Nippon Kaiji Kyokai). It belongs to the F-grade (fine-grain, fully killed) category with a guaranteed minimum yield strength of 355 MPa and excellent low-temperature toughness down to -60°C.
- Ultra-low temperature ductility ensures safe operation in arctic or ice-class vessels.
- Excellent weldability achieved through controlled low carbon equivalent (Ceq ≤ 0.38%).
- High strength-to-weight ratio reduces hull weight while maintaining structural integrity.
- Fine-grain structure refined by aluminium and microalloying elements for superior toughness.
It is primarily used in critical hull components, decks, shell plates, and stiffeners where both high strength and notch toughness at very low temperatures are required.
NK Grade F36 Shipbuilding Steel Plate Chemical Composition
The chemical composition is in accordance with ClassNK Rules Part K, Table K3.1.5 & K3.1.6. Fine-grain practice requires total aluminium content ≥ 0.015% or sufficient other grain-refining elements. The carbon equivalent Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 shall not exceed 0.38% for thickness ≤ 50 mm and 0.40% for 50–100 mm. The following values are maximum unless a range is specified.
| Element | Standard Value (%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.16 | Ladle analysis |
| Silicon (Si) | ≤ 0.50 | If required, minimum 0.10 |
| Manganese (Mn) | 0.90 – 1.60 | Depending on plate thickness |
| Phosphorus (P) | ≤ 0.025 | |
| Sulfur (S) | ≤ 0.025 | |
| Aluminium (Al) | ≥ 0.015 | Total aluminium, for fine grain |
| Niobium (Nb) | 0.02 – 0.05 | Optional microalloying |
| Vanadium (V) | 0.05 – 0.10 | Optional microalloying |
| Titanium (Ti) | ≤ 0.02 | Optional; can be used for grain refinement |
| Carbon Equivalent (Ceq) | ≤ 0.38 | For t ≤ 50 mm |
| Carbon Equivalent (Ceq) | ≤ 0.40 | For 50 < t ≤ 100 mm |
NK Grade F36 Shipbuilding Steel Plate Thermal and Electrical Physical Properties
Physical properties listed below are typical for fine-grain carbon-manganese structural steel of similar composition and processing. These values are not mandatory in the NK rules but serve as design reference. Actual properties may vary slightly with heat treatment and temperature.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At 20°C |
| Modulus of elasticity (E) | 205 | GPa | At 20°C |
| Shear modulus (G) | 80 | GPa | At 20°C, estimated from E and ν |
| Poisson's ratio (ν) | 0.30 | – | At 20°C |
| Coefficient of thermal expansion (α) | 12.5 | 10&supminus;&sup6;/K | Between 20°C and 100°C |
| Coefficient of thermal expansion (α) | 13.5 | 10&supminus;&sup6;/K | Between 20°C and 200°C |
| Coefficient of thermal expansion (α) | 14.0 | 10&supminus;&sup6;/K | Between 20°C and 400°C |
| Thermal conductivity (λ) | 51.9 | W/(m·K) | At 100°C |
| Thermal conductivity (λ) | 48.1 | W/(m·K) | At 200°C |
| Thermal conductivity (λ) | 42.0 | W/(m·K) | At 400°C |
| Specific heat capacity (cp) | 486 | J/(kg·K) | At 20°C–100°C |
| Electrical resistivity (ρe) | 0.22 | μΩ·m | At 20°C |
NK Grade F36 Shipbuilding Steel Plate Mechanical Properties
Mechanical properties are verified on test specimens taken in the transverse direction (unless otherwise agreed). The minimum yield strength reduces slightly for plates thicker than 50 mm. Impact tests are carried out on Charpy V-notch specimens at -60°C. Bending test mandrel diameter depends on plate thickness and material grade.
| Property | Required Value | Unit | Test Condition / Thickness |
|---|---|---|---|
| Yield strength (ReH) | ≥ 355 | MPa | Thickness ≤ 50 mm |
| Yield strength (ReH) | ≥ 340 | MPa | Thickness > 50 mm to ≤ 70 mm |
| Yield strength (ReH) | ≥ 325 | MPa | Thickness > 70 mm to ≤ 100 mm |
| Tensile strength (Rm) | 490 – 630 | MPa | Thickness ≤ 100 mm |
| Elongation (A, gauge length 5.65√So) | ≥ 21 | % | Thickness 5–50 mm |
| Elongation (A50, gauge length 50 mm) | ≥ 16 | % | Thickness < 5 mm |
| Elongation (A) | ≥ 21 | % | Thickness > 50 mm to ≤ 70 mm |
| Elongation (A) | ≥ 21 | % | Thickness > 70 mm to ≤ 100 mm |
| Charpy impact energy (KV2) | ≥ 34 (longitudinal) | J | At -60°C |
| Charpy impact energy (KV2) | ≥ 24 (transverse) | J | At -60°C |
| Bend test, mandrel dia. ratio | 3t | – | Thickness ≤ 25 mm, bend 180° |
| Bend test, mandrel dia. ratio | 4t | – | Thickness > 25–40 mm, bend 180° |
| Bend test, mandrel dia. ratio | 5t | – | Thickness > 40–50 mm, bend 180° |
NK Grade F36 Shipbuilding Steel Plate Fully Equivalent Material Standards and Replaceable Grades
| Country / Region | Standard / Society | Grade | Remarks |
|---|---|---|---|
| International | ABS (American Bureau of Shipping) | FH36 | Identical strength and low-temperature toughness (-60°C), fully interchangeable |
| Norway / Germany | DNV (Det Norske Veritas) | FH36 | Same yield 355 MPa, impact at -60°C, equivalent to NK F36 |
| United Kingdom | LR (Lloyd's Register) | FH36 | Matched mechanical and impact requirements |
| France | BV (Bureau Veritas) | FH36 | Recognised equivalent for hull structural applications |
| China | CCS (China Classification Society) | FH36 | Same grade designation and technical specifications |
| South Korea | KR (Korean Register) | FH36 | Equivalent to NK F36 in all regulated properties |
| Italy | RINA (Registro Italiano Navale) | FH36 | Directly replaceable in shipbuilding designs |
| Russia | RMRS (Russian Maritime Register of Shipping) | F36 | Designation F36, equivalent toughness class |
NK Grade F36 Shipbuilding Steel Plate Application Introduction
NK F36 steel plate is a premium hull construction material designed for ships operating in harsh environments. Its combination of high strength and guaranteed ductility at -60°C makes it ideal for high-stress areas of ice-class vessels, Arctic tankers, and offshore structures.
- Extensively used in shipbuilding: main hull plating, decks, bilge strakes, shell plating, longitudinal and transverse bulkheads.
- Employed in offshore engineering: jacket legs, deck structures of fixed platforms, FPSO modules, wind turbine foundations.
- Applied in naval and special vessels: pressure hulls of submarines, icebreaker hulls, and polar supply ships.
- Processing includes thermal cutting, cold forming, and welding with low-hydrogen consumables to maintain toughness.
Product Applications: Main hull plates and stiffeners, Deck and bottom shell plates, Bulkhead and tank wall plates, Ice bell and reinforcement strakes, Structural elements of jack-up rigs and semi-submersibles, Heavy-lift crane booms and bridge structures
Processed into products: Shell plating for ice zones, Bottom girder webs and flanges, Deck longitudinal stiffeners, Bilge keel and rudder horn plates, Web frames and brackets, Watertight door frames and coamings, Column and brace members of offshore jackets, Transition pieces in wind turbine monopiles
Application industries: Shipbuilding and ship repair, Offshore oil & gas platforms, Renewable energy (offshore wind foundations), Naval defence and coast guard, Heavy engineering and crane construction
NK Grade F36 Shipbuilding Steel Plate Similar / Closely Related Substitute Materials
| Country / Region | Standard / Society | Grade | Remarks |
|---|---|---|---|
| Japan / International | ClassNK | AH36, DH36, EH36 | Same base composition and strength but higher impact test temperature (0°C, -20°C, -40°C respectively); not suitable for -60°C service |
| Europe | EN 10025-4 | S355ML / S355MLO | Thermomechanically rolled weldable fine-grain structural steel with min. yield 355 MPa, impact down to -50°C; close but not identical low-temperature guarantee |
| International | API 2Y / 2W | API 2Y-60 class | Offshore structural steel plates with comparable strength and low-temperature toughness; may be considered with supplemental agreements |
| North America | ASTM A131 / A131M | Grade FH36 | Shipbuilding steel to ASTM standard; technically same strength and toughness as NK F36, but classification society approval may be required |
| Japan | JIS G 3106 | SM490B / C | General structural steel with similar tensile range but less stringent impact properties; not recommended for cryogenic hull parts without qualification |
Notes:
Certification: All plates must be delivered with a ClassNK surveyor's inspection certificate. Heat treatment: TMCP or controlled rolling is the typical delivery condition; normalizing may be applied when improved uniformity is required. Welding precautions: Preheating and interpass temperature controls should follow ClassNK guidelines to avoid cold cracking. Thickness tolerances: In accordance with NK Part K, tolerances on thickness, width and flatness apply. Optional testing: Additional ultrasonic testing, CTOD, or through-thickness (Z-grade) properties may be ordered separately.
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