KR Grade A51 Shipbuilding Steel Plate
KR Grade A51 Shipbuilding Steel Plate: High-Strength 51 ksi Yield Plate (Equivalent to AH36)
Comprehensive material data for KR Grade A51 shipbuilding steel plate, a high-strength hull structural steel equivalent to AH36, featuring minimum yield strength 355 MPa (51 ksi), excellent weldability and toughness, used in ship and offshore structures.
Hot rolling, controlled rolling, normalizing, thermo-mechanical controlled processing (TMCP)
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KR Grade A51 Shipbuilding Steel Plate Introduction
KR Grade A51 is a high-strength shipbuilding steel plate commonly designated as AH36 under the Korean Register of Shipping. It provides a minimum yield strength of 355 MPa (51 ksi) and excellent toughness at ambient temperatures, making it suitable for critical hull structures. Its chemical composition and mechanical properties comply with KR Rules Part 2 Chapter 1, ensuring reliable performance in marine and offshore environments. The steel is characterized by good weldability, controlled grain refinement, and consistent mechanical properties across thicknesses.
KR Grade A51 Shipbuilding Steel Plate Chemical Composition
The chemical composition of KR AH36/A51 steel is designed to provide high strength while maintaining good weldability and toughness. All values are in weight percent as per KR Rules. A maximum carbon equivalent (Ceq) is often imposed to ensure weldability.
| Element | Standard Value (wt%) | Remarks |
|---|---|---|
| C | ≤0.18 | |
| Mn | 0.70–1.60 | |
| Si | ≤0.50 | |
| P | ≤0.035 | |
| S | ≤0.035 | |
| Cr | ≤0.20 | |
| Ni | ≤0.40 | |
| Mo | ≤0.08 | |
| Cu | ≤0.35 | |
| Nb | 0.02–0.05 | |
| V | 0.05–0.10 | |
| Ti | ≤0.02 | |
| Al (acid soluble) | ≥0.015 | |
| N | ≤0.009 | For aluminium killed fine grain practice |
| Ceq | ≤0.38 | Ceq = C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15, typical requirement for t≤50 mm |
KR Grade A51 Shipbuilding Steel Plate Thermal and Electrical Physical Properties
These physical properties are typical for structural steels and can be used for engineering calculations. Values are valid at room temperature unless otherwise noted. Slight variations may occur depending on exact composition and heat treatment condition.
| Property | Typical Value | Unit | Condition |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | 20°C |
| Elastic Modulus (E) | 205 | GPa | 20°C |
| Shear Modulus (G) | 80 | GPa | 20°C |
| Poisson's Ratio (ν) | 0.3 | — | 20°C |
| Thermal Expansion (α) | 11.7×10⁻⁶ | /K | 20–100°C |
| Thermal Expansion (α) | 12.5×10⁻⁶ | /K | 20–200°C |
| Thermal Expansion (α) | 13.1×10⁻⁶ | /K | 20–300°C |
| Thermal Conductivity (λ) | ~50 | W/(m·K) | 20°C |
| Specific Heat | ~460 | J/(kg·K) | 20°C |
| Electrical Resistivity (ρ_e) | ~0.20 | μΩ·m | 20°C |
KR Grade A51 Shipbuilding Steel Plate Mechanical Properties
Mechanical properties for KR AH36/A51 steel plate up to 50 mm thickness, as per KR Rules. Transverse test pieces are used for tensile testing; longitudinal specimens for impact toughness. Bending test is required to verify formability.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥355 | MPa | Transverse, t≤50 mm |
| Tensile Strength (Rm) | 490–630 | MPa | Transverse, t≤50 mm |
| Elongation (A), GL=200 mm | ≥21 | % | Transverse, t≤50 mm |
| Charpy Impact (KV) at 0°C | ≥34 | J | Longitudinal, t≤50 mm |
| Bending Test (180°) | d=3a, no cracks | — | t≤50 mm |
KR Grade A51 Shipbuilding Steel Plate Fully Equivalent Materials and Replaceable Grades
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| International | IACS UR W11 | AH36 | Equivalent high strength shipbuilding steel |
| South Korea | KR Rules | AH36 (A51) | Original KR grade, A51 trade name |
| USA | ASTM A131 / ABS Rules | AH36 | Same mechanical and chemical requirements |
| Norway | DNV-OS-B101 | AH36 | Direct equivalent by DNV |
| UK | LR Rules | AH36 | Equivalent grade from Lloyd's Register |
| France | BV Rules | AH36 | Equivalent grade from Bureau Veritas |
| China | CCS Rules | AH36 | Adopted by China Classification Society |
| Japan | NK Rules | AH36 | Adopted by ClassNK |
| Germany | GL Rules (historical) | AH36 | Former Germanischer Lloyd equivalent |
| Europe | EN 10225 | S355G10+N | Offshore structural steel with similar strength, may require special certification |
KR Grade A51 Shipbuilding Steel Plate Application Introduction
KR Grade A51 (AH36) is ideal for critical structural components in shipbuilding and offshore engineering where high strength and good weldability are required. It performs well in marine environments under cyclic loading and is certified by the Korean Register for use in the hull and other primary structures.
Product Applications: Ship hull plates (bottom, side, deck, bulkhead), Offshore platform decks and legs, Jacket structures, Deckhouses and superstructures, Barge and pontoon structures, Marine cranes and lifting equipment
Processed into products: Hull shell plates, Bottom longitudinals and frames, Transverse bulkheads, Deck stringer plates, Webs and stiffeners, Bracket plates, Sea chests, Rudder plates
Application industries: Shipbuilding, Offshore Oil & Gas, Marine Engineering, Port & Harbor Construction, Pressure Vessel Manufacturing (marine service)
KR Grade A51 Shipbuilding Steel Plate Similar/Alternative Materials
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| South Korea | KR Rules | AH32 | Lower yield strength (315 MPa), otherwise similar weldability and toughness |
| South Korea | KR Rules | DH36 | Same strength, impact tested at -20°C for thicker sections or low temperature service |
| South Korea | KR Rules | EH36 | Same strength, impact tested at -40°C for Arctic/cryogenic service |
| South Korea | KR Rules | AH40 | Higher yield strength (390 MPa) for increased load capacity |
| Europe | EN 10025-4 | S355ML | Thermomechanically rolled fine grain steel, yield 355 MPa, for offshore structures |
| USA | ASTM A572 | Gr 50 | General structural steel with minimum yield 345 MPa, may be used with classification society approval |
| Japan | JIS G3106 | SM490YA | Welded structural steel with yield 365 MPa, for general use, not ship specific |
Notes:
Note: The designation "A51" is a common trade name used by POSCO to denote AH36 steel with a minimum yield strength of 51 ksi (355 MPa). This steel must be certified by the Korean Register (KR) for ship classification. Compliance with KR Rules ensures suitability for marine environments. Users should verify specific delivery condition and any supplementary requirements per project specification.
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