LR Grade B Shipbuilding Steel
LR Grade B Shipbuilding Steel - Normal Strength Marine Plate from Lloyd's Register
Comprehensive data sheet for LR Grade B shipbuilding steel plate: chemical composition, mechanical and physical properties, international equivalents, and typical applications in hull structures.
Hot rolling, controlled rolling, normalizing, cutting, cold forming, welding, drilling, machining
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LR Grade B Shipbuilding Steel Introduction
LR Grade B is a normal-strength hull structural steel graded by Lloyd's Register (LR). Widely used for ship hulls, decks, and primary components, this carbon-manganese steel is produced to strict classification society requirements, ensuring reliable strength and ductility.
- Yield strength ≥ 235 MPa (typical for thickness ≤ 100 mm)
- Tensile strength 400–520 MPa
- Good notch toughness at 0 °C (KV ≥ 27 J)
- Excellent weldability for ship fabrication
- Available as plates, sections, and flats
Delivered in hot-rolled, controlled-rolled, or normalized condition depending on thickness and application. The grade is accepted internationally by all major IACS classification societies under equivalent designations.
LR Grade B Shipbuilding Steel Chemical Composition
Typical chemical requirements for LR Grade B steel plates according to LR Rules. Trace elements are kept low to ensure weldability and toughness.
- Carbon equivalent (CEV) is generally controlled by agreement.
- Fine grain practice with aluminium is common.
- Residual elements (Cr, Ni, Cu, Mo) are limited to avoid adverse effects on mechanical properties.
| Element | Specified Value (wt%) | Notes |
|---|---|---|
| C | ≤ 0.21 | For all thicknesses |
| Si | ≤ 0.35 | Generally 0.15–0.35 for killed steel |
| Mn | ≥ 0.50 (t ≤ 12.5 mm) | Minimum based on carbon content; ≥ 2.5 × C, but not less than indicated |
| Mn | ≥ 0.80 (t > 12.5 mm) | Higher Mn for thicker plates to meet strength |
| P | ≤ 0.035 | Max |
| S | ≤ 0.035 | Max |
| Al (acid soluble) | ≥ 0.015 (if grain refined) | When aluminium is used for grain refining |
| Cr | ≤ 0.20 | Residual element |
| Ni | ≤ 0.40 | Residual element |
| Cu | ≤ 0.35 | Residual element |
| Mo | ≤ 0.08 | Residual element |
| N | ≤ 0.009 (if controlled) | May be specified for improved toughness |
| Others (total) | ≤ 0.80 | Sum of Cr + Ni + Cu + Mo |
LR Grade B Shipbuilding Steel Thermal and Electrical Physical Properties
The following values are typical for carbon‑manganese structural steels and are not part of the LR specification. They are given for design guidance.
- Density, modulus, and thermal expansion are essential for structural and thermal analysis.
| Property | Typical Value | Unit | Test Conditions / Remarks |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Modulus of elasticity (E) | 205 – 215 | GPa | At room temperature |
| Shear modulus (G) | 80 – 83 | GPa | Approximate value |
| Poisson's ratio (ν) | 0.29 – 0.30 | – | In elastic range |
| Thermal expansion coefficient (α) | 12.0 × 10⁻⁶ | 1/K | Between 20 °C and 100 °C |
| Thermal expansion coefficient (α) | 13.5 × 10⁻⁶ | 1/K | Between 20 °C and 300 °C |
| Thermal conductivity (λ) | 51 – 54 | W/(m·K) | At 20 °C |
| Thermal conductivity (λ) | 45 – 50 | W/(m·K) | At 200 °C |
| Specific heat capacity (cₚ) | 460 – 480 | J/(kg·K) | At 20 °C |
| Electrical resistivity (ρₑ) | 0.17 – 0.20 × 10⁻⁶ | Ω·m | At 20 °C |
LR Grade B Shipbuilding Steel Mechanical Properties
Tensile and impact properties are verified on test pieces taken from the finished product. Bend test ensures sufficient ductility without cracking. Impact energy is measured on Charpy V-notch specimens at the prescribed temperature.
- Values may vary slightly depending on product form and thickness.
| Property | Required Value | Unit | Test Conditions / Remarks |
|---|---|---|---|
| Yield strength (ReH) | ≥ 235 | MPa | For thickness t ≤ 50 mm, transverse or longitudinal |
| Yield strength (ReH) | ≥ 215 | MPa | For 50 mm < t ≤ 100 mm |
| Tensile strength (Rm) | 400 – 520 | MPa | All thicknesses, longitudinal or transverse |
| Elongation (A5) | ≥ 22 | % | Longitudinal, gauge length 5.65√S₀, t ≤ 50 mm |
| Elongation (A5) | ≥ 21 | % | Longitudinal, 50 mm < t ≤ 70 mm |
| Elongation (A5) | ≥ 20 | % | Longitudinal, 70 mm < t ≤ 100 mm |
| Bend test | d = 3a | – | 180° bend, mandrel diameter d, specimen thickness a, t ≤ 25 mm |
| Bend test | d = 4a | – | 180° bend, for t > 25 mm |
| Charpy V-notch impact energy | ≥ 27 (avg) | J | 0 °C, longitudinal, standard 10×10 mm specimen, min. single 20 J |
| Charpy V-notch impact energy (transverse) | ≥ 20 (avg) | J | 0 °C, if required, min. single 14 J |
LR Grade B Shipbuilding Steel Fully Equivalent Standards and Direct Substitution Grades
| Country/Region | Standard/Society | Grade | Remarks |
|---|---|---|---|
| International | LR (Lloyd's Register) | Grade B | Base specification |
| USA | ABS (American Bureau of Shipping) | Grade B | Identical technical requirements |
| Norway/Germany | DNV (Det Norske Veritas) | NV B | Equivalent normal strength grade |
| France | BV (Bureau Veritas) | Grade B | Same composition and properties |
| China | CCS (China Classification Society) | B | Fully equivalent |
| South Korea | KR (Korean Register) | B | Interchangeable |
| Japan | NK (ClassNK) | B | Equivalent shipbuilding steel |
| Italy | RINA (Registro Italiano Navale) | B | Same grade |
| Russia | RS (Russian Maritime Register) | B | Recognised equivalent |
| India | IRS (Indian Register of Shipping) | B | Equivalent normal strength |
| USA | ASTM A131 / A131M | Grade B | Common structural steel for ships, identical chemical/mechanical intent |
LR Grade B Shipbuilding Steel Application Introduction
LR Grade B is primarily intended for ship and offshore structural construction where moderate strength and good low-temperature toughness (tested at 0 °C) are required. Thanks to its reliable performance and wide classification society recognition, it serves as a standard material for hull plates and sections.
- It can be used in welded, bolted and riveted structures.
- The material is easily formable and machinable, allowing fabrication of complex components.
Product Applications: Ship hulls (bulk carriers, tankers, container ships, passenger vessels), Offshore platform decks and jackets, Barges, pontoons and floating docks, Marine cargo handling equipment, Pressure hulls of submarines (where applicable), Large storage tanks for marine service
Processed into products: Hull plating (bottom, side, deck plates), Bulkheads and watertight doors, Longitudinal and transverse stiffeners, Web frames and girders, Rudders and rudder horns, Ship masts and foundation plates, Hawse pipes, bollard and winch foundations
Application industries: Shipbuilding and repair, Offshore oil & gas engineering, Marine and coastal structures, Port and harbour equipment, Heavy civil engineering (when class certification is needed)
LR Grade B Shipbuilding Steel Similar / Alternative Materials for Non-Marine Applications
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-2 | S235JR | Comparable yield and tensile strength; impact test at +20 °C, not fully equivalent for ship certification |
| China | GB/T 700 | Q235B | Similar C-Mn steel; toughness only guaranteed at 20 °C, not for marine class |
| Japan | JIS G3101 | SS400 | Widely used general structural steel; no mandatory impact requirement |
| USA | ASTM A36 / A36M | Grade 36 | Common structural steel, yield ~250 MPa; not impact tested, not for ship classification |
Notes:
LR Grade B steel is typically supplied with classification society certificates (e.g., LR, ABS, DNV).
- Preheating may be required for thicker sections during welding to avoid cracking.
- The steel should not be used at temperatures lower than the certified impact test temperature without additional qualification.
- If improved through-thickness properties (Z-quality) are required, this must be specified separately in the order.
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