LR DH42 (DH420) High Strength Shipbuilding Steel Coil
LR DH42 (DH420) High Strength Shipbuilding Steel Coil - Comprehensive Material Data
Detailed analysis of LR DH42 (also designated as DH420) shipbuilding steel coil, including chemical composition, mechanical and physical properties, international equivalents, and application guidelines.
Hot rolling, thermomechanical rolling, normalizing, cold forming, welding, bending, cutting
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LR DH42 High Strength Shipbuilding Steel Coil Introduction
LR DH42 (commonly referred to as DH420 in the Lloyd's Register rules) is a high-strength steel grade for ship hull structures, certified by Lloyd's Register. The 'DH' designation indicates good low-temperature impact toughness at -20°C, while '42' or '420' corresponds to a minimum yield strength of 420 MPa. This normalized or thermomechanically rolled steel offers an excellent combination of strength, weldability, and toughness, making it suitable for critical structural components in shipbuilding. It complies with the latest LR Rules for the Classification of Ships, ensuring reliable performance in marine environments. The steel is typically delivered in coils and later processed into plates or profiles.
LR DH42 High Strength Shipbuilding Steel Coil Chemical Composition
The chemical composition according to LR Rules for DH420 grade (thickness ≤ 100 mm). The steel is fully killed and fine grain treated with aluminium, niobium, vanadium, and/or titanium. The carbon equivalent (Ceq) is controlled to ensure excellent weldability. All values are maximum unless a range is given.
| Element | Standard Value (max %) | Remarks |
|---|---|---|
| Carbon (C) | 0.21 | Max; lower for thicker plates |
| Silicon (Si) | 0.10 – 0.55 | Range |
| Manganese (Mn) | 1.70 | Max |
| Phosphorus (P) | 0.025 | Max; low P improves toughness |
| Sulfur (S) | 0.025 | Max; low S for cleanliness |
| Copper (Cu) | 0.35 | Max |
| Chromium (Cr) | 0.20 | Max |
| Nickel (Ni) | 0.40 | Max |
| Molybdenum (Mo) | 0.08 | Max |
| Aluminium (Als) | 0.015 min | Acid-soluble, minimum for fine grain |
| Niobium (Nb) | 0.02 – 0.05 | One or combination; sum of Nb+V+Ti ≤ 0.12% |
| Vanadium (V) | 0.05 – 0.10 | As above |
| Titanium (Ti) | 0.02 max | As above |
| Carbon Equivalent (Ceq) | 0.45 max | Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 |
LR DH42 High Strength Shipbuilding Steel Coil Physical and Thermal Properties
These values are typical for normalized high-strength low-alloy shipbuilding steel. Actual properties may vary slightly with composition and heat treatment. Data are provided for general engineering calculations and are not part of normative LR requirements.
| Property | Typical Value | Unit | Condition / Temperature |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At 20°C |
| Modulus of Elasticity (E) | 200 – 210 | GPa | At room temperature |
| Shear Modulus (G) | 80 | GPa | Estimated |
| Poisson's Ratio (ν) | 0.3 | – | Elastic range |
| Thermal Expansion Coefficient (α) | 11.5 – 12.5 | ×10⁻⁶/K | 20–100°C |
| Thermal Expansion Coefficient (α) | 12.5 – 13.5 | ×10⁻⁶/K | 20–200°C |
| Thermal Expansion Coefficient (α) | 13.5 – 14.5 | ×10⁻⁶/K | 20–400°C |
| Thermal Conductivity (λ) | 45 – 50 | W/(m·K) | At 20°C |
| Specific Heat Capacity (cp) | 460 – 500 | J/(kg·K) | At 20°C |
| Electrical Resistivity (ρe) | 0.20 – 0.25 | µΩ·m | At 20°C |
LR DH42 High Strength Shipbuilding Steel Coil Mechanical Properties
Tensile testing is performed on transverse test pieces according to LR Rules. Impact tests (Charpy V-notch) are carried out at -20°C on longitudinal specimens. For thickness > 50 mm, elongation values are slightly reduced. Minimum yield strength (ReH) applies for thickness ≤ 100 mm; for larger thickness, special agreement may be required.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | 420 min | MPa | Room temp., thickness ≤ 100 mm, transverse |
| Tensile Strength (Rm) | 530 – 680 | MPa | Transverse, all thicknesses |
| Elongation (A) | 18 min | % | 5.65√So gauge length; thickness ≤ 50 mm |
| Elongation (A) | 17 min | % | Thickness > 50 mm up to 70 mm |
| Elongation (A) | 16 min | % | Thickness > 70 mm up to 100 mm |
| Impact Energy (KV2) | 42 min (longitudinal) | J | At -20°C; average of 3 tests, single min 28 J |
| Bend Test | No cracks | - | 180° bend over former = 3 x thickness (t ≤ 35 mm) |
LR DH42 High Strength Shipbuilding Steel Coil Direct Equivalents – Same Strength & Toughness Class
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| International | Lloyd's Register (LR) | DH420 | Base grade; -20°C impact |
| Norway / International | DNV | DL420 | Same yield and toughness class |
| France / International | Bureau Veritas (BV) | A420 | -20°C impact grade |
| USA / International | American Bureau of Shipping (ABS) | AH420 | May have slight test temperature difference; verify |
| China | China Classification Society (CCS) | AH420 | Equivalent to DH420 |
| Italy / International | RINA | A420 | Technical delivery conditions aligned |
| Japan | ClassNK (NK) | K420 | Equivalent in NK rules |
| Korea | Korean Register (KR) | A420 | Same mechanical requirements |
LR DH42 High Strength Shipbuilding Steel Coil Application Introduction
LR DH420 steel coil is specifically designed for high‑stress ship and offshore structural components. Its high strength enables weight reduction without sacrificing safety, while guaranteed low‑temperature toughness ensures reliable service in cold climates and North Atlantic conditions. The material is typically processed into plates, profiles, and stiffeners during ship construction.
Product Applications: Hull shells and decks, Bottom plate assemblies, Longitudinal and transverse bulkheads, Web frames and stringers, Reinforcement plates for high‑stress areas (hatch corners, crane pedestals)
Processed into products: Ship main deck plates (coils cut to size), Side shell plates, Bilge strakes, Keel plates, Stiffeners (bulb flats, angles, T‑bars), Transverse web frame web plates, Offshore platform leg chords and bracings
Application industries: Shipbuilding (cargo vessels, tankers, bulk carriers, container ships, LNG carriers), Offshore engineering (jack‑up rigs, semi‑submersibles, FPSO modules), Marine and port constructions, Heavy civil engineering where high‑strength weldable steel is required
LR DH42 High Strength Shipbuilding Steel Coil Similar Materials – Close in Strength or Application
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| International | LR | DH40 | Lower yield strength (390 MPa); still high strength |
| International | DNV | VL D40 | Similar toughness, lower yield |
| International | EN 10025-6 | S420QL | Quenched and tempered structural steel, min yield 420 MPa, but different delivery and application |
| International | API 2W | 2W-50 | Steel for offshore platforms, similar strength level (≥414 MPa) |
| Japan | JIS G 3106 | SM490Y | For welded structures, min yield 365 MPa, not direct substitute but may be used in some less demanding structures |
Notes:
Important: The designation 'DH42' is often an industry shorthand for LR DH420. Official LR certificates will show DH420. When ordering, specify thickness, delivery condition (N or M), and required impact temperature (-20°C for DH). The material is suitable for welding with low‑hydrogen procedures; preheat may be needed for thick sections depending on carbon equivalent. Consult LR Rules for the latest edition and any supplemental requirements for specific ship types.
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