NK E70 Shipbuilding Steel Coil
NK E70 Shipbuilding Steel Coil | High Strength Offshore Plate
NK E70 is a high strength quenched and tempered steel for shipbuilding and offshore structures, certified by ClassNK, with minimum yield strength 483 MPa (70 ksi) and excellent low-temperature toughness.
Welding, cutting, cold forming, hot forming (with controlled heat treatment), machining
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NK E70 Shipbuilding Steel Coil Introduction
NK E70 is a premium high-strength, quenched and tempered (Q&T) structural steel plate and coil certified by Nippon Kaiji Kyokai (ClassNK). It delivers a minimum yield strength of 483 MPa (70 ksi) combined with excellent toughness at sub-zero temperatures (-40 °C), making it suitable for critical offshore and marine applications. The grade is designed for welded structures under heavy load and harsh environments, such as jack-up rig legs, hulls, and heavy-lift crane booms. Key features:
- Minimum yield strength 483 MPa
- Excellent impact toughness at -40 °C (≥41 J transverse)
- Good weldability with proper procedures
- Low carbon equivalent to reduce cold cracking risk
NK E70 Shipbuilding Steel Coil Chemical Composition
Typical chemical composition tailored to achieve high strength, good toughness, and weldability. Alloying elements such as Ni, Cr, Mo, and microalloys (Nb, V, Ti) are used to refine grain structure and improve hardenability. Values are ladle analysis limits as per ClassNK approved material specification, equivalent to API 2Y/2W Grade 70 and EN S500QL. Note:
- Carbon equivalent (CE) typically ≤ 0.52% to ensure weldability.
- Low sulfur and phosphorus for improved toughness.
| Element | Typical Value (max, %) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.20 | |
| Silicon (Si) | ≤ 0.80 | |
| Manganese (Mn) | ≤ 1.70 | |
| Phosphorus (P) | ≤ 0.025 | |
| Sulfur (S) | ≤ 0.010 | |
| Chromium (Cr) | ≤ 1.50 | Often 0.50-1.20 for strength and hardenability |
| Nickel (Ni) | ≤ 2.0 | Enhances low-temperature toughness |
| Molybdenum (Mo) | ≤ 0.70 | Increases strength and temper resistance |
| Copper (Cu) | ≤ 0.50 | Optional for corrosion resistance |
| Vanadium (V) | ≤ 0.12 | Microalloying for grain refinement |
| Niobium (Nb) | ≤ 0.06 | Microalloying for grain refinement |
| Titanium (Ti) | ≤ 0.05 | Grain refinement and nitrogen control |
| Boron (B) | ≤ 0.005 | Improves hardenability |
| Aluminum (Al) | ≥ 0.018 | Grain refinement and deoxidation |
NK E70 Shipbuilding Steel Coil Thermal and Electrical Physical Properties
Physical properties are typical for low-alloy quenched and tempered steels. They may vary slightly depending on exact chemical composition and heat treatment condition. These values aid in design calculations for thermal expansion, heat transfer, and electrical conductivity. Note: All values are at room temperature unless specified otherwise.
| Property | Typical Value | Unit | Test 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 Coefficient (α) | 11.7 | 10⁻⁶/K | 20 – 100 °C |
| Thermal Expansion Coefficient (α) | 12.5 | 10⁻⁶/K | 20 – 200 °C |
| Thermal Conductivity (λ) | 42 | W/(m·K) | 20 °C |
| Thermal Conductivity (λ) | 40 | W/(m·K) | 100 °C |
| Specific Heat Capacity (cp) | 475 | J/(kg·K) | 20 °C |
| Electrical Resistivity (ρe) | 0.23 | μΩ·m | 20 °C |
NK E70 Shipbuilding Steel Coil Mechanical Properties
Mechanical properties are tested in the quenched and tempered condition as per ClassNK requirements. The steel exhibits high strength with good ductility and toughness. Transverse Charpy V-notch impact tests at -40 °C ensure safe performance in cold marine environments. Note: All values apply for plate/coil thickness ≤ 50 mm unless otherwise specified. For thicker sections, properties may be slightly reduced and subject to agreement.
| Property | Mandated Value / Typical Range | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 483 | MPa | Upper yield or 0.2% offset, transverse |
| Tensile Strength (Rm) | 620 - 795 | MPa | Transverse |
| Elongation (A) | ≥ 16 | % | Gauge length 50 mm (2 in), transverse |
| Charpy Impact Toughness (KV) | ≥ 41 (transverse) | J | -40 °C, 10×10 mm specimen |
| Charpy Impact Toughness (KV) | ≥ 50 (longitudinal) | J | -40 °C, 10×10 mm specimen |
| Bend Test | 180° bend, dia = 3t | - | t = specimen thickness; no cracking |
NK E70 Shipbuilding Steel Coil Fully Equivalent Material Standards & Substitutable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ABS Rules | ABS EQ70 | Identical strength and toughness class |
| UK | LR Rules | LR EH70 | Lloyd's Register equivalent |
| France | BV Rules | BV E70 | Bureau Veritas equivalent |
| Norway/Germany | DNV Rules | DNV E70 | DNV classification equivalent |
| China | CCS Rules | CCS E70 | China Classification Society equivalent |
| Korea | KR Rules | KR EH70 | Korean Register equivalent |
| International (offshore) | API 2Y / API 2W | Grade 70 | Common offshore standard match |
NK E70 Shipbuilding Steel Coil Application Introduction
NK E70 is designed for the most demanding marine and offshore structural applications where high strength, excellent toughness, and good weldability are essential. It is widely used in critical load-bearing members of mobile offshore units and ships operating in cold climates. Application areas include:
- Leg structures of self-elevating (jack-up) drilling units
- Hull plating for ice-class vessels and arctic ships
- BOP handling and guide rails
- Heavy-lift crane booms and jibs
- Transition pieces for offshore wind turbine foundations
- Offshore platform nodes and high-stress regions
Product Applications: Jack-up rig legs (chord and rack), Heavy-lift crane booms, Arctic icebreaker hulls, Offshore subsea equipment, High-pressure vessels (offshore)
Processed into products: Rack and chord sections for jack-up legs, Stiffeners and longitudinal beams in hull structures, BOP handling arm structural components, Hydraulic cylinder mounting plates, Transition piece flanges for monopile foundations, Cutting edges and wear plates
Application industries: Shipbuilding (naval and commercial), Offshore oil and gas exploration and production, Offshore wind energy, Heavy lifting and transport equipment, Bridge and civil engineering (specialty)
NK E70 Shipbuilding Steel Coil Similar / Alternative Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| EU | EN 10025-6 | S500QL (1.8909) | Min. YS 500 MPa, Rm 590-770 MPa, KV -40 °C ≥27 J; slightly higher strength but closely matched in weldability and toughness |
| Japan | JIS G 3128 | SHY490 / SHY550? | JIS high yield strength plates for welded structures; SHY490 has YS ≥490 MPa, but toughness may vary; verify certification |
| China | GB/T 1591 | Q500E | High strength low alloy structural steel, YS ≥500 MPa, -40 °C impact; not identical, but could be considered for less critical applications with ClassNK approval |
| USA | ASTM A514/A514M | Grade Q (Type Q) | Min. YS 690 MPa, higher strength; may be an alternative if higher strength and similar toughness acceptable, but weldability differs |
Notes:
Welding: Preheating and interpass temperature control are recommended to avoid hydrogen cracking. Low-hydrogen welding consumables and proper welding procedures (e.g., SAW, FCAW) must be qualified in accordance with ClassNK rules. Post-weld heat treatment (PWHT) is normally not required for thicknesses ≤ 50 mm, but stress relieving may be applied if specified.
Inspection: Ultrasonic testing (UT) to EN 10160 Class S2/E2 or equivalent is typical for critical applications. Material must be certified by ClassNK surveyors.
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