S355NL is a thermomechanically rolled, normalized steel grade classified under the European standard EN 10025-3. It belongs to the "S355" family of structural steels but with specific toughness and composition requirements for low-temperature applications. Here's a breakdown of its key characteristics:
Key Properties & Designation Meaning
"S": Indicates "Structural steel".
"355": Specifies a minimum yield strength of 355 MPa at room temperature (thickness ≤16mm).
"N": Delivered in the normalized/normalized rolled (thermomechanically rolled) condition.
"L": Guarantees impact toughness at low temperatures (-50°C).
Technical Specifications
| Property | Requirement |
|---|---|
| Yield Strength | ≥355 MPa (for thickness ≤16mm) |
| Tensile Strength | 470–630 MPa |
| Elongation | ≥22% (minimum, varies with thickness) |
| Impact Toughness | ≥27 Joules at -50°C (tested longitudinally) |
| Delivery Condition | Normalized rolling (thermomechanical processing for refined microstructure) |
Chemical Composition (Typical Max %, EN 10025-3)
| Element | Carbon (C) | Silicon (Si) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Aluminum (Al) |
|---|---|---|---|---|---|---|
| Content | ≤0.18% | ≤0.50% | ≤1.65% | ≤0.025% | ≤0.015% | ≥0.020% |
Low impurity levels (P, S) and aluminum addition enhance weldability and low-temperature toughness.
Applications
S355NL is used in structures exposed to low temperatures, dynamic loads, or critical environments:
Offshore platforms (North Sea, Arctic projects)
Cranes & lifting equipment
Bridges in cold climates
Wind turbine towers
Mining equipment
Pressure vessels (ISO 9328-1 equivalent: P355NL)
Comparison with Related Grades
| Grade | Impact Test Temp. | Delivery | Use Case |
|---|---|---|---|
| S355J2 | -20°C | Non-normalized | General structures (mild climates) |
| S355K2 | -40°C | Non-normalized | Moderate low-temperature service |
| S355NL | -50°C | Normalized | Critical/cryogenic environments |
Equivalents in Other Standards
| Region | Equivalent Grade |
|---|---|
| ISO | S355NL (ISO 630) |
| ASTM | A572 Gr. 50 (not exact, lacks low-temp guarantee) |
| JIS | SM490YA (similar strength) |
| ISO Vessels | P355NL (ISO 9328-1) |
Critical Considerations
Welding: Preheating usually unnecessary due to low carbon equivalent (CEV ≤0.43%).
Corrosion: Not inherently weather-resistant (unlike S355J0WP). Requires coatings for corrosive environments.
Certification: Mill certificates must validate -50°C impact tests and chemical composition.
S355NL provides high strength, ductility, and verified toughness for critical infrastructure. Always verify test reports to ensure compliance with project specifications, especially for cryogenic or offshore applications.
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