1. Standard Part & Scope:
S355J2: Defined in EN 10025-2. This part covers "Non-alloy structural steels" supplied in the normalized/normalized rolled (N) condition.
S355NL: Defined in EN 10025-4. This part covers "Weldable fine grain structural steels" supplied in either the normalized/normalized rolled (N) or thermomechanically rolled (M) condition.
2. Primary Difference: Impact Toughness & Service Temperature:
S355J2: Specified for minimum service temperatures down to -20°C. Its impact toughness (ability to absorb energy without fracturing) is tested at -20°C. The "J" specifically denotes an impact energy requirement of 27 Joules (J) at -20°C. The "2" relates to thickness/testing specifics.
S355NL: Specified for minimum service temperatures down to -50°C. Its impact toughness is tested at -50°C. The "N" means Normalized/Normalized rolled condition. The "L" stands for "Low Temperature", indicating it's part of the enhanced toughness grades within Part 4. It requires a significantly higher 40 Joules (J) at -50°C impact energy (for thicknesses ≤ 50mm). This is the most crucial difference.
3. Chemical Composition & Grain Size:
S355J2: Has slightly looser compositional limits as it's covered in the "non-alloy" steels part (Part 2). It does not have a strict fine grain requirement, though normalization helps.
S355NL: Covered in the "fine grain" steels part (Part 4). It has tighter compositional limits, particularly for elements like Phosphorus (P) and Sulfur (S), which promote grain refinement and improved toughness. Must be supplied in a fine austenitic grain size condition. This fine grain structure is key to its excellent low-temperature toughness.
4. Delivery Condition:
S355J2: Only supplied in Normalized / Normalized Rolled (+N) condition.
S355NL: Can be supplied in two conditions:
Normalized / Normalized Rolled (+N)
Thermomechanically Rolled (+M) - This controlled rolling process achieves fine grain and toughness similar to normalization but without a separate heat treatment step, often making it more cost-effective.
5. Applications:
S355J2: Suitable for general structural applications (buildings, bridges, machinery frames) where low temperatures might occasionally reach down to -20°C. It's a common, versatile grade for temperate climates.
S355NL: Designed for critical applications in low-temperature environments (down to -50°C). Common uses include:
Offshore structures and platforms
Wind turbine towers (esp. in cold regions)
Lifting equipment and cranes operating in cold climates
Bridges and critical infrastructure in arctic/sub-arctic zones
Pressure vessels for low-temperature service
Any highly stressed structure where brittle fracture risk at low temperatures must be minimized.
Summary Table:
| Feature | S355J2 | S355NL |
|---|---|---|
| EN 10025 Part | Part 2 (Non-alloy steels) | Part 4 (Fine grain steels) |
| Scope | Normalized/NR structural | Fine grain, high toughness |
| Key Property | Toughness @ -20°C | High Toughness @ -50°C |
| Impact Test | -20°C | -50°C |
| Impact Energy | 27J (min @ -20°C) | 40J (min @ -50°C, ≤50mm) |
| Subgrade | J = 27J @ specified temp | L = Low temperature application |
| Grain Size | No strict requirement | Fine austenitic grain required |
| Delivery Cond. | Normalized/Normalized Rolled (+N) | Normalized/Normalized Rolled (+N) OR Thermomechanical Rolled (+M) |
| Typical Min Service Temp | Down to -20°C | Down to -50°C |
| Main Application | General structural (buildings, bridges) in temperate climates | Critical applications in cold environments (offshore, wind, arctic bridges, pressure vessels) |
In essence: Both have the same minimum yield strength (ReH >= 355 MPa for t <= 16mm) and similar strength grades for different thicknesses. The core difference lies in guaranteed toughness performance at low temperatures. S355J2 handles down to -20°C adequately, while S355NL offers vastly superior fracture resistance for critical applications where temperatures plummet to -50°C. S355NL also has finer grain structure constraints and potentially tighter composition. Choose S355NL when service temperatures are expected to be consistently below -20°C or for highly critical applications in any environment.
Just like you, 70% customers choose long-term cooperation with BBN steel not only for our good product and service quality, good reputation in the international market, but also for our experienced one-stop raw material supply and further steel processing!
