The difference between S355N and S355JR is fundamental and dictates their selection for specific engineering applications. While both share the same minimum yield strength (355 MPa), they are different material grades from different standards with distinct properties.
Here is a clear, point-by-point comparison.
At a Glance: The Core Difference
| Feature | S355JR | S355N |
|---|---|---|
| Governing Standard | EN 10025-2 (Non-alloy structural steels) | EN 10025-3 (Normalized/Normalized-rolled fine grain steels) |
| Defining Feature | Standard quality, good weldability | Normalized condition for improved toughness |
| Key Use Case | General construction in temperate climates | Critical structures in cold climates or with dynamic loads |
Detailed Breakdown of Differences
1. Material Standard & Supply Condition
S355JR (EN 10025-2):
Condition: As-rolled. The steel cools naturally after the final hot-rolling pass.
Type: A non-alloy quality steel.
S355N (EN 10025-3):
Condition: Normalized or Normalized-rolled. This is a controlled heat treatment where the steel is reheated to ~900°C and cooled in still air.
Type: A fine grain, micro-alloyed steel (often with Niobium or Vanadium).
2. Impact Toughness (The Most Critical Difference)
This is the primary reason for choosing one over the other.
S355JR: The "JR" suffix specifies Charpy V-notch impact testing at +20°C.
Requirement: 27 Joules minimum at room temperature.
Implication: Suitable for ambient temperature applications. It may become brittle in sub-zero conditions.
S355N: The "N" suffix indicates testing at -20°C.
Requirement: 40 Joules minimum at -20°C.
Implication: Guaranteed to remain tough at freezing and sub-freezing temperatures, resisting brittle fracture.
3. Mechanical & Microstructural Properties
Strength: Both have identical minimum yield (355 MPa) and tensile (470-630 MPa) strength ranges.
Homogeneity & Internal Stress: S355N's normalization process results in a more uniform, fine-grained microstructure. This evens out mechanical properties throughout the thickness of the material and relieves internal stresses from rolling. This is particularly important for thick sections and heavy welding.
Ductility: S355N generally has better elongation and ductility due to its refined grain structure.
4. Chemical Composition & Weldability
S355JR: Chemistry is controlled mainly for strength and basic weldability (Carbon Equivalent, CEV ≤ ~0.40%).
S355N: As a fine-grain steel, it has stricter controls on grain-refining elements (like Al, Nb, V). It often has a slightly lower CEV, making its weldability excellent and more predictable, especially for thick plates and critical welds.
5. Cost & Availability
S355JR: The most common and economical grade. Readily available from stock in all forms (plates, beams, sections).
S355N: More expensive due to the additional heat treatment process. It is a "special" grade and may have longer lead times. It is often supplied in plate form rather than standard sections.
Practical Application Summary: When to Use Which?
Choose S355JR when:
Building general structures (buildings, warehouses) in regions with mild winters.
The design is not governed by low-temperature impact requirements.
Cost and availability are primary concerns.
Applications are static and at ambient temperatures.
Choose S355N when:
The structure will operate in cold climates (e.g., outdoor bridges in continental Europe, support structures in Scandinavia).
The component is subject to dynamic/vibrating loads (e.g., crane runways, lifting equipment, wind turbine sections).
You are working with thick plates (> 40-50 mm) where material homogeneity is critical to prevent lamellar tearing during welding.
The application is safety-critical and requires guaranteed low-temperature toughness (e.g., parts of transportation equipment, essential infrastructure).
Analogy
Think of it like two types of glass:
S355JR is like standard window glass. It's perfectly strong for its intended use at normal temperatures.
S355N is like toughened safety glass. It has been through an extra process (heat treatment) to make it much more resistant to shock and impact, especially in harsh conditions. You pay more for this enhanced performance where it's needed.
Conclusion: The choice isn't about strength-it's about toughness, reliability under specific service conditions, and the safety margin required for the structure. S355N is the engineered, premium solution for demanding environments.