S355NL and S355ML are both high-strength structural steels with minimum yield strength of 355 MPa, but differ in their production: S355NL uses Normalizing (N) or controlled rolling for thicker plates, offering good low-temp toughness at -50°C, while S355ML uses Thermomechanical Rolling (M) for thinner plates, resulting in better weldability (lower Carbon Equivalent Value - CEV) and cost-effectiveness.
Chemical Composition Comparison
Element | S355NL (EN 10025-3, Ladle, max %) | S355ML (EN 10025-4, Ladle, max %) |
|---|---|---|
Carbon (C) | 0.18 | 0.14 |
Silicon (Si) | 0.50 | 0.50 |
Manganese (Mn) | 0.90-1.65 | 1.60 |
Phosphorus (P) | 0.025 | 0.025 |
Sulfur (S) | 0.015 | 0.020 |
Nitrogen (N) | 0.015 | 0.015 |
Aluminum (Al) | 0.02 (min, total) | 0.02 (min, total) |
Niobium (Nb) | 0.05 | 0.05 |
Vanadium (V) | 0.12 | 0.10 |
Titanium (Ti) | 0.05 | 0.05 |
Chromium (Cr) | 0.30 | 0.30 |
Nickel (Ni) | 0.30 | 0.30 |
Molybdenum (Mo) | 0.10 | 0.20 |
Copper (Cu) | 0.55 | 0.55 |
Mechanical Properties Comparison
Property | S355NL (EN 10025-3) | S355ML (EN 10025-4) |
|---|---|---|
Yield Strength (min, MPa) | ||
≤16 mm | 355 | 355 |
16<t≤40 mm | 345 | 355 |
40<t≤63 mm | 335 | 345 |
Tensile Strength (MPa) | 470-630 | 450-610 |
Elongation (min, %) | 22 (≤63 mm) | 22 (≤40 mm) |
Impact Energy (min, J) | 27 @ -50°C (longitudinal) | 27 @ -50°C (longitudinal) |
Welding and Heat Treatment
S355NL: CEV ≤0.43% supports GMAW or SAW (EN 1011-2). Preheating (100-150°C) for >20 mm; PWHT (550-650°C) optional. Consumables: ER70S-6 (GMAW), EM12K flux with EH14 wire (SAW).
S355ML: Lower CEV (≤0.39%) enhances weldability, often requiring less preheating (50-100°C for >20 mm). Same consumables apply.
The S355NL vs S355ML welding comparison favors S355ML for cost-efficient fabrication due to its TMCP process.
Applications
S355NL:
Offshore platforms in cold marine environments.
Wind towers in sub-zero climates.
Bridges and cranes in northern regions.
Its normalization ensures reliability across a wide thickness range (up to 250 mm).
S355ML:
Similar applications (offshore, wind towers, bridges) but preferred in projects prioritizing weldability and cost.
Limited to thinner sections (≤120 mm), suitable for lighter structures.
The S355ML S355NL application difference highlights S355NL's versatility for thicker plates and S355ML's cost-effectiveness for thinner ones.
Equivalent Grades
S355NL: ASTM A633 Grade E, Q345E (China), StE 355 (DIN).
S355ML: ASTM A633 Grade E, Q345E (China), StE 355 TM (DIN).
See EN 10025-3 S355N normalized structural steel plate.
