S355ML vs S355NL is a common comparison in structural steel selection, as both grades are high-strength, low-alloy steels under the EN 10025 standard but differ in processing and performance. S355NL, specified under EN 10025-3, is a normalized fine-grain steel, while S355ML, under EN 10025-4, is thermomechanically rolled (TMCP).
S355NL (EN 10025-3)
S355NL is a normalized or normalized rolled fine-grain structural steel with:
S: Structural steel.
355: Minimum yield strength of 355 MPa (≤16 mm).
NL: Normalized, with impact toughness tested at -50°C for low-temperature applications.
Its normalization process ensures a refined microstructure, ideal for cold climates like offshore platforms.
S355ML (EN 10025-4)
S355ML is a thermomechanically rolled (TMCP) fine-grain structural steel with:
S: Structural steel.
355: Minimum yield strength of 355 MPa (≤16 mm).
ML: Thermomechanically rolled, with impact toughness tested at -50°C.
TMCP produces finer grains, enhancing strength and weldability, often at a lower cost than normalization.
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.
