S355M and S355ML are European standard structural steel plates (EN 10025-4) with the same strength (minimum yield 355 MPa) and chemistry, differing only in their specified impact toughness, with S355ML offering superior low-temperature performance (tested at -50°C) compared to S355M (tested at -20°C). The 'M' signifies Thermo-Mechanical Controlled (TMCP) rolling, making them excellent for heavy, welded structures like bridges and offshore platforms, but S355ML is chosen for colder environments where sub-zero toughness is critical.
S355M vs S355ML – The Only Real Difference is Impact Temperature
In the EN 10025-4 standard, S355M and S355ML are essentially the same steel – identical chemical composition, identical strength requirements, identical weldability, identical TMCP delivery condition.
The only difference is the Charpy impact test temperature:
S355M → tested at –20 °C (minimum 40 J longitudinal)
S355ML → tested at –50 °C (minimum 27 J longitudinal)
Everything else is 100 % the same.
This single difference makes S355ML the mandatory choice when the design temperature or service temperature is below –20 °C (offshore wind towers, Arctic structures, cold-region bridges, jack-up rigs, penstocks in alpine areas, etc.). S355M is perfectly sufficient for normal structural applications where the lowest service temperature stays above –20 °C.
In practice, S355ML has become the dominant grade because most modern projects (especially offshore wind and oil & gas) specify –40 °C or –50 °C design temperature to be on the safe side.
Chemical Composition – Ladle Analysis vs Product Analysis
|
Element |
C |
Si |
Mn |
P |
S |
Nb |
V |
Al total |
Ti |
Cr |
Ni |
Mo |
Cu |
N |
CEV max |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
S355M & S355ML |
0.14 |
0.50 |
1.60 |
0.025 |
0.020 |
0.05 |
0.10 |
≥0.020 |
0.05 |
0.30 |
0.50 |
0.10 |
0.55 |
0.015 |
0.39 |
Product Analysis– Permitted deviations
|
Element |
C |
Si |
Mn |
P |
S |
Nb |
V |
Al total |
Ti |
Cr |
Ni |
Mo |
Cu |
N |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Permitted deviation |
+0.02 |
+0.05 |
+0.10 |
+0.005 |
+0.005 |
+0.01 |
+0.02 |
+0.03* |
+0.03 |
+0.01 |
+0.05 |
+0.05 |
+0.03 |
+0.03 |
Mechanical Properties
|
Thickness t (mm) |
Min Yield ReH (MPa) |
Tensile Rm (MPa) |
Min Elongation A (%) |
Impact KV min (J) longitudinal |
|---|---|---|---|---|
|
≤ 16 |
355 |
470–630 |
22 |
S355M: 40 J @ –20 °C S355ML: 27 J @ –50 °C |
|
>16 ≤ 40 |
345 |
470–630 |
22 |
same |
|
>40 ≤ 63 |
335 |
470–630 |
22 |
same |
|
>63 ≤ 80 |
325 |
470–630 |
22 |
same |
|
>80 ≤ 100 |
315 |
470–630 |
22 |
same |
|
>100 ≤ 120 |
305 |
450–610 |
22 |
same |
|
>120 ≤ 150 |
295 |
450–610 |
22 |
same (option 3 required for t > 120 mm) |
|
>150 ≤ 200 |
285–295** |
450–610 |
22 |
same (by agreement with mill) |
Application
|
Factor |
S355M |
S355ML |
Recommendation |
|---|---|---|---|
|
Service Temperature |
≥ –20 °C |
≥ –50 °C |
Use S355ML for offshore wind, Arctic, cold regions |
|
Impact Energy Required |
40 J @ –20 °C |
27 J @ –50 °C |
S355ML mandatory if spec calls for –40/–50 °C design temp |
|
Price Difference |
Baseline |
+80–150 USD/ton (2025 average) |
S355ML premium easily justified by weight saving & safety |
|
Stock Availability |
Very high |
Highest (most demanded grade worldwide) |
Both always in Gangsteel stock |
|
Weldability |
Identical (CEV ≤ 0.39) |
Identical |
No difference |
|
Weight Saving vs S355J2 |
~15–20 % |
~15–20 % |
Same |
Weldability & Fabrication – Identical Performance
Both grades have the same very low CEV (typical 0.34–0.37 actual), so welding behaviour is identical:
No preheating required up to 80 mm thickness (even 100 mm in many cases)
Low-hydrogen consumables recommended (H10 max diffusible hydrogen)
Maximum heat input 3.5–4.5 kJ/mm to preserve HAZ toughness
PWHT not required unless specified
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