S355MLO vs S355NLO EN 10025-4 Low Temp Supplier

 

 

S355MLO vs S355NLO – EN 10025-4 Low Temperature Structural Steels

S355MLO and S355NLO are both low-temperature structural steel grades under EN 10025-4, designed for engineering, offshore, and cold-climate applications. While they share the same strength level and similar chemical composition, their delivery conditions, toughness, welding behavior, and structural performance are different.
Gangsteel supplies both grades with EN 10204 3.1/3.2 certification and TMCP rolling technology.

 

Chemical Composition Comparison

The chemical composition of the two grades is generally similar because both belong to the S355 family. However, S355MLO normally has lower carbon equivalent (CEV) due to TMCP rolling, which improves weldability.

Element	S355MLO (max %)	S355NLO (max %)	Technical Notes
C	0.12	0.17	S355NLO may have slightly higher carbon
Mn	1.70	1.60	Minor differences
P	0.025	0.025	Same requirement
S	0.020	0.020	Same requirement
Nb / V / Ti	Allowed	Allowed	Micro-alloying for strength
CEV (typical)	0.40–0.43	0.47–0.52	S355MLO has better weldability

 

Mechanical Properties Comparison

Property	S355MLO	S355NLO	Notes
Yield Strength	355–420 MPa	355–420 MPa	Same strength class
Tensile Strength	470–630 MPa	470–630 MPa	Same
Elongation	≥ 22%	≥ 22%	Similar ductility
Impact Energy	27 J at –40°C	27 J at –40°C	Both “O” = –40°C grade
Thickness Range	6–150 mm	6–150 mm	Plate sizes available from Gangsteel

 

Difference in Delivery Condition (Core Distinction)

This is the most important difference:

Grade	Delivery Condition	Standard Code	Description
S355MLO	Thermomechanically Rolled	M	Best toughness, lowest CEV, excellent weldability
S355NLO	Normalized / Normalized Rolled	N	Traditional heat treatment, higher CEV

 

Summary:

• S355MLO → Modern TMCP steel
• S355NLO → Conventional normalized steel

TMCP steels like S355MLO have finer grain structure and better performance in cold-temperature environments.

 

Weldability Comparison

S355MLO

• Lower carbon equivalent (CEV)
• Less preheat needed
• Suitable for thick plates
• Excellent for complex welding structures

S355NLO

• Higher carbon equivalent
• May require preheating for thick or high-heat-input welding
• Weld toughness not as strong as TMCP grades

Overall, S355MLO is significantly better for welding, especially for heavy offshore modules and pressure-bearing structures.

 

Impact Toughness and Low-Temperature Performance

Both grades have the suffix “O”, meaning:

• Charpy V-notch 27J at –40°C

However, due to TMCP technology:

• S355MLO shows higher actual toughness values in practice
• Better crack resistance in dynamic or impact conditions

This is important for offshore wind towers, cold storage tanks, and Arctic engineering.

 

Applications Comparison

S355MLO Typical Applications

• Offshore platforms, subsea modules
• Wind tower sections
• Arctic structural steel
• High-load welded frames
• Low-temperature pressure vessels

S355NLO Typical Applications

• Bridges
• Construction steel structures
• Welded components in moderate thickness
• General engineering applications requiring –40°C toughness

Which Grade Should You Choose? (Engineering Recommendation)

Choose S355MLO if you need:

• Best weldability
• Low-temperature impact resistance
• Heavy or thick steel plates
• Offshore or Arctic-grade performance
• Reduced plate weight with high safety margin

Choose S355NLO if you need:

• Normalized structural steel
• Stable mechanical properties
• Cost-sensitive applications
• Projects without complex welding requirements

Gangsteel Supply Range

• Thickness: 6–150 mm
• Width: 1500–3200 mm
• Length: 6000–12000 mm
• Certificates: EN 10204 3.1 / 3.2, DNV, ABS, LR, BV
• UT Testing: EN 10160 S1–S3
• Z-direction: Z15 / Z25 / Z35 (optional)

Gangsteel supplies both S355MLO and S355NLO with full traceability, low-temperature test data, and stable TMCP or normalized rolling quality.

 

Others relative propery of en 10025-4 S355ML