Difference between S355ML and S460ML steel plate

S355ML and S460ML are thermomechanically rolled (TMCP) weldable fine-grain structural steel plates manufactured to European standard EN 10025-4 . The "M" designates thermomechanical rolling, and the "L" specifies guaranteed low-temperature impact toughness (minimum 27 J at –50°C) . These grades are engineered for demanding welded structures such as offshore platforms, wind power plants, pressure vessels, Arctic vessels, and heavy construction equipment, where superior strength-to-weight ratio, excellent weldability, and outstanding low-temperature fracture resistance are critical .

Key Differences – Strength and Application:

The primary distinction is their minimum yield strength. S355ML provides 355 MPa (for thickness ≤16 mm), while S460ML offers a substantially higher 460 MPa under the same conditions . This 105 MPa (30%) increase allows S460ML to withstand greater design stresses, enabling significant weight reduction in highly loaded structural components .

Key Differences – Metallurgical Design:

To achieve this higher strength while maintaining the stringent –50°C toughness, S460ML requires more precise microalloying control. Both grades feature low carbon (<0.18%) and fine-grain structures via niobium, vanadium, and titanium additions. However, S460ML employs higher manganese (up to 1.8% vs. 1.7%) and microalloy content, with tighter processing parameters during TMCP rolling and accelerated cooling . Despite S460ML's slightly higher alloy content, both grades maintain exceptionally low carbon equivalents (Ceq), typically 0.35–0.43% , which is significantly lower than quenched and tempered grades of equivalent strength.

Key Differences – Fabrication Behavior:

While both grades exhibit superior weldability compared to normalized steels due to TMCP's fine, homogeneous grain structure and minimal residual stress, S460ML demands stricter welding procedure control. Its higher strength requires qualified low-hydrogen consumables and careful heat input management to preserve HAZ toughness. Nevertheless, both grades offer substantially better weldability, lower distortion (20–30% less), and superior flatness than conventional normalized steels like S355NL/S460NL .

Chemical composition for S355ML steel plate 
 

Chemical composition for S460ML steel plate 
 

Mechnical property for S355ML steel plate
 

Mechnical property for S460ML steel plate