EN 10025-4 S355ML High-strength Low-alloy (HSLA) Steel Plate

EN10025-4 S355ML is a European standard thermomechanically rolled, weldable, fine-grain structural steel plate with low-temperature toughness. It is primarily used for structural components that require mechanical properties (especially impact toughness) in low-temperature where high toughness (resistance to brittle fracture) is a critical requirement.

Standard and Grade Designation

EN 10025: The overarching European standard for hot-rolled structural steels.

-4: Part 4 of the standard, which covers "Technical delivery conditions for thermomechanically rolled weldable fine grain structural steels."

S355: Indicates the minimum yield strength of the steel is 355 Megapascals (MPa) at thicknesses ≤ 16mm.

M: Stands for "Thermomechanically rolled" (a specific controlled rolling process).

L: Stands for "Low temperature" application, meaning it is impact tested for toughness at low temperatures.

Manufacturing Process: Thermomechanical Rolling (TM)

The "M" in S355ML stands for the manufacturing process:

Thermomechanical Rolling (TMCP): The steel is rolled within a specific temperature range that is carefully controlled. This process refines the grain structure of the steel without the need for a subsequent heat treatment.



Benefits of TMCP:

Finer Grain Size: Leads to higher strength and superior toughness.

Improved Weldability: Allows for high strength with a lower carbon equivalent compared to normalized steels.

The composition is carefully controlled to achieve the fine grain structure and good weldability.

The guaranteed minimum mechanical properties are defined for different product thicknesses. The values decrease slightly as the material thickness increases.

EN 10025-4 S355ML High-strength Low-alloy (HSLA) Steel Plate is used in critical structures where failure at low temperatures is not an option:

Offshore and Marine Structures: Jack-up rigs, platforms, ship hulls for arctic waters.

Wind Turbine Towers: Especially those located in cold climates or offshore.

Mining and Excavation Equipment: For use in arctic regions.

Bridge Construction: In countries with cold winters.

Lifting and Handling Equipment: Cranes and other equipment that must operate reliably in freezing conditions.

Pressure Vessels and Storage Tanks: For storing liquids at low temperatures.

Comparison with Other S355 Grades

Summary

EN 10025-4 S355ML High-strength Low-alloy (HSLA) Steel Plate is a thermomechanically rolled, high-toughness structural steel plate with a minimum yield strength of 355 MPa. Its key characteristic is its guaranteed impact toughness at -50°C, making it an essential material for constructing safe and reliable infrastructure and equipment in arctic and other low-temperature environments.