Structural plate thick >60 mm

The thickness effect in structural steel is a well-documented phenomenon in the EN 10025 standard. As the thickness of the rolled plate increases, the cooling rate during the rolling process decreases, resulting in a larger grain size and a less refined microstructure. This coarser microstructure reduces the mechanical properties, especially the yield strength. That's why S355 J2+N at 16 mm has a yield strength of 355 MPa, but the same steel at 100 mm has 315 MPa, and at 150 mm drops to 295 MPa. This effect is inherent to the manufacturing process and must be taken into account in structural calculations according to Eurocode 3.

Preheating when welding thick S355 plate depends on the thickness, the carbon equivalent (CE) of the material, and the ambient working temperature. As a general rule: for thicknesses under 30 mm with CE ≤ 0.43 and ambient temperature ≥ 5°C, preheating is not necessary. For thicknesses of 30-60 mm with CE 0.43-0.47, preheating to 75°C is recommended. For thicknesses of 60-100 mm with CE 0.47-0.50, preheating should be 100-125°C. For thicknesses over 100 mm with CE > 0.50, preheating may require 125-175°C depending on the specific WPS (Welding Procedure Specification). These values are indicative and must be validated in the project's WPS.

The ultrasonic test according to the EN 10160 standard is a non-destructive inspection method that detects internal discontinuities in steel plate, such as inclusions, segregations, cracks, or laminations that can compromise structural integrity. The standard defines three quality classes: S0 (no specific requirements), S1 (inspection over the entire surface), and S2 (inspection in a marginal strip). UT testing is mandatory or highly recommended for: structures of execution class EXC3 and EXC4 according to EN 1090, fatigue-loaded components, critical welded joints, plates over 100 mm thick for primary structural applications, and any project where the client specifies the test in their technical requirements. Mayor Steel offers EN 10160 S1 and S2 UT testing on request with reduced lead times.

For structures of execution class EXC3 according to EN 1090-2, the documentation for thick structural plate must include: at minimum an inspection certificate 3.1 according to EN 10204 (a 3.2 certificate with third-party inspection is recommended for critical components), the manufacturer's CE certificate of conformity, a declaration of performance for the steel according to the Construction Products Regulation (CPR), a chemical analysis report of the supplied batch, a mechanical properties report including tensile and Charpy testing, and optionally an ultrasonic test report according to EN 10160 if specified in the project. Mayor Steel provides all this documentation as standard for EXC3 projects, including full traceability from the ingot to the supplied plate.

Yes, Mayor Steel maintains permanent stock of S355 J2+N structural plate in thicknesses of 100 mm, 120 mm, 150 mm and above. This availability is one of our main differentiators: very few distributors in Spain have real stock of thick plate in these thicknesses. Our warehouse in Zierbena (Bizkaia) regularly stores S355 J2+N in formats of 2000x6000 mm and 2500x8000 mm in thicknesses of 60, 80, 100, 120, 150 and 200 mm. For thicknesses of 250 mm and 300 mm, availability is on request with lead times of 2-4 weeks. All materials include EN 10204 3.1 certification and can be supplied with EN 10160 ultrasonic testing on request. Delivery is immediate for in-stock thicknesses.

Yes, S355 J2+N structural plate in thick gauges (80-200 mm) is frequently used as material for large industrial molds, especially in applications where the specific properties of mold steels (such as P20 or 1.2311) are not required. The advantages of S355 J2+N for molds are its excellent availability in large thicknesses, its good machinability after mild quenching and tempering treatment, and its significantly lower cost compared to specific mold steels. However, it is important to consider that S355 does not have the same polishability or wear resistance as a mold steel, so its use is limited to low- and medium-production molds, prototypes, or applications where the mold surface does not require a mirror finish. Mayor Steel supplies S355 J2+N for molding applications according to customer technical specifications.

The +N suffix indicates that the steel has been supplied in the normalized condition, meaning it has undergone a normalizing heat treatment that consists of heating the material to a temperature above the austenitic transformation temperature (approximately 900°C for carbon steels) and air cooling. This treatment produces a more homogeneous, fine-grained ferrite-pearlite microstructure, improving the consistency of mechanical properties and weldability. The +M suffix indicates that the steel has been supplied in the thermomechanically processed condition (TMCP - Thermo-Mechanical Controlled Process), a controlled rolling process that combines plastic deformation and thermal control to obtain very fine-grained microstructures without the need for subsequent heat treatment. +M offers better toughness and weldability properties than +N, especially in large thicknesses, but its availability is limited to certain thicknesses and grades.