S355M and S420M are high-strength, fine-grain structural steel plates from the EN 10025-4 standard, processed via Thermomechanical Controlled Processing (TMCP) for superior weldability, toughness, and finer microstructure, making them ideal for heavily loaded, welded structures like bridges, cranes, and offshore components requiring good impact energy even at low temperatures. 'S' denotes structural steel, '355' and '420' are the minimum yield strengths (in MPa), and 'M' signifies thermomechanical rolling for enhanced properties, with 'ML' offering even lower-temperature impact resistance.
Mechnical property for S355M steel plate:
| Thickness (mm) | ||||||
| S355M | ≤ 16 | > 16 ≤ 40 | > 40 ≤ 63 | > 63 ≤ 80 | > 80 ≤ 100 | > 100 |
| Yield strength (≥Mpa) | 355 | 345 | 335 | 325 | 325 | 320 |
| ≤ 40 | > 40 ≤ 63 | > 63 ≤ 80 | > 80 ≤ 100 | > 100 | ||
| Tensile strength (Mpa) | 470-630 | 450-610 | 440-600 | 440-600 | 430-590 | |
Mechnical property for S420M steel plate
| Thickness (mm) | ||||||
| S420M | ≤ 16 | > 16 ≤ 40 | > 40 ≤ 63 | > 63 ≤ 80 | > 80 ≤ 100 | > 100 |
| Yield strength (≥Mpa) | 420 | 400 | 390 | 380 | 370 | 365 |
| ≤ 40 | > 40 ≤ 63 | > 63 ≤ 80 | > 80 ≤ 100 | > 100 | ||
| Tensile strength (Mpa) | 520-680 | 500-660 | 480-640 | 470-630 | 460-620 | |
Chemical composition for S355M steel plate
| Main chemical elements composition of S355M steel plate | ||||||
| C | Si | Mn | P | S | Nb | V |
| 0.14 | 0.50 | 1.60 | 0.030 | 0.025 | 0.05 | 0.10 |
| Al(total) | Ti | Cr | Ni | Mo | Cu | N |
| ≥0.02 | 0.05 | 0.30 | 0.50 | 0.10 | 0.55 | 0.015 |
Chemical composition for S420M steel plate
| Main chemical elements composition of S420M steel plate | ||||||
| C | Si | Mn | P | S | Nb | V |
| 0.16 | 0.50 | 1.70 | 0.030 | 0.025 | 0.05 | 0.12 |
| Al(total) | Ti | Cr | Ni | Mo | Cu | N |
| ≥0.02 | 0.05 | 0.30 | 0.80 | 0.20 | 0.55 | 0.025 |
Key Characteristics
Standard: EN 10025-4 (Thermomechanical Rolled Weldable Fine Grain Structural Steels).
Processing: Thermomechanical Controlled Processing (TMCP) involving controlled rolling and water cooling (OLAC) to achieve finer grain structure, higher strength, and toughness.
Strength: S355M has a minimum yield strength of 355 MPa, while S420M has a minimum yield strength of 420 MPa.
Weldability: Excellent, with lower carbon equivalent values, reducing preheat requirements and weld cracking risk.
Toughness: Good impact strength, especially at low temperatures (M grade for -20°C, ML grade for -50°C).
Applications
Bridges & Flood Gates: Due to high strength and weldability.
Cranes & Heavy Machinery: For structural integrity and impact resistance.
Offshore Platforms: For demanding, low-temperature environments.
Storage Tanks & Water Supply Systems: For robust, reliable structures.
