Description
S355J2+N Steel is a high-strength, low-alloy structural steel grade that falls under the EN 10025-2 European standard. The “S” stands for structural steel, “355” refers to the minimum yield strength in MPa (355 MPa), and “J2” indicates that the material has a Charpy V-notch impact test of 27J at -20°C. The “+N” signifies that the material has undergone normalization, a heat treatment process that improves the steel’s toughness, ductility, and mechanical properties.
S355J2+N is widely used in heavy-duty applications where both strength and toughness are required, especially in cold or dynamic environments.
Properties of S355J2+N Steel:
- Carbon Content: 0.20% (max)
- Manganese Content: 1.60% (max)
- Tensile Strength: 490–630 MPa (71,000–91,000 psi)
- Yield Strength: 355 MPa (51,500 psi)
- Impact Toughness: 27J at -20°C (tested under J2 conditions)
- Elongation: ~22% (longitudinal)
- Hardness: 146-187 HB (Brinell)
- Weldability: Excellent (can be welded without preheating in most applications)
- Corrosion Resistance: Moderate (not inherently resistant, often requires protective coatings)
- Machinability: Good, especially in normalized form
- Formability: Good (can be formed and shaped easily)
The “+N” or normalization process refines the grain structure, making the steel tougher and more resilient. Normalization also improves the steel’s resistance to brittle fracture, which is important for applications where dynamic or impact loads are involved.
Grades of S355J2+N Steel:
S355J2+N steel is commonly available in various forms based on the type of rolling and heat treatment.
| Grade | Description |
|---|---|
| S355J2+N Hot-Rolled | Steel is produced by hot rolling and then normalized, providing high strength and toughness with a slightly rougher surface finish. Suitable for large structural components. |
| S355J2+N Cold-Rolled | This grade is cold-rolled and normalized for improved surface finish and precision, making it ideal for parts that require tighter dimensional tolerances. |
| S355J2+N Normalized | Steel is heat-treated (normalized) to improve its mechanical properties, specifically toughness and ductility, used in critical structural and machinery applications. |
Applications of S355J2+N Steel:
| Industry/Field | Applications |
|---|---|
| Construction | Widely used in heavy structural components like columns, beams, and trusses for bridges, skyscrapers, and large infrastructure projects due to its high strength and toughness. |
| Shipbuilding | Applied in ship hulls, decks, and offshore structures where strength and resistance to brittle fracture are critical in harsh, cold marine environments. |
| Machinery | Ideal for manufacturing large frames, supports, and heavy-duty equipment parts that endure dynamic loads, such as cranes, forklifts, and earth-moving machinery. |
| Energy (Wind Turbines) | Used in wind turbine towers and other structural components where fatigue resistance and toughness are essential to withstand dynamic loading and environmental conditions. |
| Mining and Quarrying | Employed in mining and quarry equipment, such as frames, crushers, and drilling equipment, which need to be both tough and strong to handle abrasive and high-load conditions. |
| Railways | Used in railway tracks, underframes, and components that require high impact toughness and durability under dynamic loading conditions. |
| Pressure Vessels | Used in the production of storage tanks and pressure vessels for moderate-pressure applications due to its ability to handle stress and dynamic loads. |
| Cranes and Heavy Lifting | Suitable for manufacturing crane parts, heavy-duty lifting equipment, and other load-bearing components where high strength and good weldability are necessary. |
Advantages of S355J2+N Steel:
- High Strength and Toughness: S355J2+N offers high tensile and yield strength, making it ideal for load-bearing and dynamic applications.
- Improved Impact Resistance: The “J2” designation ensures good impact resistance at low temperatures, while normalization further enhances toughness.
- Excellent Weldability: S355J2+N steel can be easily welded without the need for preheating, reducing fabrication costs and time.
- Good Formability: Despite its high strength, S355J2+N maintains good ductility, allowing it to be formed into complex shapes and structural components.
- Resistant to Brittle Fracture: Normalization significantly improves the material’s ability to resist brittle fracture, especially in cold or dynamic environments.
Limitations of S355J2+N Steel:
- Corrosion Resistance: Like most structural steels, S355J2+N is not inherently corrosion-resistant and requires protective coatings (such as galvanizing or painting) for outdoor or corrosive environments.
- Machinability: While S355J2+N is machinable, its higher strength compared to softer steels can result in increased tool wear and slower machining speeds.
Comparison with Other Structural Steels:
| Steel Grade | Comparison with S355J2+N Steel |
|---|---|
| S275JR | S275JR has a lower yield strength (275 MPa) compared to S355J2+N (355 MPa), making it suitable for less demanding applications where high strength is not essential. |
| S235JR | S235JR has even lower yield strength and tensile strength, making S355J2+N more suitable for structural applications requiring higher strength and impact resistance. |
| S355J2 | S355J2+N has the same chemical composition as S355J2 but with improved mechanical properties due to the normalization process, offering better toughness and ductility. |
| S460 | S460 is a high-strength steel grade with even greater yield strength (460 MPa), suitable for very demanding applications but may have lower ductility compared to S355J2+N. |
Heat Treatment and Hardening of S355J2+N Steel:
- Normalization: The normalization process is applied to S355J2+N to improve its mechanical properties. This involves heating the steel to a high temperature (typically around 900°C), then air-cooling it. This refines the grain structure, enhancing strength, toughness, and ductility.
- Tempering and Quenching: While S355J2+N is not typically heat-treated for hardening, quenching and tempering can be applied to increase hardness for specific applications where wear resistance is required.
