S355 steel is a non-alloy structural steel under the European standard (EN). It has good strength and low-temperature toughness which is widely used in various engineering and structural fields. The following is a detailed classification description of different grades in the S355 series steel (such as S355J2, S355J2G3, S355JR, etc.), covering their naming rules, performance differences and typical applications:
1. Classification Basis of S355 Series Steel (EN 10025-2)
The European standard EN 10025-2 classifies non-alloy structural steels based on the following two points:
1. Yield strength: “S355” indicates a minimum yield strength of 355 MPa.
2. Impact toughness: The impact test temperature and energy requirements are indicated by suffix letters and numbers (such as J0, J2, K2, etc.).
2. Meaning of Suffix Letters & Numbers
1. Impact toughness grade
| Suffix | Impact test temperature | Minimum impact energy (Charpy V-notch) |
| JR | +20°C | ≥27 J |
| J0 | 0°C | ≥27 J |
| J2 | -20°C | ≥27 J |
| K2 | -20°C | ≥40 J (higher toughness requirement) |
2. Other suffixes
- G3: Indicates that the steel has been normalized and rolled, with a more uniform grain structure and stability, suitable for welding and low temperature environments.
- N: Normalized, improves mechanical properties and toughness.
- M: Thermomechanical Rolling, suitable for high strength requirements.
3. Detailed Explanation of Specific Grades
1. S355JR
- Characteristics: basic grade, impact energy ≥27 J at room temperature (+20°C).
- Application:
– Ordinary building structures (non-low temperature environment).
– Factory brackets, ordinary mechanical parts.
2. S355J0
- Characteristics: impact energy ≥27 J at 0°C.
- Application:
– Light bridges in areas with low temperatures in winter.
– Engineering machinery parts in medium low temperature environments.
3. S355J2
- Characteristics: impact energy ≥27 J at -20°C.
- Application:
– Bridges and high-rise buildings in cold areas.
– Ship structures, wind power towers.
4. S355J2G3
- Characteristics: Based on S355J2, after normalizing rolling (G3), the structure is more uniform and the welding performance is better.
- Application:
– Low temperature projects with high requirements for welding quality (such as Arctic oil and gas pipelines).
– High-precision mechanical parts.
5. S355K2
- Characteristics: Impact energy ≥ 40 J at -20°C (higher toughness).
- Applications:
– Extreme low temperature or dynamic load scenarios (such as offshore platforms, heavy-duty cranes).
4. Comparison of Chemical Composition & Delivery Status
| Grade | C (max) | Mn (max) | Si (max) | P/S (max) | Delivery status |
| S355JR | 0.2% | 1.6% | 0.55% | P≤0.035% | Hot rolled (HR) |
| S355J2 | 0.2% | 1.6% | 0.55% | P≤0.03% | Hot rolled or normalized (N) |
| S355J2G3 | 0.18% | 1.6% | 0.5% | P≤0.025% | Normalized rolled (NR) |
| S355K2 | 0.16% | 1.6% | 0.5% | P≤0.025% | Normalizing (N) |
Note:
- G3 and K2 have lower carbon and phosphorus content and higher purity to improve toughness and weldability.
- Normalizing (N) can refine the grain and enhance low temperature properties.
5. Comparison of Typical Application Scenarios
| Grade | Applicable Environment | Typical Engineering Cases |
| S355JR | Normal temperature, no low temperature impact requirements | Ordinary building frames, plant structures |
| S355J0 | Low temperature environment above 0°C | Bridges and light machinery in temperate regions |
| S355J2 | -20°C cold environment | Bridges in cold regions, ship decks, wind turbine towers |
| S355J2G3 | -20°C environment with high welding requirements | Liquefied natural gas (LNG) storage tanks, precision welded structures |
| S355K2 | Extreme low temperature or high impact load | Arctic oil and gas platforms, heavy-duty crane booms |
6. International Standard Comparison
| Grade(EN) | ASTM (USA) | GB/T (China) | JIS (Japan) |
| S355JR | A283 Gr.C | Q355B | SM490A |
| S355J2 | A572 Gr.50 | Q355D | SM490YB |
| S355K2 | A633 Gr.C | Q355E | SM520 (Special Grade) |
Summary
- S355JR: Basic type, suitable for normal temperature environment.
- S355J2: Main low-temperature steel, -20°C general scenario.
- S355J2G3: Optimizes weldability and structural uniformity, used for high-demand low-temperature welding structures.
- S355K2: Ultra-high toughness, suitable for extreme low temperature or impact environment.
Material selection suggestions: Select suffixes according to the use temperature, load type and welding requirements, and pay attention to the impact of delivery status (such as normalizing) on performance.
