What is the difference between S355J2 and S355NL?

The main differences between S355J2 and S355NL are related to their toughness, temperature performance, and their intended use in specific environmental conditions. Both are grades of structural steel under the EN 10025-2 standard, but they differ in their toughness and low-temperature performance.

1. Impact Toughness:
S355J2: This grade is tough at -20°C (the“J2”indicates it can withstand an impact test at -20°C). This makes it suitable for use in moderate to cold environments, where some degree of toughness is required at low temperatures.

S355NL: The“NL”in S355NL stands for“Normalized”or “Normalized Rolling”, and this grade is designed for low-temperature applications. It has improved impact toughness at -50°C, making it ideal for use in very cold environments or in applications that may experience cryogenic temperatures.

2. Low-Temperature Performance:
S355J2: While it is designed to maintain good toughness at temperatures down to -20°C, it is not specifically intended for extremely cold environments.

S355NL: On the other hand, S355NL is specifically designed for low-temperature performance and exhibits superior toughness at -50°C, making it more suitable for harsher climates or critical applications like offshore structures or certain cryogenic equipment.

3. Heat Treatment:
S355J2: This grade is typically thermomechanically rolled, and while it offers good mechanical properties, it does not undergo a specific normalization process to enhance toughness like S355NL.

S355NL: S355NL is normalized rolled or normalized, which helps refine the steel’s microstructure and enhances its toughness, especially in low-temperature conditions.

4. Chemical Composition:
Both grades have similar chemical compositions, primarily consisting of carbon, manganese, silicon, sulfur, and phosphorus. However, S355NL may have slight adjustments in its chemical makeup to enhance its performance in low-temperature environments, while S355J2 is optimized for general structural applications in moderate climates.
5. Applications:
S355J2: It is suitable for general structural applications such as buildings, bridges, and machinery that may be exposed to lower temperatures but not extreme cold. It is commonly used in medium-strength structures.

S355NL: Because of its enhanced low-temperature toughness, S355NL is typically used in offshore platforms, tanks, and bridges where the material must maintain integrity in extreme weather or temperatures, such as in northern or polar climates.

Summary:
In summary, S355J2 is a high-strength structural steel suited for general applications in environments that may experience moderate cold (down to -20°C), while S355NL offers superior low-temperature performance (down to -50°C), making it the better choice for harsh and cryogenic environments. The key difference lies in their impact toughness at low temperatures, with S355NL providing enhanced toughness for more demanding conditions.