What is the meaning of Jo in S355Jo?

In the designation S355JO, the "Jo" indicates the steel's impact properties at a specific temperature. The "J" signifies that the steel has been tested for impact toughness at a temperature of 0°C, while the "o" denotes that the steel can withstand a minimum Charpy impact energy of 27 joules at that temperature. This classification is part of the European standard for structural steel, ensuring the material's performance in various conditions.