The S355 steel material itself is divided into many grades, so it cannot be said that S355 is equivalent to which grade of the national standard Q345, ASTM A709 low alloy steel sheet. In engineering, usually S355JR steel is equivalent to Q345B steel, S355J0 steel is equivalent to Q345C steel, S355J2 steel is equivalent to Q345D steel, S355N steel is equivalent to Q345D steel, and S355NL steel is equivalent to Q345E steel.
Z-direction steel refers to thick steel with good tensile resistance in thickness direction. In the application of steel plate, the reason for additional performance requirements on the thickness direction of steel is due to the existence of defects in the thickness direction of steel in the process of casting and rolling. This defect makes the steel prone to lamellar tearing during welding, which reduces or even loses the design bearing capacity of application. The Z-direction performance is required for ASTM A709 low alloy steel sheet and so on steel plate with the tensile force along the plate thickness direction greater than or equal to 40mm.
The main reference for structural design of steel structure engineering is the static and dynamic characteristics of the steel used under various actions, such as elasticity, plasticity, strength, toughness, fatigue and other mechanical properties. Therefore, the ASTM A709 low alloy steel sheet and so on steel used in the construction of steel structure engineering will limit its strength, plasticity, impact toughness and weldability. Steel structure engineering requires high tensile strength and yield point of steel. High yield point can reduce the cross-section of the component, so as to reduce the weight, save steel and reduce the cost. High tensile strength can increase the safety of the structure.
