What is the difference between Q345B material and Q345A steel

What is the difference between Q345B material and Q345A steel

What is the difference between Q345B material and Q345A steel?
Q345B material and Q345A steel are slightly different in chemical composition:
Q345A steel:C≤0.20, Mn ≤1.7, Si≤0.55, P≤0.045, S≤0.045, V 0.02~0.15;
Q345B material:C≤0.20, Mn ≤1.7, Si≤0.55, P≤0.040, S≤0.040, V 0.02~0.15;

The difference between Q345B material and Q345A steel is mainly in A and B behind the material:
Q345A steel, no impact;
Q345B material, 20℃ room temperature impact.

Q345B material needs impact test at 20℃ to test its toughness index. In fact, although their strength is the same, the S / P control of Q345B material is more strict, and the ambient temperature of Q345B material is different. The higher the quality grade, the lower the temperature range they can use. Cold impact test refers to the impact test at a certain temperature to obtain the energy consumed by the punching pattern. The more energy consumed, the higher the toughness of the material. So Q345B material is better than Q345A steel.