Q345 is a material of steel. It is a low alloy steel (C<0.2%), widely used in bridges, vehicles, ships, buildings, pressure vessels, etc. Q stands for the yield of this material, followed by 345, which means that the yield value of this material, at about 345. And will increase with the thickness of the material and its yield value decreases.
Analogous to the nomenclature of Q235.
Q345A, Q345B, Q345C, Q345D, Q345E. This is the distinction between the grades, represented by the main impact temperature is different and carry on!
Q345A level, is not to do impact; Q345B level, is 20 degrees room temperature impact; Q345C level, is 0 degrees impact; Q345D level, is -20 degrees impact; Q345E level, is -40 degrees impact. At different impact temperatures, the value of the impact is also different.