What does ABCDER stand for behind Q345 steel plate

What does ABCDER behind Q345 steel plate stand for respectively?

Q345 can be divided into Q345A, Q345B, Q345C, Q345D and Q345E. What they represent is that the impact temperature is different.

Q345A, no impact;
Q345B, 20℃ room temperature impact;
Q345C, 0 degree impact;
Q345D, - 20 degree impact;
Q345E, - 40 degree impact.
At different impact temperature, the impact value is also different.

The R behind Q345 steel plate represents that it is steel plate for high pressure vessel, and R is the initial letter of vessel.