What is the difference between Q345B material and Q420B steel

What is the difference between Q345B material and Q420B steel?

The chemical constituents of Q345B material and Q420B steel were different:
Chemical composition of Q420B steel: C ≤ 0.20, Si ≤ 0.50, Mn ≤ 1.70, P ≤ 0.035, S ≤ 0.035, Nb ≤ 0.07, V ≤ 0.20, Ti ≤ 0.20, Cr ≤ 0.30, Ni ≤ 0.80, Cu ≤ 0.30, N ≤ 0.015, Mo ≤ 0.20.
Chemical composition of Q345B material: C ≤ 0.18-0.20, Si ≤ 0.50, Mn ≤ 1.70, P ≤ 0.035, S ≤ 0.035, Nb ≤ 0.07, V ≤ 0.15, Ti ≤ 0.20, Cr ≤ 0.30, Ni ≤ 0.50, Cu ≤ 0.30, N ≤ 0.012, Mo ≤ 0.10.

The mechanical properties of Q345B material and Q420B steel are different:
The mechanical properties of Q345B material are: yield strength ≥ 265 MPa, tensile strength 450-600 MPa, elongation after fracture ≥ 17%, impact energy ≥ 27J.
The mechanical properties of Q420B steel are: yield strength ≥ 340 MPa, tensile strength 500-680 MPa, elongation after fracture ≥ 18%, impact energy ≥ 34J.

Q345B material is widely used in bridges, vehicles, ships, buildings, pressure vessels, etc. The yield value decreases with the increase of material thickness.

Q420B steel is suitable for power tower, all kinds of crane, heavy truck, oil derrick, high temperature fan, large shovel, dump truck and drilling rig, coal mine hydraulic support, steel structure, etc.