What is the difference between Q420B and Q345 plate

What is the difference between Q420B and Q345 plate?

First of all, both Q420B plate and Q345 plate belong to low-alloy high-strength steel plate, and are used for building and engineering structures.

1. The chemical compositions of Q420B and Q345 plate are different:
Chemical composition of Q420B plate: 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 Q345 plate: 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.

2. The mechanical properties of Q420B and Q345 plate are different:
The mechanical properties of Q345 plate are: yield strength ≥ 265 MPa, tensile strength 450-600 MPa, elongation after fracture ≥ 17%, impact energy 27J.
The mechanical properties of Q420B plate are: yield strength ≥ 340 MPa, tensile strength 500-680 MPa, elongation after fracture ≥ 18%, impact energy 34J.

Q420B plate is the steel plate with yield strength of 420 MPa, the latter B means low temperature impact at 20℃, and Q345 plate is steel plate with yield strength of 345 MPa.