What is the difference between Q420 and C45 steel

What is the difference between Q420 and C45 steel?
Q420 steel belongs to low alloy high strength steel, and C45 steel belongs to high quality carbon structural steel.

Differences in chemical composition between Q420 and C45 steel:
The chemical composition of Q420 steel is 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 C45 steel:
C: 0.42%-0.50%, Si: 0.17%-0.37%, Mn: 0.50%-0.80%, Cr: ≤0.25%, Ni: ≤0.30%, Cu: ≤0.25%.