What is the difference between 20Mn2 seamless steel pipe and Q345 seamless steel pipe?

Chemical composition difference between 20Mn2 seamless steel pipe and Q345 seamless steel pipe:
Chemical composition of 20Mn2 seamless steel pipe: C: 0.17-0.24, Si: 0.17-0.37, Mn: 1.40-1.80.
The chemical composition of Q345 seamless steel pipe is as follows: C ≤ 0.18, Si ≤ 0.50, Mn ≤ 1.70, P ≤ 0.030, S ≤ 0.025, Nb ≤ 0.07, V ≤ 0.15, Ti ≤ 0.20, Cr ≤ 0.30, Ni ≤ 0.50, Cu ≤ 0.30, N ≤ 0.012, Mo ≤ 0.10, Al ≥ 0.015.

Mechanical properties difference between 20Mn2 seamless steel pipe and Q345 seamless steel pipe:
Mechanical properties of 20Mn2 seamless steel pipe: tensile strength ≥ 785 MPa, yield strength ≥ 590 MPa, elongation after fracture ≥ 10%, section expansion rate ≥ 40%, impact absorption energy ≥ 47J.

The mechanical properties of Q345 seamless steel pipe are: yield strength ≥ 265 MPa, tensile strength 450-600 MPa, elongation after fracture ≥ 17%, impact energy 27J. Q345D seamless pipe has good comprehensive mechanical properties, low-temperature impact toughness, cold stamping, machinability and weldability.