What are the differences between 15CrMoR and Q345R steel

The chemical constituents of 15CrMoR and Q345R steel are different:
Chemical composition of 15CrMoR steel: C: 0.12-0.18, Si: 0.15-0.40, Mn: 0.40-0.70, P: ≤ 0.025, S: ≤ 0.010, Cr: 0.80-1.20, Mo: 0.30-0.60.

Chemical composition of Q345R steel: C: ≤ 0.20, Si: ≤ 0.55, Mn: 1.20-1.70, P: ≤ 0.025, S: ≤ 0.010, Cu: ≤ 0.30, Ni: ≤ 0.30, Cr: ≤ 0.30, Mo: ≤ 0.08.

The mechanical properties of 15CrMoR and Q345R steel are different:
15CrMoR steel yield strength: 6-60mm: ≥ 295 MPa, 60-100mm: ≥ 275 MPa, 100-150mm: ≥ 255 MPa.
Tensile strength: 440-590 MPa.
Impact energy: temperature: 0℃: ≥ 31J.
Elongation: ≥ 19%.

Q345R steel mechanical properties: yield strength: ≤ 16mm: ≥ 345 MPa, 16-36mm: ≥ 325 MPa, 36-60mm: ≥ 315 MPa, 60-100mm: ≥ 305 MPa, 100-150mm: ≥ 285 MPa, 150-200mm: ≥ 265 MPa.
Tensile strength: 470-640 MPa.
Impact energy: temperature: 0℃: ≥ 34J.
Elongation: ≥ 21%.

15CrMoR is pressure vessel steel. Q345R steel is a kind of medium temperature hydrogen resistant steel; Q345R steel plate is widely used in petroleum, chemical industry, power station, boiler and other industries, and is generally used to make reactors, heat exchangers, separators, gas pipes, liquefied gas tanks, liquefied petroleum gas cylinders, etc.