What is the difference between Q420R and Q345R plates

Q420R and Q345R are steel plates for medium and low temperature pressure vessels.
Q420R and Q345R plates implementation standards: GB/T713.
Q420R and Q345R delivery status: hot rolling, controlled rolling, normalizing.

Chemical composition analysis of Q420R and Q345R plates:
Q420R plates: C: no more than 0.20, Si: not greater than 0.55, Mn:1.30-1.70, Cu: not greater than 0.3, Ni: 0.2-0.5, Cr: no more than 0.3, Mo: not greater than 0.08, P: not greater than 0.02, S: not greater than 0.01.

Q345R plates: carbon C: no more than 0.2, silicon Si: not greater than 0.55, manganese Mn:1.20-1.70, P: no more than 0.025, sulfur S: no more than 0.01, Ni: no more than 0.3, Cr: no more than 0.3, Mo: not greater than 0.08, Nb: not greater than 0.05, V: not greater than 0.05, Ti: not greater than 0.03.

Mechanical properties analysis of Q420R and Q345R plates:
Q420R yield strength: thickness: 10-20mm: yield strength is not less than 420
Q420R yield strength: thickness: 20mm-30mm: yield strength is not less than 400
Q420R tensile strength: 570-720
Q420R elongation: not less than 18
Q420R impact temperature: - 20℃

Q345R yield strength: thickness not more than 16mm: yield strength not less than 345
Q345R yield strength: thickness 16mm-36mm: yield strength not less than 325
Q345R yield strength: thickness 36mm-60mm: yield strength is not less than 315
Q345R yield strength: thickness 60mm-100mm: yield strength not less than 305
Q345R yield strength: thickness 100mm-150 mm: yield strength not less than 285
Q345R yield strength: thickness: 150-200mm: yield strength is not less than 265
Q345R tensile strength: 470-640
Q345R elongation: not less than 21
Q345R impact temperature: - 20℃

Q420R and Q345R plates are mainly used in petroleum, chemical industry, power station, boiler and other industries. They are generally used for the production of reactors, heat exchangers, separators, air guide pipes, liquefied gas tanks, boiler gas bags and liquefied petroleum cylinders.