Abstract: The high heat input welding steel 12MnNiVR was trial-produced by two different production processes.The microstructure and mechanical properties of the tested steel were obtained by optical microscope,tensile testing machine and low-temperature impact toughness testing machine,and the post-welding heat treatment behavior of the test steel was simulated by heat treatment test furnace.The results show that the tested steel produced by on-line quenching and off-line tempering process has a large amount of tempered sorbite and a small amount of tempered bainite,and a large number of carbides are evenly distributed on the ferrite matrix.In the quenched and tempered steel,the microstructure at room temperature changes from as-rolled ferrite and pearlite to more homogeneous tempered sorbite with more dispersed carbide after quenching and tempering.The tested steels produced by the two processes both exhibit excellent comprehensive mechanical properties,and after simulated post-weld heat treatment test,their properties did not decrease significantly.The on-line quenching and off-line tempering process has the advantage of eliminating reheat procedure,then can replace the quenching and tempering process,and has a positive and important role in reducing the production cost.