400MPa-grade TMCP steel plate with excellent welding performance and production method of 400MPa-grade TMCP steel plate

The invention discloses a 400MPa-grade TMCP steel plate with excellent welding performance and a manufacturing method thereof, and belongs to the technical field of metal material production. The steel plate is produced through a continuous casting billet with the thickness of 150-250 mm, in the smelting process, SiMn alloy is used for pre-deoxidation, TiFe is used for deep deoxidation, then NiMg alloy wires are fed, white slag is made in the LF refining treatment procedure, the content of alloy elements is finely adjusted, then RH degassing treatment is conducted, and the content of N is adjusted. And controlling the section equiaxed crystal zone proportion of the continuous casting billet to be less than or equal to 25%. And heating the continuous casting billet, and then manufacturing the continuous casting billet into a steel plate with the thickness of 6-60mm through a controlled rolling and controlled cooling process. The steel plate ReH is larger than or equal to 390 MPa, the Rm is larger than or equal