Grain size refining manufacturing method of large-diameter TP316H stainless steel seamless steel pipe

The invention relates to a grain size refining manufacturing method of a large-diameter TP316H stainless steel seamless steel pipe. Integrated innovative technologies such as fine high-melting-point rare earth inclusions, increase of carbonitride nucleation particles, low-melting-speed rapid solidification for eliminating thick dendritic crystals, blank grain coarsening control through blank temperature gradient high-temperature heating, large-die-angle large-deformation, on-line rapid lubrication complete dynamic recrystallization low-temperature extrusion, rapid cooling after extrusion, temperature gradient high-temperature solid solution and the like are adopted. Under the process condition that cold deformation is not adopted, the grain size of the large-section thick-wall TP316H extruded seamless steel pipe is controlled to be 4.0-6.0 grade, the requirement for uniform grain refinement of the product is met, the technical problem of industry necks is solved, and the manufacturing technical level of large