Method for improving performance of large-caliber thick-wall pipe obtained by casting and extrusion compound forming

The invention relates to a method for improving performance of a large-caliber thick-wall pipe obtained by casting and extrusion compound forming, and belongs to the technical field of methods for improving the performance of the large-caliber thick-wall pipe. Through the adoption of the method disclosed by the invention, the technical problems that the microscopic structure of a formed part is uneven and the grain size is overlarge existing in a casting and extrusion compound forming technology of a large-caliber thick-wall pipe. The technical scheme adopted by the invention lies in that the method for improving the performance of the large-caliber thick-wall pipe by casting and extrusion compound forming comprises the following steps of (1) melting alloys; (2) refining molten steel; (3) performing riser casting on the refined molten steel to obtain a hollow casting blank; (4) performing homogenizing treatment on the obtained hollow casting blank; (5) performing dephosphorization on the homogenized hollow ca