The invention relates to a manufacturing method for a G115 large-
caliber thick-wall seamless steel
pipe of a 630 DEG C ultra-supercritical unit, and belongs to the field of manufacturing of
heat resistant steel pipes. In the method, for the long-term problem of weak
impact toughness in production of the G115 large-
caliber thick-wall seamless steel
pipe, the following processes of preparation of araw material (
forging stocks / steel ingots), closed upsetting, backward
extrusion punching,
extrusion moulding, heat treatment (rapid cooling and annealing) after
extrusion and property heat treatmentare organically combined, and technological parameters of the patent CN103045962B are broken through, so that the
impact toughness after heat treatment is performed on the steel
pipe is greatly improved, and all properties can meet standard requirements of a T / CISA 003-2017 standard. Different specifications of G115 large-
caliber thick-wall seamless steel pipes with the outer
diameter of 325-1,200mm, the wall thickness of 20-180mm and the length of 12,500mm or below 12,500mm can be produced by adopting the method and can be applied to different fields of four major pipelines of an advanced ultra-supercritical boiler, a
power station and the like. The steel ingots are adopted as the
raw material, so that the production cost can be greatly reduced.