CN-121988710-A - Processing method of large-caliber seamless steel tube for nuclear power conventional island

CN121988710ACN 121988710 ACN121988710 ACN 121988710ACN-121988710-A

Abstract

The invention discloses a processing method of a large-caliber seamless steel tube for a nuclear power conventional island, which comprises the following steps of raw material preparation and smelting, centrifugal casting, tube blank post-treatment, finish machining and detection, wherein centrifugal casting comprises the following steps of casting pretreatment, centrifugal casting, tube blank cooling and solidification, namely, a rotary heat extrusion piece is introduced into an inner cavity of a tube blank, a heat insulation coating is further coated on the outer wall of the rotary heat extrusion piece, and periodic radial approaching and separating movement occurs between at least one working part on the outer wall of the rotary heat extrusion piece and the inner wall of the tube blank when the rotary heat extrusion piece rotates, so that the rotary heat extrusion piece can apply periodic radial compaction force to the inner wall of the tube blank. The invention can directly apply acting force to the inner wall of the hollow pipe blank in the cooling and solidifying stage, thereby fundamentally improving the quality of the inner wall so as to produce the hollow pipe blank of the high-quality large-caliber seamless steel pipe with smooth inner wall, compact structure and uniform performance.

Inventors

Han Junshuai
WU LIPENG
XU LUJUN
LUO JIADONG
DING ENLAI

Assignees

浙江泰富无缝钢管有限公司

Dates

Publication Date: 20260508
Application Date: 20260129

Claims (10)

1. The processing method of the large-caliber seamless steel tube for the nuclear power conventional island is characterized by comprising the following steps of: raw material preparation and smelting, namely treating the raw material by adopting a vacuum induction smelting and electroslag remelting process to obtain purified molten steel; centrifugal casting, namely pouring the smelted clean molten steel into a casting mould to form a hollow pipe blank by a centrifugal casting technology; Performing multidirectional die forging on the hollow tube blank to obtain an initial steel tube; finishing and detecting, namely finishing the initial steel pipe into a finished steel pipe meeting the design size through finishing, and detecting the performance of the finished steel pipe; Wherein the centrifugal casting comprises the steps of: The pretreatment stage of the casting mould comprises the steps of cleaning the inner wall of the casting mould, uniformly spraying a layer of refractory coating on the inner wall of the casting mould, and then baking the sprayed casting mould to dry the refractory coating on the inner wall of the casting mould, and simultaneously preheating the whole casting mould to a set temperature; Injecting refined clean molten steel into a rotary casting mould, and uniformly throwing the molten steel to the inner wall of the casting mould under the action of centrifugal force, and spreading the molten steel along the length direction of the casting mould to form a tube blank; And in the tube blank cooling and solidifying stage, a rotary thermal extrusion piece is introduced into the inner cavity of the tube blank, the outer wall of the rotary thermal extrusion piece is further coated with a heat-insulating coating, and when the rotary thermal extrusion piece rotates, at least one working part on the outer wall of the rotary thermal extrusion piece and the inner wall of the tube blank periodically perform radial approaching and separating movement, so that the rotary thermal extrusion piece can apply periodic radial compaction force to the inner wall of the tube blank.
2. The method for processing the large-caliber seamless steel tube for the nuclear power conventional island according to claim 1, wherein the rotary hot extrusion is driven by the eccentric mechanism, the rotation axis of the rotary hot extrusion is parallel to the rotation axis of the tube blank, and a preset eccentric distance is arranged between the rotation axis of the rotary hot extrusion and the rotation axis of the tube blank, so that the rotary hot extrusion can generate periodical radial compaction force on the inner wall of the tube blank in the rotation process.
3. The method for processing a large-caliber seamless steel tube for a nuclear power conventional island according to claim 2, wherein the preset eccentric distance is 1% to 4% of the inner diameter of the tube blank.
4. The method of processing a large-caliber seamless steel pipe for a nuclear power conventional island according to claim 1, wherein the rotation axis of the rotary heat pressing member coincides with the rotation axis of the pipe blank, and the outer contour of the rotary heat pressing member is a shaped structure having at least one radial protrusion which periodically applies a radial compacting force to the inner wall of the pipe blank during rotation of the rotary compacting member.
5. The method for manufacturing a large-caliber seamless steel pipe for a nuclear power conventional island according to claim 4, wherein the number of the radial protruding parts is 2-6, and the radial protruding parts are uniformly distributed along the circumferential direction of the rotary heat extrusion.
6. The method for manufacturing a large-caliber seamless steel pipe for a nuclear power conventional island according to claim 4, wherein the ratio of the maximum circumcircle radius of the radial protrusion to the inner diameter of the tube blank is in the range of 1.01 to 1.10.
7. The method for manufacturing a large-caliber seamless steel pipe for a nuclear power conventional island according to claim 1, wherein a ratio of a rotational speed of the rotary hot extrusion to a rotational speed of the mold is 1:0.8 to 1:1.5.
8. The method for manufacturing a large-caliber seamless steel pipe for a nuclear power conventional island according to claim 1, wherein the centrifugal casting stage is characterized in that when molten steel refined is injected into a rotating casting mold, the casting mold rotates at a first rotation speed; The pipe blank cooling and solidifying stage comprises the steps of lifting the rotating speed of a casting mould from the first rotating speed to a second rotating speed in a preset time, and maintaining the second rotating speed of the casting mould until molten steel in the casting mould is completely solidified to form a hollow pipe blank; The second rotating speed is higher than the first rotating speed, so that the centrifugal force acting on molten steel in the cooling and solidifying stage of the tube blank is higher than that in the pouring stage.
9. The method for manufacturing a large-caliber seamless steel pipe for a nuclear power conventional island according to claim 1, wherein molten steel is introduced into a casting mold through a casting groove rotating synchronously with the casting mold in the centrifugal casting stage, and a liquid outlet of the casting groove is directed in a tangential direction of an inner wall of the casting mold.
10. The method for processing the large-caliber seamless steel pipe for the nuclear power conventional island according to claim 8, wherein the centrifugal force coefficient G1 corresponding to the first rotation speed is 10-40; the centrifugal force coefficient G2 corresponding to the second rotating speed meets the condition that G2 is more than or equal to 60.

Description

Processing method of large-caliber seamless steel tube for nuclear power conventional island Technical Field The invention relates to the technical field of seamless steel tube production, in particular to a method for processing a large-caliber seamless steel tube for a nuclear power conventional island. Background In a nuclear power plant, a nuclear island is the "nuclear" core portion of the plant, involving nuclear reactions and radioactive materials, whose primary function is to generate heat using nuclear fission. The conventional island is a "conventional" part of a nuclear power plant, and does not involve nuclear reactions, and its main function is to convert heat generated by the nuclear island into electrical energy. In the field of nuclear power conventional islands, a main steam/main water supply pipeline is subjected to high temperature, high pressure, high flow rate medium flushing and complex stress for a long time, so that the requirements for producing large-caliber seamless steel pipes of the main steam/main water supply pipeline are very harsh, and compared with common seamless steel pipes, the production process has obvious differences in material, process precision and quality control. The production process of the large-caliber seamless steel tube for the nuclear power conventional island in the prior art mainly comprises the following steps of: Duplex smelting, namely adopting a vacuum induction smelting (VIM) and electroslag remelting (ESR) duplex process, wherein the step can obtain pure molten steel with high purity, low gas and harmful element content and uniform components. Centrifugal casting, namely directly casting the refined purified molten steel into a hollow tube blank with a specific inner cavity (such as a hexagon) through a centrifugal casting technology. Multi-directional forging, i.e., multi-directional forging is performed on a multi-directional forging press, and the die can simultaneously or sequentially apply pressure to the hollow tube blank from multiple directions (usually horizontal and vertical), and through multi-directional forging, the hollow tube blank is converted from an as-cast blank into an initial steel tube with compact structure, fine grains and a shape approaching the final size. Finishing and detecting, namely ensuring the final dimensional accuracy and the structural performance of the steel pipe through finishing. In the production process of the large-caliber seamless steel tube for the nuclear power conventional island, centrifugal casting is one of key processes for manufacturing a blank of the large-caliber seamless steel tube for the nuclear power conventional island, and the principle is that liquid metal is tightly attached to the inner wall of a casting mold by utilizing centrifugal force generated by a high-speed rotary casting mold, so that a hollow tube blank is formed. The process has the outstanding advantages that the hollow pipe blank close to the final shape can be directly obtained, the metal yield is high, and the process is particularly suitable for difficult-to-deform materials such as high alloy steel and the like. However, the quality of the inner surface and the internal metallurgical integrity of the hollow shell obtained are always technical difficulties, subject to the physical characteristics of the process itself. Specifically, the inner wall of the tube blank is extremely prone to the following prominent problems during processing. Firstly, the quality of the inner surface of the hollow shell is a problem. Because of improper control of casting parameters or poor casting state, macroscopic defects such as wrinkled skin, cold shut and the like often appear on the inner wall, so that the surface roughness is far beyond the machining requirement. The second is an internal metallurgical defect, which is directly related to the intrinsic properties of the material. In the directional solidification process from outside to inside, shrinkage porosity and shrinkage cavity are easily formed due to the interruption of the feeding channel in the central area of the tube blank. The defects seriously damage the compactness of the metal, so that the metal is easy to generate medium permeation and crack early expansion under the pressure-bearing working condition. Meanwhile, gas and impurities which cannot be completely removed in the smelting process are enriched towards the inner wall under the action of centrifugal force, so that air holes, pinholes and inclusion bands are formed, and the mechanical property and the corrosion resistance of the material are further deteriorated. In addition, segregation of alloy elements in the solidification process also causes differences in chemical composition and structure between the inner wall and the outer wall, and the overall performance of the tube blank is uneven. Moreover, the problems of uneven wall thickness, excessive ovality and the like caused by uneven vibration, deformation