Preparation method of sealing ring material for ultra-supercritical steam turbine

Abstract

A method for preparing a sealing ring material for ultra-supercritical steam turbines belongs to the field of metallic materials. A master alloy is prepared by vacuum induction melting, followed by gas-supported electroslag remelting to obtain an electroslag ingot. The composition of the electroslag ingot is (3.5–4 wt%) Fe, (7.5–8 wt%) Mn, (1.8–2.0 wt%) Nb, (1.5–1.8 wt%) Si, (1.9–2.1 wt%) Ti, (17–18 wt%) B, with the remainder being Co. The electroslag ingot is then processed into a sealing ring blank of the required size using conventional hot deformation technology, held at 250–280°C for 60–90 minutes, and then precision-machined to obtain the finished sealing ring. The material of this invention exhibits excellent wear resistance, corrosion resistance, and high-temperature resistance. Two highly hard submicron-scale dispersed reinforcing phases are formed in the Co matrix. These two reinforcing phases possess high hardness and high strength, and are small in size, ensuring excellent high-temperature resistance of the sealing ring. At application temperatures above 400°C, some Co... 54 B 40 Fe6 can dissolve into the matrix, causing the amorphous matrix lattice to expand, which is beneficial to improving the sealing performance of the sealing ring.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials and relates to a method for preparing a sealing ring material for ultra-supercritical steam turbines. Background Technology

[0002] In steam turbines, sealing rings primarily function to reduce gas leakage and are used extensively in various parts of the turbine. As steam temperatures gradually increase, higher demands are placed on the performance of these sealing rings, requiring them to be more wear-resistant, corrosion-resistant, and possess higher strength under high-temperature conditions. Currently, widely used materials for sealing rings include alloys such as HAYNES 25 and HAYNES 188. While these alloys exhibit excellent high-temperature performance, their relatively poor wear resistance during prolonged high-temperature use can easily lead to increased steam leakage due to wear. Therefore, developing a material with excellent resistance to steam corrosion, wear resistance, and high-temperature strength is crucial for improving the reliability of steam turbines. Summary of the Invention

[0003] This invention designs a novel cobalt-based alloy material for fabricating sealing rings in ultra-supercritical steam turbines. The design concept involves creating multiple submicron-scale reinforcing phases within a cobalt-based amorphous matrix through compositional design. These reinforcing phases possess high hardness and high-temperature stability, and are dispersed throughout the matrix. This results in excellent high-temperature resistance, wear resistance, and corrosion resistance in the sealing ring layer. Partially, under high-temperature conditions, the precipitated phases can partially melt back into the amorphous matrix, causing a 0.1%–0.15% expansion of the sealing ring, which is beneficial for improving its sealing performance. The higher the temperature, the more the precipitated phases melt back, resulting in greater dimensional expansion of the sealing ring and further enhancing its sealing performance.

[0004] A method for preparing a sealing ring material for an ultra-supercritical steam turbine is characterized by: preparing a master alloy by vacuum induction melting, and then obtaining an electroslag ingot by gas-supported electroslag remelting. The composition of the electroslag ingot is (3.5-4 wt%) Fe, (7.5-8 wt%) Mn, (1.8-2.0 wt%) Nb, (1.5-1.8 wt%) Si, (1.9-2.1 wt%) Ti, (17-18 wt%) B, with the remainder being Co. The electroslag ingot is then processed into a sealing ring blank of the required size by conventional hot deformation process. The blank is held at 250-280℃ for 60-90 minutes, and then finished to obtain the finished sealing ring.

[0005] The main mechanism of the alloy composition design in this invention is that by adding alloying elements such as Fe, Mn, Nb, Si, Ti, and B to Co, the matrix becomes amorphous. Furthermore, by strictly controlling the content and proportion of each element, two submicron-scale dispersed strengthening phases with high hardness can be formed in the Co matrix, namely 45-47 wt% Co.54 B 40 Fe6 precipitate, 15-16 wt% B 66 Mn 23 The Ti7Nb4 precipitate and the amorphous matrix exhibit excellent corrosion resistance and high-temperature resistance. The two reinforcing phases possess high hardness and strength, and their small size ensures the sealing ring exhibits excellent high-temperature resistance, wear resistance, and corrosion resistance, especially at operating temperatures above 400℃. Partial Co... 54 B 40 Fe6 can dissolve into the matrix, causing the amorphous matrix lattice to expand. The sealing ring size expands by 0.1% to 0.15%, which is beneficial for improving the sealing performance of the sealing ring. For example, at 500℃, there is 8% Co... 54 B 40 The Fe6 phase dissolves into the matrix, causing a 0.12% expansion of the matrix. This significantly improves the overall performance compared to conventional materials, reducing leakage by more than 10%, which further ensures the safety and reliability of the steam turbine. Detailed Implementation

[0006] Example 1: Preparation of a sealing ring with an inner diameter of Φ40mm, a wall thickness of 1cm, and a height of 2cm.

[0007] The master alloy was prepared by conventional vacuum induction melting, and then electroslag remelting under gas-supported conditions was used to obtain an electroslag ingot. The composition of the electroslag ingot was 3.5 wt% Fe, 7.5 wt% Mn, and 1.8 wt% Nb.

[0008] The mixture consists of 1.5wt% Si, 1.9wt% Ti, 17wt% B, with the remainder being Co. The electroslag ingot is then processed into a sealing ring blank with an inner diameter of Φ39.5mm, a wall thickness of 1.2cm, and a height of 2.1cm using conventional forging and ring rolling processes. The blank is then placed in a heat treatment furnace and held at 250℃ for 60 minutes. Finally, it is precision machined to obtain a finished sealing ring with an inner diameter of Φ40mm, a wall thickness of 1cm, and a height of 2cm.

[0009] Example 2: Preparation of a sealing ring with an inner diameter of Φ50mm, a wall thickness of 1.5cm, and a height of 2cm.

[0010] A master alloy was prepared by vacuum induction melting, and then electroslag remelting under gas-supported conditions was used to obtain an electroslag ingot. The composition of the electroslag ingot was 4 wt% Fe, 8 wt% Mn, 2.0 wt% Nb, 1.8 wt% Si, 2.1 wt% Ti, 18 wt% B, and the remainder was Co. The electroslag ingot was then processed by conventional hot deformation process into a sealing ring blank with an inner diameter of Φ49.5 mm, a wall thickness of 1.7 cm, and a height of 2.1 cm. The blank was held at 280℃ for 90 minutes and then finished to obtain a finished sealing ring with an inner diameter of Φ50 mm, a wall thickness of 1.5 cm, and a height of 2 cm.

Claims

1. A method for preparing a sealing ring material for an ultra-supercritical steam turbine, characterized in that: A master alloy was prepared by vacuum induction melting, and then electroslag remelting under gas-supported conditions was used to obtain an electroslag ingot. The composition of the electroslag ingot was (3.5-4 wt%) Fe, (7.5-8 wt%) Mn, (1.8-2.0 wt%) Nb, (1.5-1.8 wt%) Si, (1.9-2.1 wt%) Ti, (17-18 wt%) B, with the remainder being Co. The electroslag ingot was then processed into a sealing ring blank of the required size by conventional hot deformation process. The blank was held at 250-280℃ for 60-90 minutes, and then finished to obtain the finished sealing ring. Two highly hard submicron-scale dispersed reinforcing phases are formed in the Co matrix, consisting of 45-47 wt% Co. 54 B 40 Fe6 precipitate, 15-16 wt% B 66 Mn 23 Ti7Nb4 precipitate.