Preparation method of regulating stage blade root gasket material for gas turbine

Abstract

The invention discloses a preparation method of a regulating stage blade root gasket material for a gas turbine, and belongs to the field of metal materials. According to the invention, Ni is used as a matrix, six alloy elements of Cr, Co, Nb, Zr, Si and B are added, in order to form different types of boride phases stably existing at a high temperature, particularly, the content of B is controlled to be 2.8-3 wt%, so that about 15 wt% of (Cr, Ni) 3B2 phase, about 6 wt% of ZrB2 phase and about 8 wt% of Ni14Nb5Si6G phase are formed in the matrix by optimizing the component content and combining subsequent solid solution and aging heat treatment, and a powder metallurgy process is adopted for preparation. According to the invention, three dispersively distributed strengthening phases, namely 15 wt% of a (Cr, Ni) 3B2 phase, 6 wt% of a ZrB2 phase and 8 wt% of a Ni14Nb5Si6G phase, are formed in a matrix, so that the alloy has high hardness and strength, and also has high toughness. The hardness of the alloy reaches 40 HRC or above, the yield strength reaches 1180 MPa, the ductility reaches 14%, the performance of the alloy far exceeds that of Nimonic90 alloy which is widely used at present, and the service life of the blade root gasket prepared through the technology exceeds 20 months and is two times or above that of a common Nimonic90 alloy gasket.

Description

Technical Field

[0001] The invention belongs to the field of metal materials and relates to a method for preparing a blade root gasket material for a gas turbine regulating stage. Background Art

[0002] Blades are key parts of gas turbines, and are also one of the most delicate and important parts. They are subjected to high temperature, high pressure, huge centrifugal force, steam force, steam excitation force, corrosion and vibration, and water drop erosion in the wet steam zone under extremely harsh conditions. Their aerodynamic performance, processing geometry, surface roughness, installation clearance, operating conditions, scaling and other factors all affect the efficiency and output of the steam turbine, while their structural design, vibration intensity and operating mode have a decisive influence on the safety and reliability of the unit. When installing the blades, there is a gap between them, and they are fixed by adding a gasket between the two blades. The gasket has two functions: one is to protect the root of the blade from being scratched by external forces; the other is to achieve a close fit of the blades to prevent loosening.

[0003] In actual use, the main failure form of blade root gaskets is plastic deformation caused by stress, which leads to thickness reduction, gaps between blades, and easy vibration of blades. Therefore, the ideal gasket material should have high high temperature compressive strength and yield strength to resist extrusion deformation from the blade root. At present, the materials used to make gaskets are all mature nickel-based alloys, such as Nimonic90. Although these alloys have excellent high temperature performance, they are not ideal choices for gaskets, because when used as gaskets, a slight deformation in the thickness direction will cause a gap between the two blade roots, and the main reason for this slight deformation is related to the strengthening mechanism. The main strength mechanism of nickel-based alloys is γ´ phase and carbide strengthening. With the extension of service time or temperature fluctuations, the γ´ phase and carbide strengthening phase will aggregate and grow, causing a decrease in strength, resulting in deformation failure due to the decrease in strength when the stress remains unchanged. Therefore, the development of nickel-based high temperature alloys based on new strengthening mechanisms, where the strengthening phase can be stably present at the service temperature, is an important way to increase the life of blade root gaskets. Summary of the invention

[0004] The present invention designs a new nickel-based high-temperature alloy, which is strengthened by three strengthening phases and prepared by powder metallurgy. The three strengthening phases are uniform and fine, can stably exist at 600°C to 900°C, and will not cause the strengthening phases to aggregate and grow due to long-term service, resulting in a decrease in strength, thereby ensuring that the blade root gasket has a long service life.

[0005] A method for preparing a blade root gasket material for a gas turbine regulating stage, characterized in that the gasket material comprises the following components: Ni~(17-18wt%)Cr~(5.5-6wt%)Co~(4.5-6wt%)Nb~(4.5-5.0wt%)Zr~(2.8-3.0wt%)Si~(2.8-3wt%)B, and the main production process of the blade root gasket comprises the preparation of water-gas combined atomization alloy powder, hot isostatic pressing sintering, precision hot rolling, solution and aging heat treatment, plate cold rolling and flattening, and laser cutting.

[0006] Furthermore, the method for preparing the gas turbine regulating stage blade root gasket material is characterized in that:

[0007] The specific preparation steps are as follows:

[0008] (1) Preparation of water vapor atomization powder: Alloy smelting is carried out according to the composition of Ni~(17-18wt%)Cr~(5.5-6wt%)Co~(4.5-6wt%)Nb~(4.5-5.0wt%)Zr~(2.8-3.0wt%)Si~(2.8-3wt%)B, and then the powder is prepared by water vapor combined atomization process. The average particle size of the powder is required to be controlled at 5-6 microns, and the oxygen content is controlled below 1000ppm;

[0009] (2) hot isostatic pressing the alloy powder at a sintering temperature of 1100° C. to 1120° C. to obtain a hot isostatic pressed ingot;

[0010] (3) hot rolling the block into a plate, the hot rolling start temperature is 1030 to 1100 ° C, the stop temperature is greater than 1000 ° C, the thickness of the plate after hot rolling ranges from 0.5 mm to 2.0 mm, and the tolerance accuracy is ± 0.05 mm;

[0011] (4) Solution and aging heat treatment: After hot rolling, the plate is subjected to solution heat treatment at a temperature of 1090-1100°C. The holding time is set according to 3-5 minutes / mm thickness. After solution heat treatment, it is air-cooled; then aging treatment is carried out at an aging temperature of 910-920°C for 60-90 minutes.

[0012] (5) Cold rolling and leveling: The hot-rolled plate that has undergone solution and aging treatment is cold-rolled and leveled, and its tolerance accuracy is increased from ±0.05mm in the hot-rolled state to ±0.02mm;

[0013] (6) Laser cutting: The cold-rolled sheet that has been cold-rolled to the required thickness is cut into the required size and shape by laser to obtain the finished blade root gasket.

[0014] The principle of the invention is as follows: Ni is used as the matrix, and six alloy elements, Cr, Co, Nb, Zr, Si, and B, are added. In order to form different types of boride phases that can exist stably at high temperatures, the B content is particularly controlled to be 2.8-3wt%. By optimizing the component content and combining subsequent solid solution and aging heat treatment, about 15wt% (Cr, Ni)3B2 phase, about 6wt% ZrB2 phase, and about 8wt% Ni are formed in the matrix. 14 Nb5Si6 G phase, these three phases have high thermal stability and can exist stably at 600 to 900℃; in addition, the powder metallurgy process can control the size of these three phases to less than 1 micron, so that they are dispersed in the matrix, ensuring strength while the alloy has high toughness. The hardness of the alloy reaches more than 40HRC, the yield strength reaches 1180MPa, and the elongation reaches 14%. The performance is far superior to the widely used Nimonic90 alloy. The blade root gasket prepared by the above process has a service life of more than 20 months, which is more than twice the life of ordinary Nimonic90 alloy gaskets. DETAILED DESCRIPTION

[0015] (1) Since the thickness of the blade root gasket is usually a series of thicknesses from 0.5 mm to 2.0 mm, three typical thicknesses of 0.5 mm, 1.0 mm and 2.0 mm are selected in the specific implementation for illustration, and 100 gaskets with a manufacturing specification of 3 cm (length) × 2 cm (width) × 2.0 ± 0.02 mm (thickness), 100 gaskets with a specification of 3.5 cm (length) × 2.5 cm (width) × 1.0 ± 0.02 mm (thickness), and 100 gaskets with a specification of 2.5 cm (length) × 1.5 cm (width) × 0.5 mm ± 0.02 mm thickness are respectively manufactured.

[0016] The specific manufacturing steps are:

[0017] In the first step, the alloy powder is prepared by a water-gas combined atomization process. The powder composition is Ni~(17-18wt%)Cr~(5.5-6wt%)Co~(4.5-6wt%)Nb~(4.5-5.0wt%)Zr~(2.8-3.0wt%)Si~(2.8-3wt%)B. The average particle size of the prepared powder is controlled at 5-6 microns, and the oxygen content is controlled below 1000ppm.

[0018] The second step is to put the alloy powder into a bag for hot isostatic pressing sintering at a sintering temperature of 1100° C. to 1120° C. to obtain a hot isostatic pressing ingot block;

[0019] The third step is to hot roll the block into a plate. The hot rolling start temperature is 1030 to 1100°C, and the stop temperature is greater than 1000°C. The thickness range of the plate after hot rolling is 0.5mm, 1.5mm, 2.0mm, and the tolerance accuracy is ±0.05mm.

[0020] The fourth step is to carry out solution heat treatment on the plate after hot rolling at a temperature of 1090-1100°C, with the holding time set at 3-5 minutes / mm thickness, and air cooling after solution heat treatment; then carry out aging treatment at an aging temperature of 910-920°C for 60-90 minutes.

[0021] The fifth step is to perform cold rolling and leveling treatment on the hot-rolled plate after solid solution treatment, and improve its tolerance accuracy from ±0.05mm in hot-rolled state to ±0.02mm.

[0022] In the sixth step, the cold-rolled plates of three thicknesses are cut into the required size and shape by laser to obtain the finished blade root gaskets.

Claims

1. A method for preparing a gas turbine regulating stage blade root gasket material, characterized in that: The composition of the gasket material is: Ni~(17-18wt%)Cr~(5.5-6wt%)Co~(4.5-6wt%)Nb~(4.5-5.0wt%)Zr~(2.8-3.0wt%)Si~(2.8-3wt%)B. The main production process of the blade root gasket includes the preparation of water-gas atomized alloy powder, hot isostatic pressing sintering, precision hot rolling, solution and aging heat treatment, plate cold rolling and flattening, and laser cutting.

2. The method for preparing the gas turbine regulating stage blade root gasket material according to claim 1, characterized in that: The specific preparation steps are as follows: (1) Preparation of powder by water-gas atomization: Alloy smelting is carried out according to the composition of Ni~(17-18wt%)Cr~(5.5-6wt%)Co~(4.5-6wt%)Nb~(4.5-5.0wt%)Zr~(2.8-3.0wt%)Si~(2.8-3wt%)B, and then powder is prepared by water-gas atomization process. The average particle size of the powder is required to be controlled at 5-6 microns, and the oxygen content is controlled below 1000ppm; (2) hot isostatic pressing the alloy powder at a sintering temperature of 1100° C. to 1120° C. to obtain a hot isostatic pressed ingot; (3) hot rolling the block into a plate, the hot rolling start temperature is 1030 to 1100 ° C, the stop temperature is greater than 1000 ° C, the thickness of the plate after hot rolling ranges from 0.5 mm to 2.0 mm, and the tolerance accuracy is ± 0.05 mm; (4) Solution and aging heat treatment: After hot rolling, the plate is subjected to solution heat treatment at a temperature of 1090-1100°C, and the holding time is set according to 3-5 minutes / mm thickness. After solution heat treatment, it is air-cooled; then aging treatment is carried out at an aging temperature of 910-920°C and the holding time is 60-90 minutes; (5) Cold rolling and leveling: The hot-rolled plate that has undergone solid solution treatment is subjected to cold rolling and leveling treatment, and its tolerance accuracy is increased from ±0.05mm in the hot-rolled state to ±0.02mm; (6) Laser cutting: The cold-rolled sheet that has been cold-rolled to the required thickness is cut into the required size and shape by laser to obtain the finished blade root gasket.