Preparation method for optimizing carbide distribution of Ni-Fe-based high-temperature alloy bar billet for ultra-supercritical thermal power generating unit

Abstract

The invention discloses a preparation method for optimizing carbide distribution of a Ni-Fe-based high-temperature alloy bar billet for an ultra-supercritical thermal power generating unit. The Ni-Fe-based high-temperature alloy bar billet comprises the following materials: 0.045-0.055% of C, 18.0-20.0% of Cr, 0.4-0.6% of Mo and 0.2-0.4% of W; the high-temperature alloy comprises the following components in percentage by weight: 0.002 to 0.005 percent of B, 1.5 to 2.5 percent of Co, 25.0 to 27.0 percent of Fe, 1.9 to 2.1 percent of Al, 2.0 to 2.2 percent of Ti and the balance of Fe. The preparation method comprises the following steps: S1, obtaining a uniform and compact high-temperature alloy cast ingot through vacuum induction and vacuum self consumption; and S2, cogging is conducted, specifically, the high-temperature alloy cast ingot obtained in the step S1 is put into a heating furnace to be heated, the temperature is slowly increased to 1170 DEG C, the heat preservation time is longer than or equal to 150 h after the cast ingot reaches the temperature, then the furnace is cooled to 1100-1150 DEG C, heat preservation is conducted, and cogging forging is conducted. According to the method, the microcracks are generated in the low-temperature forging process of the bar, the diffusion channel of the carbon element is improved, the microcracks are closed in the forming stage, and finally the Ni-Fe-based high-temperature alloy bar billet with evenly-distributed carbides is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of nonferrous metal processing, in particular to a preparation method for optimizing carbide distribution of Ni-Fe based high temperature alloy rod blanks for ultra-supercritical thermal power units. Background Art

[0002] At present, ultra-supercritical thermal power units are one of the most technologically advanced power generation equipment in the thermal power industry. They have the characteristics of high main steam temperature and pressure, low coal consumption, and low pollutant emissions. Their extremely harsh service environment places high demands on the performance of materials. Since ordinary heat-resistant steels are no longer sufficient for the design temperature and pressure of ultra-supercritical thermal power units, China has developed a type of Ni-Fe-based deformable high-temperature alloy material suitable for important components of ultra-supercritical thermal power units, such as high-temperature superheaters / reheaters, main steam and reheat steam pipelines, turbine rotors, etc.

[0003] Ni-Fe based deformed high temperature alloy promotes the formation of γ′ phase and carbides TiC, M by adding Ti, Al and Cr elements. 23 C6 precipitation strengthening, adding a large amount of Fe elements, reducing the use of precious metal elements such as Ni and Co, has good high-temperature creep resistance and excellent high-temperature oxidation resistance, while also having a high cost-effectiveness. However, during the preparation process, due to the high carbon content of the alloy, the carbides in the alloy bars are prone to uneven distribution and high density, which will cause the alloy to crack during subsequent processing, seriously affecting the service life of the material. Therefore, how to reduce the density and size of carbides in the bars during the production process is an urgent problem to be solved. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a Ni-Fe based high temperature alloy rod for an ultra-supercritical thermal power unit for optimizing the carbide distribution, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a preparation method for optimizing the carbide distribution of Ni-Fe-based high-temperature alloy rod billet for ultra-supercritical thermal power units, comprising the following materials: C: 0.045-0.055, Cr: 18.0-20.0, Mo: 0.4-0.6, W: 0.2-0.4; B: 0.002-0.005, Co: 1.5-2.5, Fe: 25.0-27.0, Al: 1.9-2.1, Ti: 2.0-2.2, and the rest is Fe, comprising the following steps:

[0006] S1. Vacuum induction + vacuum self-consumption to obtain uniform and dense high-temperature alloy ingots;

[0007] S2, open the blank, put the high temperature alloy ingot obtained in S1 into the heating furnace for heating, slowly raise the temperature to 1170℃, keep the ingot warm for ≥150h, then cool the furnace to 1100℃-1150℃ for insulation, and perform open forging, the starting forging temperature is ≥950℃, the final forging temperature is ≥850℃, after the forging is completed, the material is returned to the furnace and kept warm in the range of 850-900℃ for 8-10h;

[0008] S3, forming, subjecting the ingot obtained in S2 to 2-5 fire forming forging, the forging heating temperature is 950°C-1060°C, and the deformation amount of each forging is 30%-45%;

[0009] S4, air cooling the forged rod obtained in step S3 to obtain a Ni-Fe-based high-temperature alloy rod blank that can be directly used for ultra-supercritical thermal power unit parts.

[0010] Preferably, the specification of the high-temperature alloy bar billet is Φ200mm-Φ500mm.

[0011] Preferably, the billet forging described in S2 adopts continuous re-forging, and the deformation amount of each fire is 15%-35%.

[0012] Preferably, the forming stage described in S3 is divided into 2-5 fires, the heating temperature of the second fire is 950-1000°C, the first 2-4 fires are radial upsetting and drawing, the deformation is 30%-45%, the heating temperature of the 3rd-4th fires is 1020°C-1060°C, the last 1-2 fires are drawing forming, the deformation of each fire is 15%-25%, and the heating temperature range is 1000°C-1040°C.

[0013] Preferably, the final two-fire forging reduction rate is ≥80 mm / s, and the last 1-2 fire forging adopts a round-to-round deformation method.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention prepares Ni-Fe-based high-temperature alloy rod blanks by double vacuum smelting + rapid forging, and by controlling the overaging and forging temperatures, microcracks are generated in the rods during low-temperature forging, the diffusion channels of carbon elements are improved, and the microcracks are closed in the forming stage, and finally a Ni-Fe-based high-temperature alloy rod blank with uniform carbide distribution is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a photo of carbides in a Φ213mm rod.

[0016] Among them: (a) is the edge 100×; (b) is R / 2100×; (c) is the center 100×. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] like Figure 1 As shown, the present invention provides a technical solution:

[0019] Example 1

[0020] A method for preparing a Ni-Fe-based high-temperature alloy bar billet for optimizing carbide distribution for an ultra-supercritical thermal power unit comprises the following materials:

[0021] C: 0.05, Cr: 19.0, Mo: 0.5, W: 0.3; B: 0.0035, Co: 2.0, Fe: 26.0, Al: 2.0, Ti: 2.1, and the rest is Fe, comprising the following steps:

[0022] S1. Vacuum induction + vacuum self-consumption to obtain uniform and dense high-temperature alloy ingots;

[0023] S2, open the blank, put the high temperature alloy ingot obtained in S1 into a heating furnace for heating, slowly raise the temperature to 1170°C, keep the ingot warm for 150h, then cool the furnace to 1200°C for insulation, and perform open forging, the starting forging temperature is ≥950°C, and the final forging temperature is ≥850°C;

[0024] S3, forming, subjecting the ingot obtained in S2 to 2-5 fire forming forging, the forging heating temperature is 950°C-1060°C, and the deformation amount of each forging is 30%-45%;

[0025] S4, the forged rod obtained in step S3 is air-cooled to obtain a Ni-Fe-based high-temperature alloy rod blank that can be directly used for ultra-supercritical thermal power unit parts.

[0026] Among them, the specification of high-temperature alloy rod billet is Φ213mm.

[0027] Among them, the billet forging in S2 adopts continuous re-forging, and the deformation amount of each fire is 25%.

[0028] Among them, the forming stage in S3 is divided into 2-5 fires. The first 2-4 fires are radial upsetting and drawing with a deformation of 40%. The heating temperature of the 2-4 fires is 1040℃. The last 1-2 fires are drawing forming, with a deformation of 20% in each fire and a heating temperature of 1020℃.

[0029] Among them, the final two-fire forging reduction rate is 100mm / s, and the last 1-2 fire forging adopts a round-to-round deformation method.

[0030] The obtained Ni-Fe-based high-temperature alloy bar blank for ultra-supercritical thermal power unit parts has carbide grade 4-5 as a whole according to GB / T 14999.6 rating.

[0031] Example 2

[0032] A method for preparing a Ni-Fe-based high-temperature alloy bar billet for optimizing carbide distribution for an ultra-supercritical thermal power unit comprises the following materials:

[0033] C: 0.05, Cr: 19.0, Mo: 0.5, W: 0.3; B: 0.0035, Co: 2.0, Fe: 26.0, Al: 2.0, Ti: 2.1, and the rest is Fe, comprising the following steps:

[0034] S1. Vacuum induction + vacuum self-consumption to obtain uniform and dense high-temperature alloy ingots;

[0035] S2, open the blank, put the high temperature alloy ingot obtained in S1 into the heating furnace for heating, slowly raise the temperature to 1170℃, keep the temperature for 150h after the ingot reaches the temperature, then cool the furnace to 1200℃ and keep the temperature, and then open the blank forging, the starting forging temperature is ≥950℃, the final forging temperature is ≥850℃, after the forging is completed, the material is returned to the furnace and kept at 890℃ for 9h;

[0036] S3, forming, subjecting the ingot obtained in S2 to 2-5 fire forming forging, the forging heating temperature is 950°C-1060°C, and the deformation amount of each forging is 30%-45%;

[0037] S4, the forged rod obtained in step S3 is air-cooled to obtain a Ni-Fe-based high-temperature alloy rod blank that can be directly used for ultra-supercritical thermal power unit parts.

[0038] Among them, the specification of high-temperature alloy rod billet is Φ213mm.

[0039] Among them, the billet forging in S2 adopts continuous re-forging, and the deformation amount of each fire is 25%.

[0040] Among them, the forming stage in S3 is divided into 2-5 fires, the heating temperature of the second fire is 1000℃, the first 2-4 fires are radial upsetting and drawing with a deformation of 40%, the heating temperature of the 3rd-4th fires is 1040℃, and the last 1-2 fires are drawing forming, with a deformation of 20% in each fire and a heating temperature of 1020℃.

[0041] Among them, the final two-fire forging reduction rate is 100mm / s, and the last 1-2 fire forging adopts a round-to-round deformation method.

[0042] The obtained Ni-Fe-based high-temperature alloy bar blank for ultra-supercritical thermal power unit parts has carbide grade 1-2 as a whole according to GB / T 14999.6 rating.

[0043] Comparative Example 1 and Example 2: In Example 2, the steps of the present invention are strictly followed to prepare the Ni-Fe-based high-temperature alloy rod blank for an ultra-supercritical thermal power unit, while in Example 1, only in S3, the second fire of the ingot is subjected to normal forming forging, and the deformation amount of the second fire is not strictly controlled.

[0044] Experimental results: The primary carbide distribution at the grain boundary of the Ni-Fe-based high-temperature alloy rod blank finally obtained in Example 2 is more uniform and meets the requirements, while the carbides of the Ni-Fe-based high-temperature alloy rod blank finally obtained in Example 1 are uneven and have a large number, which does not meet the requirements.

[0045] Conclusion: The present invention prepares Ni-Fe-based high-temperature alloy rod blanks by double vacuum smelting + fast forging. By controlling the overaging and forging temperature, microcracks are generated in the rod during low-temperature forging, the diffusion channel of the carbon element is improved, and the microcracks are closed in the forming stage, finally obtaining a Ni-Fe-based high-temperature alloy rod blank with uniform carbide distribution.

[0046] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a Ni-Fe-based high-temperature alloy billet for optimizing the carbide distribution of an ultra-supercritical thermal power unit, comprising the following materials: C: 0.045-0.055, Cr: 18.0-20.0, Mo: 0.4-0.6, W: 0.2-0.4; B: 0.002-0.005, Co: 1.5-2.5, Fe: 25.0-27.0, Al: 1.9-2.1, Ti: 2.0-2.2, and the rest is Fe, comprising the following steps: S1. Vacuum induction + vacuum self-consumption to obtain uniform and dense high-temperature alloy ingots; S2, open the blank, put the high temperature alloy ingot obtained in S1 into the heating furnace for heating, slowly raise the temperature to 1170℃, keep the ingot warm for ≥150h, then cool the furnace to 1100℃-1150℃ for insulation, and perform open forging, the starting forging temperature is ≥950℃, the final forging temperature is ≥850℃, after the forging is completed, the material is returned to the furnace and kept warm in the range of 850-900℃ for 8-10h; S3, forming, subjecting the ingot obtained in S2 to 2-5 fire forming forging, the forging heating temperature is 950°C-1060°C, and the deformation amount of each forging is 30%-45%; S4, air cooling the forged rod obtained in step S3 to obtain a Ni-Fe-based high-temperature alloy rod blank that can be directly used for ultra-supercritical thermal power unit parts.

2. The method for preparing a Ni-Fe-based high-temperature alloy bar billet for optimizing carbide distribution for ultra-supercritical thermal power generation units according to claim 1, characterized in that: The specifications of the high-temperature alloy bar blank are Φ200mm-Φ500mm.

3. The method for preparing a Ni-Fe-based high-temperature alloy bar billet for optimizing carbide distribution for an ultra-supercritical thermal power unit according to claim 1, characterized in that: The billet forging described in S2 adopts continuous re-forging, and the deformation amount of each fire is 15%-35%.

4. The method for preparing a Ni-Fe-based high-temperature alloy bar billet for optimizing carbide distribution for an ultra-supercritical thermal power unit according to claim 1, characterized in that: The forming stages described in S3 are divided into 2-5 fires, the heating temperature of the second fire is 950-1000°C, the first 2-4 fires are radial upsetting and drawing, the deformation is 30%-45%, the heating temperature of the 3rd-4th fires is 1020°C-1060°C, the last 1-2 fires are drawing forming, the deformation of each fire is 15%-25%, and the heating temperature range is 1000°C-1040°C.

5. The method for preparing a Ni-Fe-based high-temperature alloy bar billet for optimizing carbide distribution for ultra-supercritical thermal power generation units according to claim 1, characterized in that: The final two-fire forging reduction rate is ≥80mm / s, and the last 1-2 fire forging adopts a round-to-round deformation method.

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