High-temperature alloy material for turbine fastener and preparation method of high-temperature alloy material

Abstract

The invention provides a high-temperature alloy material for a steam turbine fastener and a preparation method of the high-temperature alloy material, and belongs to the technical field of high-temperature alloy preparation. By optimizing heat preservation measures of a heating system, a forging process, a rolling process, a heating temperature and a forging process, a rolled bar with a uniform structure being larger than or equal to phi 30 mm is prepared, after special heat treatment, the room-temperature tensile yield strength of a rolled material is larger than or equal to 770 Mpa, the tensile strength is larger than or equal to 1200 Mpa, the elongation is larger than or equal to 26%, the end face shrinkage rate is larger than or equal to 45%, the hardness is 300-325 HB, the duration at the high temperature of 650 DEG C is larger than or equal to 300 h, and the difference of Ti components at the head and the tail of the bar is smaller than or equal to 0.1%. After heat treatment, the grain size level difference of the cross section and the longitudinal surface does not exceed 1.5 level, the average grain size reaches 6.0-7.0 level, and the class A primary carbide and the class B primary carbide are both smaller than or equal to 1.5 level. The high-temperature alloy material solves the problems of excessive hardness, excessive primary carbide and the like in the machining process of a high-temperature alloy for a steam turbine fastener, and solves the problem of non-uniform Al and Ti components at the head and the tail.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature alloy preparation, and in particular relates to a high-temperature alloy material for a steam turbine fastener and a preparation method thereof. Background Art

[0002] The high-temperature alloys used in steam turbine fasteners must withstand high temperatures and high loads in their operating environment, as well as high-temperature oxidation and torsional cyclic stresses. Therefore, the high-temperature alloys used in steam turbine fasteners not only require high strength, high plasticity and good high-temperature creep properties at the operating temperature, but also the mechanical properties of the materials must meet the requirements.

[0003] At present, the hardness of high-temperature alloy rolled materials used in steam turbine fasteners is too high during the processing process, which makes the machining process difficult; the difference in Al and Ti between the head and tail of the ingot is too large, the primary carbide does not meet the standard, and the grain size difference is too large, resulting in large differences in various performances during use. The strength and plasticity indicators cannot be used stably in the working environment and cannot meet the requirements for service in the required working environment. Therefore, the development of high-temperature alloy bars for steam turbine fasteners is of great significance.

[0004] However, the existing smelting methods for high-temperature alloy materials for turbine fasteners are difficult to achieve the above-mentioned properties. There are problems such as large differences in Al and Ti between the head and tail of the ingot, substandard primary carbides, large grain size differences, large differences in various properties during use, and substandard strength and plasticity indicators.

[0005] Therefore, how to provide a high-temperature alloy material for steam turbine fasteners and a preparation method thereof to overcome the above-mentioned defects has become a technical problem to be solved urgently. Summary of the invention

[0006] The present invention is to solve the above technical problems, thereby providing a high-temperature alloy material for steam turbine fasteners and a preparation method thereof. The technical purpose of the present invention is to provide a high-temperature alloy with small difference in Al and Ti between the head and tail of the steel ingot, qualified primary carbides, small grain size difference, small performance difference during use, qualified strength and plasticity indicators, stable use in the working environment, and satisfactory service performance under the required working environment.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A high-temperature alloy material for a steam turbine fastener and a preparation method thereof. The high-temperature alloy comprises, by weight percentage, C: 0.02%-0.055%, S: ≤0.002%, P: ≤0.015%, Cr: 16.0%-19.0%, Ni: 37.0%-39.0%, Co: 19.0%-22.0%, Mo: 2.5%-3.5%, Al: ≤0.25%, Ti: 2.5%-3.0%, Mn: 0.2%-0.5%, Si: ≤0.4%, B: 0.003%-0.009%, Mg≤0.01%, Zr: 0.03%-0.10%, N≤30ppm, and the balance is Fe.

[0009] A high temperature alloy material for a steam turbine fastener and a preparation method thereof, characterized in that the preparation method comprises the following steps:

[0010] Step A, melting and homogenizing in a 6t vacuum induction furnace, preparing an alloy according to the above element composition ratio, the melting temperature is 1470-1490°C, and adjusting the content of each element during the melting process so that its weight ratio meets the design requirements to produce molten steel;

[0011] Step B, heating the molten steel in step A to 1480-1500° C. for refining, continuing deoxidation and degassing, volatilizing harmful impurity elements, adjusting the content of alloy elements, making it uniform, and reducing component segregation; determining the refining time according to the change of leakage rate, powering off and cooling in the late stage of refining, adding aluminum and titanium, sampling and analyzing after 20 minutes, adjusting the composition, and making high-quality molten steel;

[0012] Step C, pouring the high-quality molten steel from step B into electrode rods under vacuum conditions;

[0013] Step D: The electrode rods from step C are used as electrodes. After polishing, they are placed in a protective atmosphere electroslag furnace for secondary remelting and purification. The slag system is No. 66. In addition, 1.5-3.5 kg TiO2 is added to the slag system to form Electroslag ingot;

[0014] Step E: heating the electroslag ingot prepared in step D to 1190-1200° C. and keeping the temperature for 60 hours for homogenization treatment;

[0015] Step F, heating the steel ingot of step E to 1160° C., keeping the temperature for 4 hours, forging and blanking by means of a press, cooling, heating and other measures, and air cooling;

[0016] Step G, heating the billet of step F to 1150°C, keeping it warm for 2 hours, rolling it into shape by a rolling mill, and taking heat preservation measures such as high-temperature coating, and keeping it warm in an induction furnace at 1020-1040°C for 20 minutes after rolling, and then cooling it in air;

[0017] Step H, performing post-rolling heat treatment on the rolled material after rolling in step G: cool to room temperature after rolling, put it back into the furnace, heat it to 1015-1035°C, keep it warm for 2 hours, air cool it to less than 300°C, heat it to 835-855°C in the furnace, keep it warm for 24 hours, cool it in the furnace to 700°C, keep it warm for 16 hours, and then air cool it to room temperature to obtain the desired material.

[0018] Preferably, in step A, smelting of molten steel is carried out in a 6T vacuum induction furnace.

[0019] Preferably, in step B, the vacuum induction furnace is used for refining and the leakage rate is controlled for a long time, and a leak detection is performed at intervals of 10 minutes. The first leak rate is ≤2 Pa, the difference between two consecutive leak rates is <0.3 Pa, and the difference between two consecutive leak rates / the second leak rate is <10%, and the leak detection is qualified.

[0020] Preferably, in step C, refining is performed in a 6T vacuum induction furnace, C is controlled at 0.02% to 0.055%, and 8.0 to 12.0 kg Ni-Mg, 3.5 to 4.5 kg Zr and 1.5 to 2.5 kg B-Fe are added before tapping.

[0021] Preferably, in step D, remelting is performed in a 6T protective atmosphere electric slag furnace, slag system 66# (CaF2:Al2O3:CaO:MgO=65:20:10:5) is used, and 1.5-3.5 kg TiO2 is added to the slag system.

[0022] Preferably, in step E, the homogenization treatment needs to be carried out in a high-temperature diffusion furnace, first at 1120-1160° C. for 24 hours and then heated to a homogenization temperature of 1190-1200° C. for 60 hours.

[0023] Preferably, in step F, when heat preservation measures such as cooling forging and heating are adopted, the firing temperatures are cooled to 1160° C., 1140° C., and 1120° C. respectively and the rapid forming forging is performed.

[0024] Preferably, in step G, the temperature is raised to 1140° C. and kept for 2 hours using heat preservation measures such as high-temperature paint coating, and then rolled to form. After rolling, the induction furnace is kept at 1020-1040° C. for 20 minutes and then taken out of the furnace for air cooling.

[0025] Preferably, in step H, the heat treatment is carried out in an 8t resistance furnace, the temperature is uniformly raised to 1015-1035°C, kept at this temperature for 2 hours, then air-cooled to room temperature, reheated to 835-855°C, kept at this temperature for 24 hours, furnace-cooled to 700°C, kept at this temperature for 16 hours, and then air-cooled to room temperature.

[0026] Preferably, the impurities are: in weight percentage, S≤0.0020%, N≤30ppm, and the S content is controlled at ≤10ppm and N≤20ppm during the preparation process.

[0027] The beneficial effects of the present invention are as follows:

[0028] The high-temperature alloy bar material for steam turbine fasteners and the preparation method thereof has uniform structure and composition. The smelting is carried out in a 6T vacuum induction furnace. All raw materials are used after annealing to reduce gas content and improve the purity of molten steel. Before steelmaking, 8.0-12.0kg Ni-Mg, 3.5-4.5kg Zr and 1.5-2.5kg B-Fe and other trace elements are added, and the alloy C is controlled at 0.02%-0.055%, so that the plasticity and yield strength of the material are enhanced under low temperature, room temperature and high temperature conditions. The protective atmosphere electroslag is remelted for the second time, and the slag system is 66#. In addition, 1.5-3.5kg TiO is added to the slag. 2 , reduce the content of gas and inclusions, ensure the uniform Al and Ti composition at the head and tail of the steel ingot and ensure the density of the whole steel ingot. The steel ingot is homogenized to ensure that there is no dendrite segregation in the steel ingot. It is forged by a 6000T press and forged by one upsetting and one drawing, cooling forging, and the last three fires are respectively forged at 1160℃, 1140℃, and 1120℃. The deformation of the fire is controlled at 36%~45%, and the forging is carried out. After forging, it is slowly cooled to room temperature, re-entered into the furnace and heated to 1140℃ for 2h before rolling. High-temperature paint coating is used for insulation. After rolling, the induction furnace is kept at 1020~1040℃ for 20min, then taken out of the furnace for air cooling, and re-heated to 1015~1035℃ at a uniform speed for 2h. After 2 hours of heat treatment, air cool to room temperature, reheat to 835-855℃, keep warm for 24 hours, furnace cool to 700℃, keep warm for 16 hours, and then air cool to room temperature to obtain the required material. The room temperature tensile yield strength is ≥770Mpa, the tensile strength is ≥1200Mpa, the elongation is ≥26%, the end shrinkage is ≥45%, the hardness is 300-325HB, the high temperature endurance at 650℃ is ≥300h, the difference in Ti composition between the head and tail of the rod is ≤0.1%, the grain size difference of the cross section and the longitudinal surface after heat treatment does not exceed 1.5 levels, the average grain size reaches 6.0-7.0 levels, and the A primary carbide and the B primary carbide are both ≤1.5 levels; under the working environment, the mechanical properties and high temperature creep properties are less different.

[0029] The high-temperature alloy material for steam turbine fasteners and the preparation method thereof are produced by the present invention, which solves the problems of excessive hardness and excessive primary carbide in the machining process of the high-temperature alloy for steam turbine fasteners; solves the problem of uneven Al and Ti components at the head and tail; solves the requirements for high strength and high plasticity of steam turbine fasteners; solves the problem that the performance of steam turbine fasteners in a high-temperature working environment is unstable and cannot meet the problem of stable service in the required working environment, has good economic and social benefits, and is suitable for popularization and use. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described in detail below in conjunction with the embodiments. It is necessary to point out that the following embodiments are only used to explain and illustrate the present invention and are not used to limit the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content still belong to the protection scope of the present invention.

[0031] Example 1

[0032] The following examples respectively provide four high-temperature alloy materials for steam turbine fasteners, and the raw materials are prepared according to the element composition of Example 1 in Table 1.

[0033] Table 1 Element composition of high temperature alloy materials for steam turbine fasteners

[0034]

[0035] The preparation method steps are as follows:

[0036] Step A, melting and homogenizing in a 6T vacuum induction furnace, preparing an alloy according to the above element composition ratio, the melting temperature is 1470°C, and adjusting the content of each element during the melting process so that its weight ratio meets the design requirements to produce molten steel;

[0037] Step B, heating the molten steel in step A to 1480°C for refining, continuing deoxidation and degassing, volatilizing harmful impurity elements, adjusting the content of alloy elements, making it uniform, and reducing component segregation; determining the refining time according to the change of the leakage rate, power off and cool down in the later stage of refining to add aluminum and titanium, sampling and analyzing after 20 minutes, adjusting the composition, and making high-quality molten steel; the refining time of the vacuum induction furnace is controlled according to the leakage rate, leak detection is performed at intervals of 10 minutes, the leakage degree of one time is ≤2Pa, the difference between two consecutive leakage degrees is <0.3Pa, the difference between two consecutive leakage degrees / the second leakage degree is <10%, and the leak detection is qualified;

[0038] Step C, pouring the high-quality molten steel from step B into electrode rods under vacuum conditions; refining in a 6T vacuum induction furnace, controlling C at 0.02-0.055%, adding 8.0kg Ni-Mg (mass ratio 1:1), 3.5kg Zr and 1.5kg B-Fe (mass ratio 1:2) before tapping;

[0039] Step D: The electrode rods prepared in step C are used as electrodes. After polishing, they are placed in a protective atmosphere electroslag furnace for secondary remelting and purification. The slag system is No. 66. In addition, 1.5 kg TiO 2 ,form Electroslag ingot; remelting in 6T protective atmosphere electroslag furnace, slag system using 66# (CaF 2 :Al 2 O 3:CaO:MgO=65:20:10:5), and 1.5kgTiO 2 ;

[0040] Step E, heating the electroslag ingot prepared in step D to 1190° C. and keeping it at that temperature for 60 hours for homogenization treatment; the homogenization treatment needs to be carried out in a high-temperature diffusion furnace, first keeping it at 1120° C. for 24 hours and then heating it to a homogenization temperature of 1190° C. and keeping it at that temperature for 60 hours;

[0041] Step F, heating the steel ingot of step E to 1160°C, keeping the temperature for 4 hours, forging and opening the blank by means of a press through upsetting and drawing, cooling, heating and other measures, and air cooling; when adopting the heat preservation measures such as cooling forging and heating, the temperature of the fire is cooled at 1160°C, 1140°C and 1120°C respectively, and the blank is forged and formed quickly;

[0042] Step G, heating the billet of step F to 1150°C, keeping it warm for 2 hours, rolling it into shape through a rolling mill, and taking heat preservation measures such as high-temperature coating, and then taking it out of the furnace and air cooling after being kept at 1020°C in an induction furnace for 20 minutes; when taking heat preservation measures such as high-temperature paint coating, heating it to 1140°C and keeping it warm for 2 hours, and then rolling it into shape, and then taking it out of the furnace and air cooling after being kept at 1020°C in an induction furnace for 20 minutes;

[0043] Step H, performing post-rolling heat treatment on the rolled material after rolling in step G: cooling to room temperature after rolling, re-entering the furnace, heating to 1015°C, keeping warm for 2 hours, air cooling to less than 300°C, heating to 835°C in the furnace, keeping warm for 24 hours, furnace cooling to 700°C, keeping warm for 16 hours, and then air cooling to room temperature to obtain the desired material; wherein, the heat treatment is carried out in an 8T resistance furnace.

[0044] During the smelting process, the impurity content is controlled to be S≤10ppm, N≤20ppm.

[0045] Example 2

[0046] Prepare raw materials according to the element composition of Example 2 in Table 1. The preparation method steps are as follows:

[0047] Step A, melting and homogenizing in a 6T vacuum induction furnace, preparing an alloy according to the above element composition ratio, the melting temperature is 1476°C, and adjusting the content of each element during the melting process so that its weight ratio meets the design requirements to produce molten steel;

[0048] Step B, heating the molten steel in step A to 1488°C for refining, continuing deoxidation and degassing, volatilizing harmful impurity elements, adjusting the content of alloy elements, making it uniform, and reducing component segregation; determining the refining time according to the change of the leakage rate, power off and cool down in the later stage of refining to add aluminum and titanium, sampling and analyzing after 20 minutes, adjusting the composition, and making high-quality molten steel; the refining time of the vacuum induction furnace is controlled according to the leakage rate, leak detection is carried out at intervals of 10 minutes, the leakage degree of one time is ≤2Pa, the difference between two consecutive leakage degrees is <0.3Pa, the difference between two consecutive leakage degrees / the second leakage degree is <10%, and the leak detection is qualified;

[0049] Step C, pouring the high-quality molten steel from step B into electrode rods under vacuum conditions; refining in a 6T vacuum induction furnace, controlling C at 0.02-0.055%, adding 9.8kg Ni-Mg (mass ratio 1:1), 3.8kg Zr and 1.9kg B-Fe (mass ratio 1:2) before tapping;

[0050] Step D: The electrode rods prepared in step C are used as electrodes. After polishing, they are placed in a protective atmosphere electroslag furnace for secondary remelting and purification. The slag system is No. 66. In addition, 1.9 kg TiO 2 ,form Electroslag ingot; remelting in 6T protective atmosphere electroslag furnace, slag system using 66# (CaF 2 :Al 2 O 3 :CaO:MgO=65:20:10:5), and 1.7kgTiO was added to the slag system 2 ;

[0051] Step E, heating the electroslag ingot prepared in step D to 1195°C and keeping it at that temperature for 60 hours for homogenization treatment; the homogenization treatment needs to be carried out in a high-temperature diffusion furnace, first keeping it at 1137°C for 24 hours and then heating it to a homogenization temperature of 1195°C and keeping it at that temperature for 60 hours;

[0052] Step F, heating the steel ingot of step E to 1160°C, keeping the temperature for 4 hours, forging and opening the blank by means of a press through upsetting and drawing, cooling, heating and other measures, and air cooling; when adopting the heat preservation measures such as cooling forging and heating, the temperature of the fire is cooled at 1160°C, 1140°C and 1120°C respectively, and the blank is forged and formed quickly;

[0053] Step G, heating the billet of step F to 1150°C, keeping it warm for 2 hours, rolling it into shape through a rolling mill, and taking heat preservation measures such as high-temperature coating, and keeping it warm at 1030°C in an induction furnace for 20 minutes after rolling, and then cooling it in air; when taking heat preservation measures such as high-temperature paint coating, heating it to 1140°C and keeping it warm for 2 hours, and then rolling it into shape, and keeping it warm at 1030°C in an induction furnace for 20 minutes after rolling, and then cooling it in air;

[0054] Step H, heat treatment after rolling in step G: cool to room temperature after rolling, put into furnace again, heat to 1022°C, keep warm for 2 hours, air cool to less than 300°C, heat to 840°C in furnace, keep warm for 24 hours, cool to 700°C in furnace, keep warm for 16 hours, and then air cool to room temperature to obtain the required material. The heat treatment is carried out in 8T resistance furnace.

[0055] During the smelting process, the impurity content is controlled to be S≤10ppm, N≤20ppm.

[0056] Example 3

[0057] Prepare raw materials according to the element composition of Example 3 in Table 1. The preparation method steps are as follows:

[0058] Step A, melting and homogenizing in a 6T vacuum induction furnace, preparing an alloy according to the above element composition ratio, the melting temperature is 1488°C, and adjusting the content of each element during the melting process so that its weight ratio meets the design requirements to produce molten steel;

[0059] Step B, heating the molten steel in step A to 1495°C for refining, continuing deoxidation and degassing, volatilizing harmful impurity elements, adjusting the content of alloy elements, making it uniform, and reducing component segregation; determining the refining time according to the change of the leakage rate, power off and cool down in the later stage of refining to add aluminum and titanium, sampling and analyzing after 20 minutes, adjusting the composition, and making high-quality molten steel; the refining time of the vacuum induction furnace is controlled according to the leakage rate, leak detection is carried out at intervals of 10 minutes, the leakage degree of one time is ≤2pa, the difference between two consecutive leakage degrees is <0.3pa, the difference between two consecutive leakage degrees / the second leakage degree is <10%, and the leak detection is qualified;

[0060] Step C, casting the high-quality molten steel in step B into electrode rods under vacuum conditions; refining in a 6T vacuum induction furnace, controlling C at 0.02% to 0.055%, adding 11.0kg Ni-Mg (mass ratio 1:1), 4.0kg Zr and 2.0kg B-Fe (mass ratio 1:2) before tapping;

[0061] Step D: The electrode rods prepared in step C are used as electrodes. After polishing, they are placed in a protective atmosphere electroslag furnace for secondary remelting and purification. The slag system is No. 66. In addition, 2.5 kg of TiO 2 ,form Electroslag ingot; remelting in 6T protective atmosphere electroslag furnace, slag system using 66# (CaF 2 :Al 2 O 3 :CaO:MgO=65:20:10:5), and 2.5kgTiO 2 ;

[0062] Step E, heating the electroslag ingot prepared in step D to 1196°C and keeping it at that temperature for 60 hours for homogenization treatment; the homogenization treatment needs to be carried out in a high-temperature diffusion furnace, first keeping it at 1152°C for 24 hours and then heating it to the homogenization temperature of 1196°C and keeping it at that temperature for 60 hours;

[0063] Step F, heating the steel ingot of step E to 1160°C, keeping the temperature for 4 hours, forging and opening the blank by means of a press through upsetting and drawing, cooling, heating and other measures, and air cooling; when adopting the heat preservation measures such as cooling forging and heating, the temperature of the fire is cooled at 1160°C, 1140°C and 1120°C respectively, and the blank is forged and formed quickly;

[0064] Step G, heating the billet of step F to 1150°C, keeping it warm for 2 hours, rolling it into shape through a rolling mill, and taking heat preservation measures such as high-temperature coating, and then taking it out of the furnace and air cooling after being kept at 1035°C in an induction furnace for 20 minutes; when taking heat preservation measures such as high-temperature paint coating, heating it to 1140°C and keeping it warm for 2 hours, and then rolling it into shape, and then taking it out of the furnace and air cooling after being kept at 1035°C in an induction furnace for 20 minutes;

[0065] Step H, heat treatment after rolling in step G: cool to room temperature after rolling, put into furnace again, heat to 1031°C, keep warm for 2 hours, air cool to less than 300°C, heat to 850°C in furnace, keep warm for 24 hours, cool to 700°C in furnace, keep warm for 16 hours, and then air cool to room temperature to obtain the desired material. The heat treatment is carried out in 8T resistance furnace.

[0066] During the smelting process, the impurity content is controlled to be S≤10ppm, N≤20ppm.

[0067] Example 4

[0068] Prepare raw materials according to the element composition of Example 4 in Table 1. The preparation method steps are as follows:

[0069] Step A, melting and homogenizing in a 6T vacuum induction furnace, preparing an alloy according to the above element composition ratio, the melting temperature is 1490°C, and adjusting the content of each element during the melting process so that its weight ratio meets the design requirements to produce molten steel;

[0070] Step B, heating the molten steel in step A to 1500°C for refining, continuing deoxidation and degassing, volatilizing harmful impurity elements, adjusting the content of alloy elements, making it uniform, and reducing component segregation; determining the refining time according to the change of leakage rate, power off and cool down in the later stage of refining to add aluminum and titanium, sampling and analyzing after 20 minutes, adjusting the composition, and making high-quality molten steel; the refining time of the vacuum induction furnace is controlled according to the leakage rate, leak detection is carried out at intervals of 10 minutes, the leakage degree of one time is ≤2pa, the difference between two consecutive leakage degrees is <0.3pa, the difference between two consecutive leakage degrees / the second leakage degree is <10%, and the leak detection is qualified;

[0071] Step C, casting the high-quality molten steel in step B into electrode rods under vacuum conditions; refining in a 6T vacuum induction furnace, controlling C at 0.02% to 0.055%, adding 12.0kg Ni-Mg (mass ratio 1:1), 4.5kg Zr and 2.5kg B-Fe (mass ratio 1:2) before tapping;

[0072] Step D: The electrode rods prepared in step C are used as electrodes. After polishing, they are placed in a protective atmosphere electroslag furnace for secondary remelting and purification. The slag system is No. 66. In addition, 3.5 kg of TiO 2 ,form Electroslag ingot; remelting in 6T protective atmosphere electroslag furnace, slag system using 66# (CaF 2 :Al 2 O 3 :CaO:MgO=65:20:10:5), and 3.5kgTiO 2 ;

[0073] Step E: The electroslag ingot prepared in step D is heated to 1200° C. and kept at this temperature for 60 hours for homogenization treatment; the homogenization treatment needs to be carried out in a high-temperature diffusion furnace, firstly keeping it at 1160° C. for 24 hours and then heating it to the homogenization temperature of 1200° C. and keeping it at this temperature for 60 hours;

[0074] Step F, heating the steel ingot of step E to 1160°C, keeping the temperature for 4 hours, forging and opening the blank by means of a press through upsetting and drawing, cooling, heating and other measures, and air cooling; when adopting the heat preservation measures such as cooling forging and heating, the temperature of the fire is cooled at 1160°C, 1140°C and 1120°C respectively, and the blank is forged and formed quickly;

[0075] Step G, heating the billet of step F to 1150°C, keeping it warm for 2 hours, rolling it into shape through a rolling mill, and taking heat preservation measures such as high-temperature coating, and then taking it out of the furnace and air cooling after being kept at 1040°C in an induction furnace for 20 minutes; when taking heat preservation measures such as high-temperature paint coating, heating it to 1140°C and keeping it warm for 2 hours, and then rolling it into shape, and then taking it out of the furnace and air cooling after being kept at 1040°C in an induction furnace for 20 minutes;

[0076] Step H, heat treatment after rolling in step G: cool to room temperature after rolling, put into furnace again, heat to 1035°C, keep warm for 2 hours, air cool to less than 300°C, heat to 855°C in furnace, keep warm for 24 hours, cool to 700°C in furnace, keep warm for 16 hours, and then air cool to room temperature to obtain the desired material. The heat treatment is carried out in 8T resistance furnace.

[0077] During the smelting process, the impurity content is controlled to be S≤10ppm, N≤20ppm.

[0078] Comparative Example 1

[0079] Referring to the method of Example 1, in step C, 8.0 kg Ni, 3.5 kg Zr and 1.5 kg B are added before tapping.

[0080] Comparative Example 2

[0081] Referring to the method of Example 2, in step C, 9.8 kg Mg, 3.8 kg Zr and 1.9 kg Fe are added before tapping.

[0082] Comparative Example 3

[0083] Referring to the method of Example 3, in step C, 11.0 kg Ni-Mg (mass ratio 1:2), 4.0 kg Zr and 2.0 kg B-Fe (mass ratio 1:1) were added before tapping.

[0084] Comparative Example 4

[0085] Referring to the method of Example 4, in step D, 2.0 kg TiO 2 .

[0086] Test Example 1

[0087] The properties of the high temperature alloy samples prepared in the above examples 1-4 were tested to obtain The rods were tested and the results are shown in Table 2:

[0088] Table 2 High temperature alloy performance test

[0089]

[0090] As can be seen from Table 2, the room temperature tensile yield strength of the high temperature alloy sample obtained in the embodiment of the present invention is ≥770Mpa, the tensile strength is ≥1200Mpa, the elongation is ≥26%, the end shrinkage is ≥45%, and the hardness is 300-325HB. In addition, the high temperature endurance of 650℃ is ≥300h, the difference in Ti composition between the head and tail of the bar is ≤0.1%, the grain size difference of the cross section and the longitudinal surface after heat treatment does not exceed 1.5 levels, the average grain size reaches 6.0-7.0 levels, and the primary carbides of type A and type B are both ≤1.5 levels; under the working environment, the mechanical properties and high temperature creep properties are less different.

[0091] However, the room temperature mechanical properties of the high-temperature alloy specimens prepared in Comparative Examples 1-4 are relatively poor. At the same time, the high temperature endurance of 650°C is ≤220h, the difference in Ti composition between the head and tail of the rod is ≥1%, the grain size difference between the cross section and the longitudinal surface after heat treatment exceeds 3.5 levels, the average grain size is 3.0-4.0 levels, and both Class A primary carbides and Class B primary carbides are ≥2.5 levels; their mechanical properties and high-temperature creep properties are quite different.

[0092] Therefore, by producing the high-temperature alloy material for turbine fasteners and the preparation method thereof, the problems of excessive hardness and excessive primary carbide in the machining process of the high-temperature alloy for turbine fasteners are solved; the problem of uneven Al and Ti components at the head and tail is solved; the requirements for high strength and high plasticity of turbine fasteners are solved; the problem of unstable performance of turbine fasteners in high-temperature working environments and inability to meet the requirements for stable service in the working environment required by the fasteners is solved, the fasteners have good economic and social benefits, and are suitable for popularization and use.

Claims

1. A method for preparing a high temperature alloy material for a steam turbine fastener, characterized in that: The element composition of the high temperature alloy is calculated by weight percentage, C: 0.02% to 0.055%, S: ≤0.002%, P: ≤0.015%, Cr: 16.0% to 19.0%, Ni: 37.0% to 39.0%, Co: 19.0% to 22.0%, Mo: 2.5% to 3.5%, Al: ≤0.25%, Ti: 2.5% to 3.0%, Mn: 0.2% to 0.5%, Si: ≤0.4%, B: 0.003% to 0.009%, Mg≤0.01%, Zr: 0.03% to 0.10%, N≤30ppm, and the balance is Fe; The preparation method comprises the following steps: Step A, melting and homogenizing in a 6T vacuum induction furnace, preparing an alloy according to the above element composition ratio, the melting temperature is 1470-1490°C, adjusting the content of each element during the melting process so that its weight ratio meets the design requirements, and preparing molten steel; Step B, heating the molten steel in step A to 1480-1500° C. for refining, continuing deoxidation and degassing, volatilizing harmful impurity elements, adjusting the content of alloy elements, making it uniform, and reducing component segregation; determining the refining time according to the change of leakage rate, powering off and cooling in the late stage of refining, adding aluminum and titanium, sampling and analyzing after 20 minutes, adjusting the composition, and making high-quality molten steel; Step C, pouring the high-quality molten steel from step B into electrode rods under vacuum conditions; Step D: The electrode rods from step C are used as electrodes. After polishing, they are placed in a protective atmosphere electroslag furnace for secondary remelting and purification. The slag system is No.

66. In addition, 1.5-3.5 kg TiO2 is added to the slag system to form Electroslag ingot; Step E: heating the electroslag ingot prepared in step D to 1190-1200° C. and keeping the temperature for 60 hours for homogenization treatment; Step F, heating the steel ingot of step E to 1160° C., keeping the temperature for 4 hours, forging and blanking by means of a press, cooling, heating and other measures, and air cooling; Step G, heating the billet of step F to 1150°C, keeping it warm for 2 hours, rolling it into shape by a rolling mill, and taking heat preservation measures such as high-temperature coating, and keeping it warm in an induction furnace at 1020-1040°C for 20 minutes after rolling, and then cooling it in air; Step H, performing post-rolling heat treatment on the rolled material after rolling in step G: cool to room temperature after rolling, put it back into the furnace, heat it to 1015-1035°C, keep it warm for 2 hours, air cool it to less than 300°C, heat it to 835-855°C in the furnace, keep it warm for 24 hours, cool it in the furnace to 700°C, keep it warm for 16 hours, and then air cool it to room temperature to obtain the desired material.

2. The preparation method according to claim 1, characterized in that: In step B, the vacuum induction furnace is used for refining under the control of leakage rate, and leak detection is performed at intervals of 10 minutes. The first leak rate is ≤2Pa, the difference between two consecutive leak rates is <0.3Pa, and the difference between two consecutive leak rates / the second leak rate is <10%, indicating that the leak detection is qualified.

3. The preparation method according to claim 1, characterized in that: In step C, high-quality molten steel is refined in a 6T vacuum induction furnace, alloy C is controlled at 0.02% to 0.055%, and 8.0 to 12.0 kg Ni-Mg, 3.5 to 4.5 kg Zr and 1.5 to 2.5 kg B-Fe are added before tapping.

4. The preparation method according to claim 1, characterized in that: In step D, remelting is performed in a 6T protective atmosphere electric slag furnace, and 66# slag is used, and its composition by weight ratio is: CaF2:Al2O3:CaO:MgO=65:20:10:5, and 1.5-3.5kg TiO2 is added to the slag.

5. The preparation method according to claim 1, characterized in that: In step E, the homogenization treatment needs to be carried out in a high-temperature diffusion furnace, first at 1120-1160° C. for 24 hours and then heated to a homogenization temperature of 1190-1200° C. for 60 hours.

6. The preparation method according to claim 1, characterized in that: In step F, when heat preservation measures such as cooling forging and heating are adopted, the fire temperatures are cooled to 1160° C., 1140° C., and 1120° C. respectively, and the rapid forming forging is performed.

7. The preparation method according to claim 1, characterized in that: In step G, the temperature is raised to 1140°C and kept for 2 hours using heat preservation measures such as high temperature paint coating, and then rolled to form. After rolling, the induction furnace is kept at 1020-1040°C for 20 minutes and then taken out of the furnace for air cooling.

8. The preparation method according to claim 1, characterized in that: In step H, the heat treatment is carried out in an 8T resistance furnace, the temperature is uniformly raised to 1015-1035°C, kept for 2 hours, air-cooled to room temperature, reheated to 835-855°C, kept for 24 hours, furnace-cooled to 700°C, kept for 16 hours, and air-cooled to room temperature.

9. The preparation method according to claim 1, characterized in that: During the preparation process, the impurity content is controlled to be S≤10ppm and N≤20ppm.

10. A high temperature alloy material for steam turbine fasteners prepared by the method according to any one of claims 1 to 9.

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