NiCr20TiAl high-temperature alloy rolled material and forming method thereof

Abstract

The invention belongs to the technical field of high-temperature alloys. Specifically, the invention provides a forming method of the NiCr20TiAl high-temperature alloy rolled metal, and the invention further provides the NiCr20TiAl high-temperature alloy rolled metal prepared by the forming method. The forming method comprises the following steps: heating a NiCr20TiAl high-temperature alloy square billet to about gt; the method comprises the following steps: heating a billet to a temperature in the range of 1120 DEG C to about 1200 DEG C, holding the billet at the temperature for about 1 to about 2 hours, and then subjecting the held billet to rolling. According to the forming method, the grain size uniformity of the rolled NiCr20TiAl high-temperature alloy bar can be improved, the total cross-section grain size of the bar ranges from 3 grades to 8 grades, the total cross-section grain size grade difference is smaller than or equal to 3 grades, and therefore the optimal high-temperature durability performance is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of superalloys. Specifically, the present invention relates to a method for producing NiCr20TiAl superalloy rolled products, and in addition, the present invention also relates to NiCr20TiAl superalloy rolled products prepared by the said production method. Background Art

[0002] In recent years, with the continuous growth of power supply demand, the development of ultra-supercritical steam turbines has become an inevitable trend of future thermal power generation technology, which is of great significance for energy conservation, emission reduction and environmental pollution reduction. With the increase of steam turbine parameters, mainly the significant increase of steam temperature and pressure, and in order to improve the service life of steam turbines, higher requirements are put forward for the performance of high-temperature alloy materials used in ultra-supercritical steam turbines, and the requirements for the application evaluation of materials in subsequent service are also getting higher and higher.

[0003] The NiCr20TiAl alloy is a nickel-based superalloy with nickel-chromium as the matrix and aluminum and titanium added to form age-hardening phases. It is a superalloy with excellent high-temperature mechanical properties, high creep strength, high corrosion resistance and oxidation resistance under high temperature and high pressure, and is commonly used for high-temperature fasteners of ultra-supercritical steam turbines in thermal power plants. At present, small-sized bars are mostly selected for steam turbine fasteners and are formed by rolling.

[0004] Due to the complex alloy elements and high alloy content of the NiCr20TiAl alloy, the thermal effect during its hot rolling process is very significant, and the range of dynamic recrystallization is significantly affected by process parameters. The internal structure change of the metal during rolling directly affects the mechanical properties of the hot-rolled finished product, especially the grain size and creep properties.

[0005] The common phases of the NiCr20TiAl alloy are γ, γ’, M(C,N), M7C3 and M 23 C6 and other phases. Since there is no precipitated phase to pin the grain boundaries to prevent grain growth, abnormally grown grains will appear at the edge position of the bar formed after high-temperature solution treatment, and double grains will also appear in the range from the bar edge to the 1 / 4D position. Considering the service conditions of steam turbines, high standards are required for the NiCr20TiAl alloy, requiring the full-section grain size to be between 3 and 8 levels, and the full-section grain size grade difference ≤ 3 levels.

[0006] As a fastener material, the creep property is a key index. Considering the specific service conditions of steam turbines, it is required that the NiCr20TiAl alloy reaches a creep test time of ≥ 30 hours under the conditions of 750°C / 340MPa. The creep fracture time of the NiCr20TiAl alloy increases with the increase of grain size, while the NiCr20TiAl alloy is prone to mixed grains after heat treatment, and the mixed grains will seriously reduce the high-temperature creep property of the NiCr20TiAl alloy.

[0007] How to improve the grain size uniformity of NiCr20TiAl alloy and further improve its high-temperature creep properties is an urgent problem to be solved in the existing technology. Summary of the Invention

[0008] Purpose of the Invention

[0009] In view of the problems existing in the prior art described in the above Background Art section, the object of the present invention is to provide a method for producing NiCr20TiAl high-temperature alloy rolled products. Another object of the present invention is to provide NiCr20TiAl high-temperature alloy rolled products prepared by the rolling method.

[0010] Technical Solution

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] Solution 1: A method for producing NiCr20TiAl high-temperature alloy rolled products, wherein the method includes: heating a NiCr20TiAl high-temperature alloy bloom to a temperature range of about >1120°C to about 1200°C, and holding at this temperature for about 1 to about 2 hours, and then subjecting the held bloom to a first rolling to obtain a first rolled product, and the first rolling preferably includes tandem rolling.

[0013] Solution 2: The method for producing rolled products according to Solution 1 above, wherein the elemental composition weight percentage content of the NiCr20TiAl high-temperature alloy is:

[0014] C: about 0.04 to about 0.10 wt%;

[0015] Cr: about 18.00 to about 21.00 wt%;

[0016] Al: about 1.00 to about 1.80 wt%;

[0017] Ti: about 1.80 to about 2.70 wt%;

[0018] Si: about ≤0.80 wt%;

[0019] Mn: about ≤0.40 wt%;

[0020] P: about ≤0.015 wt%;

[0021] Fe: about ≤1.5 wt%;

[0022] B: about ≤0.008 wt%;

[0023] Cu: about ≤0.20 wt%;

[0024] Co: about ≤ 2.00 wt%;

[0025] S: to about ≤0.020 wt%;

[0026] The balance is Ni and inevitable impurities.

[0027] Option 3: The material forming method according to the above-mentioned Option 1 or 2, wherein the NiCr20TiAl high-temperature alloy billet is heated to a temperature range of about >1120°C to about 1200°C within a time of about ≥3 hours.

[0028] Option 4: The timber forming method according to any one of the above options 1 to 3, wherein the first rolling is performed at a temperature in the range of about >1120°C to about 1200°C.

[0029] Option 5: The material forming method according to any one of the above options 1 to 4, wherein the cross-sectional specifications of the NiCr20TiAl high-temperature alloy billet are approximately (115-125)×(115-125) mm.

[0030] Option 6: The material forming method according to any one of the above options 1 to 5, wherein the deformation rate of the NiCr20TiAl high-temperature alloy billet formed into the first rolled material by the first rolling is in the range of about 70% to about 80%.

[0031] Option 7: The material forming method according to any one of the above options 1 to 6, wherein the first rolled material is a cylindrical bar with a cross-sectional diameter ranging from about 60 to about 90 mm.

[0032] Scheme 8: The method for forming a product according to any one of the above schemes 1 to 7, wherein the method further comprises cooling the obtained first rolled product to room temperature by slow cooling in a slow cooling pit, and then performing solution treatment and aging heat treatment in sequence, wherein

[0033] The solution heat treatment comprises holding the first rolled material at a temperature of about 1030 to about 1080° C. for about 7 to about 9 hours, and then air cooling to room temperature, and

[0034] The aging heat treatment includes keeping the first rolled material at a temperature of about 825 to about 865° C. for about 23 to about 25 hours, then air cooling to room temperature, and further keeping it at a temperature of about 680 to about 720° C. for about 15 to about 17 hours, and finally air cooling to room temperature.

[0035] Option 9: The material forming method according to any one of the above options 1 to 8, wherein the method further includes subjecting the obtained first rolled material to further second rolling to obtain a second rolled material, and the second rolling preferably includes semi-continuous rolling.

[0036] Option 10: The material forming method according to the above-mentioned Option 9, wherein the second rolling is carried out in a temperature range of about >1130 to about 1200°C.

[0037] Option 11: The timber forming method according to Option 9 or 10 above, wherein online heating is performed during the second rolling process, and the temperature of the online heating is about >1130 to about 1200°C.

[0038] Option 12: The material forming method according to any one of the above options 9 to 11, wherein the deformation rate of the first rolled material formed by the second rolling to form the second rolled material is in the range of about 45% to about 75%.

[0039] Option 13: A material forming method according to any one of the above options 9 to 12, wherein the second rolled material is a cylindrical bar with a cross-sectional diameter ranging from about 20 to about <60 mm.

[0040] Solution 14: The method for forming a product according to any one of the above solutions 9 to 13, wherein the method further comprises cooling the obtained second rolled product to room temperature by slow cooling in a slow cooling pit, and then performing solution treatment and aging heat treatment in sequence, wherein

[0041] The solution heat treatment comprises holding the second rolled material at a temperature of about 1030 to about 1080° C. for about 7 to about 9 hours, and then air cooling to room temperature, and

[0042] The aging heat treatment includes keeping the second rolled material at a temperature of about 825 to about 865° C. for about 23 to about 25 hours, then air cooling to room temperature, and further keeping it at a temperature of about 680 to about 720° C. for about 15 to about 17 hours, and finally air cooling to room temperature.

[0043] Option 15: NiCr20TiAl high-temperature alloy rolled material prepared by the material forming method according to any one of the above options 1 to 14.

[0044] Technical Effect

[0045] The rolling method of the present invention can improve the grain size uniformity of the rolled NiCr20TiAl high-temperature alloy bar, wherein the bar has a full-cross-section grain size between 3 and 8, preferably between 5 and 8, and a full-cross-section grain size difference of ≤3, preferably ≤2, thereby achieving optimal high-temperature endurance performance. It should be noted that larger grains have smaller grain size fractions, and smaller grains have larger grain size fractions. For example, a grain size of 5.5 is finer than a grain size of 3. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments and the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 Fig. 4 is a micrograph of the as-rolled state of the first rolled material of NiCr20TiAl superalloy (cylindrical bar before slow cooling) obtained from Comparative Example 1 of the present invention, taken at different positions of the cross-section. The left figure is the position close to the edge, the middle figure is the position at about 1 / 4D, and the right figure is the position at about 1 / 2D.

[0048] Figure 2 Fig. 8 is a micrograph of the as-rolled state of the first rolled material of NiCr20TiAl superalloy (cylindrical bar before slow cooling) obtained from Example 1 of the present invention, taken at different positions of the cross-section. The left figure is the position close to the edge, the middle figure is the position at about 1 / 4D, and the right figure is the position at about 1 / 2D.

[0049] Figure 3 Fig. 12 is a micrograph of the microstructure of the first rolled material of NiCr20TiAl superalloy (cylindrical bar after slow cooling and solution + aging treatment) obtained from Comparative Example 2 of the present invention, taken at different positions of the cross-section. The left figure is the position close to the edge, the middle figure is the position at about 1 / 4D, and the right figure is the position at about 1 / 2D.

[0050] Figure 4 Fig. 16 is a micrograph of the microstructure of the first rolled material of NiCr20TiAl superalloy (cylindrical bar after slow cooling and solution + aging treatment) obtained from Example 2 of the present invention, taken at different positions of the cross-section. The left figure is the position close to the edge, the middle figure is the position at about 1 / 4D, and the right figure is the position at about 1 / 2D.

[0051] Figure 5 Fig. 20 is a low-magnification optical photograph of the cross-section of the first rolled material of NiCr20TiAl superalloy (cylindrical bar after slow cooling and solution + aging treatment) obtained from Comparative Example 2 of the present invention.

[0052] Figure 6 Fig. 24 is a low-magnification optical photograph of the cross-section of the first rolled material of NiCr20TiAl superalloy (cylindrical bar after slow cooling and solution + aging treatment) obtained from Example 2 of the present invention.

[0053] Figure 7Microstructure photographs taken at different positions of the cross-section of the second rolled material of NiCr20TiAl superalloy (cylindrical bar before slow cooling) obtained in Example 3 of the present invention. The left figure is the position close to the edge, the middle figure is the position at about 1 / 4D, and the right figure is the position at about 1 / 2D.

[0054] Figure 8 Microstructure photographs taken at different positions of the cross-section of the second rolled material of NiCr20TiAl superalloy (cylindrical bar after slow cooling and solution + aging treatment) obtained in Example 4 of the present invention. The left figure is the position close to the edge, the middle figure is the position at about 1 / 4D, and the right figure is the position at about 1 / 2D. Detailed implementation manners

[0055] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters not specified in the following embodiments are usually according to conventional conditions.

[0056] In the present invention, the endpoints and any values within the disclosed ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. The term "about" used in the present invention means that the modified number can fluctuate within the range of ±20%, ±15%, ±10%, ±5% or ±2% of the number. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0057] According to the first aspect of the present invention, the present invention provides a method for forming a rolled material of NiCr20TiAl superalloy.

[0058] The method for forming a rolled material according to the first aspect of the present invention includes heating a NiCr20TiAl superalloy billet to a temperature range of about >1120°C to about 1200°C (for example, about 1140°C, about 1160°C or about 1180°C), and holding at this temperature for about 1 to about 2 hours (for example, about 1.5 hours), and then subjecting the held billet to a first rolling to obtain a first rolled material.

[0059] Here, the holding temperature should not be too high, for example, not exceeding approximately 1200°C, otherwise the low-melting-point phases at the grain boundaries within the workpiece may dissolve during subsequent rolling, causing overburning during the rolling process and leading to cracking in the core. It should also not be too low, for example, not below 1120°C, otherwise the billet's deformation resistance may increase, making successful rolling impossible or causing cracks to form at the edges. Furthermore, the holding time should not be too long, for example, not exceeding approximately 2 hours, otherwise grain growth or precipitation of harmful phases within the billet may occur, making deformation difficult. It should also not be too short, for example, not less than approximately 1 hour, otherwise the billet's core may not be fully burned, resulting in uneven microstructure and a large temperature difference between the surface and core during rolling, leading to cracking in the rolled material.

[0060] In the material forming method according to the first aspect of the present invention, the NiCr20TiAl superalloy is a nickel-based superalloy having a nickel-chromium matrix and aluminum and titanium added to form an aging-strengthening phase. For example, in some preferred embodiments, the NiCr20TiAl superalloy comprises the following elemental components in weight percentage:

[0061] C: about 0.04 to about 0.10 wt %;

[0062] Cr: about 18.00 to about 21.00 wt %;

[0063] Al: about 1.00 to about 1.80 wt%;

[0064] Ti: about 1.80 to about 2.70 wt%;

[0065] Si: about ≤0.80 wt%;

[0066] Mn: about ≤0.40 wt%;

[0067] P: about ≤0.015 wt%;

[0068] Fe: about ≤1.5 wt%;

[0069] B: about ≤0.008 wt%;

[0070] Cu: about ≤0.20 wt%;

[0071] Co: about ≤ 2.00 wt%;

[0072] S: to about ≤0.020 wt%;

[0073] The balance is Ni and inevitable impurities.

[0074] In some preferred embodiments of the method for forming a billet according to the first aspect of the present invention, the NiCr20TiAl superalloy billet is preferably heated to a temperature within a range of approximately >1120°C to approximately 1200°C, such as approximately 1140°C, approximately 1160°C, or approximately 1180°C, within a period of approximately 3 hours or longer. The heating time, which refers to the time from charging the furnace to the holding temperature, is preferably greater than approximately 3 hours. This is primarily due to limitations of the heating furnace, which typically has a startup temperature of approximately 600°C. Furthermore, a rapid heating rate may result in a significant temperature difference between the surface and core of the resulting bar.

[0075] In other preferred embodiments of the material forming method according to the first aspect of the present invention, after the holding process, the held billet undergoes a first rolling process to obtain a first rolled product. The first rolling process may preferably include, for example, horizontal rolling. The first rolling process may be performed at a temperature ranging from approximately >1120°C to approximately 1200°C, for example, at approximately 1140°C, approximately 1160°C, or approximately 1180°C. In theory, the rolling temperature during the first rolling process is slightly lower than the holding temperature, as several seconds elapse between exiting the furnace and rolling, allowing the surface temperature to decrease slightly. The rolling temperature should not be too high, for example, not exceeding approximately 1200°C, as this will cause dissolution of the low-melting-point phases at the grain boundaries within the rolled product, leading to overheating during the rolling process and resulting in cracking in the core. The rolling temperature should also not be too low, for example, not below 1120°C, as this may increase the deformation resistance of the rolled product, prevent successful rolling, or cause cracks to form at the edges.

[0076] In other preferred embodiments of the billet forming method according to the first aspect of the present invention, the specifications of the NiCr20TiAl superalloy billet are not particularly limited. However, typically, a NiCr20TiAl superalloy billet having a cross-sectional specification of approximately (115-125) × (115-125) mm, for example, approximately 120 × 120 mm, can be used. This cross-sectional specification is primarily determined by the rolling pass profiles commonly used in the art. Exceeding this specification may result in excessive or insufficient billet deformation, or may prevent successful rolling.

[0077] In other preferred embodiments of the material forming method according to the first aspect of the present invention, the deformation rate of the NiCr20TiAl high-temperature alloy billet to form the first rolled product through the first rolling process is in the range of about 70% to about 80%, for example, about 75%. During the first rolling process, the deformation rate refers to the percentage of the cross-sectional area reduction from the billet to the first rolled product as a percentage of the cross-sectional area of the billet. Here, the deformation rate caused by the first rolling process should not be too large, for example, it should not exceed about 80%, otherwise the deformation will be too large and may cause local excessive temperatures, resulting in abnormal grain growth; nor should it be too small, for example, it should not be less than about 70%, otherwise the deformation will be insufficient and may result in insufficient dynamic recrystallization within the rolled product.

[0078] For example, in some exemplary embodiments, the first rolled product obtained by the first rolling is a cylindrical bar having a cross-sectional diameter in the range of about 60 to about 90 mm (e.g., about 65 mm, about 70 mm, about 75 mm, about 80 mm, or about 85 mm).

[0079] In other preferred embodiments of the timber forming method according to the first aspect of the present invention, the timber forming method further comprises cooling the obtained first rolled material to room temperature by slow cooling in a slow cooling pit, and then performing solid solution + aging heat treatment in sequence.

[0080] Here, there is no specific requirement for the slow cooling speed of the slow cooling pit, as long as it is slower than air cooling.

[0081] In addition, the solution heat treatment includes keeping the first rolled material at a temperature of about 1030 to about 1080°C (for example, about 1050°C) for about 7 to about 9 hours (for example, about 8 hours), and then air cooling to room temperature, and the aging heat treatment includes keeping the first rolled material at a temperature of about 825 to about 865°C (for example, about 845°C) for about 23 to about 25 hours (for example, about 24 hours), and then air cooling to room temperature, and further keeping it at a temperature of about 680 to about 720°C (for example, about 700°C) for about 15 to about 17 hours (for example, about 16 hours), and finally air cooling to room temperature.

[0082] Here, the purpose of performing solution + aging heat treatment on the first rolled material in sequence is to make the rolled material obtained by the treatment have the characteristics of high strength, creep resistance and stable structure through the synergistic mechanism of "dissolution-supersaturation-precipitation".

[0083] Here, inappropriate temperature and time of solution + aging heat treatment will cause imbalance in the mechanical properties of the rolled material, increase the risk of product failure, and increase processing difficulty.

[0084] Specifically, the solution treatment temperature should not be too low and the time should not be too short, otherwise the alloying elements in the rolled material cannot be fully dissolved, resulting in substandard mechanical properties and uneven structure. In addition, the solution treatment temperature should not be too high and the time should not be too long, otherwise the grains in the rolled material will easily coarsen. In addition, the aging treatment temperature should not be too low and the time should not be too short (under-aging), otherwise the precipitate phase in the rolled material will be insufficient and the performance will be unstable. Furthermore, the aging treatment temperature should not be too high and the time should not be too long (over-aging), otherwise the precipitate phase in the rolled material will easily coarsen.

[0085] In some other preferred embodiments of the material forming method according to the first aspect of the present invention, the method further comprises subjecting the obtained first rolled material to a second rolling process to obtain a second rolled material.

[0086] Here, the second rolling preferably includes semi-continuous rolling. The second rolling is preferably performed within a temperature range of approximately >1130°C to approximately 1200°C (e.g., approximately 1140°C, approximately 1160°C, or approximately 1180°C). The temperature of the second rolling should not be too high, for example, not exceeding approximately 1200°C, as this can easily cause grain boundary melting, resulting in overheating and cracking. It should also not be too low, for example, not below 1130°C, as this can prevent the first rolled product from being successfully rolled into the second rolled product or may cause cracking.

[0087] In another preferred alternative, online heating may be performed during the second rolling process, wherein the temperature of the online heating is from about >1130°C to about 1200°C.

[0088] During the second rolling process, the deformation rate of the first rolled material to form the second rolled material by the second rolling process is in the range of about 45% to about 75%, for example, about 50%, about 60% or about 70%. During the second rolling process, the deformation rate refers to the percentage of the cross-sectional area reduction from the first rolled material to the second rolled material to the cross-sectional area of the first rolled material. Here, the deformation rate caused by the second rolling should not be too large, for example, it should not exceed about 75%, otherwise the deformation of the rolled material will be too large, which may cause the local temperature to be too high and cause abnormal grain growth; it should not be too small, for example, it should not be less than about 45%, otherwise the deformation of the rolled material will be insufficient, which may cause dynamic recrystallization to fail to occur sufficiently in the rolled material.

[0089] For example, in some exemplary embodiments, the second rolled product obtained after the second rolling process is a cylindrical bar having a cross-sectional diameter in the range of 20 to about <60 mm (e.g., about 30 mm, about 40 mm, or about 50 mm).

[0090] After the second rolling, the material forming method preferably further comprises cooling the obtained second rolled material to room temperature by slow cooling in a slow cooling pit, and then performing solid solution + aging heat treatment in sequence.

[0091] Here, there is no specific requirement for the slow cooling speed of the slow cooling pit, as long as it is slower than air cooling.

[0092] In addition, the solution heat treatment includes keeping the second rolled material at a temperature of about 1030 to about 1080°C (e.g., about 1050°C) for about 7 to about 9 hours (e.g., about 8 hours), and then air cooling to room temperature, and the aging heat treatment includes keeping the second rolled material at a temperature of about 825 to about 865°C (e.g., about 845°C) for about 23 to about 25 hours (e.g., about 24 hours), and then air cooling to room temperature, and further keeping it at a temperature of about 680 to about 720°C (e.g., about 700°C) for about 15 to about 17 hours (e.g., about 16 hours), and finally air cooling to room temperature.

[0093] Here, the purpose of sequentially performing solution treatment and aging heat treatment on the second rolled material and setting its process parameters is similar to the purpose described above for the first rolled material.

[0094] According to a second aspect of the present invention, the present invention provides a NiCr20TiAl high-temperature alloy rolled product prepared by the product forming method as described above in the first aspect of the present invention, comprising a first rolled product (i.e., a cylindrical bar before slow cooling and a cylindrical bar after slow cooling and solid solution + aging treatment) and a second rolled product (i.e., a cylindrical bar before slow cooling and a cylindrical bar after slow cooling and solid solution + aging treatment).

[0095] In the NiCr20TiAl high-temperature alloy rolled products described in the second aspect of the present invention, the full-section grain size of the first and second rolled products after slow cooling and solution + aging treatment (especially the cylindrical bars after slow cooling and solution + aging treatment) is between 3 and 8 levels, preferably between 5 and 8 levels, and the full-section grain size difference is ≤3 levels, preferably ≤2 levels, and therefore has the best high-temperature endurance performance, for example, the endurance test time reaches at least about 55 hours.

[0096] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0097] The element components in the NiCr20TiAl high-temperature alloy billet with a specification of 120×120 mm used in the following examples are as follows:

[0098] C: about 0.04 to about 0.10 wt %;

[0099] Cr: about 18.00 to about 21.00 wt %;

[0100] Al: about 1.00 to about 1.80 wt%;

[0101] Ti: about 1.80 to about 2.70 wt%;

[0102] Si: about ≤ 0.80 wt%;

[0103] Mn: about ≤ 0.40 wt%;

[0104] P: about ≤ 0.015 wt%;

[0105] Fe: about ≤ 1.5 wt%;

[0106] B: about ≤ 0.008 wt%;

[0107] Cu: about ≤ 0.20 wt%;

[0108] Co: about ≤ 2.00 wt%;

[0109] S: up to about ≤ 0.020 wt%;

[0110] The balance is Ni and unavoidable impurities.

[0111] The bloom is obtained through the following process sequence: vacuum induction furnace smelting - electrode peeling - electroslag remelting under protective atmosphere - high-temperature diffusion treatment - cogging - rotary forging to produce rolled billets.

[0112] Example 1

[0113] Heat the NiCr20TiAl superalloy bloom in a heating furnace to a temperature of about 1160 °C, where the heating time from charging to the target temperature is controlled to be more than about 3 hours. After the NiCr20TiAl bloom reaches a temperature of about 1160 °C, hold it at a temperature of about 1160 °C for about 1.5 hours. Then take out the heat-preserved NiCr20TiAl bloom and enter the transverse rolling to obtain the first rolled product. The obtained first rolled product is a cylindrical bar with a cross-sectional diameter of about 70 mm and a deformation rate of about 73.3%.

[0114] Example 2

[0115] After Example 1, slow-cool the first rolled product obtained from Example 1 to room temperature by slow cooling in a slow-cooling pit, and then perform solution + aging heat treatment on the first rolled product cooled to room temperature. The solution heat treatment includes holding the first rolled product at a temperature of about 1030 to about 1080 °C for about 8 hours and then air-cooling to room temperature. The aging heat treatment includes holding at a temperature of about 825 to about 865 °C for about 24 hours, then air-cooling to room temperature, and further holding at a temperature of about 680 to about 720 °C for about 16 hours, and finally air-cooling to room temperature.

[0116] Comparative Example 1

[0117] Heat the NiCr20TiAl superalloy billet in a heating furnace to a temperature of about 1050 °C, and control the heating time from charging to the target temperature to be more than about 3 hours. After the NiCr20TiAl billet reaches a temperature of about 1050 °C, keep it at a temperature of about 1050 °C for about 2.5 hours. Then take out the heat-insulated NiCr20TiAl billet from the furnace and enter the tandem rolling to obtain the first rolled material. The obtained first rolled material is a cylindrical bar with a cross-sectional diameter of about 70 mm and a deformation rate of about 73.3%.

[0118] Comparative Example 2

[0119] After Comparative Example 1, slowly cool the first rolled material obtained from Comparative Example 1 to room temperature by means of slow cooling in a slow cooling pit, and then perform solution + aging heat treatment on the first rolled material cooled to room temperature. The solution heat treatment includes keeping the first rolled material at a temperature of about 1030 to about 1080 °C for about 8 hours, and then air-cooling to room temperature. The aging heat treatment includes keeping it at a temperature of about 825 to about 865 °C for about 24 hours, then air-cooling to room temperature, and further keeping it at a temperature of about 680 to about 720 °C for about 16 hours, and finally air-cooling to room temperature.

[0120] Example 3

[0121] After Example 1, directly feed the first rolled material obtained from Example 1 into semi-continuous rolling to obtain the second rolled material. The semi-continuous rolling process uses on-line temperature compensation, and the compensation temperature is about 1160 °C. The obtained second rolled material is a cylindrical bar with a cross-sectional diameter of about 40 mm and a deformation rate of about 67.3%.

[0122] Example 4

[0123] After Example 3, slowly cool the second rolled material obtained from Example 3 to room temperature by means of slow cooling in a slow cooling pit, and then perform solution + aging heat treatment on the second rolled material cooled to room temperature. The solution heat treatment includes keeping the second rolled material at a temperature of about 1030 to about 1080 °C for about 8 hours, and then air-cooling to room temperature. The aging heat treatment includes keeping it at a temperature of about 825 to about 865 °C for about 24 hours, then air-cooling to room temperature, and further keeping it at a temperature of about 680 to about 720 °C for about 16 hours, and finally air-cooling to room temperature.

[0124] Comparative Example 3

[0125] After Comparative Example 1, the first rolled material obtained from Comparative Example 1 was directly fed into semi - continuous rolling to obtain a second rolled material. In the semi - continuous rolling process, on - line temperature compensation was adopted, and the compensation temperature was about 1160 °C. The obtained second rolled material was a cylindrical bar with a cross - sectional diameter of about 40 mm and a deformation rate of about 67.3%.

[0126] Comparative Example 4

[0127] After Comparative Example 3, the second rolled material obtained from Comparative Example 3 was slowly cooled to room temperature by slow cooling in a slow - cooling pit, and then the second rolled material cooled to room temperature was subjected to solution + aging heat treatment. The solution heat treatment included holding the second rolled material at a temperature of about 1030 to about 1080 °C for about 8 hours and then air - cooling to room temperature. The aging heat treatment included holding at a temperature of about 825 to about 865 °C for about 24 hours and then air - cooling to room temperature, and further holding at a temperature of about 680 to about 720 °C for about 16 hours, and finally air - cooling to room temperature.

[0128] Comparative Example 5

[0129] After Example 3, the second rolled material obtained from Example 3 was cooled to room temperature by air - cooling, and then the second rolled material cooled to room temperature was subjected to solution + aging heat treatment. The solution heat treatment included holding the second rolled material at a temperature of about 1030 to about 1080 °C for about 8 hours and then air - cooling to room temperature. The aging heat treatment included holding at a temperature of about 825 to about 865 °C for about 24 hours and then air - cooling to room temperature, and further holding at a temperature of about 680 to about 720 °C for about 16 hours, and finally air - cooling to room temperature.

[0130] Comparative Example 6

[0131] After Example 1, the first rolled material obtained from Example 1 was directly fed into semi - continuous rolling to obtain a second rolled material. In the semi - continuous rolling process, on - line temperature compensation was not adopted, resulting in the temperature dropping to less than about 1130 °C during semi - continuous rolling. The obtained second rolled material was a cylindrical bar with a cross - sectional diameter of about 40 mm and a deformation rate of about 67.3%. The obtained second rolled material was slowly cooled to room temperature by slow cooling in a slow - cooling pit, and then the second rolled material cooled to room temperature was subjected to solution + aging heat treatment. The solution heat treatment included holding the second rolled material at a temperature of about 1030 to about 1080 °C for about 8 hours and then air - cooling to room temperature. The aging heat treatment included holding at a temperature of about 825 to about 865 °C for about 24 hours and then air - cooling to room temperature, and further holding at a temperature of about 680 to about 720 °C for about 16 hours, and finally air - cooling to room temperature.

[0132] For easy comparison, the process conditions of the above examples and comparative examples are summarized in Table 1 below.

[0133] Table 1

[0134]

[0135] Obtain the as-rolled microstructure photos of the first rolled materials of NiCr20TiAl superalloy from Comparative Example 1 and Example 1 (cylindrical bars before slow cooling) taken at different positions of the cross-section. See Figure 1 and 2 .

[0136] Obtain the microstructure photos of the first rolled materials of NiCr20TiAl superalloy from Comparative Example 2 and Example 2 (cylindrical bars after slow cooling and solution + aging heat treatment) taken at different positions of the cross-section. See Figure 3 and 4 .

[0137] Obtain the low-magnification optical photos of the cross-sections of the first rolled materials of NiCr20TiAl superalloy from Comparative Example 2 and Example 2 (cylindrical bars after slow cooling and solution + aging heat treatment). See Figure 5 and 6 .

[0138] Obtain the as-rolled microstructure photos of the second rolled materials of NiCr20TiAl superalloy from Example 3 (cylindrical bars before slow cooling) taken at different positions of the cross-section. See Figure 7 .

[0139] Obtain the microstructure photos of the second rolled materials of NiCr20TiAl superalloy from Example 4 (cylindrical bars after slow cooling and solution + aging heat treatment) taken at different positions of the cross-section. See Figure 8 .

[0140] From the comparison of the microstructure photos obtained from Comparative Example 1 and Example 1 ( Figure 1 and Figure 2 ), it can be seen that since the elevated rolling temperature can effectively reduce the temperature difference between the surface and the core of the rolled material, compared with Comparative Example 1 using the existing technology for heat preservation and rolling process, the as-rolled grain size of the first rolled material (cylindrical bar before slow cooling) obtained in Example 1 of the present invention is significantly improved. The grain sizes of the cylindrical bar at the position close to the edge, 1 / 4D position, and 1 / 2D position of the cross-section are improved from Grade 9, Grade 9, and Grade 9 in Comparative Example 1 to Grade 8, Grade 6, and Grade 5.5 in Example 1 of the present invention respectively. In the present invention, the 1 / 4D position or 1 / 2D position refers to: this position is located within the cross-section of the cylindrical bar, the diameter length (D) of the circular cross-section passing through this position is measured, and the shortest distance from this position to the edge is 1 / 4 times D (i.e., in the middle or near the middle between the center and the edge) or 1 / 2 times D (i.e., at the center or near the center).

[0141] It can be seen that Figure 4 for the first rolled material (cylindrical bar after slow cooling and solution + aging heat treatment) obtained in Example 2 of the present invention, the grain sizes at the position close to the edge, 1 / 4D position, and 1 / 2D position are 7-1 level, 6 level, and 5.5 level respectively. Compared with the corresponding Figure 2 as-rolled microstructure photograph of the first rolled material (cylindrical bar before slow cooling) obtained in Example 1( Figure 2 ), the grain size does not grow, and the grain size at the position close to the edge is improved from 8 level to 7-1 level.

[0142] It can be seen that Figure 3 for the first rolled material (cylindrical bar after slow cooling and solution + aging heat treatment) obtained in Comparative Example 2, the grain sizes at the position close to the edge, 1 / 4D position, and 1 / 2D position are 8-1 level, 7.5 level, and 7 level respectively. Compared with the as-rolled microstructure photograph of the first rolled material (cylindrical bar before slow cooling) obtained in Comparative Example 1( Figure 1 ), the grain sizes are all improved (from 9 level to 8-1 level, 7.5 level, and 7 level respectively).

[0143] It can be seen that Figure 5 and Figure 6 for the first rolled material of NiCr20TiAl superalloy obtained in Example 2 of the present invention( Figure 6 ), the depth of the edge coarse grain ring (i.e., the width that the coarse grain ring extends from the edge of the rolled material into the rolled material) is shallower than that of the first rolled material of NiCr20TiAl superalloy obtained in Comparative Example 2( Figure 5 ). Specifically, for the first rolled material (cylindrical bar after slow cooling and solution + aging heat treatment) obtained in Example 2 of the present invention, there is a coarse grain ring of about 2 mm at the edge( Figure 6 ); while for the first rolled material (cylindrical bar after slow cooling and solution + aging heat treatment) obtained in Comparative Example 2, there is a coarse grain ring with a depth of about 25 mm at the edge( Figure 5 ), and the depth of the coarse grain ring is significantly greater than about 2 mm of the first rolled material in Example 2 of the present invention( Figure 6 ).

[0144] It can be seen that Figure 7 for the second rolled material of NiCr20TiAl superalloy obtained in Example 3 of the present invention (cylindrical bar before slow cooling), the grain sizes at the position close to the edge, 1 / 4D position, and 1 / 2D position are 7 level, 6 level, and 5.5 level respectively. Compared with the as-rolled microstructure photograph of the first rolled material (cylindrical bar before slow cooling) obtained in Example 1( Figure 2 ), the grain size does not grow, and the grain size at the position close to the edge is improved from 8 level to 7 level.

[0145] It can be seen from Figure 8 that the grain sizes of the second rolled material of NiCr20TiAl superalloy (cylindrical bars after slow cooling and solution + aging treatment) obtained in Example 4 of the present invention at the position close to the edge, 1 / 4D position, and 1 / 2D position are 6, 4, and 4 respectively. Compared with the as-rolled microstructure photograph of the first rolled material (cylindrical bars after slow cooling and solution + aging treatment) obtained in Example 2 ( Figure 4 ), the grain sizes of the cylindrical bars at the position close to the edge, 1 / 4D position, and 1 / 2D position of the cross-section are increased from 7-1, 6, and 5.5 in Example 2 to 6, 4, and 4 in Example 4 respectively.

[0146] The above results show that the full-section grain sizes of the first rolled material (i.e., cylindrical bars before slow cooling and cylindrical bars after slow cooling and solution + aging treatment) and the second rolled material (i.e., cylindrical bars before slow cooling and cylindrical bars after slow cooling and solution + aging treatment) obtained in Examples 1 to 4 of the present invention are all between 5 and 8 levels, and the full-section grain size grade difference ≤ 3 levels, and thus the high-temperature creep rupture performance can be improved.

[0147] The second rolled materials obtained in Example 4 of the present invention and Comparative Examples 4 to 6 were respectively subjected to a 750°C / 340 MPa creep rupture test according to Chinese national standard GB / T2039-2024 "Metallic materials—Uniaxial tensile creep testing method". The test results are shown in Table 2 below.

[0148] Table 2: 750°C / 340 MPa creep rupture test results

[0149]

[0150] It can be seen from the test results in Table 2 that the 750°C / 340 MPa creep rupture test time of the second rolled material (cylindrical bar with a cross-sectional diameter of 40 mm after slow cooling and solution + aging treatment) in Example 4 of the present invention is increased to about 55 hours, which is greater than the general technical requirement (about ≥ 30 hours). However, the second rolled materials in Comparative Examples 4 to 6 do not meet the said technical requirement.

[0151] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions required to be protected by the present invention.

Claims

1. A method for producing NiCr20TiAl superalloy rolled products, characterized in that, The method comprises: heating a NiCr20TiAl high-temperature alloy billet to a temperature range of >1120° C. to 1200° C., maintaining the temperature at the temperature for 1 to 2 hours, and then subjecting the maintained billet to a first rolling process to obtain a first rolled product.

2. The method for forming timber according to claim 1, characterized in that: The element composition weight percentage content of the NiCr20TiAl high temperature alloy is: C: 0.04-0.10 wt%; Cr: 18.00-21.00 wt%; Al: 1.00-1.80 wt%; Ti: 1.80-2.70 wt%; Si: ≤0.80 wt%; Mn: ≤0.40 wt%; P: ≤ 0.015 wt%; Fe: ≤1.5 wt%; B: ≤0.008 wt%; Cu: ≤0.20 wt%; Co: ≤2.00 wt%; S: ≤0.020 wt%; The balance is Ni and inevitable impurities.

3. The method for forming timber according to claim 1, wherein: Heating the NiCr20TiAl high temperature alloy billet to a temperature range of >1120°C to 1200°C within ≥3 hours; and / or The first rolling is performed at a temperature in the range of >1120°C to 1200°C.

4. The timber forming method according to claim 1, characterized in that: The cross-sectional specifications of the NiCr20TiAl high-temperature alloy billet are (115-125)×(115-125) mm; and / or The deformation rate of the NiCr20TiAl high temperature alloy billet formed into the first rolled material by the first rolling is in the range of 70% to 80%, and / or The first rolled material is a cylindrical bar with a cross-sectional diameter ranging from 60 to 90 mm.

5. The timber forming method according to any one of claims 1 to 4, characterized in that: The method further comprises cooling the obtained first rolled product to room temperature by slow cooling in a slow cooling pit, and then performing solution treatment and aging heat treatment in sequence, wherein: The solution heat treatment comprises holding the first rolled material at a temperature of 1030 to 1080° C. for 7 to 9 hours, and then air cooling to room temperature, and The aging heat treatment includes keeping the first rolled material at a temperature of 825 to 865° C. for 23 to 25 hours, then air cooling it to room temperature, and further keeping it at a temperature of 680 to 720° C. for 15 to 17 hours, and finally air cooling it to room temperature.

6. The timber forming method according to any one of claims 1 to 4, characterized in that: The method further includes subjecting the obtained first rolled product to further second rolling to obtain a second rolled product.

7. The timber forming method according to claim 6, characterized in that: The second rolling is performed in a temperature range of >1130 to 1200°C; and / or During the second rolling process, online heating is performed, and the temperature of the online heating is in the range of >1130 to 1200°C.

8. The timber forming method according to claim 6, characterized in that: The deformation rate of the first rolled material to form the second rolled material after the second rolling is in the range of 45% to 75%; and / or The second rolled product is a cylindrical bar with a cross-sectional diameter ranging from 20 to <60 mm.

9. The timber forming method according to claim 6, characterized in that: The method further comprises cooling the obtained second rolled material to room temperature by slow cooling in a slow cooling pit, and then performing solution treatment and aging heat treatment in sequence, wherein The solution heat treatment comprises holding the second rolled material at a temperature of 1030 to 1080° C. for 7 to 9 hours, and then air cooling to room temperature, and The aging heat treatment includes keeping the second rolled material at a temperature of 825 to 865° C. for 23 to 25 hours, then air cooling it to room temperature, and further keeping it at a temperature of 680 to 720° C. for 15 to 17 hours, and finally air cooling it to room temperature.

10. NiCr20TiAl high temperature alloy rolled product produced by the product forming method according to any one of claims 1 to 9.

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