A low hot working cracking rate nickel-based alloy and a preparation method and application thereof

Abstract

The present application belongs to the technical field of nickel-based superalloys, and particularly relates to a nickel-based alloy with low hot working cracking rate, and a preparation method and application thereof. The nickel-based alloy comprises the following components in mass fraction: Mo 15.0%-17.0%, Cr 6.0%-8.0%, Fe≤5.0%, Mn≤1.0%, Si≤1.0%, C≤0.08%, P≤0.005%, S≤0.005%, O≤0.0020%, and the balance of Ni, wherein P+S+O≤0.012%, and the mass ratio of P / S is controlled to be 1.5-2.5. By strictly controlling the total amount of P, S and O impurities and the phosphorus-sulfur ratio, cooperating with the grain boundary strengthening effect of trace B and Mg, combining with high-temperature step homogenization and temperature-controlled forging process, the present application effectively eliminates dendritic segregation and carbide aggregation, significantly reduces the cracking tendency of the nickel-based alloy in the hot working process, and obtains a forged piece with uniform grain structure.

Description

Technical Field

[0001] This invention belongs to the field of nickel-based high-temperature alloy technology, specifically relating to a nickel-based alloy with low hot working cracking rate, its preparation method, and its application. Background Technology

[0002] UNS N10003 alloy is a nickel-based alloy with Ni as the matrix and solid solution strengthening by adding elements such as Mo, Cr, and Fe. Due to its excellent corrosion resistance, good high-temperature mechanical properties, and structural stability in high-temperature fluoride molten salt environments, this alloy has been selected as a structural material for molten salt reactor nuclear power plants. However, large-ingot UNS N10003 alloy faces two major technical bottlenecks in actual industrial production: (1) High tendency for hot working cracking: The alloy contains 15.0%-17.0% Mo and 6.0%-8.0% Cr by mass, with a high content of refractory elements and a wide solidification range, which leads to severe dendritic segregation during casting and subsequent forging and rolling. At the same time, the segregation of low-melting-point impurity elements (such as P and S) at the grain boundaries forms a liquid film, which induces intergranular cracks under thermal stress.

[0003] (2) Non-uniform grain structure: When the conventional homogenization treatment temperature is too low or the time is insufficient, the Mo-rich carbides are difficult to completely dissolve. During the subsequent hot deformation process, mixed grain structure and carbide aggregation are easily formed, which reduces the anisotropy, durability and creep resistance of the material.

[0004] While there are reports in the literature on the smelting methods of UNS N10003 alloy, crack control technology for large-scale (ton-level) ingots used in nuclear power plants still needs improvement. This invention proposes a systematic solution to the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a nickel-based alloy with low hot working cracking rate, its preparation method, and its application. This invention optimizes the proportion of trace elements in the alloy, strictly controls the content of impurity elements, and combines a "high-temperature step homogenization + temperature-controlled forging" process to eliminate element segregation, refine grains, and significantly reduce the risk of cracking during hot working.

[0006] To achieve the above technical objectives, the technical solution adopted in the embodiments of the present invention is as follows: In a first aspect, embodiments of the present invention provide a nickel-based alloy with low hot working cracking rate, comprising the following components by mass fraction: Mo 15.0%-17.0%, Cr 6.0%-8.0%, Fe≤5.0%, Mn≤1.0%, Si≤1.0%, C≤0.08%, P≤0.005%, S≤0.005%, O≤0.0020%, with the balance being Ni, wherein P+S+O≤0.012%, and the P / S mass ratio is controlled at 1.5-2.5.

[0007] Further, by mass fraction, it includes the following components: Mo 15.7%-16.3%, Cr 6.7%-7.3%, Fe 4.2%-4.8%, Mn 0.20%-0.40%, Si 0.15%-0.35%, C 0.04%-0.05%, P≤0.005%, S≤0.005%, O≤0.0020%, with the balance being Ni, wherein P+S+O≤0.012%, and the P / S mass ratio is controlled at 1.5-2.5.

[0008] Ni is used as the matrix element; Mo is used for solid solution strengthening to improve high-temperature strength; Cr is used for solid solution strengthening to improve oxidation resistance; Fe is used for solid solution strengthening to stabilize the microstructure and reduce costs; Mn is used for deoxidation and sulfur fixation; Si is used as a deoxidizer; and C is used to form second-phase carbides and strengthen grain boundaries.

[0009] The limiting mechanism of the phosphorus-sulfur ratio is as follows: when the P / S mass ratio is too low, sulfur (S) readily forms a low-melting-point eutectic phase with Ni and Mo, which preferentially melts during hot working to form an intergranular liquid film; when the P / S ratio is too high, the non-equilibrium segregation of sulfur at grain boundaries intensifies, reducing grain boundary bonding strength. Therefore, controlling the P / S ratio within the range of 1.5-2.5 allows the segregation behavior of P and S at grain boundaries to mutually restrain each other, avoiding excessive enrichment of a single element.

[0010] Furthermore, the nickel-based alloy also contains 0.001%-0.002% B and 0.002%-0.008% Mg. Both B and Mg have a tendency to segregate at grain boundaries, which can fill grain boundary vacancies, reduce grain boundary energy, and inhibit grain boundary wetting of low-melting-point impurities, thereby improving thermoplasticity.

[0011] Secondly, embodiments of the present invention provide a method for preparing the nickel-based alloy with low hot working cracking rate described in the first aspect, comprising the following steps: Step S1: Vacuum induction melting The raw materials are loaded into a vacuum induction melting furnace according to the proportion, the vacuum is drawn to ≤1Pa, and the furnace is powered to melt. After the molten pool is formed, the furnace is refined. After the refining is completed, argon gas is introduced to 20-30 kPa, and carbon powder is added for final deoxidation. The final C content is controlled to be 0.04%-0.05%. The molten steel is cast into electrode rods at a casting temperature of 1440-1460℃. Step S2: Vacuum consumable arc melting The electrode rods were placed in a vacuum consumable arc furnace and evacuated to ≤0.1 Pa. A steady-state melting process was used for melting. During the melting process, the arc stabilizing coil was turned on with an arc stabilizing current of 5-10 A and a frequency of 30-50 Hz to stir the molten pool and refine the solidification structure. After melting, the furnace was kept under vacuum for 20-40 minutes to allow the shrinkage cavities to solidify fully. Then, the furnace was cooled to below 200°C by argon gas to obtain a consumable remelted ingot. Step S3: High-temperature stepped homogenization heat treatment The consumable remelted ingot is loaded into a heat treatment furnace and heated to 700-900℃ at a rate of ≤80℃ / h. It is held at this temperature for 2-4 hours for preheating. Then, it is heated to 1180-1220℃ at a rate of ≤100℃ / h for homogenization. After homogenization, it is cooled to 600℃ or below in the furnace and then removed from the furnace and air-cooled. The principle of this stepped homogenization process is as follows: First, preheating at 700-900℃ reduces the temperature difference between the inside and outside of the ingot, avoiding thermal stress cracking caused by rapid heating; then, holding at a high temperature of 1180-1220℃ for a long time promotes the bulk diffusion of Mo, reduces the dendrite segregation index, and at the same time, spheroidizes and partially dissolves the primary carbides at the grain boundaries, resulting in a more uniform distribution of carbides.

[0012] Step S4, Temperature-controlled forging The homogenized consumable remelted ingot is reheated to 1150-1180℃ and held for 2-4 hours; multi-pass forging is carried out using a high-speed forging machine with an initial forging temperature ≥1120℃ and a final forging temperature ≥950℃. Step S5, Solution treatment The forged billet undergoes solution treatment: heated to 1170-1180℃, held for 1-2 hours per 100mm thickness, followed by air cooling. After solution treatment, the alloy grain size is controlled to ASTM 5-7 level.

[0013] Furthermore, in step S1, the refining temperature is controlled at 1520-1550℃, and the refining time is 30-60 minutes.

[0014] Furthermore, in step S2, the melting current is 8000-12000 A, the voltage is 22-28 V, and the melting rate is controlled at 5-8 kg / min.

[0015] Furthermore, in step S2, the electrode insertion depth is controlled at 30-50 mm, the voltage at 45-55 V, and the current at 6000-10000 A during the remelting process.

[0016] Furthermore, in step S3, the holding time for homogenization treatment is calculated based on the maximum cross-sectional thickness of the ingot: t = (0.06 - 0.08) × D, where t is the holding time in hours and D is the ingot thickness in millimeters.

[0017] Furthermore, in step S4, the deformation amount of each pass is controlled as follows: the deformation amount of the first three passes is controlled at 15%-20%, the deformation amount of subsequent passes is controlled at 20%-30%, the total forging ratio is ≥4, and a reheating is performed once between every two passes. The reheating temperature is 1100±20℃, and the holding time is 0.5-1 hour.

[0018] Thirdly, the embodiments of the present invention provide applications of the nickel-based alloys prepared by the preparation method described in the second aspect, wherein the nickel-based alloys are used in the industrial manufacturing of large-size forgings, pipes and plates for nuclear power.

[0019] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: (1) In the preparation of the nickel-based alloy of the present invention, by strictly controlling the total amount of P, S and O impurities and the P / S mass ratio, and with the grain boundary strengthening effect of trace amounts of B and Mg, the forging cracking rate of the nickel-based alloy within the hot working window is greatly reduced.

[0020] (2) The preparation method of the present invention adopts a high-temperature step homogenization process to effectively eliminate the dendritic segregation of Mo element and improve the uniformity of carbide distribution.

[0021] (3) The present invention uses temperature-controlled forging process to ensure that dynamic recrystallization is fully carried out, resulting in uniform grain size and no mixed crystal phenomenon. Attached Figure Description

[0022] Figure 1 This is a physical image of the UNS N10003 nickel-based alloy obtained in Example 1 of the present invention.

[0023] Figure 2 This is a physical image of the UNS N10003 nickel-based alloy obtained in Example 2 of the present invention.

[0024] Figure 3 This is a physical image of the UNS N10003 nickel-based alloy obtained in Example 3 of the present invention.

[0025] Figure 4 This is a physical image of the UNS N10003 nickel-based alloy obtained in the comparative example of this invention.

[0026] Figure 5 This is a comparison chart of the forging cracking rates of Examples 1-3 and the comparative example UNS N10003 nickel-based alloy.

[0027] Figure 6a and Figure 6bThese are comparison images of the microstructures of Embodiment 2 and the comparative example after homogenization treatment, respectively. Figure 6a This is a microstructure image of Example 2 after homogenization treatment. Figure 6b This is a microstructure image of the comparative model after homogenization. Detailed Implementation

[0028] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "inner" and "outer", "upper" and "lower", "left" and "right" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention.

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] Example 1 A low hot work cracking rate UNS N10003 nickel-based alloy, comprising the following components by mass fraction: Mo 16.20%, Cr 7.20%, Fe 4.50%, Mn 0.30%, Si 0.20%, C 0.045%, P 0.003%, S 0.002%, O 0.0012%, B 0.002%, Mg 0.005%, wherein the mass ratio of P / S is 1.5, and the balance is Ni.

[0031] The preparation method of the above-mentioned UNS N10003 nickel-based alloy with low hot working cracking rate includes the following steps: Step S1: Vacuum induction melting The raw materials are loaded into a vacuum induction melting furnace according to the proportion, the vacuum is drawn to 0.8 Pa, and the furnace is powered to melt. After the molten pool is formed, the furnace is refined at a temperature of 1540℃ for 40 minutes. After the refining is completed, argon gas is introduced to 22 kPa, and carbon powder is added for final deoxidation. The final C content is controlled to be 0.045%. The molten steel is then cast into Φ440 mm electrode rods at a casting temperature of 1450℃. Step S2: Vacuum consumable arc melting The electrode rods were placed in a vacuum consumable arc furnace and evacuated to 0.8 Pa. A steady-state melting process was used for melting, with a melting current of 10000 A, a voltage of 25 V, and a melting rate of 6 kg / min. During the melting process, an arc stabilizing coil was turned on with an arc stabilizing current of 8 A and a frequency of 40 Hz to stir the molten pool and refine the solidification structure. After melting, the furnace was kept under vacuum for 30 minutes to allow the shrinkage cavities to solidify fully. Then, the furnace was cooled to below 200 °C by argon gas and the ingot was removed from the furnace to obtain a Φ560 mm consumable remelted ingot. Step S3: High-temperature stepped homogenization heat treatment The consumable remelted ingot is loaded into a heat treatment furnace and heated to 800°C at a rate of 60°C / h. It is held at this temperature for 3 hours for preheating, and then heated to a homogenization temperature of 1200°C at a rate of 80°C / h. The holding time is calculated based on the maximum cross-sectional thickness of the ingot: t = 0.07 × D, where t is the holding time in hours and D is the thickness of the ingot, D = 560 mm. After homogenization, the ingot is cooled to 600°C in the furnace and then removed from the furnace and air-cooled. Where t = 0.07 × 560 = 39.2 h, and 39 h is actually taken; Step S4, Temperature-controlled forging The homogenized consumable remelted ingot was reheated to 1170℃ and held for 2.5 hours. Multi-pass forging was performed using a high-speed forging mill, with an initial forging temperature of 1150℃ and a final forging temperature of 980℃. The deformation per pass was controlled as follows: the first three passes had a deformation of 18%, and the last five passes had a deformation of 25%, with a total forging ratio of 5. A reheating process (1100℃, held for 1 hour) was performed between every two passes to restore plasticity and refine the grain size.

[0032] Step S5, Solution treatment The forged billet undergoes solution treatment: heating to 1175℃, holding for 2 hours per 100mm thickness, followed by air cooling. After solution treatment, the grain size of the resulting UNS N10003 nickel-based alloy is controlled to ASTM grade 5-7. Figure 1 As shown, the UNS N10003 nickel-based alloy has no visible cracks on its surface.

[0033] Example 2 A low hot work cracking rate UNS N10003 nickel-based alloy comprises the following components by mass fraction: Mo 16.20%, Cr 7.20%, Fe 4.50%, Mn 0.30%, Si 0.20%, C 0.045%, P 0.004%, S 0.002%, O 0.0012%, B 0.002%, Mg 0.005%, wherein the mass ratio of P / S is 1.5, and the balance is Ni.

[0034] The preparation method and parameters of the UNS N10003 nickel-based alloy with low hot working cracking rate are the same as in Example 1. The grain size of the obtained UNS N10003 nickel-based alloy is controlled at ASTM level 5-7. Figure 2 As shown, the UNS N10003 nickel-based alloy has no visible cracks on its surface.

[0035] Example 3 A low hot work cracking rate UNS N10003 nickel-based alloy comprises the following components by mass fraction: Mo 16.20%, Cr 7.20%, Fe 4.50%, Mn 0.30%, Si 0.20%, C 0.045%, P 0.005%, S 0.002%, O 0.0012%, B 0.002%, Mg 0.005%, wherein the mass ratio of P / S is 2.5, and the balance is Ni.

[0036] The preparation method and parameters of the UNS N10003 nickel-based alloy with low hot working cracking rate are the same as in Example 1. The grain size of the obtained UNS N10003 nickel-based alloy is controlled at ASTM level 5-7. Figure 3 As shown, the UNS N10003 nickel-based alloy has no visible cracks on its surface.

[0037] Comparative Example A low hot work cracking rate UNS N10003 nickel-based alloy, by mass fraction, comprises the following components: Mo 16.20%, Cr 7.20%, Fe 4.50%, Mn 0.30%, Si 0.20%, C 0.045%, P 0.002%, S 0.002%, O 0.0012%, B 0.002%, Mg 0.005%, with calculated P / S = 1.0, and the balance being Ni.

[0038] The preparation method and parameters of the UNS N10003 nickel-based alloy with low hot working cracking rate are the same as in Example 1. The grain size of the obtained UNS N10003 nickel-based alloy is controlled at ASTM level 5-7. Figure 4 As shown, the UNS N10003 nickel-based alloy exhibits obvious surface cracks.

[0039] like Figure 5 The figure shown is a comparison of the forging cracking rates of Examples 1-3 and the comparative example UNS N10003 nickel-based alloy. Figure 5 It can be seen that the cracking rate of the UNS N10003 nickel-based alloys prepared in Examples 1-3 is much lower than that of the comparative examples.

[0040] like Figure 6a and Figure 6bThe image shown is a comparison of the microstructures of Example 2 and the comparative example after homogenization treatment. Figure 6a This is a microstructure image of Example 2 after homogenization treatment, which shows that the carbides are fine and dispersed. Figure 6b The image shows a microstructure after homogenization, which can be seen that the carbides are distributed in coarse chain form at the grain boundaries and within the grains.

[0041] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A nickel-based alloy with low hot working cracking rate, characterized in that, The composition by mass fraction includes the following components: Mo 15.0%-17.0%, Cr 6.0%-8.0%, Fe≤5.0%, Mn≤1.0%, Si≤1.0%, C≤0.08%, P≤0.005%, S≤0.005%, O≤0.0020%, with the balance being Ni, wherein P+S+O≤0.012%, and the P / S mass ratio is controlled at 1.5-2.

5.

2. The nickel-based alloy with low hot working cracking rate according to claim 1, characterized in that, The composition by mass fraction includes the following components: Mo 15.7%-16.3%, Cr 6.7%-7.3%, Fe 4.2%-4.8%, Mn 0.20%-0.40%, Si 0.15%-0.35%, C 0.04%-0.05%, P≤0.005%, S≤0.005%, O≤0.0020%, with the balance being Ni, wherein P+S+O≤0.012%, and the P / S mass ratio is controlled at 1.5-2.

5.

3. The nickel-based alloy with low hot working cracking rate according to claim 1 or 2, characterized in that, It also contains 0.001%-0.002% B and 0.002%-0.008% Mg.

4. The method for preparing the nickel-based alloy with low hot working cracking rate according to any one of claims 1-3, characterized in that, Includes the following steps: Step S1: Vacuum induction melting The raw materials are loaded into a vacuum induction melting furnace according to the proportion, the vacuum is drawn to ≤1Pa, and the furnace is powered to melt. After the molten pool is formed, the furnace is refined. After the refining is completed, argon gas is introduced to 20-30 kPa, and carbon powder is added for final deoxidation. The final C content is controlled to be 0.04%-0.05%. The molten steel is cast into electrode rods at a casting temperature of 1440-1460℃. Step S2: Vacuum consumable arc melting The electrode rods were placed in a vacuum consumable arc furnace and evacuated to ≤0.1 Pa. A steady-state melting process was used for melting. During the melting process, the arc stabilizing coil was turned on with an arc stabilizing current of 5-10 A and a frequency of 30-50 Hz. After melting, the furnace was kept under vacuum for 20-40 minutes to allow the shrinkage cavity to solidify fully. Then, argon gas was used to cool the furnace to below 200°C to obtain a consumable remelted ingot. Step S3: High-temperature stepped homogenization heat treatment The consumable remelted ingot is loaded into a heat treatment furnace and heated to 700-900℃ at a rate of ≤80℃ / h. It is held at this temperature for 2-4 hours for preheating. Then, it is heated to 1180-1220℃ at a rate of ≤100℃ / h for homogenization. After homogenization, it is cooled to 600℃ or below in the furnace and then removed from the furnace and air-cooled. Step S4, Temperature-controlled forging The homogenized consumable remelted ingot is reheated to 1150-1180℃ and held for 2-4 hours; multi-pass forging is carried out using a high-speed forging machine with an initial forging temperature ≥1120℃ and a final forging temperature ≥950℃. Step S5, Solution treatment The forged billet undergoes solution treatment: heated to 1170-1180℃, held for 1-2 hours per 100mm thickness, followed by air cooling. After solution treatment, the alloy grain size is controlled to ASTM 5-7 level.

5. The method for preparing a nickel-based alloy with low hot working cracking rate according to claim 4, characterized in that, In step S1, the refining temperature is controlled at 1520-1550℃, and the refining time is 30-60 minutes.

6. The method for preparing a nickel-based alloy with low hot working cracking rate according to claim 4, characterized in that, In step S2, the melting current is 8000-12000 A, the voltage is 22-28 V, and the melting rate is controlled at 5-8 kg / min.

7. The method for preparing a nickel-based alloy with low hot working cracking rate according to claim 4, characterized in that, In step S2, the electrode insertion depth is controlled at 30-50 mm, the voltage at 45-55 V, and the current at 6000-10000 A during the remelting process.

8. The method for preparing a nickel-based alloy with low hot working cracking rate according to claim 4, characterized in that, In step S3, the holding time for homogenization treatment is calculated based on the maximum cross-sectional thickness of the ingot: t = (0.06 - 0.08) × D, where t is the holding time in hours and D is the thickness of the ingot in millimeters.

9. The method for preparing a nickel-based alloy with low hot working cracking rate according to claim 4, characterized in that, In step S4, the deformation amount of each pass is controlled as follows: the deformation amount of the first three passes is controlled at 15%-20%, the deformation amount of subsequent passes is controlled at 20%-30%, the total forging ratio is ≥4, and a reheating is performed once between every two passes. The reheating temperature is 1100±20℃, and the holding time is 0.5-1 hour.

10. The application of the nickel-based alloy prepared by the method according to any one of claims 4-9, characterized in that, The nickel-based alloy is used in the industrial manufacturing of large-size forgings, pipes, and plates for nuclear power plants.

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