A preparation method for strengthening and toughening NCu30-4-2-1 alloy by adding rare earth element Ce

Abstract

The present invention belongs to the field of toughened nickel-copper alloys, and particularly relates to a preparation method for toughening NCu30-4-2-1 alloy by adding rare earth element Ce. By using vacuum induction melting technology, first, graphite, Cu plates, Ni plates, and Fe blocks are loaded into a crucible, and the above raw materials are refined. The vacuum degree during the refining period is 0.5-1.0 Pa, the refining temperature is 1480°C-1520°C, and the refining time is 20 min. After the molten metal surface forms a film, argon gas is filled into the furnace at 30000-40000 Pa, and then the Si block and Mn sheet wrapped with Ni plates are added into the melt, and high-power stirring is carried out for 5 min. Finally, the melt temperature is controlled at 1250-1300°C, the Ce block wrapped with Ni plates is added into the melt, high-power stirring is carried out for 5 min, and when the power supply is raised to 1360±10°C, casting is carried out to obtain an ingot with high purity and uniform composition. The present invention determines the feeding method and smelting process of alloy melting, and improves the recovery rate of rare earth element Ce. In addition, by adjusting the content of Ce element, the microstructure of the alloy is regulated to obtain better strength-plasticity matching.

Description

Technical Field

[0001] The present invention belongs to the field of toughened nickel - copper alloys, and particularly relates to a preparation method for toughening NCu30 - 4 - 2 - 1 alloy by adding rare - earth element Ce. Background Art

[0002] NCu30 - 4 - 2 - 1 alloy is a nickel - based alloy with high wear resistance. This alloy has high hardness, high strength, excellent wear resistance and anti - adhesion properties, and is used to manufacture aviation fuel devices and other precision friction parts that require stable operation. The prominent problems during the melting process of NCu30 - 4 - 2 - 1 alloy are that alloying elements are prone to oxidation and have an air - absorption tendency. Therefore, effective measures must be taken in many aspects to obtain a high - quality alloy melt with low gas content, few inclusions and qualified and uniform chemical composition. The melting of NCu30 - 4 - 2 - 1 alloy mainly uses vacuum induction furnaces and vacuum arc furnaces. Elements such as Cu, Si and Mn in the alloy composition are extremely easy to oxidize under high - temperature melting conditions. Therefore, when the alloy solidifies, a large number of inclusions will be generated at the grain boundaries, resulting in a decline in the performance of the alloy and a reduction in the finished - product rate.

[0003] Rare - earth elements can improve the properties of traditional materials such as steel and aluminum, playing a role like turning stone into gold. Adding a trace amount of rare - earth element Ce to NCu30 - 4 - 2 - 1 alloy can form non - metallic inclusions with O, N and S elements in the steel. As a dispersion body for pinning grain boundaries, it can refine the microstructure and thus improve the mechanical properties of the alloy. In addition, due to the relatively large atomic radius of rare - earth elements, it will cause relatively large lattice distortion, thus achieving the effect of solid - solution strengthening. However, excessive O, N and S contents in the melt not only affect the mechanical properties of the alloy, but also significantly affect the recovery rate of Ce. In addition, the feeding method of Ce and the melt temperature also affect the recovery rate of Ce. In order to improve the mechanical properties of the alloy, the present invention mainly controls the content of rare - earth element Ce by improving the feeding method and smelting process, and at the same time toughens NCu30 - 4 - 2 - 1 alloy by adding Ce element. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method for toughening NCu30 - 4 - 2 - 1 alloy by adding rare - earth element Ce. By using the feeding method and smelting process provided by the present invention, the O content in the NCu30 - 4 - 2 - 1 alloy prepared by melting is ≤0.0030%, the N content is ≤0.0010%, and the S content is ≤0.0015%. At the same time, by adjusting the content of Ce, the ability of rare - earth elements to regulate the microstructure is exerted, so that the prepared NCu30 - 4 - 2 - 1 alloy has a good match of high strength and high plasticity.

[0005] The technical solution of the present invention is as follows:

[0006] A preparation method for strengthening and toughening NCu30-4-2-1 alloy by adding rare earth element Ce. By weight percentage, the composition of NCu30-4-2-1 alloy is as follows: C≤0.03, Cu 30~32, Si 3.9~4.3, Fe 1.5~2.8, Mn 0.5~1.5, Ce 0.01~0.06, and the balance is Ni and inevitable impurity elements; among the impurity elements, the content of O is ≤0.0030%, the content of N is ≤0.0010%, and the content of S is ≤0.0015%.

[0007] The specific preparation method includes the following steps:

[0008] (1) Raw material selection: Select Ni plates, Cu plates, Si blocks, Fe rods, Mn sheets, graphite rods and Ce blocks as raw materials, and calculate and prepare the raw materials of each element according to the composition control requirements.

[0009] (2) Charging: For the NCu30-4-2-1 alloy containing Ce, batch charging is carried out according to factors such as the melting point of the raw materials, the degree of easy oxidation, density, addition quantity and the degree of easy volatility; for the first batch of charging, first put graphite, Cu plates, Ni plates, and Fe blocks into the crucible; for the second batch of charging, first put the Si block and Mn sheet wrapped with nickel plates into the crucible; for the third batch of charging, put the Ce block wrapped with nickel plates into the crucible.

[0010] (3) Melting period: When the vacuum degree in the melting period is ≤10 Pa, start power supply. Gradually increase the power to 25~30 kW in the early stage of melting the first batch of materials. After ensuring the formation of the molten pool, reduce the power supply to 20±1 kW to melt the materials, and ensure that the melting period is 35~45 min; after melting is complete, raise the temperature to 1480℃~1520℃ and enter the refining period.

[0011] (4) Refining period: Control the vacuum degree at 0.5~1.0 Pa and the power range at 13~17 kW in the refining period, control the refining temperature at 1480℃~1520℃, and the refining time at 15~25 min.

[0012] (5) Alloying period: After the refining is completed, enter the alloying period. Cut off the power and form a film. Fill the furnace with argon gas at 30000~40000 Pa, add the second batch of materials into the melt, stir at high power for 4~6 min, and finally control the melt temperature at 1250~1300℃ to add the third batch of materials, stir at high power for 4~6 min, and supply power to raise the temperature to 1360±10℃ for casting.

[0013] (6) Casting: The inner wall of the ingot mold should be cleaned with a steel shovel and a steel brush, and the remaining steel slag and scale should be removed with compressed air. The casting temperature is 1360 ± 10 °C. A sprue cup with an inner diameter of Φ20 mm at the lower end is used to control the casting speed, ensuring that the casting time for each ingot is 40 - 60 s. The recovery rate of Ce element is stably maintained at 85% - 90%, and ingots with high purity and uniform composition are obtained.

[0014] In the preparation method of strengthening and toughening NCu30 - 4 - 2 - 1 alloy by adding rare earth element Ce, in step (1), it is necessary to ensure that the total O content brought in by the raw materials ≤ 0.020% and the S content ≤ 0.0015%.

[0015] In the preparation method of strengthening and toughening NCu30 - 4 - 2 - 1 alloy by adding rare earth element Ce, in step (1), all raw materials are removed of surface oxides, oil stains and impurities.

[0016] In the preparation method of strengthening and toughening NCu30 - 4 - 2 - 1 alloy by adding rare earth element Ce, in step (1), industrial purity Si blocks and Mn sheets are used as raw materials, and the raw material purity of the remaining alloying elements is not less than 99.9 wt.%.

[0017] In the preparation method of strengthening and toughening NCu30 - 4 - 2 - 1 alloy by adding rare earth element Ce, after step (3) melting period and step (4) refining period, when the O content in the melt ≤ 0.0050%, N content ≤ 0.0020%, and S content ≤ 0.0015%, it enters the alloying period.

[0018] In the preparation method of strengthening and toughening NCu30 - 4 - 2 - 1 alloy by adding rare earth element Ce, in step (5), the high power is 30 kW.

[0019] The design concept of the present invention is:

[0020] Based on the above technical solution, the present invention ensures that the total O content brought in by the raw materials ≤ 0.020% and the S content ≤ 0.0015%. By controlling the O and S content entering the furnace, the reaction with Ce element to form oxysulfide is reduced, which affects the recovery rate of Ce element. All of the high - purity graphite is added in the first batch of charging to ensure the C concentration in the molten pool, which is beneficial to promoting the C - O reaction during the melting process and improving the degassing effect during the melting period. Controlling the vacuum degree and time during the melting period and the vacuum degree and refining time during the refining period can provide good thermodynamic and kinetic conditions for the C - O reaction, promote the degassing during the vacuum induction process, and ensure that when the O content ≤ 0.0050%, N content ≤ 0.0020%, and S content ≤ 0.0015%, it enters the alloying period.

[0021] In the alloying stage of the present invention, low temperature and argon filling are adopted to reduce the volatilization of Mn element. Adding Ce blocks at a relatively low temperature of 1250 - 1300 °C can reduce the burning loss; adopting the method of wrapping Mn sheets, Si blocks and Ce blocks with nickel plates can make the above elements sink rapidly in the melt. At the same time, the nickel plates melt first in the melt, avoiding the oxidation and burning loss of the above elements when added to the melt. Adopting high-power stirring can quickly involve Mn, Si and Ce elements into the interior of the melt and dissolve them evenly, further reducing the burning loss of the elements and obtaining an alloy ingot with uniform composition.

[0022] The advantages and beneficial effects of the present invention are as follows:

[0023] (1) By controlling the contents of O, N and S in the furnace, the present invention reduces the pressure of deoxidation, denitrification and desulfurization in the vacuum melting process.

[0024] (2) Through the process control of charging, melting stage and refining stage, the present invention ensures that the O content in the melt entering the alloying stage is ≤0.0050%, the N content is ≤0.0020%, and the S content is ≤0.0015%, creating basic conditions for the accurate and stable control of Ce content.

[0025] (3) Through the feeding method of Ce and controlling the melt temperature and stirring process, the present invention realizes the accurate and stable control of Ce content in the vacuum induction melting of NCu30 - 4 - 2 - 1 alloy, and the recovery rate of Ce is stably maintained at 85% - 90%.

[0026] (4) By adding trace rare earth element Ce, the present invention adsorbs impurity elements such as O, N and S, forms non-metallic oxides and sulfides to pin the grain boundaries, hinders the grain boundary migration, achieves the effects of refining the microstructure and removing impurities, and finally makes the strength and plasticity of NCu30 - 4 - 2 - 1 alloy well coordinated.

[0027] (5) The preparation method of strengthening and toughening NCu30 - 4 - 2 - 1 alloy by adding rare earth element Ce provided by the present invention has a simple process flow.

[0028] In summary, the present invention determines the feeding method and smelting process of alloy melting, improving the recovery rate of rare earth element Ce. The addition of rare earth element Ce can effectively degas and remove impurities, improving the metallurgical quality of the alloy; in addition, by adjusting the content of Ce element, the microstructure of the alloy is regulated to obtain better strength-plasticity matching. The performance indexes of NCu30 - 4 - 2 - 1 alloy strengthened and toughened by adding rare earth element Ce are as follows: the tensile strength R m is 910 - 980 MPa, the yield strength R p0.2 is 550 - 590 MPa, the elongation after fracture A is 9.0 - 13.5%, and the volume fraction of dendritic region in the alloy is 46 - 63%. Description of the Drawings

[0029] Figure 1 X-ray diffraction spectra of the as-cast NCu30-4-2-1 alloy prepared in the comparative example and the examples.

[0030] Figure 2 Microstructure morphologies of the as-cast NCu30-4-2-1 alloy prepared in the comparative example and the examples. Among them, in Figure (a), the Ce0 alloy shows a dendritic morphology, in Figure (b), the Ce1 alloy shows a dendritic morphology, in Figure (c), the Ce3 alloy shows a dendritic morphology, in Figure (d), the Ce6 alloy shows a dendritic morphology, and the inset is a partial enlarged view.

[0031] Figure 3 Tensile engineering stress-strain curves of the as-cast NCu30-4-2-1 alloy prepared in the comparative example and the examples. Specific embodiments

[0032] In the specific implementation process, the composition (wt.%) of the NCu30-4-2-1 alloy in the examples is as follows: C ≤ 0.03, Cu 30-32, Si 3.9-4.3, Fe 1.5-2.8, Mn 0.5-1.5, Ce 0.01-0.06, and the balance is Ni and unavoidable impurity elements; among the impurity elements, the O content ≤ 0.0030%, the N content ≤ 0.0010%, and the S content ≤ 0.0015%. The composition (wt.%) of the NCu30-4-2-1 alloy in the comparative example is as follows: C ≤ 0.03, Cu 30-32, Si 3.9-4.3, Fe 1.5-2.8, Mn 0.5-1.5, Ce 0, and the balance is Ni and unavoidable impurity elements; among the impurity elements, the O content ≤ 0.0050%, the N content ≤ 0.0020%, and the S content ≤ 0.0015%.

[0033] Using vacuum induction melting technology, first put graphite, Cu plates, Ni plates, and Fe blocks into the crucible, refine the above raw materials, the vacuum degree during the refining period is 0.5-1.0 Pa, the refining temperature is 1480°C-1520°C, and the refining time is 20 min; after the melt surface forms a film, fill the furnace with argon at 30000-40000 Pa, then add the Si block and Mn sheet wrapped in a nickel plate to the melt, and stir at high power for 5 min; finally, control the melt temperature at 1250-1300°C, add the Ce block wrapped in a nickel plate to the melt, stir at high power for 5 min, and pour when the power supply raises the temperature to 1360 ± 10°C to obtain an ingot with high purity and uniform composition.

[0034] The raw materials are industrial purity Si block (>99.37wt.%) and Mn sheet (>97.45wt.%), and the purity of the raw materials of the remaining alloy elements is not less than 99.9wt.%. The ingredient list of the NCu30-4-2-1 alloy is shown in Table 1; the content of each element of the NCu30-4-2-1 alloy is obtained by plasma emission spectrometer, oxygen, nitrogen and hydrogen analyzer and carbon and sulfur analyzer, see Table 2; the composition phase composition of the NCu30-4-2-1 alloy is obtained by scanning electron microscope spectrometer, see Table 3.

[0035] Table 1 Ingredients of comparative examples and example alloys

[0036]

[0037] Table 2 Comparative Example and Example Alloys The contents of various elements obtained by plasma emission spectrometer, oxygen, nitrogen and hydrogen analyzer and carbon and sulfur analyzer

[0038]

[0039] Table 3 Phase composition of comparative example and example alloys obtained by scanning electron microscope energy dispersive spectrometer

[0040]

[0041] Below, the technical scheme of the present invention is further described in detail in combination with comparative examples and embodiments.

[0042] Comparative Example 1

[0043] In this comparative example, the NCu30-4-2-1 alloy was not added with the rare earth element Ce, and was referred to as Ce0 alloy for short. 10 kg of the alloy was smelted in a single furnace, and 0 wt.% of Ce element was added during batching, see Table 1.

[0044] The preparation method of the NCu30-4-2-1 alloy comprises the following specific steps:

[0045] (1) Raw material selection: Select Ni plate, Cu plate, Si block, Fe rod, Mn sheet and graphite as raw materials, ensure that the total O content of the raw materials is ≤0.020%, and the S content is ≤0.0015%. According to the composition control requirements, calculate and prepare the raw materials of each element; remove oxides, oil stains and impurities on the surface of all raw materials;

[0046] (2) Loading: The NCu30-4-2-1 alloy was loaded in batches. In the first batch, graphite, Cu plate, Ni plate, and Fe block were loaded into the crucible in sequence; in the second batch, Si block and Mn sheet wrapped with nickel plate were loaded into the crucible;

[0047] (3) Melting period: During the melting period, power is supplied when the vacuum degree is 5Pa. In the early stage of melting of the first batch of materials, the power is gradually increased to 28kW to ensure that the molten pool is formed, and then the power supply is reduced to 20±1kW to ensure that the melting period is 40min. After melting, the temperature is raised to 1500℃ to enter the refining period.

[0048] (4) Refining stage: During the refining stage, the vacuum degree is controlled at 0.8 Pa, the power is 15 kW, the refining temperature is controlled at 1500°C, the refining time is 20 min, and the O content, N content and S content in the melt are controlled to be ≤0.0050%, ≤0.0020% and ≤0.0015%, and then the alloying stage is entered;

[0049] (5) Alloying period: After refining, the alloying period begins. The power is turned off and the furnace is filled with argon gas at 35,000 Pa. The second batch of materials is added to the melt. The furnace is stirred at a high power of 30 kW for 5 minutes. Then the power is turned on and the temperature is raised to 1360 ± 10 °C for casting.

[0050] (6) Casting: The inner wall of the ingot mold should be cleaned with a steel shovel and a steel brush, and compressed air should be used to remove residual steel slag and oxide scale. The casting temperature is 1360±10℃. A pouring cup with a lower inner diameter of Φ20mm is used to control the casting speed. The casting time of each ingot is guaranteed to be 40 to 60s, and a NCu30-4-2-1 alloy ingot with uniform composition is obtained.

[0051] The microstructure of the as-cast Ce0 alloy was characterized. Figure 1 As shown in the XRD diffraction pattern of Ce0 alloy, Ce0 alloy has two phases, α phase and β phase, both of which are face-centered cubic structures; Figure 2 As shown in (a), the Ce0 alloy exhibits a dendrite morphology. Both the dendrite and the interdendrite contain the matrix α phase and the granular secondary β phase dispersed in the matrix. However, the color difference between the two regions is due to the difference in the content of solid solution elements, that is, the content of Si element in the interdendrite is higher, as shown in Table 3. In addition, there is a eutectic (α+β) phase between the dendrites, and black spots are clearly visible on the eutectic β phase. This spot is the eutectic α phase. Due to the small size of the eutectic α phase, the analysis results of the energy spectrometer of the scanning electron microscope will have a large error due to size limitations, but the analysis results can show that there are differences in the composition of the two phases. Relatively speaking, the composition analysis of the eutectic β phase is more accurate, and the chemical analysis results show that the β phase is enriched in Ni and Si elements, but poor in Cu, Fe and Mn elements; the composition analysis error of the eutectic α phase is large, but its Si content is significantly lower than that of the eutectic β phase, as shown in Table 3.

[0052] like Figure 3 As shown in the figure, from the tensile engineering stress-strain curve of Ce0 alloy, it can be seen that the tensile strength R m The yield strength R is 961MPa. p0.2 It is 591MPa and the elongation after break A is 14.75%.

[0053] Example 1

[0054] In this example, the NCu30-4-2-1 alloy was strengthened and toughened by adding 0.01 wt.% of rare earth element Ce, abbreviated as Ce1 alloy, and 10 kg of alloy was melted in a single furnace. Considering the loss of rare earth element Ce during melting, 0.0125 wt.% of Ce element was added during batching, as shown in Table 1.

[0055] The preparation method of the NCu30-4-2-1 alloy is as follows:

[0056] (1) Raw material selection: Ni plates, Cu plates, Si blocks, Fe rods, Mn sheets, graphite and Ce blocks were selected as raw materials to ensure that the total O content brought in by the raw materials ≤ 0.020% and the S content ≤ 0.0015%. According to the composition control requirements, the raw materials of each element were calculated and prepared; all raw materials were removed of surface oxides, oil stains and impurities;

[0057] (2) Charging: The NCu30-4-2-1 alloy containing Ce was charged in batches. For the first batch of charging, graphite, Cu plates, Ni plates and Fe blocks were successively put into the crucible; for the second batch of charging, the Si block and Mn sheet wrapped with nickel plates were put into the crucible; for the third batch of charging, the Ce block wrapped with nickel plates was put into the crucible;

[0058] (3) Melting period: Power was supplied when the vacuum degree in the melting period reached 5 Pa. The power was gradually increased to 28 kW in the early stage of melting the first batch of materials. After ensuring the formation of the molten pool, the power supply was reduced to 20 ± 1 kW to melt the materials, ensuring that the melting period was 40 min; after melting was complete, the temperature was raised to 1500 °C and the refining period was entered;

[0059] (4) Refining period: The vacuum degree was controlled at 0.8 Pa and the power was 15 kW in the refining period. The refining temperature was controlled at 1500 °C and the refining time was 20 min. After controlling the O content in the melt ≤ 0.0050%, the N content ≤ 0.0020% and the S content ≤ 0.0015%, the alloying period was entered;

[0060] (5) Alloying period: After the refining was completed, the alloying period was entered. The power was cut off to form a film, and argon gas was filled into the furnace at 35000 Pa. The second batch of materials was added to the melt, and stirred at a high power of 30 kW for 5 min. Finally, the Ce block wrapped with nickel plates was added to the melt at a temperature of 1270 °C, stirred at a high power of 30 kW for 5 min, and the power supply was increased to raise the temperature to 1360 ± 10 °C for casting;

[0061] (6) Casting: The inner wall of the ingot mold should be cleaned with a steel shovel and a steel brush, and compressed air should be used to remove residual steel slag and oxide scale. The casting temperature is 1360±10℃, and a pouring cup with a lower inner diameter of Φ20mm is used to control the casting speed. The casting time of each ingot is guaranteed to be 40 to 60s. The yield of Ce element is stabilized at 85% to 90%, and a NCu30-4-2-1 alloy ingot with uniform composition is obtained.

[0062] The microstructure of the as-cast Ce1 alloy was characterized. Figure 1 As shown in the figure, the XRD diffraction pattern of Ce1 alloy is the same as that of Ce0 alloy. Ce1 alloy has two phases, α phase and β phase, both of which are face-centered cubic structures. Figure 2 As shown in (b), the Ce1 alloy exhibits a dendrite morphology. Both the dendrite and the interdendritic region have matrix α phase and granular secondary β phase dispersed in the matrix. The size of the secondary β phase particles in the interdendritic region is relatively large, mainly because the content of Si in the interdendritic region is relatively high, as shown in Table 3. Similarly, there is a eutectic (α+β) phase between dendrites. Black spots can be clearly seen on the eutectic β phase. This spot is the eutectic α phase. Due to the small size of the eutectic α phase, the analysis results of the energy spectrometer of the scanning electron microscope will have a large error due to the size limitation, but the analysis results can show that there are differences in the composition of the two phases. Relatively speaking, the composition analysis of the eutectic β phase is more accurate. The chemical analysis results show that the β phase is enriched in Ni and Si elements, but poor in Cu, Fe and Mn elements; the composition analysis error of the eutectic α phase is large, but its Si content is significantly lower than that of the eutectic β phase, as shown in Table 3. Compared with the Ce0 alloy, 0.01wt.% of Ce element is added to the Ce1 alloy, and the structure of the alloy is refined, which can reduce dendrite segregation. In addition, the addition of Ce element can improve the metallurgical quality of the alloy. The main reason is that Ce element plays the role of a modifier in the alloy. After entering the alloy liquid, Ce element quickly reacts with O, N, S, etc. to generate high-melting-point rare earth Ce-rich compounds, which remain solid during the solidification process. Some compounds enter the slag phase and are removed, achieving the purpose of removing impurities, as shown in Table 2; another part of the fine high-melting-point compound particles remain in the alloy liquid and are dispersed. When the alloy liquid solidifies, it becomes a crystalline alloy, which generates non-spontaneous crystal nuclei during the crystallization process, thereby refining the organization.

[0063] like Figure 3 As shown in the tensile engineering stress-strain curve of Ce1 alloy, it can be seen that the tensile strength R m The yield strength is 918MPa, and the yield strength R p0.2 The tensile strength, yield strength and elongation after fracture of Ce1 alloy are all reduced compared with the tensile properties of Ce0 alloy. The main reason is that the regional volume fraction of dendrites in Ce1 alloy is small (about 59% for Ce0 and about 46% for Ce1), which reduces the tensile properties of the alloy.

[0064] Example 2

[0065] In this example, the NCu30-4-2-1 alloy was strengthened and toughened by adding 0.03 wt.% of rare earth element Ce, abbreviated as Ce3 alloy, and 10 kg of alloy was melted in a single furnace. Considering the loss of rare earth element Ce during melting, 0.0375 wt.% of Ce element was added during batching, as shown in Table 1.

[0066] The preparation method of the NCu30-4-2-1 alloy is as follows:

[0067] (1) Raw material selection: Select Ni plates, Cu plates, Si blocks, Fe rods, Mn sheets, graphite, and Ce blocks as raw materials, ensuring that the total O content and S content brought in by the raw materials are ≤0.020% and ≤0.0015% respectively. Calculate and prepare the raw materials of each element according to the composition control requirements; remove the surface oxides, oil stains, and impurities from all raw materials;

[0068] (2) Charging: Charge the NCu30-4-2-1 alloy containing Ce in batches. For the first batch of charging, first put graphite, Cu plates, Ni plates, and Fe blocks into the crucible; for the second batch of charging, put the Si block and Mn sheet wrapped with nickel plates into the crucible; for the third batch of charging, put the Ce block wrapped with nickel plates into the crucible;

[0069] (3) Melting period: Start power supply when the vacuum degree in the melting period is 8 Pa. Gradually increase the power to 26 kW in the early stage of melting the first batch of materials. After ensuring the formation of the molten pool, reduce the power supply to 20 ± 1 kW to melt the materials, ensuring that the melting period is 35 min; after melting is complete, raise the temperature to 1480 °C and enter the refining period;

[0070] (4) Refining period: Control the vacuum degree at 0.5 Pa and the power at 13 kW in the refining period. Control the refining temperature at 1480 °C and the refining time at 20 min. After controlling the O content ≤0.0050%, N content ≤0.0020%, and S content ≤0.0015% in the melt, enter the alloying period;

[0071] (5) Alloying period: After the refining is completed, enter the alloying period. Cut off the power and form a film. Fill the furnace with argon gas at 30000 Pa. Add the second batch of materials to the melt, stir with a high power of 30 kW for 5 min. Finally, control the melt temperature at 1250 °C and add the Ce block wrapped with nickel plates, stir with a high power of 30 kW for 5 min, and supply power to raise the temperature to 1360 ± 10 °C for casting;

[0072] (6) Casting: The inner wall of the ingot mold should be cleaned with a steel shovel and a steel brush, and the remaining steel slag and scale should be removed with compressed air. The casting temperature is 1360 ± 10 °C. A sprue cup with an inner diameter of Φ20 mm at the lower end is used to control the casting speed, ensuring that the casting time for each ingot is 40 - 60 s. The recovery rate of Ce element is stably maintained at 85% - 90%, and an NCu30 - 4 - 2 - 1 alloy ingot with uniform composition is obtained.

[0073] Characterize the microstructure of the as - cast Ce3 alloy. As Figure 1 shown, the XRD diffraction pattern of the Ce3 alloy is the same as that of the Ce0 and Ce1 alloys. The Ce3 alloy has two phases, the α - phase and the β - phase, both of which are face - centered cubic structures; as Figure 2 (c) shows, the Ce3 alloy exhibits a dendritic morphology. There are matrix α - phases and granular secondary β - phases precipitated diffusely in the matrix both in the dendrites and between the dendrites. Moreover, the secondary β - phase particles in the interdendritic region are larger in size. The main reason is that the content of Si element in the interdendritic region is higher, as shown in Table 3. Similarly, there is a eutectic (α + β) phase between the dendrites. Black spots can be clearly seen on the eutectic β - phase, and these spots are eutectic α - phases. Since the size of the eutectic α - phase is small, the energy - dispersive spectrometer (EDS) built into the scanning electron microscope will have a large error in the analysis results due to size limitations, but the analysis results can show that there are differences in the compositions of the two phases. Relatively speaking, the composition analysis of the eutectic β - phase is more accurate. The chemical analysis results show that the β - phase is enriched with Ni and Si elements and depleted in Cu, Fe, and Mn elements; the composition analysis of the eutectic α - phase has a large error, but its Si content is significantly lower than that of the eutectic β - phase, as shown in Table 3. Comparing with the Ce1 alloy, when the Ce content in the Ce3 alloy reaches 0.03 wt.%, the dendritic microstructure morphology coarsens. The main reasons are as follows: When more Ce elements are added to the alloy, the Ce elements alloy with other elements beneficial to heterogeneous nucleation, forming a large number of rare - earth compounds. These compounds aggregate and enter the slag phase in the form of blocks and are removed; in addition, when more Ce elements are added, the constitutional supercooling effect of rare - earth Ce atoms is reduced, resulting in over - modification. Comparing the O and N contents in the Ce1 alloy, more Ce elements in the alloy can further remove harmful impurities in the alloy, which is of great significance for improving the metallurgical quality of the alloy, as shown in Table 2.

[0074] As Figure 3 shown, it can be seen from the tensile engineering stress - strain curve of the Ce3 alloy that the tensile strength R m of the Ce3 alloy is 923 MPa, the yield strength R p0.2 is 565 MPa, and the elongation after fracture A is 10.12%. Comparing with the Ce1 alloy, both the tensile strength and the elongation after fracture of the Ce3 alloy are improved, while the yield strength remains almost unchanged. The main reason is that the volume fraction of the dendritic region in the Ce3 alloy (about 54%) has increased.

[0075] Example 3

[0076] In this embodiment, the NCu30-4-2-1 alloy is strengthened by adding 0.06 wt.% of rare earth element Ce, which is simply referred to as Ce6 alloy, and 10 kg of alloy is melted in a single furnace. Considering the loss of rare earth element Ce during melting, 0.075 wt.% of Ce element is added during batching, as shown in Table 1.

[0077] The preparation method of the NCu30-4-2-1 alloy is as follows:

[0078] (1) Raw material selection: Select Ni plates, Cu plates, Si blocks, Fe rods, Mn flakes, graphite, and Ce blocks as raw materials, ensuring that the total O content brought in by the raw materials is ≤ 0.020% and the S content is ≤ 0.0015%. Calculate and prepare the raw materials of each element according to the composition control requirements; remove the oxides, oil stains, and impurities on the surface of all raw materials.

[0079] (2) Charging: Charge the NCu30-4-2-1 alloy containing Ce in batches. For the first batch of charging, first put graphite, Cu plates, Ni plates, and Fe blocks into the crucible; for the second batch of charging, put the Si block and Mn flake wrapped with nickel plates into the crucible; for the third batch of charging, put the Ce block wrapped with nickel plates into the crucible.

[0080] (3) Melting stage: Start power supply when the vacuum degree in the melting stage is 2 Pa. Gradually increase the power to 30 kW in the early stage of melting the first batch of materials. After ensuring the formation of the molten pool, reduce the power supply to 20 ± 1 kW to melt the materials, ensuring that the melting time is 45 min; after melting is complete, raise the temperature to 1520 °C and enter the refining stage.

[0081] (4) Refining stage: Control the vacuum degree at 1.0 Pa and the power at 17 kW in the refining stage. Control the refining temperature at 1520 °C and the refining time at 20 min. After controlling the O content in the melt to be ≤ 0.0050%, the N content to be ≤ 0.0020%, and the S content to be ≤ 0.0015%, enter the alloying stage.

[0082] (5) Alloying stage: After the refining is completed, enter the alloying stage. Cut off the power and form a film. Fill the furnace with argon gas at 40000 Pa. Add the second batch of materials to the melt, stir at high power for 5 min. Finally, control the melt temperature at 1300 °C and add the Ce block wrapped with nickel plates, stir at high power for 5 min, and supply power to raise the temperature to 1360 ± 10 °C for casting.

[0083] (6) Casting: Use a steel shovel and steel brush to clean the inner wall of the ingot mold, and use compressed air to remove the residual steel slag and oxide scale. The casting temperature is 1360 ± 10 °C. Use a pouring cup with an inner diameter of Φ20 mm at the lower end to control the casting speed, ensuring that the casting time for each ingot is 40 - 60 s, the recovery rate of Ce element is stable at 85% - 90%, and an NCu30-4-2-1 alloy ingot with uniform composition is obtained.

[0084] The microstructure of the as-cast Ce6 alloy was characterized. Figure 1 As shown in the figure, the XRD diffraction pattern of Ce6 alloy is the same as that of Ce0, Ce1 and Ce3 alloys. Ce6 alloy has two phases, α phase and β phase, both of which are face-centered cubic structures. Figure 2 As shown in (d), the Ce6 alloy exhibits a dendrite morphology. Both the dendrite and the interdendritic region contain the matrix α phase and the granular secondary β phase dispersed in the matrix. The secondary β phase particles in the interdendritic region are larger in size, mainly because the Si content in the interdendritic region is higher, as shown in Table 3. Similarly, there is a eutectic (α+β) phase between the dendrites. Black spots can be clearly seen on the eutectic β phase. This spot is the eutectic α phase. Due to the small size of the eutectic α phase, the analysis results of the energy spectrometer of the scanning electron microscope will have a large error due to the size limitation, but the analysis results can show that there are differences in the composition of the two phases. Relatively speaking, the composition analysis of the eutectic β phase is more accurate. The chemical analysis results show that the β phase is enriched in Ni and Si elements, but poor in Cu, Fe and Mn elements; the composition analysis error of the eutectic α phase is larger, but its Si content is significantly lower than that of the eutectic β phase, as shown in Table 3. Comparing Ce1 and Ce3 alloys, when the Ce content of this series of alloys reaches 0.06wt.%, the dendrite structure coarsens again, even exceeding that of Ce0 alloy without Ce element added. The main reason is that the addition of a large amount of Ce element to the alloy makes Ce element alloyed with other elements beneficial to heterogeneous nucleation, forming a large number of rare earth compounds, which gather into the slag phase in the form of blocks and are removed; in addition, the addition of a large amount of Ce element reduces the supercooling effect of rare earth Ce atomic components, resulting in over-metamorphism. Comparing the O and N contents in Ce1, Ce3 and Ce6 alloys, it can be seen that the increase of Ce element can further remove harmful impurities in the alloy and improve the metallurgical quality of the alloy, as shown in Table 2.

[0085] like Figure 3 As shown in the tensile engineering stress-strain curve of Ce6 alloy, it can be seen that the tensile strength R m The yield strength is 979MPa, and the yield strength R p0.2 The tensile strength, yield strength and elongation after fracture of Ce6 alloy are improved, mainly because the volume fraction of dendrite region in Ce6 alloy (about 63%) is the largest.

[0086] In summary, the present invention determines the feeding method and smelting process, improving the recovery rate of rare earth element Ce. By adjusting the content of rare earth element Ce, without changing the type of phase, it effectively degasses, removes impurities and refines the microstructure, enabling the NCu30-4-2-1 alloy to obtain good strength and plasticity matching. It can be seen from this study that the tensile properties of this series of NCu30-4-2-1 alloys mainly depend on the volume fraction of the dendritic region. The larger the volume fraction, the better the comprehensive tensile properties of the alloy; with the increase of the Ce element content, the O and N contents of the alloy decrease, improving the metallurgical quality of the alloy.

[0087] 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 them; 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 described 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 of the embodiments of the present invention.

Claims

1. A preparation method for strengthening and toughening NCu30-4-2-1 alloy by adding rare earth element Ce, characterized in that, By weight percentage, the composition of the NCu30-4-2-1 alloy is as follows: C ≤ 0.03, Cu 30 - 32, Si 3.9 - 4.3, Fe 1.5 - 2.8, Mn 0.5 - 1.5, Ce 0.01 - 0.06, and the balance is Ni and inevitable impurity elements; among the impurity elements, the O content ≤ 0.0030%, the N content ≤ 0.0010%, and the S content ≤ 0.0015%. The preparation method specifically includes the following steps: (1) Raw material selection: Select Ni plates, Cu plates, Si blocks, Fe rods, Mn sheets, graphite rods, and Ce blocks as raw materials, and calculate and prepare the raw materials of each element according to the composition control requirements. (2) Loading: For the NCu30-4-2-1 alloy containing Ce, batch loading is carried out according to factors such as the melting point of the raw materials, the degree of oxidation susceptibility, density, addition quantity, and volatility; for the first batch loading, first put graphite, Cu plates, Ni plates, and Fe blocks into the crucible; for the second batch loading, put the Si block and Mn sheet wrapped with nickel plates into the crucible successively; for the third batch loading, put the Ce block wrapped with nickel plates into the crucible. (3) Melting period: When the vacuum degree in the melting period ≤ 10 Pa, power is supplied. In the early stage of melting the first batch of materials, the power is gradually increased to 25 - 30 kW. After ensuring the formation of the molten pool, the power supply is reduced to 20 ± 1 kW for melting the materials, and the melting period is ensured to be 35 - 45 min; after melting is complete, the temperature is raised to 1480 °C - 1520 °C and enter the refining period. (4) Refining period: Control the vacuum degree at 0.5 - 1.0 Pa and the power range at 13 - 17 kW in the refining period, control the refining temperature at 1480 °C - 1520 °C, and the refining time at 15 - 25 min. (5) Alloying period: After the refining is completed, enter the alloying period. Cut off the power and form a film, fill the furnace with argon at 30000 - 40000 Pa, add the second batch of materials into the melt, stir at high power for 4 - 6 min, and finally control the melt temperature at 1250 - 1300 °C and add the third batch of materials, stir at high power for 4 - 6 min, supply power to raise the temperature to 1360 ± 10 °C for casting. (6) Casting: The inner wall of the ingot mold should be cleaned with a steel shovel and a steel brush, and the residual steel slag and scale should be removed with compressed air. The casting temperature is 1360 ± 10 °C, and a sprue cup with an inner diameter of Φ20 mm at the lower end is used to control the casting speed, ensuring that the casting time for each ingot is 40 - 60 s, and the recovery rate of the Ce element is stable at 85% - 90%, obtaining ingots with high purity and uniform composition. In step (1), it is necessary to ensure that the total O content brought in by the raw materials ≤ 0.020% and the S content ≤ 0.0015%. After passing through the melting period in step (3) and the refining period in step (4), control the O content in the melt ≤ 0.0050%, the N content ≤ 0.0020%, and the S content ≤ 0.0015% before entering the alloying period.

2. The preparation method of the NCu30-4-2-1 alloy toughened by adding rare earth element Ce according to claim 1, characterized in that, In step (1), the oxides, oil stains, and impurities on the surfaces of all raw materials are removed.

3. The preparation method of the NCu30-4-2-1 alloy strengthened by adding rare earth element Ce according to claim 1, characterized in that, In step (1), industrial purity Si blocks and Mn sheets are used as raw materials, and the raw material purity of the remaining alloy elements is not less than 99.9 wt.%.

4. The preparation method of strengthening NCu30-4-2-1 alloy by adding rare earth element Ce according to claim 1, characterized in that, In step (5), the high power is 30 kW.

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