A rare earth-containing valve alloy with excellent performance and a preparation method thereof

Abstract

This invention discloses a high-performance rare-earth-containing valve alloy and its preparation method. The chemical composition of the valve alloy, by weight percentage, is: C: 0.04-0.1%, Si≤0.3%, Mn≤1.0%, Cr: 19.0-21.0%, Fe≤1.0%, Al: 1.6%-1.8%, Ti: 2.5-2.7%, Ce: 0.05-0.1%, O≤0.0010%, N≤0.0015%, with the balance being nickel and unavoidable impurities. The preparation method includes vacuum induction melting, electroslag remelting, hot working, solution heat treatment, and aging heat treatment. The electroslag remelting involves adding 3%-5% Ce₂O₃ to a quaternary slag system. The valve alloy provided by this invention exhibits high high-temperature strength and high-temperature creep resistance, solving the problems of cracking and breakage in the exhaust valve head of current domestic internal combustion engines, leading to short engine life.

Description

Technical Field

[0001] This invention belongs to the field of rare earth-containing high-temperature alloy production technology, specifically relating to a high-performance rare earth-containing valve alloy and its preparation method. Background Technology

[0002] Internal combustion engines, as key power equipment in modern industry and transportation, are widely used in many industries such as automobiles, ships, power generation equipment, and construction machinery, playing an irreplaceable role in promoting social development and economic growth. Among various types of internal combustion engines, the valve, as the core component controlling the entry and exit of gas into the combustion chamber, directly affects the engine's power output, fuel economy, emission levels, and overall service life.

[0003] With the rapid development of modern industry and transportation, the operating conditions of internal combustion engines are becoming increasingly demanding, placing higher requirements on valve performance. Under the combined effects of high temperature, high pressure, high mechanical load, and corrosive gases, valves need to possess excellent high-temperature strength, high-temperature durability, oxidation resistance, corrosion resistance, and good thermal fatigue resistance. However, the traditional valve alloys widely used in China currently exhibit many problems when facing these harsh operating conditions. For example, high-temperature strength and high-temperature durability cannot be simultaneously satisfied, resulting in internal combustion engines being unable to operate stably at high temperatures for extended periods.

[0004] Due to insufficient high-temperature strength and poor durability, traditional valve alloys frequently cause cracks and breakage of the exhaust valve head in internal combustion engines during practical applications, significantly shortening the engine's service life. These problems severely restrict the widespread application and efficient operation of internal combustion engines in various fields. Therefore, there is an urgent need for a new type of valve alloy to solve these problems and improve the performance and reliability of internal combustion engines. Summary of the Invention

[0005] The purpose of this invention is to provide a high-performance rare earth-containing valve alloy and its preparation method, which not only has high high-temperature strength but also good high-temperature durability, thus having the advantage of simultaneously achieving both high-temperature strength and durability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A high-performance rare-earth-containing valve alloy has the following chemical composition by mass percentage: C: 0.04–0.1%, Si ≤ 0.3%, Mn ≤ 1.0%, Cr: 19.0–21.0%, Fe ≤ 1.0%, Al: 1.6%–1.8%, Ti: 2.5–2.7%, Ce: 0.05–0.1%, O ≤ 0.0010%, N ≤ 0.0015%, with the balance being nickel and unavoidable impurities.

[0007] Preferably, in the chemical composition, the mass ratio of Al+Ti is 4.2–4.35, and the Al:Ti ratio is 0.6–0.72. Al and Ti are important elements for forming the γ′ phase, which is beneficial for improving the high-temperature oxidation resistance of the alloy and preventing over-aging. According to the proportion, mass, and addition of Al and Ti elements in this invention, it can be ensured that an ordered γ′ phase precipitates in the alloy matrix. The increase in the lattice mismatch degree between the γ′ phase and the γ matrix phase and the increase in the volume fraction of the γ′ phase can increase the yield strength caused by precipitation strengthening. Furthermore, combined with the subsequent heat treatment of this invention, the optimal size of the γ′ phase precipitation is 10–40 nm, which not only ensures the high-temperature creep resistance of the alloy but also ensures the high-temperature strength of the alloy.

[0008] Preferably, the mass ratio of Al to Ce in the chemical composition is 16–36:1. By adjusting the mass ratio of Al to Ce, it is possible to refine the grain size, improve the high-temperature strength of the valve alloy, and ensure its high-temperature creep resistance. This may be due to their synergistic effects. Ce can inhibit grain growth at high temperatures and refine the grain size; at the same time, it can regulate the morphology, size, and distribution of strengthening phases (such as γ′ phase) in the alloy, making them more uniform and stable, thereby enhancing the high-temperature strength and creep resistance of the alloy. Cerium can promote the formation of a denser, continuous, and strongly bonded oxide film (such as Al2O3, Cr2O3) on the alloy surface; this oxide film can effectively block the diffusion of oxygen and corrosive media into the matrix, significantly improving the lifespan of the alloy under high-temperature oxidation and corrosion environments. In addition to refining the grain size, Al can also affect the precipitation of the γ′ phase. According to the formulation of the present invention, not only can the γ′ phase be fully precipitated, but also the square γ′ phase can be precipitated uniformly and finely, thereby enabling the alloy to maintain good stability at high temperatures.

[0009] Furthermore, the total inclusion rating of the rare earth-containing valve alloy of the present invention is less than 0.5.

[0010] Furthermore, the rare earth-containing valve alloy of the present invention has a high temperature strength of ≥900MPa at 650℃, a high temperature strength of ≥800MPa at 750℃, a creep rupture performance of ≥50h at 750℃ / 340MPa, a creep rupture performance of ≥100h at 750℃ / 310MPa, and an impact energy of ≥63J.

[0011] Furthermore, the preparation method of the high-performance rare-earth-containing gas valve alloy of the present invention includes the following steps: S1. Vacuum induction melting: The raw materials are vacuum induction melted according to the chemical composition ratio. Rare earth elements are added 3 to 5 minutes before tapping and the mixture is stirred thoroughly. The amount of rare earth elements added is 5 to 7 times the composition ratio.

[0012] S2, Electroslag Remelting: Add 3% to 5% Ce2O3 to the quaternary slag system; the quaternary slag system is composed of CaF, Al2O3, CaO, TiO2 and Ce2O3.

[0013] S3. Hot working: After holding at 1180~1200℃ for 3~4h, forging is carried out. The final forging temperature shall not be lower than 930℃, and slow cooling is performed. After the surface is ground, it is held at 1130~1150℃, and the final rolling temperature is 970~990℃.

[0014] S4. Solution heat treatment: Hot-rolled bars are held at 1020±10℃ for 1 to 1.5 hours and then rapidly water-cooled.

[0015] S5. Aging heat treatment: After solution treatment, the bar is kept at 700±10℃ for 16 hours and then air-cooled to room temperature.

[0016] Furthermore, in the electroslag remelting of the present invention, the slag system further includes aluminum particles; the amount of aluminum particles added is 0.5 to 1% of the mass of Ce2O3.

[0017] Furthermore, the forging process described in this invention is a unidirectional drawing process involving one forging and one drawing.

[0018] This invention further improves the various properties of valve alloys, especially their high-temperature creep resistance, through a specific production process.

[0019] First, during the vacuum induction melting process, the loss of Ce element during subsequent electroslag remelting was ensured, the timing of Ce addition was determined, and the amount of Ce added was effectively increased, thus fully ensuring that the Ce element content in the finished alloy is basically consistent with the set value.

[0020] Secondly, the addition of 3% to 5% Ce2O3 during electroslag remelting further ensures the burn-off of Ce.

[0021] In the hot forging stage, a specific temperature is used in conjunction with one upsetting and one drawing, which, compared to two upsetting and two drawing or three upsetting and three drawing, can effectively refine the grains, improve the microstructure, reduce the number of forging passes, lower the production cost of the alloy, and provide a good rolled billet. In the hot rolling stage, by combining an appropriate final rolling temperature and a rapid cooling method, the fine and uniform microstructure of the alloy is fully guaranteed, improving the overall performance of the material.

[0022] The solution heat treatment described in this invention promotes the full dissolution of the strengthening phase in the alloy, and the rapid cooling method also ensures the full dissolution of the strengthening phase, improving the ability of the alloy to precipitate and grow in large quantities during subsequent aging heat treatment. The final aging heat treatment enables the uniform and fine precipitation of square γ′ in the material, further improving the stability of the alloy's high-temperature strength, ensuring that the alloy maintains both good high-temperature strength and high-temperature creep strength at high temperatures, and ensuring the lifespan of the material.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial technical effects: (1) By adding a certain amount of Ce element and changing the Al and Ti ratio in the alloy, and by adjusting its smelting and hot processing technology, the present invention fully ensures the purity of the alloy, improves the number of square γ′ precipitation morphologies, thereby improving the high-temperature creep performance and high-temperature strength of the alloy, and ensures that the material simultaneously takes into account both high-temperature strength and high-temperature creep performance.

[0024] (2) The rare earth elements added in this invention can not only achieve the precipitation of the γ′ phase, but also make the square γ′ phase precipitate uniformly and finely, so that the alloy maintains good stability at high temperature.

[0025] (3) The dual smelting process (vacuum induction + electroslag remelting) adopted in this invention fully guarantees the metallurgical quality and cleanliness of the alloy, with the total inclusions being less than grade 0.5, laying a good foundation for subsequent hot processing.

[0026] (4) The preparation process used in this invention not only ensures the comprehensive performance of the alloy, but also reduces the production cost of the material. Attached Figure Description

[0027] Figure 1 The γ´ precipitate of rare earth gas valve alloy gold is shown in Example 1. Detailed Implementation

[0028] The present invention will be further described clearly and completely below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0029] The chemical composition of the rare earth-containing valve alloy in this embodiment, by mass percentage, is as follows: C: 0.06%, Si: 0.2%, Mn: 0.91%, Cr: 20.1%, Fe: 0.56%, Al: 1.69%, Ti: 2.61%, Ce: 0.0676%, O: 0.0010%, N: 0.0014%, with the balance being nickel and unavoidable impurities; wherein Al+Ti=4.3, Al:Ti=0.6475, and Al:Ce=25.

[0030] The preparation method of the rare earth gas valve alloy in this embodiment includes the following steps: S1. Vacuum induction melting: The raw materials are vacuum induction melted according to the chemical composition ratio. Rare earth elements are added 4 minutes before tapping and the mixture is stirred thoroughly. The amount of rare earth elements added is 5 times the composition ratio.

[0031] S2, Electroslag Remelting: Add 4.1% Ce2O3 and 0.041% Al particles to the quaternary slag system of CaF 50%, Al2O3 20%, CaO 20%, TiO2 5.8%.

[0032] S3. Hot working: After holding at 1190℃ for 5 hours, forging is carried out. The forging process is unidirectional drawing after one upsetting and one drawing. The final forging temperature is 950℃, followed by slow cooling. After the surface is ground, it is held at 1140℃, and the final rolling temperature is 975℃.

[0033] S4. Solution heat treatment: After holding the hot-rolled bar at 1020℃ for 1 hour, it is rapidly water-cooled.

[0034] S5. Aging heat treatment: After solution treatment, the bar is kept at 700℃ for 16 hours and then air-cooled to room temperature. Example 2

[0035] The chemical composition of the rare earth-containing valve alloy in this embodiment, by mass percentage, is as follows: C: 0.07%, Si: 0.15%, Mn: 0.89%, Cr: 19.8%, Fe: 0.66%, Al: 1.72%, Ti: 2.53%, Ce: 0.0573%, O: 0.0008%, N: 0.0013%, with the balance being nickel and unavoidable impurities; wherein Al+Ti=4.25, Al:Ti=0.679, and Al:Ce=30.

[0036] The preparation method of the rare earth gas valve alloy in this embodiment includes the following steps: S1. Vacuum induction melting: The raw materials are vacuum induction melted according to the chemical composition ratio. Rare earth elements are added 4 minutes before tapping and the mixture is stirred thoroughly. The amount of rare earth elements added is 5 times the composition ratio.

[0037] S2, Electroslag Remelting: Add 3.3% Ce2O3 and 0.033% Al particles to the quaternary slag system of CaF 50%, Al2O3 20%, CaO 20%, TiO2 6.6%.

[0038] S3. Hot working: After holding at 1196℃ for 3 hours, forging is carried out. The forging process is unidirectional drawing after one upsetting and one drawing. The final forging temperature is 945℃, followed by slow cooling. After the surface is ground, it is held at 1150℃, and the final rolling temperature is 988℃.

[0039] S4. Solution heat treatment: After holding the hot-rolled bar at 1030℃ for 1 hour, it is rapidly water-cooled. S5. Aging heat treatment: After solution treatment, the bar is kept at 710℃ for 16 hours and then air-cooled to room temperature. Example 3

[0040] The chemical composition of the rare earth-containing valve alloy in this embodiment, by mass percentage, is as follows: C: 0.04%, Si: 0.22%, Mn: 0.86%, Cr: 20.3%, Fe: 0.72%, Al: 1.65%, Ti: 2.68%, Ce: 0.0916%, O: 0.0006%, N: 0.0012%, with the balance being nickel and unavoidable impurities; wherein Al+Ti=4.33, Al:Ti=0.6156, and Al:Ce=18.

[0041] The preparation method of the rare earth gas valve alloy in this embodiment includes the following steps: S1. Vacuum induction melting: The raw materials are vacuum induction melted according to the chemical composition ratio. Rare earth elements are added 4 minutes before tapping and the mixture is stirred thoroughly. The amount of rare earth elements added is 6 times the composition ratio.

[0042] S2, Electroslag Remelting: Add 4.9% Ce2O3 and 0.049% Al particles to the quaternary slag system of CaF 50%, Al2O3 20%, CaO 20%, TiO2 5.0%.

[0043] S3. Hot working: After holding at 1180℃ for 3 hours, forging is carried out. The forging process is unidirectional drawing after one upsetting and one drawing. The final forging temperature is 953℃, followed by slow cooling. After the surface is ground, it is held at 1130℃, and the final rolling temperature is 982℃.

[0044] S4. Solution heat treatment: After holding the hot-rolled bar at 1010℃ for 1 hour, it is rapidly water-cooled.

[0045] S5. Aging heat treatment: After solution treatment, the bar is kept at 700℃ for 16 hours and then air-cooled to room temperature. Example 4

[0046] The chemical composition of the rare earth-containing valve alloy in this embodiment, by mass percentage, is as follows: C: 0.09%, Si: 0.18%, Mn: 0.95%, Cr: 19.4%, Fe: 0.59%, Al: 1.80%, Ti: 2.51%, Ce: 0.0502%, O: 0.0009%, N: 0.0013%, with the balance being nickel and unavoidable impurities; wherein Al+Ti=4.31, Al:Ti=0.717, and Al:Ce=36.

[0047] The preparation method of the rare earth gas valve alloy in this embodiment includes the following steps: S1. Vacuum induction melting: The raw materials are vacuum induction melted according to the chemical composition ratio. Rare earth elements are added 4 minutes before tapping and the mixture is stirred thoroughly. The amount of rare earth elements added is 7 times the composition ratio.

[0048] S2, Electroslag Remelting: Add 3.6% Ce2O3 and 0.036% Al particles to a quaternary slag system consisting of 50% CaF, 20% Al2O3, 20% CaO, and 6.3% TiO2.

[0049] S3. Hot working: After holding at 1188℃ for 4 hours, forging is carried out. The forging process is unidirectional drawing after one upsetting and one drawing. The final forging temperature is 952℃, followed by slow cooling. After the surface is ground, it is held at 1145℃, and the final rolling temperature is 976℃.

[0050] S4. Solution heat treatment: After holding the hot-rolled bar at 1036℃ for 1 hour, it is rapidly water-cooled.

[0051] S5. Aging heat treatment: After solution treatment, the bar is kept at 708℃ for 16 hours and then air-cooled to room temperature. Comparative Example 1

[0052] The chemical composition of the comparative valve alloy, by mass percentage, is as follows: C: 0.07%, Si: 0.15%, Mn: 0.89%, Cr: 19.8%, Fe: 0.66%, Al: 1.55%, Ti: 2.61%, O: 0.0008%, N: 0.0013%, with the balance being nickel and unavoidable impurities; wherein Al+Ti=4.16, Al:Ti=0.5938.

[0053] The preparation method of this comparative gas valve alloy includes the following steps: S1. Vacuum induction melting: The raw materials are vacuum induction melted according to the chemical composition ratio. Rare earth elements are added 4 minutes before tapping and the mixture is stirred thoroughly. The amount of rare earth elements added is 5 times the composition ratio.

[0054] S2, Electroslag Remelting: Add 4.1% Ce2O3 and 0.041% Al particles to the quaternary slag system of CaF 50%, Al2O3 20%, CaO 20%, TiO2 5.8%.

[0055] S3. Hot working: After holding at 1190℃ for 3 hours, forging is carried out. The forging process is unidirectional drawing after one upsetting and one drawing. The final forging temperature is 950℃, followed by slow cooling. After the surface is ground, it is held at 1140℃, and the final rolling temperature is 975℃.

[0056] S4. Solution heat treatment: After holding the hot-rolled bar at 1020℃ for 1 hour, it is rapidly water-cooled.

[0057] S5. Aging heat treatment: After solution treatment, the bar is kept at 700℃ for 16 hours and then air-cooled to room temperature. Comparative Example 2

[0058] The difference between this comparative example and Example 1 is as follows: S2. Ce2O3 was not added to the quaternary slag system during the electroslag remelting process.

[0059] S3. The forging billet was directly drawn without upsetting. Comparative Example 3

[0060] The difference between this comparative example and Example 1 is as follows: S2, Electroslag Remelting: Add 10% Ce2O3 to the quaternary slag system; S3. Forging blanks are formed by two blocks and two pulls.

[0061] The performance of rare earth-containing valve alloys in each embodiment and comparative example was tested, and the results are shown in Table 1.

[0062] Table 1 Mechanical properties of valve alloys in each embodiment and comparative example

[0063] Example 1: γ' precipitates of rare earth gas valve alloys, as shown in Example 1 Figure 1 As shown; by Figure 1 It can be seen that the γ′ phase is fully precipitated, and after heat treatment, the square γ′ precipitates are uniformly fine, with most having a size of 20-30 nm. The metallographic structure of the rare earth valve alloys in the other embodiments is the same as that in Example 1.

[0064] As shown in Table 1, compared with the comparative example, the rare earth-containing valve alloy provided by the present invention has higher hardness, high temperature strength and high temperature creep strength.

[0065] Comparative Examples 1 and 2 did not contain rare earth Ce; Comparative Example 3 did not contain Ce2O3 in the electroslag and the forging process did not involve upsetting and drawing; Comparative Example 4 contained 10% Ce2O3 in the electroslag and the forging process involved two upsetting and two drawing. The valve alloys prepared in the above comparative examples all showed certain differences from the present invention in various properties.

[0066] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make similar improvements and refinements without departing from the principles of the present invention, and these improvements and refinements should also be considered within the scope of protection of the present invention.

Claims

1. A rare earth-containing valve alloy having excellent properties, characterized by comprising, in mass %, Its chemical composition by weight percentage is as follows: C: 0.04-0.1%, Si≤0.3%, Mn≤1.0%, Cr: 19.0-21.0%, Fe≤1.0%, Al: 1.6%-1.8%, Ti: 2.5-2.7%, Ce: 0.05-0.1%, O≤0.0010%, N≤0.0015%, with the balance being nickel and unavoidable impurities.

2. The high-performance rare-earth-containing gas valve alloy according to claim 1, characterized in that, In the chemical composition, the mass ratio of Al+Ti is 4.2 to 4.35, and the Al:Ti ratio is 0.6 to 0.

72.

3. The high-performance rare-earth-containing gas valve alloy according to claim 1, characterized in that, In the chemical composition, the mass ratio of Al to Ce is 16 to 36:

1.

4. The high-performance rare-earth-containing gas valve alloy according to claim 1, characterized in that, The total inclusion rating of the valve alloy is less than or equal to 0.

5.

5. The high-performance rare-earth-containing gas valve alloy according to claim 1, characterized in that, The valve alloy has a high-temperature strength of ≥900MPa at 650℃, a high-temperature strength of ≥800MPa at 750℃, a creep rupture performance of ≥50h at 750℃ / 340MPa, a creep rupture performance of ≥100h at 750℃ / 310MPa, and an impact energy of ≥63J.

6. A method for preparing the high-performance rare-earth-containing gas valve alloy according to any one of claims 1 to 5, characterized in that, It includes vacuum induction melting, electroslag remelting, hot working, solution heat treatment and aging heat treatment; the electroslag remelting involves adding 3% to 5% Ce2O3 to the quaternary slag system; the quaternary slag system is composed of CaF, Al2O3, CaO, TiO2 and Ce2O3.

7. The method for preparing the high-performance rare-earth-containing gas valve alloy according to claim 6, characterized in that, The electroslag remelting process includes aluminum particles in the slag system; the amount of aluminum particles added is 0.5 to 1% of the mass of Ce2O3.

8. The method for preparing the high-performance rare-earth-containing gas valve alloy according to claim 6, characterized in that, The vacuum induction melting process involves melting the raw materials in a vacuum induction process according to the chemical composition ratio. Rare earth elements are added 3 to 5 minutes before tapping the steel and the mixture is stirred thoroughly. The amount of rare earth elements added is 5 to 7 times the composition ratio.

9. The method for preparing the high-performance rare-earth-containing gas valve alloy according to claim 6, characterized in that, The hot working process involves holding the material at 1180–1200℃ for 3–5 hours, followed by forging. The final forging temperature must not be lower than 930℃, and the material is cooled slowly. After surface grinding, the material is held at 1130–1150℃, and the final rolling temperature is 970–990℃.

10. The method for preparing the high-performance rare-earth-containing gas valve alloy according to claim 9, characterized in that, The forging process involves a single forging and drawing followed by unidirectional elongation.

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