Cobalt-based alloy for turbocharger assembly and preparation method of cobalt-based alloy

Abstract

The invention discloses a cobalt-based alloy for a turbocharger assembly and a preparation method of the cobalt-based alloy. The cobalt-based alloy is prepared from the following elemental components in percentage by mass: 14%-18% of nickel Ni, 15%-20% of chromium Cr, 21.5%-25% of molybdenum Mo, 0-0.1% of carbon C, 1.5%-3.0% of silicon Si, 0-0.02% of phosphorus P, 0-0.02% of sulfur S, less than or equal to 100 PPM of nitrogen N, less than or equal to 50 PPM of oxygen O and the balance of cobalt Co. The exhaust gas regulating valve assembly formed by the cobalt-based alloy for the turbocharger assembly through a precision casting process has excellent corrosion resistance and high-temperature performance through bench testing.

Description

Technical Field

[0001] The invention belongs to the technical field of special cobalt-based alloys, and in particular relates to a cobalt-based alloy for a turbocharger component and a preparation method thereof. Background Art

[0002] A turbocharger is an air compressor that uses the exhaust gas from the engine to do work. Turbochargers can not only save energy and reduce emissions, but also effectively increase engine power. With the rapid development of internal combustion engine technology, the energy-saving and environmentally friendly characteristics of turbocharging have been widely accepted by many automobile manufacturers. The working environment temperature of the turbocharger is relatively high. The working temperature of the diesel engine supercharger is generally around 600°C, the working temperature of the gasoline engine supercharger is as high as 800-900°C, and the working temperature of the special vehicle engine supercharger is as high as 900-950°C. With the improvement of engine performance requirements, the working temperature of the turbocharger will be further increased, and the temperature resistance, corrosion resistance, high temperature friction performance and other requirements of the material are extremely high.

[0003] Natural gas engine is an internal combustion engine that uses the energy generated by natural gas combustion to drive the piston movement to complete its work. With increasingly stringent environmental protection requirements, natural gas engines have become an important development direction. The exhaust gas regulating valve is one of the main components of the turbocharger for natural gas engines, and has high requirements for the corrosion resistance of the material.

[0004] Many researchers use nickel-based alloys as materials for turbocharger components, such as patent documents CN104946933A, CN104736731A, etc. However, nickel-based high-temperature alloys are difficult to serve for a long time at temperatures above 750°C.

[0005] At present, there are many technologies related to cobalt-based superalloys. Cobalt-based alloys are composed of cobalt and one or more of the elements chromium, tungsten, iron, nickel, etc. It is a hard alloy that can withstand various wear, corrosion and high-temperature oxidation, and has the highest strength among superalloys. Cobalt-based superalloys have higher melting points, better high-temperature strength, hot corrosion resistance, oxidation resistance, good fatigue resistance, fracture toughness and better hardness index than nickel-based superalloys.

[0006] For example: Patent document CN111041281A discloses a chromium-containing cobalt-based high-temperature alloy, with an atomic percentage of Cr of (1-2) at.%, Ni of (24-34) at.%, Al of (6.5-7.5) at.%, Ti of (2.5) at.%, and the remainder of Co; the sum of the atomic percentages of Al and Ti is not more than 10 at.%; the microstructure of the chromium-containing cobalt-based high-temperature alloy is a dendritic structure, consisting of a γ-Co matrix phase and a γ'-(Co, Ni)3(Al, Ti) phase located on the dendrites; Ni, Al and Ti elements segregate in the γ' phase, and Co and Cr elements segregate in the γ phase; and it contains η phase and δ phase. Patent document CN111004945A discloses a molybdenum-containing cobalt-based high-temperature alloy, with the atomic percentage of Mo being 2 at.%, Ni being 24 at.%, Al being 6.5 at.%, Ti being 1.5 at.%, and the remainder being Co; the sum of the atomic percentages of Al and Ti being not greater than 10 at.%; the microstructure of the molybdenum-containing cobalt-based high-temperature alloy is a dendritic structure, consisting of a γ-Co matrix phase and a γ'-(Co, Ni)3(Al, Ti) phase located on the dendrites; it contains a γ phase and a γ' phase, with Ni, Al, Ti and Mo elements segregating into the γ' phase, and the Co element segregating into the γ phase; it contains an η phase, a δ phase and a μ phase. Patent document CN113699414A discloses a γ' phase strengthened cobalt-based high-temperature alloy with excellent high-temperature tensile properties, C0.02-0.1, Cr6.82-9, Ni24-28, Mo2-6, Ti1-3, Al2.5-5, B0.005-0.01, Ta4-8, W2-6, Zr0.05-0.2, and Co as the balance; the alloy is a cast polycrystalline alloy, the microstructure is a dendritic structure, and the phase composition is γ-Co matrix, γ'-Co3 (Al, Me), MC type carbide, eutectic (γ+γ'), wherein Me is W, Ta, Ti, Mo; the alloy has a tensile elongation of 7-12% at 800-1000°C and a tensile elongation of 15.6% at room temperature. Patent document CN115821118A discloses a high-titanium cobalt-based high-temperature alloy, wherein the atomic percentage of Ti is 12-14 at.%, Mo is 4-5 at.%, Al is 5.5-6.5 at.%, and the balance is Co; the sum of the atomic percentages of Mo and Ti is not greater than 18 at.%. However, the alloy material in the above document has relatively low molybdenum and silicon contents, resulting in low performance indicators such as high-temperature corrosion resistance and high-temperature oxidation resistance. Summary of the invention

[0007] The object of the present invention is to provide a cobalt-based alloy for a turbocharger component and a preparation method thereof, so as to solve the problems of the turbocharger component in the prior art that the turbocharger component is not resistant to corrosion, has insufficient wear resistance or has insufficient hardness.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] The invention discloses a cobalt-based alloy for a turbocharger component, which is composed of the following element components in mass fraction: nickel Ni: 14%-18%, chromium Cr: 15%-20%, molybdenum Mo: 21.5%-25%, carbon C: 0-0.1%, silicon Si: 1.5%-3.0%, phosphorus P: 0-0.02%, sulfur S: 0-0.02%, nitrogen N: ≤100PPM, oxygen O: ≤50PPM, and the balance is cobalt Co.

[0010] Preferably, the cobalt-based alloy for a turbocharger component described in the present invention is composed of the following elemental components in mass fraction: Ni: 15% to 17%, Cr: 16% to 19%, Mo: 23% to 25%, C: 0.01% to 0.06%, Si: 1.8% to 2.8%, P: 0 to 0.02%, S: 0 to 0.02%, N: ≤100ppm, O: ≤50ppm, and the balance is cobalt Co.

[0011] The metallographic structure of the cobalt-based alloy for the turbocharger component is that laves phases are evenly distributed on an austenite matrix; the yield strength at a temperature of 20±2° C. is ≥700 MPa, and the Rockwell hardness is 47-55 HRC.

[0012] Preferably, the room temperature density of the cobalt-based casting alloy is 8.70±0.10 g / cm 3 .

[0013] The method for preparing a cobalt-based alloy for a turbocharger component of the present invention comprises the following steps:

[0014] (1) Loading the charge in accordance with the formula ratio into a vacuum furnace for smelting: first using a metal nickel bar as the bottom, then adding a metal chromium bar and a molybdenum bar, and then adding metal silicon and electric cobalt; electrically heating to melt the charge;

[0015] (2) pouring the molten steel into master alloy bars; taking samples to test the chemical composition;

[0016] (3) cutting and grinding the master alloy rod to make a standard master alloy;

[0017] (4) The standard master alloy is melted again in a vacuum fast melting furnace and cast into products of specific shapes.

[0018] Preferably, the melting temperature of the charge in step (1) is 1480-1550°C.

[0019] Preferably, the secondary melting temperature in step (4) is 1420-1480°C.

[0020] The cobalt-based alloy for a turbocharger assembly of the present invention is suitable for a turbocharger assembly for a natural gas engine, in particular, an exhaust gas regulating valve assembly of a turbocharger.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] In the cobalt-based alloy for the turbocharger assembly of the present invention, the nickel element is mainly used to improve the impact toughness and corrosion resistance of the material; the optimized content of the molybdenum element and the silicon element can significantly improve the corrosion resistance and high-temperature strength of the material; the exhaust gas regulating valve assembly formed by the cobalt-based alloy material through the precision casting process has excellent corrosion resistance and high-temperature performance after bench testing. DETAILED DESCRIPTION

[0023] Those skilled in the art should recognize that the present embodiment is only used to illustrate the present invention, and is not used to limit the present invention. Any changes or modifications to the embodiment within the scope of the present invention are within the scope of the claims of the present invention.

[0024] Example 1

[0025] A cobalt-based alloy for a turbocharger component, the preparation method of which comprises the following steps:

[0026] (1) Charge the furnace charge in the formula ratio into a vacuum furnace for smelting: first use 15.5 parts (by weight, the same below) of metal nickel bars as the bottom, then add 18 parts of metal chromium bars and 23.5 parts of molybdenum bars, and then add 2 parts of metal silicon and 41 parts of electric cobalt; supply electricity for heating to melt the charge, and the melting temperature of the charge is 1520°C;

[0027] (2) pouring the molten steel into master alloy rods through a steel tube mold; taking samples to test the chemical composition;

[0028] (3) cutting and grinding the master alloy rod to make a standard master alloy;

[0029] (4) The standard master alloy is melted for a second time in a vacuum fast melting furnace at a melting temperature of 1460°C, and the molten steel is poured into an exhaust gas regulating valve for a turbocharger.

[0030] The cobalt-based alloy obtained in this embodiment 1 is measured by metallography, and the mass fractions of the elemental components are as follows: Ni: 15.5%, Cr: 17.9%, Mo: 23.4%, C: 0.02%, Si: 1.9%, P: 0.012%, S: 0.003%, N: 13ppm, O: 8PPM, and the balance is Co.

[0031] According to the GB / T 230.1-2018 standard, the Rockwell hardness of the exhaust gas regulating valve was measured three times to be 49HRC, 51HRC, and 50.5HRC; the room temperature density was measured by the water displacement method to be 8.72g / cm 3 .

[0032] According to the provisions of GB / T 2423.51 standard, the corrosion resistance of the exhaust gas control valve was measured at 950℃, and the corrosion weight loss rate was 0.734mg / (cm 2 .h);

[0033] According to the provisions of GB / T 13303 standard, the high temperature oxidation test of the exhaust gas control valve was measured at 950℃, and the oxidation rate value was 0.0413g / (m 2 .h).

[0034] Example 2

[0035] A cobalt-based alloy for a turbocharger component, the preparation method of which comprises the following steps:

[0036] (1) Charge the furnace charge in the formula ratio into a vacuum furnace for smelting: first use 16.5 parts of metal nickel bars as the bottom, then add 16.5 parts of metal chromium bars and 23.5 parts of molybdenum bars, and then add 2.7 parts of metal silicon and 40.8 parts of electric cobalt; supply electricity for heating to melt the charge, and the melting temperature of the charge is 1510°C;

[0037] (2) pouring the molten steel into master alloy rods through a steel tube mold; taking samples to test the chemical composition;

[0038] (3) cutting and grinding the master alloy rod to make a standard master alloy;

[0039] (4) The standard master alloy is melted for a second time in a vacuum fast melting furnace at a melting temperature of 1470°C, and the molten steel is poured into an exhaust gas regulating valve for a turbocharger.

[0040] The cobalt-based alloy obtained in this embodiment 2 is measured by metallographic structure, and the mass fractions of the elemental components are as follows: Ni: 16.5%, Cr: 16.3%, Mo: 23.4%, C: 0.04%, Si: 2.6%, P: 0.011%, S: 0.004%, N: 15ppm, O: 8PPM, and the remainder is Co.

[0041] According to the GB / T 230.1-2018 standard, the Rockwell hardness of the exhaust gas regulating valve was measured to be 49HRC, 52HRC and 51HRC three times; the room temperature density was measured by the water displacement method to be 8.72g / cm 3 .

[0042] According to the provisions of GB / T 2423.51 standard, the corrosion resistance of the exhaust gas control valve was measured at 950°C, and the corrosion weight loss rate was 0.712mg / (cm 2 .h).

[0043] According to the provisions of GB / T13303 standard, the high temperature oxidation test of the exhaust gas control valve at 950°C was tested, and the oxidation rate value was 0.0402g / (m 2 .h).

[0044] Example 3

[0045] A cobalt-based alloy for a turbocharger component, the preparation method of which comprises the following steps:

[0046] (1) Charge the furnace charge in accordance with the formula ratio into a vacuum furnace for smelting: first use 16 parts of metal nickel bars as the bottom, then add 18.5 parts of metal chromium bars and 24.7 parts of molybdenum bars, and then add 2.2 parts of metal silicon and 38.6 parts of electric cobalt; supply electricity for heating to melt the charge, and the melting temperature of the charge is 1530°C;

[0047] (2) pouring the molten steel into master alloy rods through a steel tube mold; taking samples to test the chemical composition;

[0048] (3) cutting and grinding the master alloy rod to make a standard master alloy;

[0049] (4) The standard master alloy is melted for a second time in a vacuum fast melting furnace at a melting temperature of 1440°C, and the molten steel is poured into an exhaust gas regulating valve for a turbocharger.

[0050] The cobalt-based alloy obtained in this embodiment 3 is determined by metallographic structure, and the mass fractions of the elemental components are as follows: Ni: 16%, Cr: 18.4%, Mo: 24.6%, C: 0.05%, Si: 2%, P: 0.013%, S: 0.002%, N: 12ppm, O: 10PPM, and the remainder is Co.

[0051] According to the provisions of GB / T 230.1-2018 standard, the Rockwell hardness of the exhaust gas regulating valve was measured three times to be 49HRC, 50HRC, and 49HRC; the room temperature density was measured by the water displacement method to be 8.75g / cm 3 .

[0052] According to the provisions of GB / T 2423.51 standard, the corrosion resistance of the exhaust gas control valve was measured at 950℃, and the corrosion weight loss rate was 0.703mg / (cm 2 .h).

[0053] According to the provisions of GB / T13303 standard, the high temperature oxidation test of the exhaust gas control valve at 950°C was tested, and the oxidation rate value was 0.039g / (m2 .h).

[0054] Comparative Example 1

[0055] A cobalt-based alloy for a turbocharger component, the preparation method of which comprises the following steps:

[0056] (1) Charge the furnace charge in the formula ratio into a vacuum furnace for smelting: first use 16.5 parts of metal nickel bars as the bottom, then add 16.5 parts of metal chromium bars and 23.5 parts of molybdenum bars, and then add 1 part of metal silicon and 42.4 parts of electric cobalt; supply electricity for heating to melt the charge, and the melting temperature of the charge is 1510°C;

[0057] (2) pouring the molten steel into master alloy rods through a steel tube mold; taking samples to test the chemical composition;

[0058] (3) cutting and grinding the master alloy rod to make a standard master alloy;

[0059] (4) The standard master alloy is melted for a second time in a vacuum fast melting furnace at a melting temperature of 1470°C, and the molten steel is poured into an exhaust gas regulating valve for a turbocharger.

[0060] Comparative Example 1 is a comparative example of Example 2, except that the silicon content is reduced. The cobalt-based alloy obtained in Comparative Example 1, through metallographic determination, has the following mass fractions of elemental components: Ni: 16.5%, Cr: 16.3%, Mo: 23.4%, C: 0.04%, Si: 0.8%, P: 0.011%, S: 0.004%, N: 15ppm, O: 8PPM, and the balance is Co.

[0061] According to the GB / T 230.1-2018 standard, the Rockwell hardness of the exhaust gas regulating valve was measured to be 48HRC, 52HRC and 51HRC three times; the room temperature density was measured by the water displacement method to be 8.74g / cm 3 .

[0062] According to the provisions of GB / T 2423.51 standard, the corrosion resistance of the exhaust gas control valve was measured at 950℃, and the corrosion weight loss rate was 0.86mg / (cm 2 .h).

[0063] According to the provisions of GB / T13303 standard, the high temperature oxidation test of the exhaust gas control valve at 950°C was tested, and the oxidation rate value was 0.055g / (m 2 .h).

[0064] Comparative Example 2

[0065] A cobalt-based alloy for a turbocharger component, the preparation method of which comprises the following steps:

[0066] (1) Charge the furnace charge in the formula ratio into a vacuum furnace for smelting: first use 16 parts of metal nickel bars as the bottom, then add 18.5 parts of metal chromium bars and 20 parts of molybdenum bars, and then add 2.2 parts of metal silicon and 43.3 parts of electric cobalt; supply electricity for heating to melt the charge, and the melting temperature of the charge is 1530°C;

[0067] (2) pouring the molten steel into master alloy rods through a steel tube mold; taking samples to test the chemical composition;

[0068] (3) cutting and grinding the master alloy rod to make a standard master alloy;

[0069] (4) The standard master alloy is melted for a second time in a vacuum fast melting furnace at a melting temperature of 1440°C, and the molten steel is poured into an exhaust gas regulating valve for a turbocharger.

[0070] Comparative Example 2 is a comparative example of Example 3, except that the molybdenum content is reduced. The cobalt-based alloy obtained in Comparative Example 2, through metallographic determination, has the following mass fractions of elemental components: Ni: 16%, Cr: 18.4%, Mo: 19.9%, C: 0.05%, Si: 2%, P: 0.013%, S: 0.002%, N: 12ppm, O: 10PPM, and the balance is Co.

[0071] According to the GB / T 230.1-2018 standard, the Rockwell hardness of the exhaust gas regulating valve was measured to be 46HRC, 49HRC and 45HRC three times; the room temperature density was measured by the water displacement method to be 8.7g / cm 3 .

[0072] According to the provisions of GB / T 2423.51 standard, the corrosion resistance of the exhaust gas control valve was measured at 950℃, and the corrosion weight loss rate was 0.89mg / (cm 2 .h).

[0073] According to the provisions of GB / T13303 standard, the high temperature oxidation test of the exhaust gas control valve at 950°C was tested, and the oxidation rate value was 0.058g / (m 2 .h).

[0074] Table 1 Performance test results of Examples 1 to 3 and Comparative Examples 1 to 2

[0075]

[0076] It can be seen from Table 1 that the exhaust gas regulating valve components formed by the cobalt-based alloy materials of Examples 1 to 3 through the precision casting process have excellent corrosion resistance and high temperature performance after bench testing. Compared with Comparative Examples 1 to 3, the molybdenum content and silicon content of Examples 1 to 3 have a great influence on the hardness, corrosion resistance, and high temperature oxidation resistance of the materials.

Claims

1. A cobalt-based alloy for a turbocharger component, characterized in that: It is composed of the following element components in mass fraction: nickel Ni: 14% ~ 18%, chromium Cr: 15% ~ 20%, molybdenum Mo: 21.5% ~ 25%, carbon C: 0 ~ 0.1%, silicon Si: 1.5% ~ 3.0%, phosphorus P: 0 ~ 0.02%, sulfur S: 0 ~ 0.02%, nitrogen N: ≤ 100PPM, oxygen O: ≤ 50PPM, and the balance is cobalt Co.

2. The cobalt-based alloy for turbocharger components according to claim 1, characterized in that: It is composed of the following element components in mass fraction: Ni: 15%~17%, Cr: 16%~19%, Mo: 23%~25%, C: 0.01%~0.06%, Si: 1.8%~2.8%, P: 0~0.02%, S: 0~0.02%, N: ≤100ppm, O: ≤50ppm, and the balance is cobalt Co.

3. The cobalt-based alloy for turbocharger components according to claim 1, characterized in that: The metallographic structure of the cobalt-based alloy for the turbocharger component is that laves phase is evenly distributed on an austenite matrix; the yield strength at a temperature of 20±2° C. is ≥700 MPa, and the Rockwell hardness is 47-55 HRC.

4. The cobalt-based alloy for turbocharger components according to claim 1, characterized in that: The room temperature density of the cobalt-based casting alloy is 8.70±0.10 g / cm 3 .

5. The method for preparing a cobalt-based alloy for a turbocharger component according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Loading the charge in the formula ratio into the vacuum furnace for smelting: first use metal nickel bars as the bottom, then add metal chromium bars and molybdenum bars, and then add metal silicon and electric cobalt; electrically heating to melt the charge; (2) pouring the molten steel into master alloy bars; taking samples to test the chemical composition; (3) Cutting and grinding the master alloy rod to make a standard master alloy; (4) The standard master alloy is melted again in a vacuum fast melting furnace and cast into products of specific shapes.

6. The method for preparing a cobalt-based alloy for a turbocharger component according to claim 5, characterized in that: The melting temperature of the charge in step (1) is 1480-1550°C.

7. The method for preparing a cobalt-based alloy for a turbocharger component according to claim 5, characterized in that: The secondary melting temperature in step (4) is 1420-1480°C.

8. The use of the cobalt-based alloy for turbocharger components according to any one of claims 1 to 4, characterized in that: For use in turbocharger components for natural gas engines.

9. The use of the cobalt-based alloy for turbocharger components according to claim 8, characterized in that: Waste gas regulating valve assembly for turbocharger.

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