A vacuum induction melting method for reducing the oxygen content of nickel-based high-temperature alloys

Abstract

The present invention belongs to the technical field of high temperature alloys, and specifically relates to a vacuum induction melting method for reducing the oxygen content of a nickel-based high temperature alloy, comprising the following steps: selecting a raw material with a low O content according to the content requirements of each element in the Hastelloy X alloy, and calculating the theoretical value of the O content of the batch; adding the prepared raw material element material with low affinity for O into a crucible, heating it to above the melting point of the alloy under high vacuum, and refining after the alloy components are completely melted; adding an element with high affinity for O and an intermediate material of B for secondary refining after primary refining, and obtaining molten steel after refining; after the smelting is completed, cooling to the alloy liquid surface conjunctiva, pouring the molten steel after passing argon gas, and demolding after pouring to complete the preparation of the Hastelloy X alloy ingot. The present invention can effectively reduce the oxygen content in the Hastelloy X alloy, and improve its high temperature performance, oxidation resistance and corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature alloy smelting, and in particular relates to a vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy. Background Art

[0002] Hastelloy X alloy is a typical nickel-based high-temperature alloy with excellent high-temperature strength, oxidation resistance and corrosion resistance. It is widely used in extreme high-temperature environments. Since Hastelloy X alloy needs to be used for a long time at high temperatures, the purity of the material is crucial to its performance. However, during the smelting process, oxygen in the air or impurity oxygen in the raw materials easily enters the alloy to form oxide inclusions. These inclusions will not only weaken the mechanical properties of the alloy, but may also cause structural defects such as cracks, especially in high-temperature environments, which will aggravate the embrittlement and failure of the alloy, seriously reducing the service life of the hot end components.

[0003] Vacuum induction melting is a commonly used melting method for high-temperature alloys. Vacuum induction melting has the characteristics of pure alloy, low gas content, easy control of easily burned elements, and volatilization of low-melting point harmful inclusions. Although the oxygen content of Hastelloy X alloy can be controlled within a certain range by vacuum induction melting, there are still certain oxide residues. In addition, some elements used in the alloy, such as Ti, Al, etc., are easy to react with oxygen, further increasing the generation of oxide inclusions, but it is difficult to effectively control the oxygen content of Hastelloy X alloy below 10ppm by only one vacuum induction melting. Therefore, how to provide a method that is simple to operate, easy to implement, and can effectively reduce the oxygen content of Hastelloy X alloy under the premise of ensuring industrial production has become an important challenge to improve the quality of Hastelloy X alloy. In order to solve the deficiencies of the prior art, the present invention provides a new melting method, which effectively reduces the oxygen content in the alloy through reasonable process control, significantly reduces oxide inclusions, and improves the overall performance of the material. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy. By using high-purity raw materials, precise refining processes and casting processes, the oxygen content in the Hastelloy X alloy can be effectively reduced, and its high-temperature performance, oxidation resistance and corrosion resistance can be improved. While simplifying the operation process, the method can be applied in industrial production, providing a feasible technical route for the preparation of high-performance Hastelloy X alloy materials.

[0005] To achieve the above technical objectives, the technical solution adopted in the embodiment of the present invention is: a vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy, comprising the following steps:

[0006] Step S1. Selecting raw materials: selecting raw materials with low O content according to the content requirements of each element in Hastelloy X alloy, and calculating the theoretical value of O content in the ingredients;

[0007] Step S2. Vacuum induction melting: Add the prepared raw material elements with low affinity for O into a crucible, heat to above the melting point of the alloy under high vacuum, and refine after the alloy components are completely melted;

[0008] Step S3. Refining: After the primary refining, an element with high affinity to O and an intermediate material of B are added for secondary refining, and molten steel is obtained after refining;

[0009] Step S4. Pouring: After smelting, the temperature is lowered to the alloy liquid surface to form a film, and the molten steel is poured after passing argon gas. After pouring, the mold is removed to complete the preparation of the Hastelloy X alloy ingot.

[0010] Furthermore, the raw materials in step S1 include Ni, Fe, Cr, Mo, Al, Ti, C and nickel-boron alloy, and the theoretical value of the total content of O in the raw materials is controlled within 50 ppm.

[0011] Furthermore, in step S2, the raw material elements with low affinity to O include Ni, Fe, Cr, Mo and 1 / 2 of C;

[0012] When the raw material C is added, the C particles are wrapped with Ni foil, and the raw material C covers the liquid surface of the molten steel when added;

[0013] The vacuum degree should be kept within 8Pa during vacuum induction melting.

[0014] Furthermore, the elements with high affinity for O in step S3 include Al and Ti; the intermediate material of B is a nickel-boron alloy, and the remaining 1 / 2 of C is added together with the nickel-boron alloy. When the raw material C is added, the C particles are wrapped with Ni foil, and the raw material C covers the liquid surface of the molten steel when added.

[0015] Furthermore, during refining in step S3, the vacuum degree is maintained within 4 Pa, and a two-time refining method is adopted, with the first refining temperature being 1550±10°C, the refining time being 40±5min, the second refining temperature being 1580±10°C, the refining time being 8±2min, and sufficient stirring being performed during the refining process.

[0016] Furthermore, in step S4, the casting mold tube adopts a carbon steel mold tube; the mold tube baking temperature is 300-400°C, and the insulation time is 4h; the pouring nozzle diameter is 16-20mm; and the pouring temperature is 1480-1500°C.

[0017] Furthermore, the oxygen content of the Hastelloy X alloy ingot in step S4 is ≤10ppm.

[0018] Furthermore, the Hastelloy X alloy ingot in step S4 comprises the following components: C 0.05-0.20wt%, Cr20.5-23.0wt%, Mo 8-10wt%, Fe 17-20wt%, B≤0.01wt%, Al≤0.5wt%, Ti≤0.15wt%, and the balance is Ni and unavoidable impurities.

[0019] The technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0020] The present invention adopts a method for accurately controlling the refining process and the pouring process, and the introduction of O in the raw material can be effectively avoided through the raw material oxygen content refining process; in addition, by increasing the secondary refining temperature and reducing the secondary refining time, the oxide formation of elements such as Al and Ti can be reduced, and the crucible can be prevented from supplying oxygen to the molten steel; in addition, reducing the pouring temperature and increasing the pouring nozzle diameter can promote the volatilization of the O element, and finally reduce the oxygen content of the Hastelloy X high-temperature alloy to less than 10ppm, effectively solving the problem that the oxygen content of the Hastelloy X alloy cannot be further reduced by only using vacuum induction melting technology, improving the purity of the Hastelloy X alloy ingot, and then improving the high-temperature performance of the Hastelloy X alloy. In addition, the present invention has a simple process, is convenient for industrial production, and is suitable for large-scale manufacturing of high-performance nickel-based alloy materials. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] Example 1

[0023] A vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy, wherein a single furnace melts an alloy weighing 2000 kg, comprising the following steps:

[0024] Step S1. Raw materials: weigh the raw materials according to the content requirements of each element in the Hastelloy X alloy, the raw materials include Ni, Fe, Cr, Mo, Al, Ti, C and nickel-boron alloy, and theoretically calculate the total oxygen content in the raw materials. The theoretical value of the total oxygen content is 28 ppm;

[0025] Step S2. Vacuum induction melting: Add the raw material elements Ni, Fe, Cr, Mo and 1 / 2 of C prepared in step S1 into a crucible, heat to above the melting point of the alloy under a vacuum condition of 5 Pa, and melt the alloy components completely;

[0026] When the raw material C is added, the C particles are wrapped with Ni foil, and the raw material C covers the liquid surface of the molten steel when added;

[0027] Step S3. Refining: During the refining process, the vacuum degree is maintained at 2Pa, the primary refining temperature is 1560°C, the refining time is 40min, after the primary refining, the intermediate material nickel-boron alloy of the prepared raw material elements Al, Ti, B and the remaining 1 / 2 of C are added, and the secondary refining is performed, the secondary refining temperature is 1585°C, and the refining time is 10min;

[0028] Step S4. Pouring: After refining, stop the power and cool down until the alloy liquid surface forms a film, and use a carbon steel mold tube for pouring. The mold tube baking temperature is 350°C and the insulation time is 4h; the nozzle diameter is 16mm and the pouring temperature is 1500°C.

[0029] Example 2

[0030] A vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy, wherein a single furnace melts an alloy weighing 2000 kg, comprising the following steps:

[0031] Step S1. Raw materials: weigh the raw materials according to the content requirements of each element in the Hastelloy X alloy, the raw materials include Ni, Fe, Cr, Mo, Al, Ti, C and nickel-boron alloy, and theoretically calculate the total oxygen content in the raw materials. The theoretical value of the total oxygen content is 43 ppm;

[0032] Step S2. Vacuum induction melting: Add the raw material elements Ni, Fe, Cr, Mo and 1 / 2 of C prepared in step S1 into a crucible, heat to above the melting point of the alloy under a vacuum condition of 4 Pa, and melt the alloy components completely;

[0033] When the raw material C is added, the C particles are wrapped with Ni foil, and the raw material C covers the liquid surface of the molten steel when added;

[0034] Step S3. During the refining process, the vacuum degree is maintained at 1Pa, the primary refining temperature is 1550°C, the refining time is 40min, and after the primary refining, the intermediate material nickel-boron alloy of the prepared raw material elements Al, Ti, and B and the remaining 1 / 2 of C are added for secondary refining, the secondary refining temperature is 1580°C, and the refining time is 8min;

[0035] Step S4. Pouring: After refining, stop the power and cool down until the alloy liquid surface forms a film, and use a carbon steel mold tube for pouring. The pouring mold tube uses a carbon steel mold tube, the mold tube baking temperature is 350°C, the insulation time is 4h, the pouring temperature is 1500°C, and the nozzle diameter is 16mm.

[0036] Example 3

[0037] A vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy, wherein a single furnace melts an alloy weighing 2000 kg, comprising the following steps:

[0038] Step S1. Raw materials: weigh the raw materials according to the content requirements of each element in the Hastelloy X alloy, the raw materials include Ni, Fe, Cr, Mo, Al, Ti, C and nickel-boron alloy, and theoretically calculate the total oxygen content in the raw materials. The theoretical value of the total oxygen content is 22ppm;

[0039] Step S2. Vacuum induction melting: Add the raw material elements Ni, Fe, Cr, Mo and 1 / 2 of C prepared in step S1 into a crucible, heat to above the melting point of the alloy under a vacuum condition of 6Pa, and melt the alloy components completely;

[0040] When the raw material C is added, the C particles are wrapped with Ni foil, and the raw material C covers the liquid surface of the molten steel when added;

[0041] Step S3. During the refining process, the vacuum degree is maintained at 3Pa, the primary refining temperature is 1550°C, the refining time is 40min, and after the primary refining, the intermediate material nickel-boron alloy of the prepared raw material elements Al, Ti, and B and the remaining 1 / 2 of C are added for secondary refining, the secondary refining temperature is 1580°C, and the refining time is 8min;

[0042] Step S4. Pouring: After refining, stop the power and cool down until the alloy liquid surface forms a film, and use a carbon steel mold tube for pouring. The pouring mold tube uses a carbon steel mold tube, the mold tube baking temperature is 350°C, and the insulation time is 4h; the pouring temperature is 1490°C, and the nozzle diameter is 20mm.

[0043] Comparative Example 1

[0044] The difference between Comparative Example 1 and Example 1 is that the theoretical value of the total oxygen content calculated for the raw materials used is 143 ppm, the secondary refining temperature is 1560°C, and the pouring temperature is 1520°C.

[0045] Related experimental results:

[0046] The theoretical values ​​of O content calculated for the Hastelloy X alloy raw materials of Examples 1-3 and Comparative Example 1, the actual O content measured in the alloy ingots, and the composition of each element in the alloy ingots are shown in Table 1.

[0047] Table 1 Element composition and O content of Hastelloy X alloy in various embodiments and comparative examples

[0048] Test results Comparative Example 1 Example 1 Example 2 Example 3 C (wt%) 0.09 0.11 0.12 0.12 Cr(wt%) 21.8 21.9 22.2 22.0 Mo (wt%) 9 8.9 9.2 9.0 Fe(wt%) 19 18 18 19 B (wt%) 0.005 0.005 0.006 0.005 Al(wt%) 0.10 0.15 0.12 0.20 Ti(wt%) 0.03 0.03 0.03 0.03 Ni(wt%) margin margin margin margin Theoretical value of O content (ppm) 143 28 43 22 O content of finished product sample (ppm) 17 10 8 7

[0049] It can be seen from Table 1 that the O content in the finished product sample of the embodiment of the present invention is significantly reduced compared with that of the comparative example 1, and the oxygen content of the Hastelloy X alloy finished product can be effectively controlled within 10 ppm.

[0050] The smelting method of the present invention comprises: selecting raw materials, controlling the amount of O content introduced, and controlling the theoretical value of the O content of the ingredients within 50ppm; specifying the feeding order of the raw materials, preferentially adding raw materials of elements (Ni, Fe, Cr, Mo and 1 / 2C) with low affinity to O and graphite carbon for deoxidation, designing the adding method of graphite carbon, adding the graphite carbon in a covering manner, and performing a refining and purification after the alloy components are completely melted; after the raw materials are purified once, O is also removed, and then raw materials of elements (Al, Ti) with high affinity to O, intermediate materials of B and remaining 1 / 2C are added for secondary refining, and graphite carbon is added again during the secondary refining for further deoxidation; after the refining is completed, heating is stopped and the temperature is lowered to the alloy liquid surface for film formation, and argon is passed for pouring. The method effectively controls the oxygen content of the Hastelloy X alloy melted by vacuum induction melting within 10ppm by controlling the purity of the raw materials, optimizing the feeding order of the materials, the number of times and refining time of the alloy solution, and controlling the pouring temperature and speed. This method can be applied in industrial production while simplifying the operation process, and provides a feasible technical route for the preparation of Hastelloy X alloy materials with low O content.

[0051] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy, characterized in that: The following steps are involved: Step S1. Select raw materials: select raw materials with low O content according to the content requirements of each element in Hastelloy X alloy, and calculate the theoretical value of O content in the ingredients; Step S2. Vacuum induction melting: Add the prepared raw material elements with low affinity for O into a crucible, heat to above the melting point of the alloy under high vacuum, and refine after the alloy components are completely melted; Step S3. Refining: After the primary refining, an element with high affinity to O and an intermediate material of B are added for secondary refining, and molten steel is obtained after refining; Step S4. Pouring: After smelting, the temperature is lowered to the alloy liquid surface to form a film, and the molten steel is poured after passing argon gas. After pouring, the mold is removed to complete the preparation of the Hastelloy X alloy ingot.

2. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: The raw materials in step S1 include Ni, Fe, Cr, Mo, Al, Ti, C and nickel-boron alloy, and the theoretical value of the total content of O in the raw materials is controlled within 50 ppm.

3. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: In step S2, the raw material elements with low affinity to O include Ni, Fe, Cr, Mo and 1 / 2 of C; When the raw material C is added, the C particles are wrapped with Ni foil, and the raw material C covers the liquid surface of the molten steel when added; The vacuum degree should be kept within 8Pa during vacuum induction melting.

4. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: The elements with high affinity for O in step S3 include Al and Ti; the intermediate material of B is a nickel-boron alloy, and the remaining 1 / 2 of C is added together with the nickel-boron alloy. When the raw material C is added, Ni foil is used to wrap the C particles, and the raw material C covers the liquid surface of the molten steel when added.

5. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: During refining in step S3, the vacuum degree is maintained within 4 Pa, and a two-time refining method is adopted. The first refining temperature is 1550±10°C, the refining time is 40±5min, the second refining temperature is 1580±10°C, the refining time is 8±2min, and sufficient stirring is performed during the refining process.

6. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: In step S4, the casting mold tube adopts a carbon steel mold tube; the mold tube baking temperature is 300-400°C, and the insulation time is 4h; the pouring nozzle diameter is 16-20mm; and the pouring temperature is 1480-1500°C.

7. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: The oxygen content of the Hastelloy X alloy ingot in step S4 is ≤10ppm.

8. The vacuum induction melting method for reducing the oxygen content of a nickel-based high-temperature alloy according to claim 1, characterized in that: The Hastelloy X alloy ingot in step S4 comprises the following components: C 0.05-0.20wt%, Cr 20.5-23.0wt%, Mo8-10wt%, Fe 17-20wt%, B≤0.01wt%, Al≤0.5wt%, Ti≤0.15wt%, and the balance is Ni and unavoidable impurities.