Vacuum smelting method of nitrogen-containing cobalt-based alloy

Abstract

The invention discloses a vacuum smelting method of a nitrogen-containing cobalt-based alloy. The vacuum smelting method comprises the processes of smelting, refining and oxygen control, gas-phase nitrogen increase and pouring tapping. In the refining oxygen control process, the vacuum degree is kept to be 5 Pa or below, the refining temperature is controlled to be 80-100 DEG C above an alloy liquidus, and the relation between the refining time t and the smelting rated furnace capacity M is shown in the formula (A); the gas phase nitrogen increasing process comprises the steps that after refining oxygen control is finished, the temperature of alloy liquid is reduced to 40-60 DEG C above a liquidus, nitrogen is filled into a furnace for nitrogen increasing, electrolytic manganese is added after gas filling is finished, and the nitrogen filling pressure is obtained according to a formula (B); the relation between the nitrogen increasing time tN and the smelting rated furnace capacity M is shown in the formula (C). According to the method, the oxygen content in alloy liquid is remarkably reduced, rare earth burning loss is reduced, and the rare earth control precision is improved; the nitrogen content deviation is accurately controlled within + / -5%, the rare earth burning loss amount is stably controlled within the target content of 15%, and the alloy component uniformity and the mechanical property stability are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of vacuum smelting technology, and in particular to a vacuum smelting method for nitrogen-containing cobalt-based alloys. Background Technology

[0002] Cobalt-based alloys are widely used in high-end fields such as aero-engine blades, gas turbine components, nuclear reactor structural materials, and biomedical implants due to their excellent high-temperature strength, corrosion resistance, and creep resistance. However, with increasingly harsh service environments for equipment (such as ultra-high temperatures and highly corrosive media), the mechanical properties and stability of traditional cobalt-based alloys face greater challenges.

[0003] Introducing nitrogen as an interstitial atom into cobalt-based alloys can significantly improve the material's strength, hardness, and corrosion resistance, while reducing grain boundary brittleness. However, nitrogen has extremely low solubility in liquid cobalt (typically below 0.1 wt%) and is significantly affected by the melting atmosphere, temperature, and alloy composition (such as Cr and Mo content), making it difficult to precisely control the nitrogen content in traditional smelting processes. Excess nitrogen may cause porosity defects, while insufficient nitrogen content will fail to provide the strengthening effect, placing extremely high demands on process control.

[0004] Currently, nitrogen enrichment in production and testing mainly involves adding nitride alloys, such as chromium nitride and vanadium nitride intermediate alloys. However, this method is costly, prone to causing component segregation, and the nitrogen release process is difficult to control precisely. Existing technologies also struggle to achieve precise control of rare earth elements, primarily because the refining process cannot achieve ultra-low oxygen content control. Residual oxygen in molten steel and raw materials reacts violently with highly reactive rare earth elements, causing significant irreversible losses. Furthermore, improper timing of rare earth element addition can lead to premature oxidation or delayed diffusion, ultimately resulting in low and fluctuating rare earth yields, making precise control impossible. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a vacuum smelting method for nitrogen-containing cobalt-based alloys that can precisely control the nitrogen content.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes smelting, refining and oxygen control, gas phase nitrogen enhancement and casting and tapping processes;

[0007] The gas-phase nitrogen enrichment process is as follows: After the refining and oxygen control are completed, the temperature of the alloy liquid is reduced to 40-60°C above the liquidus line, and nitrogen gas at a certain pressure is introduced into the furnace for nitrogen enrichment. After the gas filling is completed, electrolytic manganese is added. The nitrogen filling pressure is obtained according to formula (B).

[0008]

[0009] In the formula: P N2 Nitrogen purging pressure, Pa; N 目标The target nitrogen content (%) for smelting cobalt-based alloys;

[0010] Nitrogen enrichment time t N The relationship between the smelting rated furnace volume M and the smelting rated furnace volume is shown in equation (C);

[0011] t N =2.1×M 1 / 2 (C);

[0012] In the formula: t N , represents nitrogen addition time, in minutes; M, represents the rated furnace volume for smelting, in kg.

[0013] Furthermore, the refining oxygen control process involves maintaining a vacuum level of 5 Pa or below, controlling the refining temperature at 80–100°C above the alloy liquidus line, and a refining time of t. 精 The relationship between the smelting rated furnace volume M and the smelting rated furnace volume is shown in equation (A);

[0014] t 精 =1.4×M 1 / 2 (A);

[0015] In the formula: t 精 , where M is the refining time (min); M is the rated furnace volume for smelting (kg).

[0016] Furthermore, in the gas-phase nitrogen enrichment process, lanthanum is added 2-3 minutes before the nitrogen enrichment ends.

[0017] Furthermore, the chemical composition and mass percentage of the nitrogen-containing cobalt-based alloy are as follows: C 0.05-0.15%, Mn 1-2%, Cr 19-21%, W 14-16%, Ni 9-11%, La 0.02-0.05%, Fe≤3%, Si≤0.4%, N 0.3-0.4%, with the balance being Co and unavoidable impurities.

[0018] The beneficial effects of adopting the above technical solution are as follows: This invention achieves precise control of nitrogen content deviation in nitrogen-containing cobalt-based alloys within ±5% through a gas-phase nitrogen enrichment pressure formula and time model, significantly improving the uniformity of alloy composition and the stability of mechanical properties; the gas-phase nitrogen enrichment method not only ensures low control of impurities such as oxygen and sulfur in the solution, but also achieves precise control of nitrogen and rare earth content in the vacuum casting of the cobalt-based alloy; at the same time, through the synergistic effect of effective deoxidation and precise nitrogen enrichment, it solves the problem of large fluctuations in nitrogen content in traditional processes, providing reliable technical support for the high-performance material needs in aerospace, energy equipment, biomedicine and other fields.

[0019] This invention optimizes vacuum smelting process parameters by controlling the vacuum degree, refining temperature, and refining time during the oxygen control process. This fully utilizes the carbon-oxygen reaction to significantly reduce the oxygen content in the alloy liquid, thereby reducing rare earth burn-off and improving the control precision of rare earth in subsequent processes. Combined with the control of the timing of lanthanum addition, the rare earth burn-off can be stably controlled within 15% of the smelting target content, significantly improving the uniformity of alloy composition and the stability of mechanical properties. This achieves precise control of the rare earth content in the vacuum casting of the cobalt-based alloy, solving the problem of low rare earth yield in traditional processes.

[0020] The smelting process of this invention is simple to operate and overcomes the technical challenge of precise control of nitrogen and rare earth elements in nitrogen-containing cobalt-based alloys. It achieves breakthroughs in cost control, compositional homogeneity, and process stability. It not only provides a reliable path for the industrialized and stable production of high-performance cobalt-based alloys, but also plays an important role in promoting my country's independent supply of high-end materials, upgrading of equipment manufacturing industry, and sustainable development strategy. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to specific embodiments.

[0022] The vacuum smelting method for this nitrogen-containing cobalt-based alloy includes furnace charging, melting, refining and oxygen control, vapor-phase nitrogen enrichment, and casting and tapping processes, each of which is described below:

[0023] (1) Charging process: A vacuum induction furnace is used for smelting. First, the graphite required for smelting is evenly spread at the bottom of the crucible. Then, chromium, tungsten, nickel, and cobalt are placed into the crucible, while manganese and lanthanum are placed in secondary charging hoppers. The metal materials are mainly industrial pure materials, using electrolytic cobalt plates, electrolytic nickel plates, metallic chromium, graphite, electrolytic manganese, tungsten bars, and metallic lanthanum. The total weight of the raw materials added to the furnace should be controlled within ±10% of the rated furnace volume M of the vacuum induction furnace. The relationship between the height h and the inner diameter d (diameter) of the crucible is 1.5 ≤ h / d ≤ 1.8.

[0024] (2) Refining and oxygen control process: Maintain vacuum at 5 Pa or below, control refining temperature at 80-100℃ above the alloy liquidus line, and refining time t 精 The relationship between the rated furnace volume M of the vacuum induction furnace and the vacuum induction furnace is shown in equation (A);

[0025] t 精 =1.4×M 1 / 2 (A);

[0026] In the formula: t 精 , where M is the refining time, i.e., the total oxygen control time for refining, in min; M is the rated furnace volume of the vacuum induction furnace, in kg.

[0027] This refining and oxygen control process can fully utilize the carbon-oxygen reaction to significantly reduce the oxygen content in the solution, thereby improving the control precision of rare earth elements in subsequent processes; the refining and oxygen control process reduces the oxygen content to ≤0.003%.

[0028] (3) Gas phase nitrogen enrichment process: After the refining and oxygen control are completed, the temperature of the alloy liquid is reduced to 40-60°C above the liquidus line, and nitrogen gas at a certain pressure is introduced into the furnace for nitrogen enrichment. Electrolytic manganese is added after the gas filling is completed, and lanthanum is added 2-3 minutes before the nitrogen enrichment is completed. The nitrogen filling pressure is obtained according to formula (B).

[0029]

[0030] In the formula: P N2 Nitrogen purging pressure, Pa; N 目标 The target nitrogen content (%) for smelting nitrogen-containing cobalt-based alloys;

[0031] Nitrogen enrichment time t N The relationship between the smelting rated furnace volume M and the smelting rated furnace volume is shown in equation (C);

[0032] t N =2.1×M 1 / 2 (C).

[0033] In the formula: t N The nitrogen-increasing time is the time from the end of nitrogen charging to the start of casting and tapping, in minutes; M is the rated furnace volume for smelting, in kilograms.

[0034] (4) Casting process: After the gas phase nitrogen addition ends, the steel is cast and tapped under electric current.

[0035] Examples 1-4: A vacuum induction furnace with a rated capacity of 500 kg was used to smelt nitrogen-containing cobalt-based alloy materials. The nitrogen control target was 0.35% (wt), the rare earth lanthanum control target was 0.04% (wt), the crucible inner diameter d = 440 mm, the height h = 660 mm, and h / d = 1.5.

[0036] (1) Loading the furnace: First, spread the graphite required for smelting evenly on the bottom of the crucible, and then put chromium, tungsten, nickel and cobalt into the crucible. Manganese and lanthanum are placed in the secondary feeding hopper respectively. The metal material is mainly industrial pure material, and electrolytic cobalt plate, electrolytic nickel plate, metallic chromium, graphite, electrolytic manganese, tungsten bar and metallic lanthanum are selected.

[0037] (2) Melting: Vacuuming and heating with electricity until all the alloy material in the crucible is melted;

[0038] (3) Refining and oxygen control: Maintain the vacuum degree below 5 Pa, control the refining temperature at 80-100℃ above the liquidus line, and the refining time t 精 =1.4×M 1 / 2 =1.4 × 500 1 / 2 = 31.3 min;

[0039] (4) Gas-phase nitrogen addition: After refining and oxygen control are completed, the solution temperature is lowered to 40-60°C above the liquidus line, and nitrogen gas is introduced into the furnace at a certain pressure. Electrolytic manganese is added immediately after the gas introduction is completed. The nitrogen addition pressure is:

[0040]

[0041] Nitrogen enrichment time is: t N =2.1×M 1 / 2 =2.1 × 500 1 / 2 =47.0 min, add rare earth lanthanum 2-3 min before the end of gas phase nitrogen enhancement;

[0042] (5) Casting and tapping: After the gas phase nitrogen enrichment is completed, the steel is cast and tapped under electric current.

[0043] The parameter control of each stage of the smelting process is shown in Table 1. After demolding, the ingot was sliced ​​150 mm from the bottom. Two samples were taken from the center, R / 2 and edge of the cross section for ICP chemical composition analysis of La and oxygen and nitrogen analysis, respectively. The results are shown in Table 2.

[0044] Table 1: Parameter Control at Each Stage of the Smelting Process in Examples 1-4

[0045]

[0046] Note: TL is the liquidus temperature of this steel grade.

[0047] Table 2: Rare earth and oxygen / nitrogen content (wt%) after vacuum smelting in Examples 1-4

[0048]

[0049]

[0050] Through tissue observation and chemical composition analysis, the nitrogen enrichment results of the alloy materials obtained in Examples 1-4 were accurate, with small deviations in nitrogen content and uniform rare earth composition.

[0051] Examples 5-8: The above-mentioned nitrogen-containing cobalt-based alloy material was smelted using a vacuum induction furnace with a rated capacity of 1500 kg. The nitrogen content was controlled at 0.4% (wt), the rare earth lanthanum content was controlled at 0.02%, the crucible inner diameter d = 650 mm, the height h = 1170 mm, and the h / d = 1.8.

[0052] (1) Loading the furnace: First, spread the graphite required for smelting evenly on the bottom of the crucible, and then put chromium, tungsten, nickel and cobalt into the crucible. Manganese and lanthanum are placed in the secondary feeding hopper respectively. The metal material is mainly industrial pure material, and electrolytic cobalt plate, electrolytic nickel plate, metallic chromium, graphite, electrolytic manganese, tungsten bar and metallic lanthanum are selected.

[0053] (2) Melting: Vacuuming and heating with electricity until all the alloy material in the crucible is melted;

[0054] (3) Refining and oxygen control: Maintain the vacuum degree below 5 Pa, control the refining temperature at 80-100℃ above the liquidus line, and the refining time t 精 =1.4×M 1 / 2 =1.4 × 1500 1 / 2 =54.2min;

[0055] (4) Gas-phase nitrogen addition: After refining and oxygen control are completed, the solution temperature is lowered to 40-60°C above the liquidus line, and nitrogen gas is introduced into the furnace at a certain pressure. Electrolytic manganese is added immediately after the gas introduction is completed. The nitrogen addition pressure is:

[0056]

[0057] Nitrogen enrichment time is: t N =2.1×M 1 / 2 =2.1 × 1500 1 / 2 =81.3min, add rare earth lanthanum 2-3min before the end of gas phase nitrogen enhancement;

[0058] (5) Casting and tapping: After the gas phase nitrogen enrichment is completed, the steel is cast and tapped under electric current.

[0059] The parameter control of each stage of the smelting process is shown in Table 3. After demolding, the ingot was sliced ​​at 150 mm from the bottom. Two samples were taken from the center, R / 2 and edge of the cross section for ICP chemical composition analysis of La and oxygen and nitrogen analysis, respectively. The results are shown in Table 4.

[0060] Table 3: Parameter Control at Each Stage of the Smelting Process in Examples 5-8

[0061]

[0062] Note: TL is the liquidus temperature of this steel grade.

[0063] Table 4: Rare earth and oxygen / nitrogen content (wt%) after vacuum smelting in Examples 5-8

[0064]

[0065] Through tissue observation and chemical composition analysis, the nitrogen enrichment results of the alloy materials obtained in Examples 5-8 were accurate, with small deviations in nitrogen content and uniform rare earth composition.

[0066] Examples 9-12: The above-mentioned nitrogen-containing cobalt-based alloy material was smelted using a vacuum induction furnace with a rated capacity of 300 kg. The nitrogen content was controlled at 0.3% (wt), the rare earth lanthanum content was controlled at 0.05%, the crucible inner diameter d = 360 mm, the height h = 580 mm, and the h / d = 1.61.

[0067] (1) Loading the furnace: First, spread the graphite required for smelting evenly on the bottom of the crucible, and then put chromium, tungsten, nickel and cobalt into the crucible. Manganese and lanthanum are placed in the secondary feeding hopper respectively. The metal material is mainly industrial pure material, and electrolytic cobalt plate, electrolytic nickel plate, metallic chromium, graphite, electrolytic manganese, tungsten bar and metallic lanthanum are selected.

[0068] (2) Melting: Vacuuming and heating with electricity until all the alloy material in the crucible is melted;

[0069] (3) Refining and oxygen control: Maintain the vacuum degree below 5 Pa, control the refining temperature at 80-100℃ above the liquidus line, and the refining time t 精 =1.4×M 1 / 2 =1.4 × 300 1 / 2 =24.2min;

[0070] (4) Gas-phase nitrogen addition: After refining and oxygen control are completed, the solution temperature is lowered to 40-60°C above the liquidus line, and nitrogen gas is introduced into the furnace at a certain pressure. Electrolytic manganese is added immediately after the gas introduction is completed. The nitrogen addition pressure is:

[0071]

[0072] Nitrogen enrichment time is: t N =2.1×M 1 / 2 =2.1 × 300 1 / 2 =36.4 min, add rare earth lanthanum 2-3 min before the end of gas phase nitrogen enhancement;

[0073] (5) Casting and tapping: After the gas phase nitrogen enrichment is completed, the steel is cast and tapped under electric current.

[0074] The parameter control of each stage of the smelting process is shown in Table 5. After demolding, the ingot was sliced ​​at 150 mm from the bottom. Two samples were taken from the center, R / 2 and edge of the cross section for ICP chemical composition analysis of La and oxygen and nitrogen analysis, respectively. The results are shown in Table 6.

[0075] Table 5: Parameter Control at Each Stage of the Smelting Process in Examples 9-12

[0076]

[0077] Note: TL is the liquidus temperature of this steel grade.

[0078] Table 6: Rare earth and oxygen / nitrogen content (wt%) after vacuum smelting in Examples 9-12

[0079]

[0080]

[0081] Through tissue observation and chemical composition analysis, the nitrogen enrichment results of the alloy materials obtained in Examples 9-12 were accurate, with small deviations in nitrogen content and uniform rare earth composition.

Claims

1. A vacuum smelting method for a nitrogen-containing cobalt-based alloy, characterized in that: This includes the processes of smelting, refining with oxygen control, vapor-phase nitrogen enrichment, and casting and tapping. The gas-phase nitrogen enrichment process is as follows: After the refining and oxygen control are completed, the temperature of the alloy liquid is reduced to 40-60°C above the liquidus line, and nitrogen gas at a certain pressure is introduced into the furnace for nitrogen enrichment. After the gas filling is completed, electrolytic manganese is added. The nitrogen filling pressure is obtained according to formula (B). In the formula: P N2 Nitrogen purging pressure, Pa; N 目标 The target nitrogen content (%) for smelting cobalt-based alloys; Nitrogen enrichment time t N The relationship between the smelting rated furnace volume M and the smelting rated furnace volume is shown in equation (C); t N =2.1×M 1 / 2 (C); In the formula: t N , represents nitrogen addition time, in minutes; M, represents the rated furnace volume for smelting, in kg.

2. The vacuum smelting method for a nitrogen-containing cobalt-based alloy according to claim 1, characterized in that: The refining oxygen control process involves maintaining a vacuum level of 5 Pa or below, controlling the refining temperature at 80–100°C above the alloy liquidus line, and a refining time of t. 精 The relationship between the smelting rated furnace volume M and the smelting rated furnace volume is shown in equation (A); t 精 =1.4×M 1 / 2 (A); In the formula: t 精 , where M is the refining time (min); M is the rated furnace volume for smelting (kg).

3. The vacuum smelting method for a nitrogen-containing cobalt-based alloy according to claim 1, characterized in that: In the gas-phase nitrogen enrichment process, lanthanum is added 2-3 minutes before the nitrogen enrichment ends.

4. A vacuum smelting method for a nitrogen-containing cobalt-based alloy according to claim 1, 2, or 3, characterized in that, The chemical composition and mass percentage of the nitrogen-containing cobalt-based alloy are as follows: C 0.05-0.15%, Mn 1-2%, Cr 19-21%, W 14-16%, Ni 9-11%, La 0.02-0.05%, Fe≤3%, Si≤0.4%, N 0.3-0.4%, with the balance being Co and unavoidable impurities.

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