A nuclear power plant pressure vessel steel powder and a method of making the same

Abstract

This invention relates to the field of metal additive manufacturing, and more particularly to a pressure vessel steel powder for nuclear power plants and its preparation method. The pressure vessel steel powder comprises the following components: C: ≤0.2wt%; Si: 0.1-0.3wt%; Mn: 1.15-1.60wt%; S: ≤0.005wt%; Cr: ≤0.25wt%; Ni: 0.5-0.8wt%; P: ≤0.008wt%; Mo: 0.43-0.57wt%; V: ≤0.01wt%; Cu: ≤0.08wt%; Al: ≤0.04wt%; Co: ≤0.03wt%; with the balance being iron. This invention achieves precise control of the powder's chemical composition through targeted process design and impurity control strategies, ensuring that all performance indicators fully comply with the requirements of the "Design and Construction Rules for Mechanical Components of Pressurized Water Reactor Nuclear Island" standard.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing, and more particularly to a metal powder for pressure vessel steel used in nuclear power plants and its preparation method. Background Technology

[0002] Metal powder, as the core raw material of additive manufacturing (AM, also known as 3D printing) technology, directly determines the mechanical properties, corrosion resistance, and long-term service safety of additively manufactured parts through key performance indicators such as chemical composition uniformity, particle size distribution range, sphericity, purity, and flowability. The nuclear power industry places extreme demands on the reliability, stability, and ability to withstand harsh operating conditions of component materials; therefore, the quality control of metal powder has become a core element in ensuring the long-term safe and stable operation of nuclear power equipment. Additive manufacturing technology, with its advantages of near-net-shape forming, high design freedom, high material utilization, and short production cycle, has been gradually applied to the manufacturing and in-service repair of key components of nuclear power equipment. This technology enables the integrated molding of complex structural components, effectively overcoming the technical bottlenecks of traditional forging and casting processes in the machining of complex structures, and significantly reducing production costs and R&D cycles. Among these, nuclear power pressure vessels, as core pressure-bearing components of nuclear power equipment, operate under extreme conditions of high temperature, high pressure, and strong radiation for extended periods, placing extremely high demands on the strength, toughness, corrosion resistance, and weld compatibility of materials. 16MND5 steel is a commonly used low-alloy high-strength steel for nuclear power pressure vessels. When its components are manufactured using additive manufacturing technology, problems such as uneven microstructure and welding defects that are easily caused by traditional processes can be effectively avoided, significantly improving the structural integrity and long-term service reliability of the components.

[0003] Existing patented metal powder preparation technologies have significant limitations: their design focuses primarily on optimizing the proportions of key alloying elements, lacking targeted technical designs for controlling harmful impurity elements such as phosphorus (P) and sulfur (S). These harmful impurity elements can easily lead to fatal defects such as intergranular corrosion and hot cracking in components under extreme operating conditions. This directly results in existing powder products failing to meet the stringent control requirements for P and S element content in the Nuclear Power Industry's "Code for Design and Construction of Mechanical Components in Pressurized Water Reactors" (RCCM) standard, thus limiting their engineering application in the manufacturing of critical load-bearing components for nuclear power plants. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a pressure vessel steel metal powder for nuclear power plants and its preparation method. Through targeted process design and impurity control strategies, the chemical composition of the powder can be precisely controlled, and its various performance indicators fully meet the requirements of the "Design and Construction Rules for Mechanical Components of Pressurized Water Reactor Nuclear Island" standard.

[0005] This invention provides a method for preparing pressure vessel steel powder for nuclear power plants, comprising the following steps: Step 1: Pre-treat the raw materials to remove surface impurities and moisture; Step 2: According to the formula, various raw materials are smelted, atomized and screened in a vacuum induction melting furnace; during the smelting process, the smelting temperature is controlled at 1560~1600℃ and held for 6~12 minutes to ensure that the raw materials are completely melted and the composition is uniform. The furnace exit temperature is controlled at 1600~1640℃; CaO-Al2O3 refining slag is added to the molten steel to adsorb and remove P and S impurities by the interfacial reaction between the refining slag and the molten steel. Step 3: Powder post-processing to obtain nuclear power pressure vessel steel metal powder; The pressure vessel steel powder for nuclear power plants comprises the following components: C: ≤0.2wt%; Si: 0.1-0.3wt%; Mn: 1.15-1.60wt%; S: ≤0.005 wt%; Cr: ≤0.25 wt%; Ni: 0.5-0.8wt%; P: ≤0.008 wt%; Mo: 0.43-0.57 wt%; V: ≤0.01wt%; Cu: ≤0.08 wt%; Al: ≤0.04 wt%; Co: ≤0.03 wt%; The balance is iron.

[0006] As a further technical solution, the pretreatment includes rust removal, degreasing and drying.

[0007] As a further technical solution, step 3 specifically includes: Step 2-1: Place the proportioned raw materials into a vacuum induction melting furnace, using a corundum crucible. Step 2-2: Perform gas purging on the vacuum induction melting furnace using a vacuum pump; Steps 2-3: Melting; The smelting temperature is controlled at 1560~1600℃ and held for 6~12 minutes to ensure that the raw materials are completely melted and the composition is uniform. The tapping temperature is controlled at 1610~1630℃. CaO-Al2O3 refining slag is added to the molten steel at a rate of 2%~3% of the molten steel mass. The interface reaction between the refining slag and the molten steel is used to adsorb and remove P and S impurities. Simultaneously, argon gas with a purity ≥99.999% is introduced for bottom blowing and stirring, with the stirring intensity controlled at 0.5-1.0 L / (min·kg) to promote full contact between the refining slag and the molten steel. The refining time is 30-40 minutes. After refining, alloy additives are added to the molten steel to adjust the composition of the molten steel to the standard range of 16MND5 steel. Steps 2-4: Perform atomization treatment; Steps 2-5: After the raw powder obtained by atomization is cooled, it is first passed through a 50-mesh ultrasonic vibrating sieve at a sieve speed of 60~100kg / min; then it is further subdivided under an argon atmosphere using a two-stage gas-protected airflow classifier.

[0008] As a further technical solution, in step 2-2, the vacuum level is ensured to be less than 5*10. -3 Pa; the power of the large crucible during vacuuming should not exceed 50kW; initially, the intermediate ladle power is increased to 5kW and held for 5-8 minutes, the intermediate ladle power is increased to 10kW and held for 5-8 minutes, the intermediate ladle power is increased to 10-20kW until atomization ends; pure argon is used for gas replacement, and the pressure gauge inside the furnace is below 0.02MPa after replacement.

[0009] As a further technical solution, the mass ratio of CaO to Al2O3 in the CaO-Al2O3 refining slag is 3~5:1.

[0010] As a further technical solution, in steps 2-4, the atomizing gas is pure nitrogen, and the atomization pressure is 3.5~4.5MPa; the initial atomization pressure during the atomization process is 2.0MPa, which is increased to a maximum atomization pressure of 4.3~4.72MPa within 4~10 minutes, and the maximum argon flow rate is 1100~1300m³ / h. 3 / h, control the pouring frequency and speed when pouring liquid, keep the liquid level in the intermediate bath at 50~80% height, and keep the intermediate bath continuously warm, with a temperature range of 1630~1650℃.

[0011] As a further technical solution, in steps 2-5, the main parameters of the airflow stage are as follows: feed frequency is 6~10Hz, primary classifier frequency is 2~5Hz, secondary classifier frequency is 13~21Hz, fan frequency is 40~45Hz, air pressure is 4~7kPa, and oxygen content is ≤5%.

[0012] As a further technical solution, in steps 2-4, Atomization is achieved using VIGA atomizing equipment, with a guide tube made of corundum and a reverse-conical zirconia nozzle with a nozzle diameter of 4.0~4.5mm.

[0013] As a further technical solution, step 3 specifically involves: vacuum drying the screened powder at a temperature of 120~150℃ and a holding time of 4~6h to remove the moisture and trace gases adsorbed by the powder. The packaging uses inert gas to protect the powder from oxidation during storage and transportation.

[0014] This invention provides a pressure vessel steel powder for nuclear power plants, which is prepared by the method described above.

[0015] Compared with the prior art, the nuclear power pressure vessel steel metal powder and its preparation method of the present invention have the following beneficial effects: (1) Through precise ingredient calculation, strict raw material control and selection, and the synergistic effect of vacuum refining and gas atomization powdering, the chemical composition of the prepared 16MND5 steel powder fully meets the requirements of the "Design and Construction Rules for Mechanical Components of Pressurized Water Reactor Nuclear Island" standard. In particular, the P content is controlled at ≤0.008% and the S content is controlled at ≤0.005%, and the content error of key elements is ≤±0.05%, which meets the stringent requirements of nuclear power pressure vessels for material composition stability.

[0016] (2) Refining slag can be recycled, reducing waste emissions and conforming to the development concept of green manufacturing. Attached Figure Description

[0017] Figure 1 The image shows the scanning electron microscope (SEM) morphology of the 16MND5 steel powder prepared according to the present invention.

[0018] Figure 2 The graph shows the particle size distribution of the 16MND5 steel powder prepared according to the present invention.

[0019] Figure 2 In the diagram, the red line represents the frequency distribution, and the blue line represents the cumulative distribution. Detailed Implementation

[0020] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0021] Embodiments of the present invention disclose a pressure vessel steel powder for nuclear power plants, comprising the following components: C: ≤0.2wt% Si: 0.1-0.3wt% Mn: 1.15-1.60 wt% S: ≤0.005wt% Cr: ≤0.25wt%; Ni: 0.5-0.8wt% P: ≤0.008wt% Mo: 0.43-0.57 wt% V: ≤0.01wt%; Cu: ≤0.08wt% Al: ≤0.04wt% Co: ≤0.03wt% The balance is iron.

[0022] The present invention discloses a method for preparing pressure vessel steel powder for nuclear power plants, comprising the following steps: Step 1: Pre-treat the raw materials to remove surface impurities and moisture. The raw materials include: high-purity industrial pure iron with P content ≤0.01% and S content ≤0.008%, electrolytic manganese, electrolytic nickel, molybdenum bars, and silicon blocks.

[0023] The pretreatment includes rust removal, degreasing, and drying.

[0024] Step 2: Melt, atomize, and sieve the various raw materials in a vacuum induction melting furnace according to the formula. Specifically, it includes: Step 2-1: Place the proportioned raw materials into a vacuum induction melting furnace, using a corundum crucible.

[0025] Step 2-2: Perform gas replacement on the vacuum induction melting furnace using a vacuum pump.

[0026] Ensure a vacuum level of less than 5 × 10 -3 Pa; the power of the large crucible during vacuuming should not exceed 50kW; initially, the intermediate ladle power is increased to 5kW and held for 5-8 minutes, the intermediate ladle power is increased to 10kW and held for 5-8 minutes, the intermediate ladle power is increased to 10-20kW until atomization ends; pure nitrogen is used for gas replacement, and the pressure gauge inside the furnace is below 0.02MPa after replacement.

[0027] Steps 2-3: Melting The smelting temperature is controlled at 1560~1600℃, and held for 6~12 minutes to ensure complete melting and uniform composition of the raw materials. The tapping temperature is controlled at 1600~1640℃. The amount of CaO-Al2O3 refining slag added is 2%~3% of the mass of the molten steel after smelting. In this example, the proportion is precisely calculated based on the actual mass of the molten steel to ensure the adsorption effect of P and S impurities. The mass ratio of CaO to Al2O3 in the CaO-Al2O3 refining slag is 3:1.

[0028] Simultaneously, nitrogen gas with a purity ≥99.999% is introduced for bottom blowing and stirring, with the stirring intensity controlled at 0.5~1.0 L / (min·kg) to promote full contact between the refining slag and the molten steel. The refining time is 30~40 minutes. After refining, a trace amount of alloying agent is added to the molten steel to precisely adjust the composition of the molten steel to the standard range of 16MND5 steel.

[0029] Steps 2-4: Perform atomization treatment Atomization is achieved using a VIGA atomizing device with a corundum guide tube and a reverse-conical zirconia nozzle with a nozzle diameter of 4.0~4.5mm. The atomizing gas is pure nitrogen with a purity of 99.999%, and the atomization pressure is 3.5~4.5MPa. The initial atomization pressure is 2.0MPa, increasing to a maximum atomization pressure of 4.3~4.72MPa within 4~10 minutes, with a maximum nitrogen flow rate of 1200m³ / h. 3 / h, control the pouring frequency and speed when pouring liquid, keep the liquid level in the intermediate bath at 50~80% height, and keep the intermediate bath continuously warm, with a temperature range of 1630~1650℃.

[0030] Steps 2-5: Screening After the raw powder obtained by atomization is cooled, it is first screened by a 50-mesh ultrasonic vibrating sieve at a screening speed of 60~100kg / min; then it is further subdivided in a nitrogen atmosphere using a two-stage gas-protected airflow classifier.

[0031] The main parameters of the airflow stage are as follows: feed frequency is 6~10Hz, primary classifier frequency is 2~5Hz, secondary classifier frequency is 13~21Hz, fan frequency is 40~45Hz, air pressure is 4~7KPa, and oxygen content is ≤5%.

[0032] Step 3: Powder Post-processing The screened powder is subjected to vacuum drying at a temperature of 120~150℃ for 4~6 hours to remove the moisture and trace gases adsorbed by the powder.

[0033] The dried powder underwent key performance testing, including the following indicators: Table 1 Requirements for Powder Performance Testing All performance indicators meet the requirements for additive manufacturing metal powders for nuclear power, and after passing the test, they are packaged with inert gas protection.

[0034] The packaging uses inert gas to protect the powder from oxidation during storage and transportation.

[0035] To further understand the present invention, the following detailed description of the nuclear power pressure vessel steel powder and its preparation method provided by the present invention is provided in conjunction with embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0036] Example 1 The RCCM standard requirements for the chemical composition of 16MND5 material are confirmed as shown in Table 2.

[0037] Table 2 Technical requirements for chemical composition of 16MND5 (wt%) Confirm raw material ratio The vacuum melting / VIGA gas atomization process yielded an alloy element recovery rate of 98% and an overall powder recovery rate of 55%. The required raw materials and proportions were determined as follows: 180.12 kg of high-purity industrial pure iron, 2.43 kg of electrolytic manganese, 0.63 kg of silicon ingots, 1.35 kg of electrolytic nickel, and 1 kg of molybdenum bars. The high-purity industrial pure iron contained 0.008% P and 0.006% S; the electrolytic manganese had a purity of 99.93%; the silicon ingots contained 77% Si, 0.003% P, and 0.002% S; the electrolytic nickel had a purity of 99.92%; the molybdenum bars had a purity of 99.97%; and the remaining components were silicon dioxide and trace amounts of metal oxides (Al₂O₃ / CaO) and other inert impurities. These impurities are removed during the melting process with the refining slag and will not enter the molten steel or the final powder product. Furthermore, there were no other harmful metal impurities, meeting the purity requirements for raw materials used in nuclear power.

[0038] All raw materials are dried at 120℃ for 3 hours after rust and oil removal.

[0039] Powder preparation process Place the above ingredients into the crucible of the vacuum induction melting furnace. The prepared raw materials are then placed into the vacuum induction melting furnace; the crucible is a corundum crucible.

[0040] Vacuuming and purging. Ensure the vacuum level is less than 50 Pa; during vacuuming, the power of the large crucible is 48 kW; initially, the power of the intermediate ladle is increased to 5 kW and held for 5-8 minutes, the power of the intermediate ladle is increased to 10 kW and held for 6 minutes, and the power of the intermediate ladle is increased to 18 kW until atomization ends; pure nitrogen is used for gas purging, and the pressure gauge inside the furnace is below 0.02 MPa after purging.

[0041] Melting. Place the raw materials into a vacuum induction melting furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 Pa, the melting temperature is controlled at 1580℃, and the temperature is held for 10 minutes to ensure that the raw materials are completely melted and the composition is uniform. 2 kg of CaO-Al2O3 refining slag is added, and nitrogen is introduced for bottom blowing and stirring. The stirring intensity is 0.8 L / (min·kg). The furnace temperature is controlled at 1620℃ after refining for 35 minutes.

[0042] Atomization. Atomization was performed using a VIGA atomizer with a corundum guide tube and a 4.2mm diameter reverse-conical zirconia nozzle. The atomizing gas was pure nitrogen with a purity of 99.999%, and the atomization pressure was 4.5 MPa. The initial atomization pressure was 2.0 MPa, increasing to the maximum atomization pressure of 4.5 MPa within 4 minutes, with a maximum nitrogen flow rate of 1200 m³ / h. 3 / h, when pouring liquid, it is required to control the pouring frequency and pouring speed, keep the liquid level in the intermediate bath at 65% height, and keep the intermediate bath continuously warm, with a temperature range of 1640℃.

[0043] Sieving. After cooling for more than 2 hours, the raw powder obtained from atomization is first sieved using a 50-mesh ultrasonic vibrating sieve at a sieving speed of 80 kg / min. Then, a two-stage air classifier under nitrogen atmosphere is used for further subdivision. The main parameters of the air classifier are as follows: feed frequency 8 Hz, primary classifier frequency 3 Hz, secondary classifier frequency 17 Hz, fan frequency 43 Hz, air pressure 5 kPa, and oxygen content ≤ 5%.

[0044] Powder post-processing The screened powder was subjected to vacuum drying at a temperature of 135℃ for 5 hours to remove adsorbed moisture and trace gases.

[0045] The packaging uses inert gas to protect the powder from oxidation during storage and transportation.

[0046] Case Results: (1) Powder performance test results (2) Results of chemical composition analysis (wt%) Example 2 The RCCM standard requirements for the chemical composition of 16MND5 material are confirmed as shown in Table 2.

[0047] Confirm raw material ratio The vacuum melting / VIGA gas atomization process yielded an alloy element recovery rate of 98% and an overall powder recovery rate of 55%. The required raw materials and proportions were determined as follows: 1570.73 kg of high-purity industrial pure iron, 285.93 kg of electrolytic manganese, 84.98 kg of silicon ingots, 141.55 kg of electrolytic nickel, and 106.05 kg of molybdenum bars. The high-purity industrial pure iron contained 0.009% P and 0.007% S; the electrolytic manganese had a purity of 99.93%; the silicon ingots contained 76% Si, 0.004% P, and 0.002% S; the electrolytic nickel had a purity of 99.92%; the molybdenum bars had a purity of 99.97%; and the remaining components were silicon dioxide and trace amounts of metal oxides (Al₂O₃ / CaO) and other inert impurities. These impurities are removed during the melting process with the refining slag and will not enter the molten steel or the final powder product. Furthermore, there were no other harmful metal impurities, meeting the purity requirements for raw materials used in nuclear power.

[0048] All raw materials are dried at 120℃ for 3 hours after rust and oil removal.

[0049] Powder preparation process Place the above ingredients into the crucible of the vacuum induction melting furnace. The prepared raw materials are then placed into the vacuum induction melting furnace; the crucible is a corundum crucible.

[0050] Vacuuming and purging. Ensure the vacuum level is less than 50 Pa; during vacuuming, the power of the large crucible is 48 kW; initially, the power of the intermediate ladle is increased to 5 kW and held for 5-8 minutes, the power of the intermediate ladle is increased to 10 kW and held for 6 minutes, and the power of the intermediate ladle is increased to 18 kW until atomization ends; pure nitrogen is used for gas purging, and the pressure gauge inside the furnace is below 0.02 MPa after purging.

[0051] Melting. Place the raw materials into a vacuum induction melting furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 Pa, the melting temperature is controlled at 1580℃, and the temperature is held for 10 minutes to ensure that the raw materials are completely melted and the composition is uniform. 25 kg of CaO-Al2O3 refining slag is added, and nitrogen is introduced for bottom blowing and stirring. The stirring intensity is 0.8 L / (min·kg). The furnace temperature is controlled at 1620℃ after refining for 35 minutes.

[0052] Atomization. Atomization is performed using a VIGA atomizer with a corundum guide tube and a 4.2mm diameter reverse-conical zirconia nozzle. The atomizing gas is pure nitrogen with a purity of 99.999%, and the atomization pressure is 4.5MPa. The initial atomization pressure is 2.0MPa, increasing to the maximum atomization pressure of 4.5MPa within 4 minutes, with a maximum nitrogen flow rate of 1200m³ / h. 3 / h, when pouring liquid, it is required to control the pouring frequency and pouring speed, keep the liquid level in the intermediate bath at 65% height, and keep the intermediate bath continuously warm, with a temperature range of 1640℃.

[0053] Sieving. After cooling for 3 hours, the raw powder obtained from atomization is first sieved using a 50-mesh ultrasonic vibrating sieve at a sieving speed of 80 kg / min. Then, a two-stage air classifier under nitrogen atmosphere is used for further subdivision. The main parameters of the air classifier are as follows: feed frequency 8 Hz, primary classifier frequency 3 Hz, secondary classifier frequency 17 Hz, fan frequency 43 Hz, air pressure 5 kPa, and oxygen content ≤ 5%.

[0054] Powder post-processing The screened powder was subjected to vacuum drying at a temperature of 135℃ for 5 hours to remove adsorbed moisture and trace gases.

[0055] Case Results (1) Powder performance test results (2) Results of chemical composition analysis (wt%) The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing pressure vessel steel powder for nuclear power plants, characterized in that, Includes the following steps: Step 1: Pre-treat the raw materials to remove surface impurities and moisture; Step 2: According to the formula, various raw materials are smelted, atomized and screened in a vacuum induction melting furnace; during the smelting process, the smelting temperature is controlled at 1560~1600℃ and held for 6~12 minutes to ensure that the raw materials are completely melted and the composition is uniform. The furnace exit temperature is controlled at 1600~1640℃; CaO-Al2O3 refining slag is added to the molten steel to adsorb and remove P and S impurities by the interfacial reaction between the refining slag and the molten steel. Step 3: Powder post-processing to obtain nuclear power pressure vessel steel metal powder; The pressure vessel steel powder for nuclear power plants comprises the following components: C: ≤0.2wt% Si: 0.1-0.3wt%; Mn: 1.15-1.60wt%; S: ≤0.005 wt% Cr: ≤0.25 wt%; Ni: 0.5-0.8wt%; P: ≤0.008 wt%; Mo: 0.43-0.57 wt% V: ≤0.01wt%; Cu: ≤0.08 wt%; Al: ≤0.04 wt%; Co: ≤0.03 wt% The balance is iron.

2. The preparation method according to claim 1, characterized in that, The pretreatment includes rust removal, degreasing, and drying.

3. The preparation method according to claim 1, characterized in that, Step 2 specifically includes: Step 2-1: Place the proportioned raw materials into a vacuum induction melting furnace, using a corundum crucible. Step 2-2: Perform gas purging on the vacuum induction melting furnace using a vacuum pump; Steps 2-3: Melting; The smelting temperature is controlled at 1560~1600℃ and held for 6~12 minutes to ensure that the raw materials are completely melted and the composition is uniform. The tapping temperature is controlled at 1610~1630℃. CaO-Al2O3 refining slag is added to the molten steel at a rate of 2%~3% of the molten steel mass. The interface reaction between the refining slag and the molten steel is used to adsorb and remove P and S impurities. Simultaneously, argon gas with a purity ≥99.999% is introduced for bottom blowing and stirring, with the stirring intensity controlled at 0.5-1.0 L / (min·kg) to promote full contact between the refining slag and the molten steel. The refining time is 30-40 minutes. After refining, alloy additives are added to the molten steel to adjust the composition of the molten steel to the standard range of 16MND5 steel. Steps 2-4: Perform atomization treatment; Steps 2-5: After the raw powder obtained by atomization is cooled, it is first passed through a 50-mesh ultrasonic vibrating sieve at a sieve speed of 60~100kg / min; then it is further subdivided under an argon atmosphere using a two-stage gas-protected airflow classifier.

4. The preparation method according to claim 3, characterized in that, In step 2-2, the vacuum level is guaranteed to be less than 5*10. -3 Pa; the power of the large crucible during vacuuming should not exceed 50kW; initially, the intermediate ladle power is increased to 5kW and held for 5-8 minutes, the intermediate ladle power is increased to 10kW and held for 5-8 minutes, the intermediate ladle power is increased to 10-20kW until atomization ends; pure argon is used for gas replacement, and the pressure gauge inside the furnace is below 0.02MPa after replacement.

5. The preparation method according to claim 1, characterized in that, The mass ratio of CaO to Al2O3 in the CaO-Al2O3 refining slag is 3~5:

1.

6. The preparation method according to claim 3, characterized in that, In steps 2-4, the atomizing gas is pure nitrogen, and the atomization pressure is 3.5~4.5 MPa; the initial atomization pressure is 2.0 MPa, which increases to a maximum atomization pressure of 4.3~4.72 MPa within 4~10 minutes, and the maximum argon flow rate is 1100~1300 m³ / h. 3 / h, control the pouring frequency and speed when pouring liquid, keep the liquid level in the intermediate bath at 50~80% height, and keep the intermediate bath continuously warm, with a temperature range of 1630~1650℃.

7. The preparation method according to claim 3, characterized in that, In steps 2-5, the main parameters of the airflow stage are as follows: feed frequency is 6~10Hz, primary classifier frequency is 2~5Hz, secondary classifier frequency is 13~21Hz, fan frequency is 40~45Hz, air pressure is 4~7kPa, and oxygen content is ≤5%.

8. The preparation method according to claim 3, characterized in that, In steps 2-4, Atomization is achieved using VIGA atomizing equipment, with a guide tube made of corundum and a reverse-conical zirconia nozzle with a nozzle diameter of 4.0~4.5mm.

9. The preparation method according to claim 1, characterized in that, Step 3 specifically involves: vacuum drying the screened powder at a temperature of 120-150°C for 4-6 hours to remove the moisture and trace gases adsorbed by the powder. The packaging uses inert gas to protect the powder from oxidation during storage and transportation.

10. A metal powder for pressure vessel steel used in nuclear power plants, characterized in that, It is prepared by the method described in any one of claims 1 to 9.

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