Preparation method of metal powder suitable for MIM injection molding ultrahigh-strength steel

Abstract

The invention discloses a preparation method of metal powder suitable for MIM injection molding ultrahigh-strength steel, and the preparation method of the metal powder comprises the following steps: S1, adding ultrahigh-strength steel raw materials such as pure iron, high-purity chromium, molybdenum strips, elemental niobium, electrolytic copper, cobalt and nickel plates, high-purity silicon and micro-carbon ferrochrome into a medium-frequency induction furnace, and smelting under the protection of nitrogen to obtain molten steel; s2, water and gas combined atomization is conducted, specifically, nitrogen is adopted as a process protective atmosphere, water-soluble quenching liquid is adopted as an atomization medium, main components of the quenching liquid are separated out and wrap the surface of metal liquid drops under the high-temperature condition, and the situation that water vapor films are generated in the atomization process to oxidize the metal liquid drops is avoided; after atomization is finished, the atomization medium and the metal powder fall into water, the temperature is reduced, the quenching liquid is re-dissolved into the water, the coating is broken, and the metal liquid drops are cooled and solidified into the metal powder; the powder prepared through the method has the advantages of being low in oxygen content, accurate in alloy component, high in cleanliness, fine in powder granularity, reasonable in distribution, good in sphericity degree and the like, and can be widely applied as a raw material of MIM injection molding ultrahigh-strength steel.

Description

[0001] This invention patent application is a divisional application of Chinese patent application No. 202310689636.0. The application number of the original application is 202310689636.0, and the application date is June 12, 2023. The name of the invention is a metal powder suitable for MIM injection molding of ultra-high-strength steel, preparation method and ultra-high-strength steel. Technical Field

[0002] The present invention relates to the technical field of metal powder material preparation, and in particular to a method for preparing metal powder for MIM injection molding of ultra-high strength steel. Background Art

[0003] Metal powder injection molding is a new type of net forming technology with the fastest development and the greatest application potential in the current powder metallurgy field. It has unique advantages in the preparation of net-shaped products with complex three-dimensional structures, uniform organizational structures and high performance. With the rapid development of the automotive industry, its products such as engines, seats, seat belts, sunroofs, etc. have many small parts that require complex three-dimensional shapes and high mechanical properties. These parts generally have specific functions and must meet the requirements of high strength, high toughness, excellent fatigue performance and high precision. In order to meet the needs of lightweight products and high strength of components, the selection of materials with high specific strength, especially ultra-high strength steel, has become the main solution at present.

[0004] At present, ultra-high strength steel metal powder is usually prepared by processes such as mechanical ball milling, gas atomization, water atomization or water-gas combined atomization; among them, the advantage of the ball milling method is that it can be operated continuously, is suitable for dry grinding and wet grinding, and can be used to prepare powders of various metals and alloys; the disadvantage is that it is not very selective for materials and is difficult to mass produce; gas atomization powder making refers to the use of high-speed airflow to break up the liquid metal flow into small droplets, which are then quickly condensed to obtain a formed powder; it has a wide range of applications, and the prepared powder has the characteristics of high sphericity and low oxygen content. Its main shortcomings are coarse powder particle size, hollow spheres and other problems; water-gas combined atomization powder making technology combines the advantages of water atomization and gas atomization, and the powder produced has the advantages of fine water atomization powder and good sphericity of gas atomization powder, and is widely used in the current production of ultra-high strength steel alloy powder.

[0005] However, the current water vapor combined atomization mechanism is that the supersonic airflow pre-disperses the molten steel column to form molten metal droplets, which are then broken up by ultra-high pressure atomized water and cooled and solidified into alloy powder. During this period, the molten steel droplets are in direct contact with the atomized water to produce a large amount of water vapor. The water vapor film wraps the metal droplets, causing the oxidation of the droplets to increase sharply. In addition, the cooling speed of the molten metal droplets is too fast, causing the powder to become a spherical powder after cooling and solidification, thereby limiting its wide application in injection molded ultra-high strength steel products.

[0006] In view of this, the inventors have made in-depth considerations and actively researched, improved and trial-produced the present invention to address the many deficiencies and inconveniences caused by the imperfections in the above-mentioned preparation method of ultra-high strength steel metal powder, and have developed the present invention. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing metal powder for MIM injection molding ultra-high strength steel, the metal powder having the advantages of low oxygen content, precise alloy composition, high cleanliness, fine powder particle size and reasonable distribution, good sphericity, etc. The ultra-high strength steel prepared by the metal powder meets the market requirements for MIM ultra-high strength steel such as high strength, high toughness, excellent fatigue performance and high precision.

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

[0009] A metal powder suitable for MIM injection molding of ultra-high strength steel. The metal powder comprises the following components in percentage by weight: 10.0-11.0 wt% Cr, 8.0-9.0 wt% Mo, 0.2-0.4 wt% Nb, 0.2-0.5 wt% Cu, 17.0-18.0 wt% Co, 6.0-7.0 wt% Ni, 0.3-0.5 wt% Si, 0.05-0.1 wt% C and 54.0-58.25 wt% Fe.

[0010] Laser particle size of metal powder D90: 18-20μm, powder oxygen content ≤ 0.1wt%, powder tap density ≥ 5.0g / cm 3 .

[0011] A method for preparing metal powder for MIM injection molding of ultra-high strength steel comprises the following steps:

[0012] S1. Medium frequency induction melting: the following metal powder components are prepared according to their mass percentage: 10.0-11.0wt% Cr, 8.0-9.0wt% Mo, 0.2-0.4wt% Nb, 0.2-0.5wt% Cu, 17.0-18.0wt% Co, 6.0-7.0wt% Ni, 0.3-0.5wt% Si, 0.05-0.1wt% C, 54.0-58.25wt% Fe; pure iron, high purity chromium, molybdenum bars, elemental niobium, electrolytic copper, cobalt, nickel plates, high purity silicon and micro-carbon ferrochrome in the raw materials of ultra-high strength steel are added into a medium frequency induction furnace for melting, and the furnace mouth is provided with a ring pipeline nitrogen protection melting to obtain molten steel;

[0013] S2. Water-gas combined atomization: nitrogen is used as the process protective atmosphere, and water-soluble quenching liquid is used as the atomizing medium. During the atomization process, the water-soluble quenching liquid precipitates a film covering the surface of the metal droplets. After the atomization is completed, the atomizing medium and the metal powder fall into the water, the temperature decreases, the water-soluble quenching liquid dissolves back into the water, the film is broken, and the metal droplets are then cooled and solidified into spherical metal powders.

[0014] During the medium frequency induction melting process in step S1, a small amount of La and Ce mixed rare earth RE is gradually added to the molten steel, and the Ishikawa F2 slag remover is used to cover the molten steel to isolate the air; when the molten steel temperature reaches 1580-1620°C, SiCaMn deoxidizer is added for deoxidation; then the slag is cleaned and the pump is started to pour steel.

[0015] During the medium frequency induction melting process in step S1, a zirconia foam ceramic filter is placed at the bottom of the tundish to filter out the clean molten steel.

[0016] In step S2, three cyclones and a single exhaust water seal pipe are evenly distributed at 90 degrees on the upper cone of the atomizing barrel.

[0017] In the water vapor combined atomization process of step S2, a Hartmann resonant cavity structure annular gap type spray disc is used; the hole size of the bottom of the molten steel ladle is 4.0-4.5mm, the atomization pressure is 80-95MPa, and the flow rate is 350-380L / min.

[0018] In the water vapor combined atomization process in step S2, the water-soluble quenching liquid contains polyvinyl alcohol, rust inhibitor, preservative and defoamer, and the concentration thereof is 5-15%.

[0019] The laser particle size D90 of the prepared metal powder is 18-20 μm, the oxygen content of the powder is ≤0.1wt%, and the tap density of the powder is ≥5.0g / cm 3 .

[0020] An ultra-high strength steel is prepared by MIM using ultra-high strength steel metal powder. The ultra-high strength steel has a hardness of 54-57HRC, a tensile strength of ≥2100MPa, a yield strength of ≥2000MPa, and an elongation of 3-5%.

[0021] After adopting the above structure, the metal powder for ultra-high strength steel of the present invention has the following advantages compared with the prior art:

[0022] 1. In the present invention, a small amount of La and Ce mixed rare earth RE is added to the molten steel during the smelting process, and the molten steel is covered with Ishikawa F2 slag remover to isolate the air. The rare earth removes CrS, MnS, FeO, MnO, SiO 2 Transformed to (Ce, La, RE) 2 O 2S and other inclusions, significantly improving the purity of the molten steel and the morphology of inclusions. The ultra-high strength steel alloy powder has a very small impurity content, accurate and uniform alloy composition, and a delicate structure. Secondly, a water-soluble quenching liquid is used as the atomizing medium. Under high temperature conditions, the main components of the quenching liquid are separated out to form a film coated on the surface of the metal droplet, which avoids the water vapor film generated during the atomization process to oxidize the metal droplets, causing the droplet oxidation to increase sharply, and the powder oxygen content is ≤0.1%; after the atomization is completed, the atomizing medium and the metal powder fall into the water, the temperature drops and the quenching liquid dissolves back into the water, and the film is broken. Due to the temperature gradient change in the rapid cooling process of the metal droplet, the spheroidization ability of the metal droplet is greatly enhanced, the powder has good sphericity, and the tap density is ≥5.0g / cm 3 ; The metal powder has the advantages of low oxygen content, precise alloy composition, high cleanliness, fine powder particle size and reasonable distribution, and good sphericity;

[0023] 2. The metal powder for ultra-high strength steel prepared by the present invention adopts MIM injection molding process, and can prepare ultra-high strength and high toughness steel parts with a hardness of 54-57HRC, tensile strength ≥2100MPa, yield strength ≥2000MPa, and elongation 3-5%. It has high strength, high toughness, and excellent fatigue performance, so that it can meet the needs of smart terminals, hardware tools, automobiles and other industries for high-performance parts, and can generate huge economic benefits. DETAILED DESCRIPTION

[0024] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0025] The invention discloses a metal powder suitable for MIM injection molding of ultra-high strength steel. The metal powder comprises the following components in percentage by weight: 10.0-11.0wt% Cr, 8.0-9.0wt% Mo, 0.2-0.4wt% Nb, 0.2-0.5wt% Cu, 17.0-18.0wt% Co, 6.0-7.0wt% Ni, 0.3-0.5wt% Si, 0.05-0.1wt% C and 54.0-58.25wt% Fe.

[0026] The laser particle size D90 of the metal powder of the present invention is 18-20 μm, the oxygen content of the powder is ≤0.1 wt%, and the tap density of the powder is ≥5.0 g / cm 3 .

[0027] The invention is suitable for metal powder for MIM injection molding of ultra-high strength steel. During the smelting process, a small amount of La and Ce mixed rare earth RE is added to the molten steel, and the molten steel is covered with Ishikawa F2 slag remover to isolate the air. The rare earth removes CrS, MnS, FeO, MnO, SiO 2 Transformed to (Ce, La, RE) 2 O2 S and other inclusions, significantly improving the purity of the molten steel and the morphology of inclusions. The ultra-high strength steel alloy powder has a very small impurity content, accurate and uniform alloy composition, and a delicate structure. Secondly, a water-soluble quenching liquid is used as the atomizing medium. Under high temperature conditions, the main components of the quenching liquid are separated out to form a film coated on the surface of the metal droplet, which avoids the water vapor film oxidation and the extremely cold metal droplets causing a sharp increase in the oxidation of the droplets during the atomization process. The oxygen content of the powder is ≤0.1%; after the atomization is completed, the atomizing medium and the metal powder fall into the water, the temperature decreases, the quenching liquid dissolves back into the water, and the film is broken. Due to the temperature gradient change in the rapid cooling process of the metal droplet, the spheroidization ability of the metal droplet is greatly enhanced, the powder has good sphericity, and the tap density is ≥5.0g / cm 3 ; The metal powder has the advantages of low oxygen content, precise alloy composition, high cleanliness, fine and reasonable powder particle size distribution, and good sphericity; The metal powder for ultra-high strength steel can be used to prepare ultra-high strength steel using the MIM injection molding process, which can meet the market requirements for high strength, high toughness, excellent fatigue performance and high precision of MIM ultra-high strength steel, so that it can meet the needs of smart terminals, hardware tools, automobiles and other industries for high-performance parts, and can generate huge economic benefits.

[0028] The present invention also discloses a method for preparing metal powder for MIM injection molding of ultra-high strength steel, comprising the following steps:

[0029] S1. Medium frequency induction melting: the following metal powder components are prepared according to their mass percentage: 10.0-11.0wt% Cr, 8.0-9.0wt% Mo, 0.2-0.4wt% Nb, 0.2-0.5wt% Cu, 17.0-18.0wt% Co, 6.0-7.0wt% Ni, 0.3-0.5wt% Si, 0.05-0.1wt% C, 54.0-58.25wt% Fe; pure iron, high purity chromium, molybdenum bars, elemental niobium, electrolytic copper, cobalt, nickel plates, high purity silicon and micro-carbon ferrochrome in the raw materials of ultra-high strength steel are added into a medium frequency induction furnace for melting, and the furnace mouth is provided with a ring pipeline nitrogen protection melting to obtain molten steel;

[0030] S2. Water-gas combined atomization: nitrogen is used as the process protective atmosphere, and water-soluble quenching liquid is used as the atomizing medium; during the atomization process (800-1000°C), the water-soluble quenching liquid precipitates a film covering the surface of the metal droplets; after the atomization is completed, the atomizing medium and the metal powder fall into the water, the temperature decreases, the water-soluble quenching liquid dissolves back into the water, the film is broken, and the metal droplets are then cooled and solidified into spherical metal powders.

[0031] In the medium frequency induction melting process of step S1, a small amount of La and Ce mixed rare earth RE is gradually added to the molten steel, and the Ishikawa F2 slag remover is used to cover the molten steel to isolate the air; when the temperature of the molten steel reaches 1580-1620°C, SiCaMn deoxidizer is added for deoxidation; then the slag is removed and the pump is started to cast steel.

[0032] In the medium frequency induction smelting process of step S1 of the present invention, a zirconia foam ceramic filter is placed at the bottom of the tundish to filter the residue and clean the molten steel.

[0033] In step S2 of the present invention, three cyclones and a single exhaust water seal pipe are evenly distributed at 90 degrees on the cone of the atomizing barrel, ensuring that the flow field of the atomizing system is stable and the exhaust of the system during the atomizing process is smoother and more uniform.

[0034] In the water vapor combined atomization process in step S2, the present invention adopts a Hartmann resonant cavity structure annular gap type spray disc; the leakage hole size at the bottom of the molten steel ladle is 4.0-4.5mm, the atomization pressure is 80-95MPa, and the flow rate is 350-380L / min; the self-developed Hartmann resonant cavity structure annular gap type spray disc is adopted, when the high-speed fluid is sprayed out from the annular gap spray disc, the impact force of the fluid will excite the cross resonance cavity vibration to produce resonance, the fluid is more uniform and continuous, and the droplet breakage can be promoted, thereby obtaining better atomization quality.

[0035] In the water vapor combined atomization process in step S2 of the present invention, the water-soluble quenching liquid contains polyvinyl alcohol, rust inhibitor, preservative and defoamer, and the concentration thereof is 5-15%.

[0036] The laser particle size D90 of the metal powder prepared by the present invention is 18-20 μm, the oxygen content of the powder is ≤0.1wt%, and the tap density of the powder is ≥5.0g / cm 3 .

[0037] The present invention is applicable to the preparation method of metal powder for MIM injection molding ultra-high strength steel. The prepared metal powder has the advantages of low oxygen content, precise alloy composition, high cleanliness, fine powder particle size and reasonable distribution, good sphericity, etc.; it can be widely used as a raw material for MIM injection molding ultra-high strength steel, and the prepared ultra-high strength steel has the advantages of high strength, high toughness, excellent fatigue performance and high precision, etc.

[0038] Embodiment 1

[0039] A method for preparing metal powder for MIM injection molding ultra-high strength steel comprises the following steps:

[0040] S1. Medium frequency induction melting: the following metal powder components are prepared according to their mass percentage: 56.05wt% Fe, 10.5wt% Cr, 8.5wt% Mo, 0.3wt% Nb, 0.2wt% Cu, 17.5wt% Co, 6.5wt% Ni, 0.4wt% Si, 0.05wt% C; pure iron, high-purity chromium, molybdenum bars, elemental niobium, electrolytic copper, cobalt, nickel plates, high-purity silicon, and micro-carbon ferrochrome in the raw materials of ultra-high strength steel are added into a medium frequency induction furnace for melting, and a ring pipeline is used at the furnace mouth to protect the melting to obtain molten steel with nitrogen;

[0041] During the medium frequency induction melting process, a small amount of La and Ce mixed rare earth RE is gradually added to the molten steel, and the Ishikawa F2 slag remover is used to cover the molten steel to isolate the air; when the molten steel temperature reaches 1580-1620℃, SiCaMn deoxidizer is added for deoxidation; then the slag is removed and the pump is started to pour steel; during the steel pouring process, a zirconia foam ceramic filter is placed at the bottom of the tundish to filter the slag and clean the molten steel;

[0042] S2, water-gas combined atomization: nitrogen is used as the process protection atmosphere, and water-soluble quenching liquid is used as the atomizing medium; the self-developed Hartmann resonant cavity structure annular gap type spray disc is used; the hole size of the bottom of the molten steel tundish is 4.0-4.5mm, the atomizing pressure is 80-95MPa, and the flow rate is 350-380L / min;

[0043] Under high temperature conditions of 800-1000℃, the water-soluble quenching liquid precipitates a film covering the surface of the metal droplets; after atomization, the atomized medium and metal powder fall into the water, the temperature drops, the water-soluble quenching liquid dissolves back into the water, the film breaks, and the metal droplets then cool and solidify into spherical metal powder.

[0044] Embodiment 2

[0045] The difference between the second embodiment and the first embodiment is that the second embodiment adjusts the composition of a metal powder suitable for MIM injection molding of ultra-high strength steel, and the prepared metal powder composition is: 54.87wt% Fe, 11wt% Cr, 8.5wt% Mo, 0.35wt% Nb, 0.2wt% Cu, 18wt% Co, 6.5wt% Ni, 0.5wt% Si, 0.08wt% C, and the above components are all mass percentages.

[0046] Embodiment 3

[0047] The difference between the third embodiment and the first embodiment is that the third embodiment adjusts the composition of a metal powder suitable for MIM injection molding of ultra-high strength steel, and the prepared metal powder composition is: 54.21wt% Fe, 11wt% Cr, 9.0wt% Mo, 0.4wt% Nb, 0.3wt% Cu, 18wt% Co, 6.5wt% Ni, 0.5wt% Si, 0.09wt% C, and the above components are all mass percentages.

[0048]

[0049] The present invention further discloses an ultra-high strength steel prepared by MIM using metal powder for ultra-high strength steel. The ultra-high strength steel has a hardness of 54-57HRC, a tensile strength of ≥2100MPa, a yield strength of ≥2000MPa, and an elongation of 3-5%.

[0050] The ultra-high strength steel metal powder of the present invention can be prepared by MIM injection molding process to obtain ultra-high strength and high toughness steel parts with a hardness of 54-57HRC, a tensile strength of ≥2100MPa, a yield strength of ≥2000MPa, and an elongation of 3-5%. The ultra-high strength and high toughness steel parts have high strength, high toughness, and excellent fatigue performance, so that they can meet the needs of smart terminals, hardware tools, automobiles and other industries for high-performance parts, and can generate huge economic benefits.

[0051] After testing, the following is a material performance comparison table of product A made by the present invention and product B made by the conventional water-gas combined atomization method.

[0052]

[0053]

[0054] The above embodiments do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for preparing metal powder for MIM injection molding ultra-high strength steel, characterized in that: The following steps are involved: S1. Medium frequency induction melting: pure iron, high purity chromium, molybdenum bars, elemental niobium, electrolytic copper, cobalt, nickel plates, high purity silicon and micro-carbon ferrochrome in the raw materials of ultra-high strength steel are added into a medium frequency induction furnace for melting, and a ring pipeline nitrogen protection is used at the furnace mouth to melt and obtain molten steel; a small amount of La and Ce mixed rare earth RE is gradually added to the molten steel, and the Ishikawa F2 slag remover is used to cover the molten steel to isolate the air; the rare earth transforms CrS, MnS, FeO, MnO and SiO2 in the molten steel into inclusions such as (Ce, La, RE)2O2S; the temperature of the molten steel reaches 1580-1620℃, and SiCaMn deoxidizer is added for deoxidation; then the slag is cleaned and the pump is started to cast steel; S2. Water-gas combined atomization: nitrogen is used as the process protective atmosphere, water-soluble quenching liquid is used as the atomizing medium, the hole size of the bottom of the steel liquid ladle is 4.0-4.5mm, the atomizing pressure is 80-95MPa, and the flow rate is 350-380L / min; during the atomization process, the water-soluble quenching liquid precipitates a film covering the surface of the metal droplets; after the atomization is completed, the atomizing medium and the metal powder fall into the water, the temperature decreases, the water-soluble quenching liquid dissolves back into the water, the film is broken, and the metal droplets are then cooled and solidified into spherical metal powder.

2. A method for preparing metal powder for MIM injection molding ultra-high strength steel as claimed in claim 1, characterized in that: The ultra-high strength steel raw material is formulated according to the following metal powder component mass percentages: 10.0-11.0wt% Cr, 8.0-9.0wt% Mo, 0.2-0.4wt% Nb, 0.2-0.5wt% Cu, 17.0-18.0wt% Co, 6.0-7.0wt% Ni, 0.3-0.5wt% Si, 0.05-0.1wt% C, and 54.0-58.25wt% Fe.

3. A method for preparing metal powder for MIM injection molding ultra-high strength steel as claimed in claim 1, characterized in that: During the medium frequency induction melting process in step S1, a zirconia foam ceramic filter is placed at the bottom of the tundish to filter out the clean molten steel.

4. A method for preparing metal powder for MIM injection molding ultra-high strength steel as claimed in claim 1, characterized in that: In step S2, three cyclones and a single exhaust water seal pipe are evenly distributed at 90 degrees on the upper cone of the atomizing barrel.

5. A method for preparing metal powder for MIM injection molding ultra-high strength steel as claimed in claim 1, characterized in that: In the water vapor combined atomization process of step S2, a Hartmann resonant cavity structure annular gap type spray disc is used.

6. A method for preparing metal powder for MIM injection molding ultra-high strength steel as claimed in claim 1, characterized in that: In the water vapor combined atomization process in step S2, the water-soluble quenching liquid contains polyvinyl alcohol, rust inhibitor, preservative and defoamer, and the concentration thereof is 5-15%.

7. A method for preparing metal powder for MIM injection molding ultra-high strength steel as claimed in claim 1, characterized in that: The laser particle size D90 of the prepared metal powder is 18-20 μm, the oxygen content of the powder is ≤0.1 wt%, and the tap density of the powder is ≥5.0 g / cm 3 .

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