Preparation method of low-cost and low-pollution iron-containing alloy spherical powder

Abstract

The invention discloses a low-cost and low-pollution iron-containing alloy spherical powder preparation method, which belongs to the technical field of metal powder preparation, and comprises the following steps: (1) heating and melting the end part of a metal bar with the diameter of 90-350mm to form metal liquid drops with the size of millimeter level; the metal bar is made of pure iron or an alloy containing an iron element; (2) the metal liquid drops vertically drop to an atomization spraying disc internally provided with a liquid guide pipe under the action of gravity, meanwhile, inert gas is sprayed out through the atomization spraying disc, the metal liquid drops dropping to the spraying disc are impacted, and secondary liquid drops with the size being in the micron order are obtained; and (3) the secondary liquid drops slowly drop into the atomizing chamber along the liquid guide pipe, move and solidify under the action of gravity and airflow, and circulate in this way, so that the metal spherical powder is obtained. The method is low in cost, high in efficiency and less in pollution, and fully meets the application requirements of the fields of additive manufacturing, cladding, powder metallurgy, spraying and the like on the iron and iron alloy spherical powder.

Description

Technical Field

[0001] The invention belongs to the technical field of metal powder preparation, and in particular relates to a low-cost, low-pollution method for preparing iron-containing alloy spherical powder. Background Art

[0002] Due to the development of powder metallurgy, cladding, additive manufacturing, spraying and other fields, nearly spherical powders of iron and iron-containing alloys are needed, but the existing powder making methods are difficult to achieve low-cost and low-pollution powder preparation for the following reasons:

[0003] Iron and iron-containing alloys, especially those containing active elements, can react chemically with ceramic crucibles. In addition, the components of the crucible will also enter the liquid metal, which will cause pollution, resulting in adverse factors such as composition deviation, increased oxygen content, inclusions, etc. in the powder. In particular, the increase in oxygen content has a great impact on the performance of the alloy block obtained by subsequent powder metallurgy.

[0004] The water atomization method is a common, low-cost method for preparing iron-containing alloy powders. It relies on water flow to impact molten liquid metal to obtain metal powder. However, this method is a non-vacuum atomization method, the oxygen content of the powder remains high, and the prepared powder has an irregular morphology, is far from spherical, has poor fluidity, and is not suitable for additive manufacturing and densification powder metallurgy.

[0005] In the gas atomization method, the induction melting gas atomization (VIGA method) is difficult to obtain high-purity, low-pollution spherical powder due to the use of oxide ceramic crucibles.

[0006] The raw material of plasma wire atomization equipment (PA) must be wire, the raw material of radio frequency plasma spheroidization method must be powder, and methods such as PREP (plasma rotating electrode atomization) need to be pre-processed into round rods and made into threads. These methods have requirements on the size and morphology of the raw materials, and the processing yield of materials with poor performance such as plastic processing is low, and they also increase the necessary processes and increase the cost.

[0007] Crucible-free vacuum electrode induction melting gas atomization (EIGA method) does not contact the crucible, and the powder making process does not produce additional reactions or introduce impurities. Therefore, it is expected to produce high-quality metal powders, especially iron and iron-containing alloy powders, but its preparation cost is relatively high. Therefore, the current EIGA method mainly reduces the diameter of iron or iron-containing alloy bars (usually below 50mm) and combines gas recovery and reuse, peak electricity consumption, human resources and other measures to reduce the preparation cost, but it has gradually approached the limit and is difficult to reduce further; and the use of gas recovery and reuse, such as hydrogenation and dehydrogenation technology routes, makes it difficult to guarantee the quality of iron and iron-containing alloy powders. Summary of the invention

[0008] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a low-cost, low-pollution method for preparing ferrous alloy spherical powder.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A low-cost, low-pollution method for preparing iron-containing alloy spherical powder comprises the following steps:

[0011] (1) In a vacuum environment and an inert atmosphere, the end of a metal bar with a diameter of 90 mm to 350 mm is heated and melted to form a metal droplet with a size of millimeters; the metal bar is made of pure iron or an alloy containing iron elements;

[0012] (2) Under the action of gravity, the metal droplets vertically drip onto an atomizing spray plate with a liquid guide tube. At the same time, an inert gas is sprayed through the atomizing spray plate to impact the metal droplets dripping onto the spray plate, thereby obtaining secondary droplets of micron size; the inert gas pressure is 0.1-20 MPa, and the gas impact duration is 0.02-1000000 seconds;

[0013] (3) The secondary droplets slowly drip into the atomization chamber along the liquid guide tube, move and solidify under the action of gravity and airflow, and repeat this cycle to obtain metal spherical powder with an oxygen increment of 0.001-100000 ppm.

[0014] Furthermore, the preparation process of the metal bar material is: the raw material is prepared into a metal ingot by a smelting ingot casting or a powder metallurgy method, and then the metal ingot is obtained by surface treatment.

[0015] Preferably, in step (1), the vacuum degree of the vacuum environment is 0-10 -5 MPa.

[0016] Preferably, the inert gas in step (1) is at least one of nitrogen, argon and helium.

[0017] Furthermore, in the step (1), the power frequency used for heating and melting the end of the metal bar is 100-600 Hz.

[0018] Furthermore, in step (2), an induction heating method is used to heat and melt the end of the metal rod to form metal droplets with a size of millimeters.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention adopts a secondary gas atomization method, cooperates with the design of the taper of the end of the metal bar, and the effects of the vacuum environment, the atomizing spray disc, the inert gas, the liquid guide tube and the atomizing chamber, firstly melts the end of the metal bar into millimeter-level primary droplets, then utilizes the gas impact of the atomizing spray disc to make the primary droplets form micrometer-level secondary droplets, and then through the control of the liquid guide tube, the secondary droplets slowly drip into the atomizing chamber, and finally solidifies into powder under the action of the airflow in the atomizing chamber. This scheme designed by the present invention can not only meet the requirements of preparing spherical powders of large-diameter iron and iron alloy bars (above 90mm, up to 350mm), but also has low cost and high efficiency.

[0021] Experiments show that, since large diameter bars can be used, the scheme of the present invention greatly increases the output of iron and iron-containing alloy spherical powders. Specifically, under the same length of electrode metal bars, the output of metal powder per furnace of 100 mm diameter bars is increased by more than 300% compared with that of 50 mm diameter bars, and the output of metal powder per furnace of 350 mm diameter bars is 100 times that of 50 mm diameter bars. Therefore, the present invention fully meets the application requirements of iron and iron-containing alloy spherical powders in the fields of additive manufacturing, cladding, powder metallurgy, spraying, etc.

[0022] (2) The preparation method of the present invention does not contact the crucible, uses an inert gas to impact the metal droplets, and designs the pressure and impact duration of the inert gas, thereby reducing the pollution caused by the crucible, lowering the oxygen content, and effectively avoiding the introduction of impurities, thereby fully improving the quality of the iron and iron-containing alloy spherical powder.

[0023] (3) The raw materials required in the preparation method of the present invention can be recycled materials, thereby further reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of a 316 stainless steel electrode bar material with a diameter of 150 mm being melted into droplets in the present invention;

[0025] Figure 2 This is a diagram of the V4E electrode rod material with a diameter of 150 mm melted into a beam flow diagram of the present invention;

[0026] Figure 3 This is an optical microscope picture of the 316 stainless steel metal powder prepared in Example 3 of the present invention;

[0027] Figure 4 This is an optical microscope picture of the cross section of the iron-based alloy metal powder prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the materials and reagents used in the examples can be obtained from commercial sources.

[0030] The content of active metal elements in the metal powder finally prepared in the embodiment of the present invention is measured by a conventional chemical quantitative method in the art, and the oxygen increment and nitrogen increment are measured by an oxygen, nitrogen and hydrogen analyzer.

[0031] In the present invention, the powder raw material is Fe-alloy, the iron content is not less than 0.01wt%, and the melting point is in the range of 800°C to 2000°C. The preparation method of spherical powder is as follows:

[0032] (1) A metal ingot is prepared by smelting ingots (using vacuum magnetic levitation induction melting, vacuum induction water-cooled copper crucible condensation furnace melting, vacuum arc melting or vacuum induction melting to melt the alloy, and the melting temperature of the alloy melting is 50°C-6000°C), powder metallurgy (using sintering, hot pressing sintering and other methods; the temperature of powder metallurgy is 30°C-3000°C, and the pressure is 0-30Mpa); and then surface treatment (mechanical grinding or chemical cleaning to clean the surface oil, impurities, oxide scale pollution layer to expose the metal) to obtain a metal bar with a diameter of 90mm-350mm;

[0033] (2) Use a vacuum pump to evacuate the furnace body so that the metal bar is in a vacuum environment with a vacuum degree of 0-10 - 5 MPa, and filled with at least one of nitrogen, argon and helium with a gas purity of 99.99%, and the replacement frequency is 1;

[0034] (3) Using induction heating method, the end of the metal bar is heated and melted to obtain molten metal droplets (primary droplets, the size is millimeter level); the heating and melting temperature is 50-2000°C, and the power frequency is 100-600Hz; Figure 1 , 2 As shown, they are schematic diagrams of melting 150 mm diameter 316 stainless steel electrode rod and 150 mm diameter V4E electrode rod into droplets;

[0035] (4) A secondary gas atomization method is used to first form metal droplets into micron-sized secondary droplets, and then pass through an atomization chamber to finally solidify into spherical powders with an oxygen increment of 0.001-100000 ppm; wherein the gas atomization gas pressure for forming the secondary droplets is 0.1-20 MPa, and the gas impact duration is 0.02-1000000 seconds.

[0036] The present invention is further described below in conjunction with embodiments and drawings.

[0037] Example 1

[0038] Powder making raw material: Fe-W alloy, with a composition of 30wt% iron and 70wt% tungsten, and a melting point of 1850°C.

[0039] The preparation method is as follows:

[0040] S1. A vacuum induction melting furnace is used for smelting to obtain a master alloy ingot, and after mechanical processing, an electrode rod material with a diameter of 90 mm is obtained;

[0041] S2. Use a vacuum pump to evacuate the furnace body, so that the master alloy ingot is in a vacuum environment, and fill it with inert gas; wherein the vacuum degree is 0 MPa, and nitrogen with a gas purity of 99.99999% is filled, and the number of replacements is 1;

[0042] S3. Metal powder is prepared by induction melting gas atomization. The electrode is first heated and melted. The power frequency is 600 Hz and the melting temperature is 2000°C. Liquid metal droplets are formed. The liquid metal falls vertically into the atomizing spray plate. The inert gas atomization pressure is 0.1 MPa and the gas impact duration is 0.02 seconds.

[0043] S4. A gas atomization method is used to gas-atomize the primary metal droplets formed by induction heating and melting to form secondary droplets, which are solidified in a container to obtain spherical powder. The oxygen increment of the spherical powder is 100,000 ppm.

[0044] Example 2

[0045] Powder making raw material: Fe-Ga alloy, with a composition of 10at% iron and 90at% gallium, and a melting point of 800°C.

[0046] The preparation method is as follows:

[0047] S1. The alloy is smelted by a vacuum induction water-cooled copper crucible smelting furnace at a smelting temperature of 800° C. The obtained master alloy ingot is mechanically processed to obtain an electrode rod material with a rod diameter of 350 mm.

[0048] S2. Use a vacuum pump to evacuate the furnace body, so that the master alloy ingot is in a vacuum environment and filled with inert gas; the vacuum degree is 10 -5 MPa, filled with helium with a gas purity of 99.99999%, and the number of replacements is 1-2 times;

[0049] S3. Metal powder is prepared by induction melting gas atomization. The electrode is first heated and melted. The power frequency is 100 Hz and the melting temperature is 800°C. Liquid metal droplets are formed. The liquid metal falls vertically into the atomizing spray plate. The inert gas atomization pressure is 20 MPa and the gas impact duration is 1,000,000 seconds.

[0050] S4. A primary beam formed by induction heating and melting is atomized by gas atomization to form secondary droplets, which are solidified in a container to obtain spherical powder. The oxygen increment of the spherical powder is 0.001 ppm.

[0051] Example 3

[0052] Powder making raw materials: 316 stainless steel, 18Cr-12Ni-2.5Mo, the composition is 18wt% chromium, 12wt% nickel, 2.5wt% molybdenum, and iron as the balance, and the melting point is 1375-1400°C.

[0053] The preparation method is as follows:

[0054] S1. The alloy is melted by vacuum induction melting at a temperature of 1500° C. The obtained master alloy ingot is mechanically processed to obtain an electrode rod having a rod diameter of 150 mm.

[0055] S2. Use a vacuum pump to evacuate the furnace body, so that the master alloy ingot is in a vacuum environment and filled with inert gas; the vacuum degree is 10 -3 MPa, filled with nitrogen gas with a gas purity of 99.99999%, and the number of replacements was 1;

[0056] S3. Metal powder is prepared by induction melting gas atomization. The electrode is first heated and melted. The power frequency is 150 Hz and the melting temperature is 1800°C. Liquid metal droplets are formed. The liquid metal falls vertically into the atomizing spray plate. The inert gas atomization pressure is 4 MPa and the gas impact duration is 180 seconds.

[0057] S4. The primary metal droplets formed by induction heating and melting are atomized by gas atomization to form secondary droplets, which are solidified in a container to obtain spherical powder. The oxygen increment of the spherical powder is 100 ppm, and its optical microscope picture is as follows: Figure 3 shown.

[0058] Example 4

[0059] Powder making raw material: Fe-based alloy, with a composition of 1.4wt% carbon, 0.4wt% silicon, 0.4wt% manganese, 4.7wt% chromium, 3.5wt% molybdenum, 3.7wt% vanadium, and the balance of iron.

[0060] The preparation method is as follows:

[0061] S1. The alloy is melted by vacuum induction melting at a temperature of 1700° C. The prepared metal ingot is mechanically processed to obtain an electrode rod having a rod diameter of 200 mm.

[0062] S2. Use a vacuum pump to evacuate the furnace body, so that the master alloy ingot is in a vacuum environment and filled with inert gas; the vacuum degree is 10 -4 MPa, filled with argon gas with a gas purity of 99.999%, and the number of replacements was 2 times;

[0063] S3. Metal powder is prepared by induction melting gas atomization. The electrode is first heated and melted. The power frequency is 200 Hz and the melting temperature is 1700°C. Liquid metal droplets are formed. The liquid metal falls vertically into the atomizing spray plate. The inert gas atomization pressure is 5 MPa and the gas impact duration is 300 seconds.

[0064] S4. The primary metal droplets formed by induction heating and melting are atomized by gas atomization to form secondary droplets, which are solidified in the container to obtain spherical powder. The oxygen increment of the spherical powder is 60ppm, and its optical microscope picture is as follows: Figure 4 shown.

[0065] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A low-cost, low-pollution method for preparing ferrous alloy spherical powder, characterized in that: The following steps are involved: (1) In a vacuum environment and an inert atmosphere, the end of a metal bar with a diameter of 90 mm to 350 mm is heated and melted to form a metal droplet with a size of millimeters; the metal bar is made of pure iron or an alloy containing iron elements; (2) Under the action of gravity, the metal droplets vertically drip onto an atomizing spray plate with a liquid guide tube. At the same time, an inert gas is sprayed through the atomizing spray plate to impact the metal droplets dripping onto the spray plate, thereby obtaining secondary droplets of micron size; the inert gas pressure is 0.1-20 MPa, and the gas impact duration is 0.02-1000000 seconds; (3) The secondary droplets slowly drip into the atomization chamber along the liquid guide tube, move and solidify under the action of gravity and airflow, and repeat this cycle to obtain metal spherical powder with an oxygen increment of 0.001-100000 ppm.

2. A low-cost, low-pollution method for preparing ferrous alloy spherical powder according to claim 1, characterized in that: The preparation process of the metal bar material is: the raw material is prepared into a metal ingot by a smelting ingot casting or a powder metallurgy method, and then the metal ingot is prepared by surface treatment.

3. A low-cost, low-pollution method for preparing iron-containing alloy spherical powder according to claim 1 or 2, characterized in that: In the step (1), the vacuum degree of the vacuum environment is 0-10 -5 MPa.

4. A low-cost, low-pollution method for preparing ferrous alloy spherical powder according to claim 3, characterized in that: The inert gas in step (1) is at least one of nitrogen, argon and helium.

5. A low-cost, low-pollution method for preparing ferrous alloy spherical powder according to claim 4, characterized in that: In the step (1), the power supply frequency used to heat and melt the end of the metal bar is 100-600 Hz.

6. A low-cost, low-pollution method for preparing iron-containing alloy spherical powder according to claim 1, 2, 4 or 5, characterized in that: In the step (2), an induction heating method is used to heat and melt the end of the metal bar to form metal droplets with a size of millimeters.

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