Gas atomization method of molten steel

Abstract

The present invention relates to a process for producing steel powder comprising the steps of providing molten iron from a blast furnace, smelting the molten iron in a converter to form molten steel containing up to 600 ppm C, up to 120 ppm S, up to 125 ppm P, up to 50 ppm N and up to 1200 ppm O, pouring the molten steel into a plurality of induction furnaces, adding at least one ferroalloy to each of the plurality of induction furnaces to adjust the steel composition, pouring the molten steel at the desired composition of each induction furnace into a dedicated reservoir connected to at least one gas atomizer, feeding the molten steel under pressure from each reservoir to at least one gas atomizer of each reservoir and gas atomizing the molten steel to form steel powder with the desired composition.

Description

Technical Field

[0001] The present invention relates to the production of steel powder, and in particular, to the production of steel powder by gas atomization for additive manufacturing. The present invention also relates to the equipment for producing such steel powder.

Background Art

[0002] The demand for steel powder for additive manufacturing has been increasing, and as a result, it is necessary to adapt the manufacturing process.

[0003] In particular, it is known to melt a metal material in an electric furnace or a vacuum melting furnace, refine the composition, and pour the molten steel into a tundish connected to an atomizer. Such a batch process is not suitable for the need to produce a large amount of steel powder, preferably in continuous mode.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, an object of the present invention is to improve the disadvantages of the prior art equipment and processes by providing a general-purpose process for producing steel powder. In particular, the object is to provide a process that can use different raw materials and produce powders with different steel compositions according to requirements, while operating in continuous mode in some cases.

Means for Solving the Problems

[0005] For this purpose, the first main subject of the present invention consists of a process for producing steel powder, including the following steps. - Providing molten iron from a blast furnace; - Refining the molten iron in a converter to form molten steel containing up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O; - Pouring the molten steel into a plurality of induction furnaces; - Adding at least one type of ferroalloy to each of the plurality of induction furnaces to adjust the steel composition to the desired steel composition of the steel powder. - A step of pouring molten steel of the desired composition from each induction furnace into a dedicated reservoir connected to at least one gas atomizer, - A step of supplying molten steel from each reservoir under pressure to at least one gas atomizer in each reservoir, and gas atomizing the molten steel to form steel powder of a desired composition.

[0006] The processes according to the present invention may also have the following optional features, which may be considered individually or in combination: - This process is continuous. - Molten iron from the blast furnace is desulfurized to contain less than 50 ppm of sulfur by weight. - Molten steel contains up to 250 ppm of C and / or up to 90 ppm of P and / or up to 25 ppm of N. - After refining molten iron in a converter, molten steel is formed, and the molten steel is further refined in a ladle smelting furnace to obtain a steel composition containing up to 30 ppm of oxygen. - The temperature inside the ladle smelting furnace is maintained between 1520 and 1700°C. - The refined molten steel is poured directly from the ladle smelting furnace into multiple induction furnaces. - The refined molten steel is first poured into a tundish, and then poured from the tundish into several induction furnaces. - The tundish allows for the simultaneous pouring of refined molten steel into all induction furnaces. - The temperature inside the tundish is maintained between 1520 and 1620°C. - Purge the tundish with argon to control the oxygen content in the tundish. - Before or after refining in a ladle smelting furnace, the molten steel is further processed in a vacuum tank degasser or vacuum oxygen decarburization vessel. - The temperature inside multiple induction reactors is maintained between 1500 and 1700°C. - The temperature in at least one of the multiple induction reactors is maintained between 1620 and 1650°C. - The ferroalloys added to the induction furnace are not pre-melted. - Scrap or directly reduced iron or silicide alloy or nitride alloy or pure element or mixture thereof is added to at least one of a plurality of induction furnaces. - Induction reactors do not have an atmosphere control. - At least one of the multiple induction reactors is a vacuum induction reactor. - The atmosphere of each dedicated reservoir is argon, nitrogen, or a mixture thereof. - The temperature in each dedicated reservoir is maintained between 1300 and 1750°C. - The temperature in each dedicated reservoir is at least 150°C above the liquidus temperature of the molten steel.

[0007] A second subject of the present invention is an apparatus for producing steel powder, comprising the following: - blast furnace, - A converter capable of refining molten iron to form molten steel containing up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O. - Multiple induction reactors, - A ferroalloy supply unit capable of supplying at least one type of ferroalloy to the plurality of induction furnaces, - A dedicated reservoir for each induction reactor, each dedicated reservoir being connected to at least one gas atomizer and pressurizable.

[0008] The apparatus according to the present invention may also have the following optional features, which may be considered individually or in combination: - The facility further includes a ladle smelting furnace for refining molten steel to obtain a steel composition containing up to 30 ppm of O. - The equipment further includes a tundish that can pour molten steel into all induction furnaces simultaneously. - The tundish is positioned above multiple induction reactors. - The equipment further includes a vacuum tank degasser (VTD) or a vacuum oxygen decarburization (VOD) container.

Best Mode for Carrying Out the Invention

[0009] Other features and advantages of the present invention will be described in more detail in the following description.

[0010] This invention is provided purely for purposes of explanation and is not intended to be limiting in any way. By reading the following explanation, it will be understood more deeply.

[0011] In the first step of the process, molten iron (or pig iron) is provided from the blast furnace.

[0012] Conventionally, the blast furnace is supplied with solid materials filled in its upper part, mainly sinter, pellets, iron ore, and carbonaceous materials, generally coke, which is called the throat of the blast furnace. The iron-containing charging raw materials (sinter, pellets, and iron ore) are conventionally converted into pig iron by reducing iron oxide with a reducing gas (especially containing CO, H2, and N2), and this reducing gas is formed by the combustion of the carbonaceous material in the tuyere located at the lower part of the blast furnace, where air is preheated to a temperature between 1000 and 1300 °C, called hot air, and injected.

[0013] The pig iron and slag are discharged from the molten pool at the bottom of the blast furnace. The pig iron is poured into a ladle, and then this is conventionally poured into a converter (or BOF, meaning a basic oxygen steelmaking furnace) pre-filled with scrap.

[0014] The pig iron can be transported directly to the converter or can be pre-treated first before being poured into the converter. According to a variant of the present invention, the pig iron from the blast furnace is sent to a hot metal desulfurization station before being poured into the converter. In that case, the pig iron is preferably desulfurized to contain less than 50 ppm of S by weight. This desulfurization step facilitates the refining of the downstream molten steel, and thus the desired steel composition is obtained.

[0015] In the second step of the process, the molten iron is refined in a converter to form molten steel containing, by weight, up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O.

[0016] The process of refining iron into steel includes a step of blowing oxygen to decarburize the iron and a post-blowing step of blowing a neutral gas such as argon. Lime and / or dolomite are added to the converter to remove impurities such as silicon, phosphorus, and manganese and to reach the levels of impurities required for the desired steel composition. These additives, together with the impurities extracted from the pig iron, form converter slag.

[0017] Since the decarburization reaction releases energy, scrap is usually added to control the temperature of the liquid steel being produced. Mineral additives such as lime, dolomite, and limestone can be further added to control the chemical composition and temperature of the liquid steel being produced. These mineral additives can also be used to monitor the chemical composition of the slag, as the slag composition affects the equilibrium between the liquid steel and the slag and thus promotes the reactions occurring in the liquid steel.

[0018] In the present invention, in order to provide a general composition compatible with all possible powder compositions to be produced, the composition contains, by weight, up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O at the end of the refining step in the converter, and the balance is iron and inevitable impurities resulting from the process.

[0019] In certain cases where a demanding powder composition has to be produced, the composition is further limited to up to 250 ppm of C and / or up to 90 ppm of P and / or up to 25 ppm of N.

[0020] The molten steel from the converter is then tapped into a regenerated ladle. Preferably, to minimize slag carryover from the converter, only the first heat of the sequence is tapped into a regenerated ladle to be transported to the next step in the process according to the present invention. The remaining steel and slag are later tapped into a standard steel ladle during the tapping process and transferred to another part of the plant for another process. By minimizing slag carryover, additional deoxidation is prevented and the level of impurities in the molten steel is reduced.

[0021] At the end of the second step of the process, the molten steel is refined to obtain a steel composition containing up to 30 ppm by weight of oxygen. In other words, the oxygen content in the steel composition is limited to 30 ppm. More preferably, the molten steel is refined to obtain a steel composition containing 10 to less than 150 ppm by weight of sulfur, up to 150 ppm of phosphorus, up to 100 ppm of nitrogen, and up to 30 ppm of oxygen. The main purpose of this step is to deoxygenate the molten steel. Optionally, this step may include primary alloying of the molten steel.

[0022] In this case, the molten steel is transferred from the converter to the ladle smelting furnace (LMF). This transfer is preferably carried out without controlling the atmosphere.

[0023] In ladle smelting furnaces, the analytical quality of the liquid metal, including not only metal alloy elements but also controlled compositional trimming of metalloids (C, H, N, O, P, S), is adjusted to a different degree depending on the grade. The type and content of oxide inclusions are controlled by deoxygenation (or "killing") of the steel, generally using aluminum for sheet steel, by calcium treatment to alter their composition, and by controlled flotation. Such treatment is carried out by adding different additives such as lime, dolomite, fluorite, and / or various fluxes to the ladle furnace. The resulting impurities form slag that floats on the surface of the molten metal. Depending on the composition of the slag, additives are added to remove residual impurities.

[0024] Optionally, primary alloying of molten steel can be carried out by adding ferroalloys, silicide alloys, nitride alloys, pure metals, or mixtures thereof. This primary alloying is particularly interesting when all different steel powders to be produced in multiple gas atomizers have a given alloying element in common.

[0025] Iron alloys refer to various alloys of iron with one or more other elements in high proportions, such as silicon, niobium, boron, chromium, aluminum, manganese, and molybdenum. The main alloys are FeAl (usually containing 40-60 wt% Al), FeB (usually containing 17.5-20 wt% B), FeCa, FeCr (usually containing 50-70 wt% Cr), FeMg, FeMn, FeMo (usually containing 60-75 wt% Mo), FeNb (usually containing 60-70 wt% Nb), FeNi, FeP, FeS, FeSi (usually containing 15-90 wt% Si), FeSiMg, FeTi (usually containing 45-75 wt% Ti), FeV (usually containing 35-85 wt% V), and FeW (usually containing 70-80 wt% Mo).

[0026] Silicide alloys can be MnSi, CrSi, or CaSi in particular. Nitride alloys can be MnN.

[0027] Pure metals can include iron, copper, nickel, cobalt, chromium, calcium, and rare earth metals.

[0028] The temperature inside the ladle smelting furnace is preferably maintained between 1520 and 1700°C, more preferably between 1520 and 1620°C.

[0029] In one modification of the present invention, in order to provide a general-purpose composition that is compatible with all possible powder compositions to be manufactured, the composition contains up to 600 ppm by weight of C, 10 to less than 150 ppm of S, up to 150 ppm of P, up to 100 ppm of N, and up to 30 ppm of O at the end of the refining step in a ladle smelting furnace, with the remainder being iron and unavoidable impurities arising from the process.

[0030] In certain cases where demanding powder compositions must be produced, molten steel may be further processed in a vacuum tank degasser (VTD) or vacuum oxygen decarburization (VOD) vessel. These devices allow for further restriction of hydrogen, nitrogen, and / or carbon content. The hydrogen content may be less than 2 ppm (by weight). The nitrogen content may be less than 20 ppm (by weight). The carbon content may be less than 20 ppm (by weight).

[0031] In a vacuum tank degasser, the ladle is typically placed inside a lidless vacuum tank connected to a vacuum pump, or a vacuum cover is placed directly over the ladle. Under vacuum conditions and argon injection, carbon and oxygen react vigorously until equilibrium is reached at very low levels (allowable processing time). A variation of the vacuum tank degasser is the vacuum oxygen decarburizer (VOD), which has an oxygen lance in the center of the tank lid to improve carbon removal under vacuum. VODs are often used to reduce the carbon content of high-alloy steels without peroxidizing oxidizable alloying elements such as chromium.

[0032] The processing in the VTD or VOD vessel can be carried out before or after refining in the ladle smelting furnace.

[0033] In the third step of the process, the molten steel from the converter, or the refined molten steel from the ladle smelting furnace, and, if applicable, the VTD or VOD, is poured into several induction furnaces.

[0034] An induction furnace is an electric furnace in which heat is applied by induction heating of metal. An induction furnace consists of a non-conductive crucible that holds a filling of molten metal, surrounded by a coil of copper wire. A strong alternating current flows through the wire. The coil generates a rapidly reversing magnetic field that penetrates the metal.

[0035] Thanks to multiple induction furnaces, the steel powder manufacturing process can be easily carried out continuously.

[0036] Each induction reactor can be operated independently of the others. It can be shut down specifically for maintenance or repair while other induction reactors are still in operation. In addition, the induction lines can be supplied with ferroalloys, scrap, directly reduced iron (DRI), silicide alloys, nitride alloys, or pure elements in different quantities for each induction reactor.

[0037] The number of induction furnaces is adapted to the flow of molten steel coming from the converter, or the flow of refined molten steel coming from the ladle smelting furnace, and / or the desired flow of steel powder at the bottom of the atomizer.

[0038] According to one modification of the present invention, molten steel from a converter is poured directly into multiple induction furnaces, or, where applicable, refined molten steel is poured directly into multiple induction furnaces from a ladle smelting furnace, from a VTD, or from a VOD. "Directly" in this case includes the use of ladles for transferring the molten steel to the multiple induction furnaces.

[0039] According to another modification of the present invention, molten steel from a converter, or refined molten steel from a ladle smelter, VTD, or VOD, is first poured into a tundish, and then poured from the tundish into a plurality of induction furnaces. This configuration allows for easy distribution of molten steel to the induction furnaces as needed. The tundish is primarily used as a storage container. It can be batch-fed by the ladle smelter and supplied independently to each induction furnace. In particular, molten steel can be poured into all induction furnaces simultaneously. One way to achieve this capability is to provide the tundish with as many injection means as there are induction furnaces. The injection means may be injection holes and corresponding stopper rods.

[0040] The temperature inside the tundish is preferably maintained between 1520 and 1620°C.

[0041] The tundish is preferably purged with argon to control the oxygen content in the tundish.

[0042] In the fourth step of the process, at least one type of ferroalloy is added to each of the multiple induction furnaces to adjust the steel composition to the desired steel powder composition.

[0043] Iron alloys refer to various alloys of iron with one or more other elements in high proportions, such as silicon, niobium, boron, chromium, aluminum, manganese, and molybdenum. The main alloys are FeAl (usually containing 40-60 wt% Al), FeB (usually containing 17.5-20 wt% B), FeCa, FeCr (usually containing 50-70 wt% Cr), FeMg, FeMn, FeMo (usually containing 60-75 wt% Mo), FeNb (usually containing 60-70 wt% Nb), FeNi, FeP, FeS, FeSi (usually containing 15-90 wt% Si), FeSiMg, FeTi (usually containing 45-75 wt% Ti), FeV (usually containing 35-85 wt% V), and FeW (usually containing 70-80 wt% Mo).

[0044] The relative amounts of the ferroalloy mixture and each of the ferroalloys are, if applicable, adjusted to achieve the desired steel powder composition. The ferroalloys added to the induction furnace are preferably not pre-melted.

[0045] Optionally, scrap, directly reduced iron, silicide alloys, nitride alloys, pure elements, or mixtures thereof may be added to facilitate composition adjustment.

[0046] Directly reduced iron is produced by the direct reduction of iron ore (in the form of lumps, pellets, or powder) to iron using reducing gas or elemental carbon produced from natural gas or coal.

[0047] Silicide alloys can be MnSi, CrSi, or CaSi in particular. Nitride alloys can be MnN.

[0048] Pure elements can be, in particular, carbon and pure metals such as iron, copper, nickel, cobalt, chromium, calcium, and rare earth metals.

[0049] This step can be carried out independently and asynchronously in each induction furnace. As described above, different steel compositions can be prepared in different induction furnaces to obtain different steel powders.

[0050] To ensure proper melting of the ferroalloy and homogenization of the composition, the temperatures in the multiple induction furnaces are preferably maintained between 1500 and 1700°C, more preferably between 1620 and 1700°C. The temperature in at least one of the multiple induction furnaces is more preferably maintained between 1580 and 1650°C to extend the crucible and refractory life of the induction furnace.

[0051] It is preferable not to control the atmosphere of each induction furnace. However, in one modification of the present invention, the atmosphere of at least one induction furnace can be controlled. In particular, it is a vacuum induction furnace. It can function as an alternative to the vacuum tank degasser or vacuum oxygen decarburizer described above for further processing of molten steel.

[0052] The minimum duration in each induction furnace is controlled by the atomization rate and the rate at which the liquid steel can be discharged from the reservoir.

[0053] In the fifth step of the process, for each induction furnace, molten steel of the desired composition is poured into a dedicated reservoir connected to at least one gas atomizer. "Dedicated" means that the reservoir is paired with a given induction furnace. However, multiple reservoirs can be dedicated to one given induction furnace. For clarity, each induction furnace has its own production flow, along with at least one reservoir connected to at least one gas atomizer. Using such parallel and independent production flows, the process for producing steel powder is versatile and can be easily made continuous.

[0054] A reservoir is primarily a storage tank that allows for atmosphere control, heating of molten steel, and pressurization.

[0055] The atmosphere of each dedicated reservoir is preferably argon, nitrogen, or a mixture thereof to avoid oxidation of the molten steel.

[0056] The steel composition poured into each reservoir is heated above its liquidus temperature and maintained at this temperature. This overheating prevents clogging of the atomizer nozzles. Furthermore, the reduction in the viscosity of the molten composition helps to obtain a powder with high sphericity and no satellites, and with an appropriate particle size distribution.

[0057] The composition is preferably heated to a temperature at least 150°C above its liquidus temperature so that its viscosity is sufficiently reduced. However, since surface tension increases with temperature, it is preferable not to heat the composition to a temperature more than 450°C above its liquidus temperature.

[0058] Preferably, the composition is heated to a temperature 200 to 300°C higher than its liquidus temperature.

[0059] In one modification of the present invention, the composition is heated between 1300 and 1750°C, preferably between 1550 and 1750°C, which represents a good compromise between viscosity reduction and surface tension increase.

[0060] The reservoir is either continuously pressurized or can be pressurized when molten steel is supplied. The means for pressurizing the reservoir are designed accordingly. Continuous pressurization of each reservoir is advantageous for having a continuous flow from the reservoir to at least one atomizer connected to the reservoir. The pressure of each dedicated reservoir is adjusted to keep the metal flow constant. The pressure setting depends on several parameters, which can be adjusted as needed by those skilled in the art.

[0061] The reservoir can comprise a single chamber or multiple chambers that can be pressurized independently of each other. Multiple chambers allow the steel powder manufacturing process to be more easily continuous.

[0062] In the sixth step of the process, once the dedicated reservoir is pressurized, the molten steel can flow from the reservoir to at least one of the gas atomizers connected to the reservoir.

[0063] The molten composition is atomized into fine metal droplets by forcing a flow of molten metal through an orifice (nozzle) at the bottom of a reservoir under moderate pressure and impacting it with a jet of gas. The gas is introduced into the metal flow as it exits the nozzle, and the accompanying gas expands (due to heating), creating turbulence as it exits into the atomization tower, which has a large collection volume. The latter is filled with an inert gas to prevent the powder from oxidizing. The metal droplets are cooled as they fall within the atomization tower. Gas atomization is preferred because it is advantageous for producing powder particles with a high degree of roundness and a small amount of satellite. These particles are also less oxidized than those produced by water atomization.

[0064] The atomizing gas is preferably argon or nitrogen. Both increase the melt viscosity more slowly than other gases, such as helium, which promotes the formation of smaller particle sizes. They also play a role in controlling the purity of the chemical, avoiding undesirable impurities, and ensuring a good form of powder. Since the molar weight of nitrogen is 14.01 g / mol compared to 39.95 g / mol of argon, finer particles can be obtained by using argon rather than nitrogen. On the other hand, the specific heat capacity of nitrogen is 1.04 J / (gK) compared to 0.52 of argon. Therefore, nitrogen increases the cooling rate of the particles. In some cases, argon may be preferred over nitrogen to avoid contamination of the composition by nitrogen.

[0065] The gas flow affects the particle size distribution and microstructure of the metal powder. In particular, the cooling rate increases with higher flow rates. Therefore, the gas flow rate (m 3 The gas-to-metal ratio, defined as the ratio between the gas flow rate (kg / hour) and the metal flow rate (kg / hour), is preferably maintained between 1 and 5, more preferably between 1.5 and 3.

[0066] The nozzle diameter affects the flow rate of the molten metal, and therefore the particle size distribution and cooling rate. The maximum nozzle diameter is preferably limited to 6 mm to limit the increase in average particle size and the decrease in cooling rate. The nozzle diameter is more preferably between 2 and 3 mm to more precisely control the particle size distribution and to work favorably for the formation of the desired microstructure.

[0067] The metal powder obtained by atomization can be sieved to retain particles whose size is better suited to the subsequent technology to be used, particularly additive manufacturing. For example, in the case of additive manufacturing by powder bed fusion, a range of 15 to 50 μm is preferred. In the case of additive manufacturing by laser metal deposition or direct metal deposition, a range of 45 to 150 μm is preferred.

[0068] Parts manufactured from metal powder produced by this process can be obtained by additive manufacturing techniques such as powder bed fusion (LPBF), direct metal laser sintering (DMLS), electron beam melting (EBM), selective heating sintering (SHS), selective laser sintering (SLS), laser metal deposition (LMD), direct metal deposition (DMD), direct metal laser melting (DMLM), direct metal printing (DMP), laser cladding (LC), and binder jetting (BJ). Coatings made from metal powder according to the present invention can also be obtained by manufacturing techniques such as cold spraying, thermal spraying, and high-speed oxygen fuel spraying. They can also be obtained by conventional powder metallurgy such as press forming and sintering.

[0069] The process according to the present invention can be carried out using equipment including the following: - blast furnace, - A converter capable of refining molten iron to form molten steel containing up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O. - Multiple induction reactors, - A ferroalloy supply unit capable of supplying at least one type of ferroalloy to the plurality of induction furnaces, - A dedicated reservoir for each induction reactor, each dedicated reservoir being connected to at least one gas atomizer and pressurizable.

[0070] The equipment may further include a ladle smelting furnace capable of refining molten steel to obtain a steel composition containing up to 30 ppm of oxygen.

[0071] The equipment may further include a tundish from which molten steel or refined molten steel can be poured simultaneously into all induction furnaces. Such a tundish facilitates the storage of molten steel and the supply of induction furnaces on demand. The tundish is preferably positioned above the multiple induction furnaces to further facilitate supply.

[0072] The induction furnaces are preferably movable in and out of their positions and tiltable to deslag and pour molten steel in the reservoir. They are preferably located on one floor of the steelworks, more preferably on one floor below the tundish. They are preferably located above the corresponding reservoir and atomizer to further facilitate feeding.

[0073] At least one of the multiple induction furnaces may be a vacuum induction furnace to satisfy a particular steel composition of powder. Alternatively, the equipment may further include a vacuum tank degasser and / or a vacuum oxygen decarburization vessel to adjust the composition of a particular powder. The vacuum tank degasser and the vacuum oxygen decarburization vessel are preferably located between the ladle smelting furnace and the multiple induction furnaces, or, where applicable, the tundish.

[0074] The ferroalloy supply unit preferably comprises a storage silo for each containing one type of ferroalloy, and a transport means for transporting each ferroalloy to each induction furnace, and optionally to a ladle smelter. The ferroalloy supply unit may also comprise a storage means for silicide alloys and / or nitride alloys and / or pure elements, and a transport means for transporting these materials to each induction furnace and optionally to a ladle smelter. The transport means may be supply pipes. They may reach each induction furnace directly, or reach a mixing unit where mixtures of ferroalloys, silicide alloys, nitride alloys, and pure elements are prepared before being transported to each induction furnace. The ferroalloy supply unit may also comprise a supply means for scrap and direct reduced iron.

[0075] Each dedicated reservoir is preferably connected to at least two gas atomizers so that one gas atomizer can be stopped, for example, for maintenance or repair, to collect the powder at its bottom, while maintaining continuous production of steel powder.

[0076] Each reservoir is preferably connected to at least one gas atomizer by a supply pipe. More preferably, the supply pipe is heated, for example, by induction heating, to maintain proper overheating of the molten steel and thereby prevent clogging of the atomizer nozzle. The supply pipe can be closed by a closing mechanism such as a stopper rod operated from inside the reservoir or a stopper located inside the supply pipe.

Claims

1. A method for producing steel powder having a desired composition, comprising the following steps: - Step of supplying molten iron from the blast furnace, - A step of refining the molten iron in a converter to form refined molten steel having a composition containing up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O. - The step of pouring the refined molten steel into multiple induction furnaces, - In each of the plurality of induction furnaces, at least one type of ferroalloy is added to adjust the composition of the refined molten steel to a desired composition of steel powder, thereby obtaining adjusted and refined molten steel having a desired composition in the plurality of induction furnaces. - A step of pouring the adjusted and refined molten steel from each of the plurality of induction furnaces into each dedicated reservoir of the plurality of reservoirs, wherein each dedicated reservoir of the plurality of reservoirs is connected to each gas atomizer, - A step of supplying molten steel prepared and refined from a corresponding dedicated reservoir under pressure to the gas atomizer of each of the plurality of reservoirs, and using the gas atomizer of each dedicated reservoir to gas atomize the prepared and refined molten steel to obtain steel powder having the desired composition.

2. The method according to claim 1, wherein the composition of the refined molten steel includes up to 250 ppm of C and / or up to 90 ppm of P and / or up to 25 ppm of N.

3. The method according to claim 1 or 2, comprising the steps of refining the molten iron in the converter to form refined molten steel, and further refining the refined molten steel in a ladle refining furnace, wherein the refined molten steel after further refining in the ladle refining furnace contains up to 30 ppm of oxygen.

4. The method according to claim 3, wherein the ladle smelting furnace is maintained at a temperature between 1520 and 1700°C.

5. The method according to claim 3 or 4, wherein the refined molten steel is poured directly from the ladle smelting furnace into the plurality of induction furnaces.

6. The method according to claim 3 or 4, wherein the refined molten steel is first poured from the ladle smelting furnace into a tundish, and then poured from the tundish into the plurality of induction furnaces.

7. The method according to claim 6, wherein the tundish is configured to pour the refined molten steel into each of the plurality of induction furnaces simultaneously.

8. The method according to claim 6 or 7, wherein the tundish is maintained at a temperature between 1520 and 1620°C.

9. The method according to any one of claims 6 to 8, wherein the tundish is purged with argon to control the oxygen content in the tundish.

10. The method according to any one of claims 3 to 9, wherein the refined molten steel is further processed in a vacuum tank degasser or a vacuum oxygen decarburization vessel before or after further refining in the ladle refining furnace.

11. The method according to any one of claims 1 to 10, wherein each of the plurality of induction furnaces is maintained at a temperature between 1500 and 1700°C.

12. The method according to any one of claims 1 to 11, wherein at least one of the plurality of induction furnaces is maintained at a temperature between 1620 and 1650°C.

13. The method according to any one of claims 1 to 12, wherein the at least one ferroalloy added to each of the plurality of induction furnaces is not pre-melted.

14. The method according to any one of claims 1 to 13, wherein scrap or directly reduced iron or silicide alloy or nitride alloy or pure element or mixture thereof is added to at least one of the plurality of induction furnaces.

15. The method according to any one of claims 1 to 14, wherein none of the induction furnaces among the plurality of induction furnaces are atmosphere-controlled.

16. The method according to any one of claims 1 to 14, wherein at least one of the plurality of induction furnaces is a vacuum induction furnace.

17. The method according to any one of claims 1 to 16, wherein each of the plurality of reservoirs has an atmosphere comprising argon, nitrogen, or a mixture thereof.

18. The method according to any one of claims 1 to 17, wherein each of the plurality of reservoirs is maintained at a temperature between 1300 and 1750°C.

19. The method according to any one of claims 1 to 18, wherein each of the plurality of reservoirs is maintained at a temperature at least 150°C above the liquidus temperature of the adjusted and refined molten steel poured into the reservoir.

20. Equipment for producing steel powder having a desired composition, comprising the following: - Blast furnaces that supply molten iron, - A converter configured to refine the molten iron and form refined molten steel having a composition containing up to 600 ppm of C, up to 120 ppm of S, up to 125 ppm of P, up to 50 ppm of N, and up to 1200 ppm of O, - Multiple induction reactors, - A ferroalloy supply unit configured to supply at least one type of ferroalloy to the plurality of induction furnaces, - A plurality of reservoirs, each including a dedicated reservoir for each of the plurality of induction furnaces, wherein each of the plurality of reservoirs is connected to and pressurized by at least one gas atomizer.

21. The apparatus according to claim 20, further comprising a ladle smelting furnace configured to further refine the refined molten steel, wherein the refined molten steel after further refinement in the ladle smelting furnace contains up to 30 ppm of oxygen.

22. The apparatus according to claim 20 or 21, further comprising a tundish configured to pour the molten steel into each of the plurality of induction furnaces simultaneously.

23. The apparatus according to claim 22, wherein the tundish is positioned above the plurality of induction furnaces.

24. The apparatus according to any one of claims 20 to 23, further comprising a vacuum tank degasser (VTD) or a vacuum oxygen decarburization (VOD) container.