JP2019536901A - Self-generating protective atmosphere for liquid metals - Google Patents

Abstract

Provided is an improved method for manufacturing cast parts from powder metal materials by sand casting, permanent mold casting, investment casting, lost foam casting, die casting, or centrifugal casting, or water, gas, plasma, ultrasonic, or rotary disk atomization. Is done. The method includes adding at least one additive to the molten metal material before or during the casting or atomization process. The at least one additive forms a protective gas atmosphere surrounding the molten metal material that is at least three times greater than the volume of the melt to be treated. The protective atmosphere prevents the introduction or reintroduction of contaminants such as sulfur (S) and oxygen (O2) into the material. The cast parts or atomized particles produced include at least one of the following advantages: less internal pores, less internal oxides, median circularity of at least 0.60, median of at least 0.60. Roundness, and increased sphericity of microstructure phases and / or components.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This patent application is filed with US Provisional Patent Application No. 62 / 409,192 filed October 17, 2016, and US Utility Model Patent Application No. 15 filed September 1, 2017. No./693,747, the content of which is incorporated herein by reference in its entirety.

  The present invention relates generally to metallic materials, and more particularly to molten metal materials that have been atomized or solidified to form powdered metals or castings, and methods of forming the same.

  Powdered metal materials can be formed by various processes, such as water atomization, gas atomization, plasma atomization, ultrasonic atomization, or rotating disks. Powdered metal materials are used in a variety of different technologies, such as pressing and sintering, metal injection molding, and additive manufacturing. Metal castings are also commonly used in a variety of technologies, including both automotive and non-automotive parts, and can be used in a variety of applications, such as sand casting, permanent mold casting, investment casting, lost foam casting, die casting, or centrifugal casting. It is manufactured by a simple process. The atomization and casting processes both begin with molten metal material. A common atomization process involves applying a fluid (water, gas, oil, ultrasonic, or plasma) to a molten metal material to form a plurality of particles. The casting process typically involves pouring molten metal material into a mold having the desired shape and solidifying the liquid metal before removing the metal part from the mold.

  One aspect of the present invention provides a method of making a powdered metal material. The method comprises adding at least one additive to the molten base metal material, wherein the at least one additive surrounds the molten base metal material having at least three times the volume of the molten base metal material to be treated. Forming, adding, and atomizing the molten base metal material after adding at least some of the at least one additive to produce a plurality of particles. Another aspect of the present invention provides a powdered metal material formed from a molten metal material having a self-generated protective atmosphere.

  Another aspect of the present invention provides a method for manufacturing a cast component. The method comprises adding at least one additive to the molten base metal material, wherein the at least one additive surrounds a molten metal material having at least three times the volume of the molten base metal material to be treated. Forming, adding, and adding at least some of the at least one additive, followed by casting the molten metal material. Another aspect of the present invention provides a casting formed from a molten metal material having a self-generated protective atmosphere.

Both methods involve producing a self-generated protective atmosphere in the molten base metal material. Adding at least one additive to the molten base metal material can improve the quality of the melt. At least one additive can create a protective atmosphere that acts as a protective barrier against oxidation. The protective atmosphere also acts as a barrier to prevent impurities such as sulfur (S) and / or oxygen (O ₂ ) from entering or re-entering the molten metal material. Thus, the at least one additive may limit oxidation and limit the amount of internal oxides during the melting and pouring stages of the process. Further, the physical structure and / or microstructural characteristics of the powder particles in the solidified metallic material can be altered to improve or affect material properties. For example, at least one additive may also contribute to microstructural engineering of the precipitate, such as size and morphology.

  When the molten metal material is atomized, the at least one additive can shape the shape and morphology of the resulting powder particles. Even in the case of powder atomization, the at least one additive improves the roundness and sphericity of the resulting powder particles. The amount of internal voids in powders and castings can also be reduced.

  The nebulizing step may also include producing a plurality of particles having a spherical shape. The sphericity of the particles, and the sphericity of the shape of the microstructured phases or components in the nebulized, as-cast, or heat-treated nebulized particles or castings is given by the following equation: In accordance with the analysis index of the two images, specifically, the circularity and the roundness.

Circularity (C) = 4π × ([Area] / [Perimeter] ² )
New circularity (R) = 4 × ([area] / (π × [long axis] ² )) = 1 / AR
Where AR = [long axis] / [short axis].

  Image analysis indices can be calculated using open source software such as ImageJ (http://imagej.nih.gov/ij/). A sphericity index value of 1.0 indicates a perfect circle.

  Other advantages of the present invention will be readily understood as they become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

FIG. 3 shows additives (cells marked with “x”) that create a protective gas atmosphere for various chemical systems (Al, Cu, Mn, Ni, Co, Fe, Ti, and Cr). FIG. 3 shows additives (cells marked with “x”) that react with oxides for various chemical systems (Al, Cu, Mn, Ni, Co, Fe, Ti, and Cr). FIG. 3 shows additives (cells marked with “x”) that react with sulfur for various chemical systems (Al, Cu, Mn, Ni, Co, Fe, Ti, and Cr). FIG. 4 shows a curve of the calculated total volume of gas evolved as a function of the amount of additive for an exemplary composition. 5 is a graph showing experimentally obtained EDS spectra on a polished pure iron surface before and after exposure to the atmosphere above the tundish during the powder atomization process described in FIG. FIG. 4 is a graph showing the calculated volume of gas generated by sodium (Na) and potassium (K) additives in aluminum at different temperatures (800 degrees Celsius and 900 degrees Celsius), with the dashed line indicating the lower limit of gas. FIG. 4 is a graph showing the calculated volume of gas generated by various additives in titanium at a temperature of 1800 degrees Celsius, with the dashed line indicating the lower limit of gas. FIG. 4 is a graph showing the calculated volume of gas generated by various additives in cobalt at a temperature of 1600 degrees Celsius, with the dashed line indicating the lower limit of gas. FIG. 3 is a graph showing the calculated volume of gas generated by various additives in chromium at a temperature of 2000 degrees Celsius, with the dashed line indicating the lower limit of gas. FIG. 4 is a graph showing the calculated volume of gas generated by various additives in copper at a temperature of 1200 degrees Celsius, with the dashed line indicating the lower limit of gas. FIG. 4 is a graph showing the calculated volume of gas generated by various additives in iron at a temperature of 1650 degrees Celsius, with the dashed line indicating the lower limit of gas. 1 is a graph showing the calculated volume of gas generated by various additives in manganese at a temperature of 1400 degrees Celsius, with the dashed line indicating the lower limit of gas. FIG. 3 is a graph showing the calculated volume of gas generated by various additives in nickel at a temperature of 1600 degrees Celsius, with the dashed line indicating the lower limit of gas. FIG. 4 is a graph showing the calculated total volume of gas obtained per 100 grams of composite cobalt alloy melt at a temperature of 1600 degrees Celsius as a function of the amount of additives (K and Li). Backscattered electron micrograph of water-sprayed hypereutectic cast iron powder without added magnesium, with many irregular primary graphite nodules precipitated on the internal silicon oxide introduced into the melt during the injection step of the atomization process. is there. FIG. 3 is a backscattered electron micrograph of another water-sprayed hypereutectic cast iron powder with added magnesium, with one spherical primary graphite nodule precipitated on the heterogeneous oxide nuclei containing Mg during the atomization process. Figure 5 is a backscattered electron micrograph of a water atomized hypereutectic cast iron powder containing about 4.0% C and 2.3% Si without the addition of magnesium, the graphite nodules grown in the solid state during the post heat treatment process. 3 is a backscattered electron micrograph in which is present. FIG. 18 is a photomicrograph of another water-sprayed hypereutectic cast iron powder with added magnesium according to an exemplary embodiment, showing a more spherically grown solid state during the post heat treatment process as compared to that shown in FIG. 17. It is a microscope picture in which graphite nodule exists. FIG. 19 is a diagram showing the circularity frequency distribution of graphite nodules observed in the water atomized hypereutectic cast iron powder shown in FIGS. 17 and 18. FIG. 19 is a diagram showing the roundness frequency distribution of graphite nodules observed in the water atomized hypereutectic cast iron powder shown in FIGS. 17 and 18. 19 is a table showing numerical data on the circularity of graphite nodules grown in a solid state for the two hypereutectic cast iron powders observed in FIGS. 17 and 18. 19 is a table showing numerical data on the roundness of graphite nodules grown in a solid state with respect to the two hypereutectic cast iron powders observed in FIGS. 17 and 18. Backscattered electron micrographs of water atomized stainless steel powder without magnesium added, sieved through -80 / + 200 mesh (177-74 microns), where red arrows indicate backscattered electron micrographs pointing to internal voids. is there. 23 is a backscattered electron micrograph of another water atomized stainless steel powder with magnesium added, sieved through -80 / + 200 mesh (177-74 microns), with one red arrow comparing to that of FIG. 4 is a backscattered electron micrograph pointing to only one small internal void. Optical micrograph of water atomized high carbon steel alloyed with silicon powder containing about 1.3% C and 1.1% Si without magnesium addition, sieved through -200 mesh (74 microns or less) Wherein the red arrow is an optical micrograph pointing to the internal void. Comparative water alloyed with silicon containing about 1.4% C and 1.1% Si with magnesium added, sieved through -200 mesh (74 microns or less) according to one exemplary embodiment. 25 is an optical micrograph of the atomized high carbon steel, wherein the red arrow indicates that the internal voids are less than the powder of FIG. FIG. 3 includes a table listing the evaluated compositions.

  One aspect of the present invention is to provide water or gas atomization, or plasma atomization, by adding at least one additive to the molten metal material before and / or during the atomization process. Includes improved methods of producing powdered metal materials by any atomization process that requires going through the creation of a liquid metal bath, such as ultrasonic atomization, or rotating disk atomization. Another aspect of the invention is a process such as sand casting, permanent casting, investment casting, lost foam casting, die casting, or centrifugal casting from molten metal material by adding at least one additive to the molten metal material. Includes improved methods of manufacturing castings. The at least one additive forms a protective gas atmosphere surrounding the molten metal material that is at least three times greater than the volume of the melt to be treated.

The protective atmosphere created by the at least one additive added to the molten material is such that impurities, such as sulfur (S) and / or oxygen (O ₂ ) or others, as the protective gas comes out of the melt. Acts as a barrier to prevent intrusion or re-entry into the molten metal material by extruding them from the surface of the molten material. The additive forming the protective gas atmosphere can also react with dissolved sulfur in the melt and / or oxides suspended in the melt before the introduction of the additive. The reaction of the additive with the dissolved sulfur in the melt increases the sphericity of the atomized particles formed from the melt and / or reduces the sphericity of the microstructured phases and components in the atomized particles or casting. increase.

  When water atomization is used, the addition of an additive to the molten metal material can increase the sphericity of the atomized particles to a level close to the sphericity of the particles formed by gas atomization. The cost is low in comparison. Adding additives to the molten metal material also limits the formation and entrainment of new oxides from the surface of the melt, by reacting with those already present in the melt before the introduction of the additives. Cleaner particles can be produced. These oxides can be formed as bilayer films in which the oxide films fold over themselves, leaving a weak interface between the oxide films. Additives can also reduce the amount and size of internal voids, a problem encountered with atomized powders. Additives can also increase the sphericity of microstructural components and / or phases formed in the atomized particles and / or during the subsequent heat treatment process. For example, if the atomized particles are formed from a cast iron material, at least 50% of the graphite precipitate formed during the post heat treatment process has a circularity of at least 0.6 and a roundness of at least 0.6.

  When casting is used, additives can be added to the molten metal material to increase the sphericity of the microstructural components and / or phases formed during casting and / or during subsequent heat treatment processes. Adding additives to the molten metal material also limits the formation and entrainment of new oxides from the surface of the melt and reacts with those already present in the melt prior to the introduction of the additives. By doing so, a cleaner casting can be manufactured. These oxides can be formed as bilayer films in which the oxide films fold over themselves, leaving a weak interface between the oxide films. Additives can also reduce the amount and size of internal voids, a problem encountered in many castings.

  According to one exemplary embodiment, the method begins with melting a base metal material. Many different metal compositions can be used as the base metal material. However, in order to produce enough gas to act as a protective atmosphere, thereby obtaining the desired spherical powder and / or more spherical microstructure components and / or cleaner particles, and / or to reduce the internal pores To have, the additive must have low solubility in the metallic material. The substrate and additives should be selected such that the volume of the protective gas atmosphere generated when the additives are introduced is at least three times the volume of the molten metal material being treated. For example, if 0.22 weight percent (% by weight) of magnesium is added to an iron-rich melt, the volume of gas evolved provides a protective atmosphere defined as three times the initial volume of the melt to be treated. About 20 times the lower limit of the gas required to perform

  Base metal materials are typically aluminum (Al), copper (Cu), manganese (Mn), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), and chromium (Cr). At least one of them. The base metal material can include pure Al, Cu, Mn, Ni, Co, Fe, Ti, or Cr. Aluminum-rich, copper-rich, manganese-rich, nickel-rich, cobalt-rich, iron-rich, titanium-rich, chromium-rich alloy, or at least 50% by weight of Al, Cu, Mn, Ni, Co, Fe, Ti, and / or Cr. Containing alloys are also well suited for use as starting base metal materials. Mixtures of these base metal materials in different proportions are also used as starting materials such as Al-Cu, Fe-Ni, Fe-Co, Fe-Ni-Co, Ni-Cr, Ti-Cu and Co-Cr alloys. But is not limited to these. The alloys can also include at least one of the following as alloying elements, as long as they remain in solution in the melt of the desired alloy: silver (Ag), boron (B), barium (Ba) , Beryllium (Be), carbon (C), calcium (Ca), cerium (Ce), gallium (Ga), germanium (Ge), potassium (K), lanthanum (La), lithium (Li), magnesium (Mg) , Molybdenum (Mo), nitrogen (N), sodium (Na), niobium (Nb), phosphorus (P), sulfur (S), scandium (Sc), silicon (Si), tin (Sn), strontium (Sr) , Tantalum (Ta), vanadium (V), tungsten (W), yttrium (Y), zinc (Zn), and zirconium (Zr).

  A distinction may be made between elements described as "alloy elements" and elements described as "additives". The alloying elements remain dissolved in the base metal material and / or form different phases / components in the final part / powder. Alloying elements affect the microstructure and properties of the part. For example, C in Fe forms cementite which increases strength. Additives are defined as elements added to the melt to create a protective gas atmosphere and react with S and / or oxides. Figures 1-3 include a listing of additives for various base metal materials. One particular element may be an alloying element in one substrate, but may be an additive in a different substrate. For example, Mg is an alloy element in the Al-rich alloy, but is an additive in the Fe-rich alloy. According to one exemplary embodiment, to create a gaseous protective atmosphere in the Al-Mg alloy, K and / or Na must be used as an additive and the melting temperature selected according to the selected additive. Must. For example, since Mg is used as an alloy element of an aluminum alloy (Al-5000 series), no protective gas atmosphere is generated.

  However, the starting metal material is not limited to the above composition. Other metal compositions can be used as long as the additive has low solubility in the selected material and generates a sufficient amount of protective gas atmosphere. Some additives used to create a gaseous protective atmosphere react spontaneously with dissolved sulfur in the melt to produce more stable compounds, thereby increasing surface tension. This is the case for Mg in an Fe-rich system where solid MgS precipitates. However, some additives, while creating a protective atmosphere, do not react with dissolved sulfur, as is the case with Na in Fe-rich systems. In such situations, various additives must be used in combination to increase the surface tension and create a protective atmosphere.

  As described above, a variety of different additives can be added to the molten metal material to achieve an increased protective atmosphere and other benefits described above. The additive selected depends on the composition of the base metal material. For example, the at least one additive may include at least one of K, Na, Zn, Mg, Li, Ca, Sr, and Ba. The protective gas atmosphere generated by the additive prevents impurities from penetrating or re-entering the molten metal material.

  The above additives generate different amounts of protective gas atmosphere, depending on the chemical system in which they are used. Some additives are more suitable for some systems than others. For example, in aluminum alloys, K and Na are often preferred. In copper alloys, K and Na are often preferred. For manganese alloys, K, Na, Zn, Mg, and Li are often preferred. For nickel alloys, K and Na are often preferred. For cobalt alloys, K, Na, Li, and Ca are often preferred. For iron alloys, K, Na, Zn, Mg, Li, Sr, and Ca are often preferred. For titanium alloys, Zn, Mg, Li, Ca, and Ba are often preferred. For chromium alloys, K, Na, Zn, Mg, Li, Sr, Ca, and Ba are often preferred. An example is provided in FIG. 1 with the preferred additives marked.

  According to one particular exemplary embodiment, the metal-based material includes Mg that is rich in iron and generates a protective gas and also reacts with sulfur impurities. Alternatively, the base metal material is pure iron and the additive is Mg. According to another particular example, the metal-based material is iron-rich, and the additive comprises a mixture of K and Ba. Potassium (K) generates a protective gas atmosphere and barium (Ba) reacts with sulfur.

The protective atmosphere limits the amount of atomized particles and oxides in the casting, and also limits the size and amount of the atomized particles and internal voids in the casting. Some additives used to create a gaseous protective atmosphere, such as Mg additives in Fe-rich systems containing Si as alloying element, react spontaneously with oxides suspended in the melt. To produce more stable compounds and their morphology changes during the chemical reaction process. In these materials, the oxide of SiO ₂ , which may be in the form of a bilayer film (overlapping film of poorly bound oxide), is suspended in the melt. One of the reasons for explaining that a smaller amount of voids is observed is that Mg helps bond the interface between the overlapping films as a result of the chemical reaction between Mg and the oxide. And then to create a stronger interface that cannot be separated to form pores. The self-generated Mg gaseous atmosphere limits further oxidation of the melt surface, which limits the amount of internal oxides in the particles. However, some additives, while creating a protective atmosphere, do not react with oxides suspended in the melt, as is the case for Zn in Ti-rich systems. In such situations, different additive combinations must be used to limit the amount and size of the internal voids. For example, at least one additive can be added to create a protective gas atmosphere that prevents the intrusion or re-entry of impurities into the molten metal material, and at least one additive can be added to the molten metal material to form a protective gas atmosphere. Although it can react with oxides, it does not always create a protective gas atmosphere. Examples of such combinations of additives in a Ti-rich alloy to produce more spherical particles and / or phases and components with less internal voids do not contribute to the generation of a protective atmosphere, but and Zn to produce, may be a mixture of Sr to react with S and TiO _2.

In other words, some additives are more effective in some systems than others, depending on the type of oxide formed. As indicated above, if less internal voids having a smaller size are desired, the additive must react with oxides in suspension in the melt. These oxides are also considered as impurities in the molten base metal material, for example, Al ₂ O ₃ in aluminum-based materials or Fe ₂ O ₃ in iron-based materials. When the molten base metal material is an aluminum alloy or aluminum-based, preferred additives for reacting with the oxide include K, Na, Mg, Li, and Ca. When the molten base metal material is an iron alloy or iron-based, preferred additives for reacting with the oxide include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the molten base metal material is a titanium alloy or a titanium-based material, preferred additives for reacting with the oxide include Sr, Ca, and Ba. When the molten base metal material is a chromium alloy or chromium-based, preferred additives for reacting with the oxide include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the molten base metal material is a cobalt alloy or a cobalt-based, preferred additives for reacting with the oxide include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the molten base metal material is a copper alloy or copper-based, preferred additives for reacting with the oxide include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the molten base metal material is a manganese alloy or manganese-based, preferred additives for reacting with the oxide include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. When the molten base metal material is a nickel alloy or a nickel-based material, preferred additives for reacting with the oxide include K, Na, Zn, Mg, Li, Sr, Ca, and Ba. An example is shown in FIG.

  When the molten base material is iron-based and contains sulfur as an impurity, Zn, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. An example of such a combination of additives in an iron-based material or Fe-rich alloy to produce more spherical particles and / or phases and components may be a mixture of Na and Ba. Na produces a protective atmosphere and Ba and reacts with S. When the molten base metal material is a titanium alloy or a titanium-based material and contains sulfur as an impurity, K, Na, Zn, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. When the molten base metal material is a cobalt alloy or a cobalt-based material and contains sulfur as an impurity, Na, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. When the molten base metal material is a chromium alloy or a chromium-based material and contains sulfur as an impurity, K, Na, Zn, Mg, Sr, Ca, and Ba are preferable for reacting with sulfur. When the molten base metal material is an aluminum alloy or an aluminum-based material and contains sulfur as an impurity, K, Na, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. When the molten base metal material is a nickel alloy or a nickel-based material and contains sulfur as an impurity, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. When the molten base metal material is a copper alloy or a copper-based material and contains sulfur as an impurity, K, Na, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. When the molten base metal material is a manganese alloy or a manganese-based material and contains sulfur as an impurity, K, Na, Mg, Li, Sr, Ca, and Ba are preferable for reacting with sulfur. An example is shown in FIG.

  In addition, certain additives successfully generate a protective gas atmosphere and also react with sulfur and oxides present as impurities in the molten base metal material. For example, when the molten base metal material is an iron alloy or an iron-based additive that generates a protective gas atmosphere and reacts with sulfur and oxide impurities includes Zn, Mg, Li, Sr, and Ca. When the molten base metal material is a titanium alloy or a titanium-based material, additives that generate a protective gas atmosphere and react with sulfur and oxide impurities include Ca and Ba. When the molten base metal material is a chromium alloy or chromium-based additive that generates a protective gas atmosphere and reacts with sulfur and oxide impurities includes K, Na, Zn, Mg, Sr, Ca, and Ba. When the molten base metal material is a cobalt alloy or a cobalt-based additive that generates a protective gas atmosphere and reacts with sulfur and oxide impurities includes Na, Li, and Ca. When the molten base metal material is an aluminum alloy or an aluminum-based material, additives that generate a protective gas atmosphere and react with sulfur and oxide impurities include K and Na. When the molten base metal material is a copper alloy or a copper-based additive that generates a protective gas atmosphere and reacts with sulfur and oxide impurities includes K and Na. When the molten base metal material is a manganese alloy or manganese-based additive that generates a protective gas atmosphere and reacts with sulfur and oxide impurities includes K, Na, Mg, and Li.

  As mentioned above, the molten metal material can be atomized, for example by water or gas atomization, to form a powdered metal. Alternatively, the molten metal material can be formed into a casting.

  As suggested above, the starting base metal material selected often contains iron in an amount of at least 50.0% by weight, based on the total weight of the metal material before adding the additives. For example, cast iron, high alloy cast iron, stainless steel, non-alloyed and alloyed steel, tool steel, maraging steel, or hadfield steel can be used. According to one exemplary embodiment, the metallic material is a steel powder comprising 1.3% by weight of carbon and 1.1% by weight of silicon. According to another exemplary embodiment, the metallic material is a cast iron powder comprising 4.0 wt% carbon and 2.3 wt% silicon. According to another exemplary embodiment, the metallic material comprises: 1.2% Mn, 0.30% Si, 0.44% Cu, 0.23% Mo, 17.3% Cr, Stainless steel powder containing 9.5% Ni and other trace elements. As described above, aluminum alloys (e.g., alloys designated as 2024, 3003, 3004, 6061, 7075, 7475, 5080, and 5082), copper alloys (such as aluminum bronze, silicon bronze, and brass), manganese alloys, Nickel alloys (e.g., alloys represented as 625), cobalt alloys (e.g., Tribaloy and Haynes 188), cobalt-chromium alloys (e.g., CoCrMo alloys and stellite), titanium alloys (e.g., Ti-6Al-4V or Ti-6Al) Alloys), chromium alloys (such as the Kh65 NVFT alloy), and any hybrid alloys made from these chemical systems can also be used as starting powder metal materials (eg, Invar, Monel, Chromel, Alnico, and Ni). Alloys represented as inol60). These examples are not exhaustive and at least one additive (potassium (K), sodium (Na), zinc (Zn), magnesium (Mg), lithium (Li), strontium (Sr), calcium ( Ca), and barium (Ba)) can be used as long as their solubility in the selected material is low, resulting in the formation of a protective gas atmosphere on top of the molten material, resulting in processing. To form at least three times the initial volume of the melt to be melted. 4-14 represent the results of performed calculations and experiments showing the increase in volume of the protective gas atmosphere that occurs when additives are added to a molten metal material according to an exemplary embodiment of the present invention. FIG. 4 represents a curve of the total volume of gas obtained as a function of the amount of additive for an exemplary composition. Additives (where the additives were a mixture of 90 wt% Mg and 10 wt% Na). This alloy is a cast iron powder material (Fe rich) containing 4.0% C, 1.5% Si, 0.02% S, and 2.0% Cu. This curve was calculated using the chemical composition of one water atomized powder, the amount of additive used in this experiment was 0.11% by weight, which was Provided about 0.40 liters of protective gas (Mg and Na). The dashed line represents the lower limit of gas that should be obtained to provide a protective atmosphere that is three times the initial volume of the melt to be treated. In this example, the calculated gas volume is about five times the lower limit.

  FIG. 5 shows energy dispersive X-ray spectroscopy obtained on a polished pure iron surface before and after exposure to a gaseous atmosphere above the tundish during the powder atomization process described in FIG. 3 shows an EDS) spectrum. This confirms that the additives (in this case Mg and Na) formed a gaseous protective atmosphere generated on top of the melt and that these elements were deposited on the exposed polished iron surface.

  FIG. 6 shows examples of different amounts of gas that can be generated in an aluminum alloy at different temperatures for different additives. The basic system of calculation is Al + 0.02% S + 0.02% Al2O3. The dashed line represents the lower limit of the amount of gas that should be obtained to provide a protective atmosphere defined as three times the initial volume of the melt to be treated. In these examples, the minimum amount of additive added depends on the nature of the additive and the temperature of the melt. For example, if the melt is at a temperature of about 800 degrees Celsius, Na cannot generate enough gas regardless of the amount added. However, when the temperature of the melt rises to about 900 degrees Celsius, the minimum amount of Na to generate at least three times the initial volume of the melt to be treated is about 0.32% by weight. For K, the minimum amount is 0.36% by weight when the melt is 800 degrees Celsius and 0.26% by weight when the melt is about 900 degrees Celsius. If a mixture of half Na and half K is used in an aluminum melt at 900 degrees Celsius, the minimum amount of Na + K is about 0.29 wt% (0.16 wt% Na and 0.13 wt% % K). FIG. 7 shows an example of the minimum amount of different additives added to a titanium melt at 1800 degrees Celsius. For example, the addition of 0.11 wt% Ca provides about the same minimum amount of gas protection as the addition of 0.48 wt% Zn. 8-13 show other examples of different amounts of different additives in different systems (Co, Cr, Cu, Fe, Mn, and Ni). FIG. 14 shows the calculated minimum amount of additive (K + Li) in the composite cobalt alloy.

  After adding at least one additive to the molten base metal material, the melt can be atomized or cast. Water atomization is often preferred because it is 3 to 9 times cheaper than gas atomization and even cheaper than other atomization processes. However, for some alloys that are easily oxidized, gas atomization is preferred. Additional treatment prior to gas atomization allows for improved conditions for atomization, such as higher gas pressure, yet still achieves round particles and can also limit the amount of internal oxides and voids . In addition, the added additives can increase the sphericity of the water atomized particles so that the sphericity approaches that of the gas atomized particles.

  As mentioned above, the additives are added in such an amount that the total volume of the gas after the introduction of the additives is at least three times the initial volume of the melt to be treated. In one exemplary embodiment, the additive, in this case Mg, comprises 0.05-1.0% by weight, e.g. 0%, based on the total weight of the molten base metal material (iron-rich alloy) and the added magnesium. It is added in a single operation as a mass of pure Mg in an amount in the range of .18% by weight. Thus, the resulting atomized powder metal material or casting, as well as the material without additives, contains a very small amount of residual magnesium and total sulfur content, but with this atomized powder metal material, Is chemically bound to the additive and is not dissolved in the melt (as a solid precipitate of MgS), which results in greater surface tension, and thus more spherical particles, and / or more spherical particles. Providing microstructure phases and components and / or lesser amounts of internal voids. Thermodynamic calculations show that the free sulfur content in the Mg-treated iron-rich material is more than 10 times lower than that of the untreated material, even if the total sulfur content of both materials is similar Was done.

  The additive may be present in a single continuous step, for example up to 1.0% by weight in a single continuous step, or in multiple steps spaced from one another at certain time intervals, for example up to 0.2% by weight of the additive. Can be added in three or four steps, respectively. Additionally or alternatively, the additives can be added in a furnace or in a ladle, which can be in the form of a pure metal or as an alloy or compound containing the additives. Various techniques that are already available can be used to introduce additives into molten metal materials, such as, but not limited to, chunks / chunks of material containing the additives, the top of the melt, or It can be deposited directly on the bottom of the furnace / crucible, or in a mold, or it can be introduced into the melt by using cored wire technology or a plunger process. For example, cored wire technology uses a steel sheath filled with a Mg-rich alloy and is introduced into the melt at a rate that depends on process parameters. Plunger technology uses a vessel in which a Mg-containing master alloy is placed, which vessel is cast into liquid cast iron. Thus, the magnesium contacts the liquid cast iron deeper in the melt away from the surface.

  As described above, by adding additives to the molten metal material (in the case of Mg in a Fe-rich alloy), the number of water atomized particles having a circularity and roundness value of 0.6 or more is reduced. Increased by at least 8% compared to the same water atomized material without additives. Additives, such as magnesium, can also result in less internal oxides and close the interface of the residual oxide bilayer present in the molten metal material. This produces cleaner atomized particles and cleaner castings with fewer and smaller internal voids.

  After the atomization or casting step, the method may include a post heat treatment process. The heat treatment step can include annealing or another heating process typically applied to powdered metal materials. The heat treatment can be performed in an inert or reducing atmosphere, such as, but not limited to, an atmosphere containing nitrogen, argon, and / or hydrogen, or in a vacuum. For example, annealing in a reducing atmosphere after water atomization can reduce surface oxides. The heat treatment step can also be used to form new microstructural phases and / or components, such as graphite precipitates or nodules, carbides, or nitrides, in the atomized particles or castings. Other microstructure phases and / or components may be present, depending on the composition of the metallic material. In one exemplary embodiment, the metallic material is a hypereutectic cast iron alloy, and the cementite present in the cast iron alloy converts to ferrite and spheroidal graphite nodules during the heat treatment process, see FIGS. 17 and 18. I want to be. Spherical carbides should also form during heat treatment of high alloy steels. An external protective atmosphere or vacuum system may also be used with the self-generated protective atmosphere described herein, such as a nitrogen (N2) flow onto the melt or a argon (Ar) flow. But not limited thereto. The melt can also be enclosed in a chamber provided with a protective inert atmosphere or vacuum system. These systems can increase the effectiveness of the process.

  Additives can also increase the sphericity of the microstructured components and / or phases formed in the atomized particles or casting during post heat treatment. However, more rounded phases and / or components can be present in the powdered metal material immediately after atomization as well as in the as-cast material as well as after heat treatment. The microstructure phase can include graphite precipitates, carbides, and / or nitrides. Other microstructure phases and / or components may be present, depending on the composition of the metallic material. Typically, the microstructural components and / or phases have a median circularity of at least 0.6 and a median circularity. Also, at least 10% formed in a magnesium-treated iron-based material having a circularity and roundness value greater than 0.6 compared to the same alloy but without the additive treatment. Above, preferably at least 15%, of the components and / or phases are present.

  According to one exemplary embodiment, the powdered metal material comprises iron, such as cast iron, in an amount of at least 50% by weight, and the atomized particles comprise graphite precipitate, wherein at least 50% of the graphite precipitate comprises , 0.6 or more and circularity. In another embodiment in which the metallic material is iron-based and treated with Mg, the annealing step includes producing a graphite precipitate or nodule, wherein the graphite precipitate or nodule has a circularity of at least 0.6. It has a median and a median of roundness. In one exemplary embodiment, the metallic material is a hypereutectic cast iron alloy treated with Mg, and spheroidal graphite nodules are formed during the heat treatment process.

  As mentioned above, the self-generating protective atmosphere created after the introduction of the additives suppresses the oxidation of the surface of the melt and limits the amount of internal oxides in the powder after atomization and in the casting after solidification. . FIG. 15 shows primary graphite nodules in hypereutectic cast iron powder precipitated on silicon oxide in suspension in a melt formed during injection from a crucible into a tundish; The agent was not treated. In Fe-rich systems containing a high carbon content, carbon provides protection against oxidation of the melt in the crucible (due to the high temperatures), which prevents the formation of oxides in the crucible. Numerous graphite nodules grown on these different oxides can be observed in powders without additives. By comparison, FIG. 16 shows one of the relatively small number of primary graphite nodules that can be observed in hypereutectic cast iron powder treated with the additive (Mg). The protective atmosphere made of Mg gas limited the oxidation of the melt directly from the crucible and through the injection, so that the amount of oxides present in the melt before the introduction of the additives was free of additives Significantly less than in the melt. Thus, very little substrate is available for the graphite precipitate during solidification and less graphite nodules are present.

  As described above, the molten metal material can be atomized to form a powdered metal material or cast to form a solidified component. The powdered metal material is typically formed by water or gas atomization, but other atomization processes can be used. The powders and castings obtained with the disclosed method can be used in a variety of different automotive or non-automotive applications. For example, atomized particles can be used in a typical pressing and sintering process. Atomized particles can also be used in metal injection molding, thermal spraying, and additive manufacturing applications such as three-dimensional printing, electron beam melting, binder jetting, and selective laser sintering.

  When the molten metal material is cast, the method includes melting the base metal material and then adding at least one additive to the base metal material. The method then includes pouring the molten metal material into a mold having the desired shape and solidifying the liquid metal before removing the solidified metal part from the mold.

Experiments FIGS. 17 and 18 show microstructure phases and / or components, specifically graphite, achieved by adding an additive (magnesium in this case) before or during the water atomization process and after heat treatment. Figure 4 is a photomicrograph showing improved sphericity of nodules. Each material is a cast iron powder containing about 4.0% by weight carbon and 2.3% by weight silicon. However, the material of FIG. 17 was atomized without the addition of magnesium, whereas the material of FIG. 18 was atomized with the addition of magnesium. The median roundness of the graphite nodules shown in FIG. 17 without added magnesium was calculated to be 0.56. The median roundness of the graphite nodules containing magnesium shown in FIG. 18 was calculated to be 0.73. Other results showing an improvement in the sphericity of nodules by additive treatment are shown in FIGS.

  Figures 23 and 24 show lower internal void content according to an exemplary embodiment of the present invention. In this example, 304 stainless steel was atomized with water. The powder shown in FIG. 24 was treated with Mg and showed a smaller amount of internal voids.

  Figures 25 and 26 show a lower internal void content according to an exemplary embodiment of the present invention. In this example, high carbon steel alloyed with silicon was atomized with water. The powder shown in FIG. 26 was treated with Mg and showed a smaller amount of internal voids.

FIG. 27 shows the chemical composition of an exemplary embodiment of the invention.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings, and may be implemented in other ways than those specifically described while remaining within the scope of the following claims. In particular, all features of all claims and all embodiments can be combined with one another, as long as they do not conflict with one another.

Claims (28)

A method for producing a powder metal material, comprising:
Adding at least one additive to the molten base metal material, wherein the at least one additive surrounds the molten base metal material having a volume at least three times the volume of the molten base metal material to be treated. Forming an atmosphere, and atomizing the molten base metal material after adding at least some of the at least one additive to produce a plurality of particles.   The method of claim 1, wherein the molten base metal material is iron-based and the at least one additive comprises magnesium.   The method of claim 1, wherein the atomizing step comprises water atomization, gas atomization, plasma atomization, ultrasonic atomization, or rotating disk atomization.   The molten base metal material is at least one of aluminum (Al), copper (Cu), manganese (Mn), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), and chromium (Cr). Wherein the molten base metal material is silver (Ag), boron (B), barium (Ba), beryllium (Be), carbon (C), calcium (Ca), cerium (Ce), gallium (Ga) , Germanium (Ge), potassium (K), lanthanum (La), lithium (Li), magnesium (Mg), molybdenum (Mo), nitrogen (N), sodium (Na), niobium (Nb), phosphorus (P) , Sulfur (S), scandium (Sc), silicon (Si), tin (Sn), strontium (Sr), tantalum (Ta), vanadium (V), tungsten (W), Potassium (Y), zinc (Zn), and optionally containing at least one alloying element selected from the group consisting of zirconium (Zr), The method of claim 1.   The method of claim 4, wherein the at least one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba.   The said molten base metal material is an iron type | system | group, The said at least one additive which forms the said protective gas atmosphere contains at least one of K, Na, Zn, Mg, Li, Sr, and Ca. 5. The method according to 4.   5. The molten base metal material is iron-based, includes sulfur present as an impurity, and the at least one additive includes at least one of Zn, Mg, Li, Sr, Ca, and Ba. The method described in.   The molten base metal material is iron-based and includes at least one oxide present as an impurity, and the at least one additive includes at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba. 5. The method of claim 4, comprising one.   The molten base metal material is iron-based, includes sulfur and at least one oxide present as impurities, and the at least one additive forming the protective gas atmosphere includes Zn, Mg, Li, Sr, and Ca. 5. The method of claim 4, comprising at least one of the following.   The molten base metal material is an aluminum alloy, which contains sulfur and / or at least one oxide present as impurities, and wherein the at least one additive forming the protective gas atmosphere is at least one of K and Na And the at least one additive comprises at least one of K, Na, Mg, Li, Sr, Ca, and Ba for reacting with the sulfur, and / or the at least one additive 5. The method of claim 4, wherein comprises at least one of K, Na, Mg, Li, Ca for reacting with the at least one oxide.   The molten base metal material is titanium-based, includes sulfur present as an impurity and / or at least one oxide, and the at least one additive forming the protective gas atmosphere includes Zn, Mg, Li, Ca, and Comprising at least one of Ba, wherein the at least one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba for reacting with the sulfur. 5. The method of claim 4, wherein the at least one additive comprises at least one of Sr, Ca, and Ba for reacting with the at least one oxide.   The molten base metal material is a cobalt alloy and includes sulfur present as an impurity and / or at least one oxide, and the at least one additive forming the protective gas atmosphere includes K, Na, Li, and Ca. And at least one additive includes at least one of Na, Mg, Li, Sr, Ca, and Ba for reacting with the sulfur, and / or the at least one additive. 5. The method of claim 4, wherein the one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, Ba for reacting with the at least one oxide.   The molten base metal material is a chromium alloy, includes sulfur present as an impurity and / or at least one oxide, and the at least one additive forming the protective gas atmosphere is K, Na, Zn, Mg, Li. , Sr, Ca, and Ba, wherein the at least one additive comprises at least one of K, Na, Zn, Mg, Sr, Ca, and Ba for reacting with the sulfur. And / or the at least one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba for reacting with the at least one oxide The method of claim 4.   The method of claim 4, wherein the molten base metal material is iron-based and the at least one additive comprises Mg. A method of manufacturing a cast part, comprising:
Adding at least one additive to the molten base metal material, wherein the at least one additive surrounds the molten base metal material having a volume at least three times the volume of the molten base metal material to be treated. Forming an atmosphere, and casting the molten metal material after adding at least some of the at least one additive.   16. The method of claim 15, wherein said molten base metal material is iron-based and said at least one additive comprises magnesium.   16. The method of claim 15, wherein the casting step comprises sand casting, permanent mold casting, investment casting, lost foam casting, die casting, or centrifugal casting.   The molten base metal material is at least one of aluminum (Al), copper (Cu), manganese (Mn), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), and chromium (Cr). Wherein the molten base metal material is silver (Ag), boron (B), barium (Ba), beryllium (Be), carbon (C), calcium (Ca), cerium (Ce), gallium (Ga) , Germanium (Ge), potassium (K), lanthanum (La), lithium (Li), magnesium (Mg), molybdenum (Mo), nitrogen (N), sodium (Na), niobium (Nb), phosphorus (P) , Sulfur (S), scandium (Sc), silicon (Si), tin (Sn), strontium (Sr), tantalum (Ta), vanadium (V), tungsten (W), Potassium (Y), zinc (Zn), and optionally containing at least one alloying element selected from the group consisting of zirconium (Zr), The method of claim 15.   19. The method of claim 18, wherein the at least one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba.   The said molten base metal material is an iron type | system | group, The said at least one additive which forms the said protective gas atmosphere contains at least one of K, Na, Zn, Mg, Li, Sr, and Ca. 19. The method according to 18.   19. The molten base metal material is iron-based and includes sulfur present as an impurity, and the at least one additive includes at least one of Zn, Mg, Li, Sr, Ca, and Ba. The method described in.   The molten base metal material is iron-based and includes at least one oxide present as an impurity, and the at least one additive includes at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba. 19. The method according to claim 18, comprising one.   The molten base metal material is iron-based, includes sulfur and at least one oxide present as impurities, and the at least one additive forming the protective gas atmosphere includes Zn, Mg, Li, Sr, and Ca. 19. The method of claim 18, comprising at least one of the following.   The molten base metal material is an aluminum alloy, which contains sulfur and / or at least one oxide present as impurities, and wherein the at least one additive forming the protective gas atmosphere is at least one of K and Na And the at least one additive comprises at least one of K, Na, Mg, Li, Sr, Ca, and Ba for reacting with the sulfur, and / or the at least one additive 20. The method of claim 18, wherein comprises at least one of K, Na, Mg, Li, Ca for reacting with the at least one oxide.   The molten base metal material is titanium-based, includes sulfur present as an impurity and / or at least one oxide, and the at least one additive forming the protective gas atmosphere includes Zn, Mg, Li, Ca, and Comprising at least one of Ba, wherein the at least one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba for reacting with the sulfur. 19. The method of claim 18, wherein the at least one additive comprises at least one of Sr, Ca, and Ba for reacting with the at least one oxide.   The molten base metal material is a cobalt alloy and includes sulfur present as an impurity and / or at least one oxide, and the at least one additive forming the protective gas atmosphere includes K, Na, Li, and Ca. And at least one additive includes at least one of Na, Mg, Li, Sr, Ca, and Ba for reacting with the sulfur, and / or the at least one additive. 19. The method of claim 18, wherein one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, Ba for reacting with the at least one oxide.   The molten base metal material is a chromium alloy, includes sulfur present as an impurity and / or at least one oxide, and the at least one additive forming the protective gas atmosphere is K, Na, Zn, Mg, Li. , Sr, Ca, and Ba, wherein the at least one additive comprises at least one of K, Na, Zn, Mg, Sr, Ca, and Ba for reacting with the sulfur. And / or the at least one additive comprises at least one of K, Na, Zn, Mg, Li, Sr, Ca, and Ba for reacting with the at least one oxide The method of claim 18.   19. The method of claim 18, wherein said molten base metal material is iron-based and said at least one additive comprises Mg.