JPS5922761B2 - Method for producing water atomized raw steel powder - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing water atomized raw steel powder, and particularly to a method for producing water atomized raw steel powder, and in particular to a method for controlling the amount of oxygen and carbon. Compressibility and formability are among the most important properties of pure iron and iron-based alloy steel powder for powder metallurgy, and the higher the density and strength of a compacted material, the more its applications will expand. Furthermore, in recent years, they have been applied to applications that require heat resistance, wear resistance, and oxidation resistance, such as engine parts for automobiles and the like. This raw material is pure iron powder and Mn, Ni, Cr, Mo1
Cu1Co,,V. Water atomization is suitable as an industrial method for producing iron-based alloy steel powder containing alloying elements such as Nb and W. Conventionally, when a molten steel injection stream is water atomized with a high-speed water stream, the oxide film on the particle surface that is generated is reduced and removed, the hard water-hardened structure is annealed to soften it by recrystallization, and decarburization and denitrification are performed. Reductive annealing methods for obtaining good compressibility and formability include heat treatment in a reducing atmosphere containing hydrogen as the main component, heating in a non-oxidizing atmosphere such as reduced pressure, inert gas, etc.
There is a method in which reduction and softening are performed simultaneously using pre-alloyed carbon, or a two-stage heat treatment method in which they are combined. When performing reduction annealing in a reducing atmosphere containing hydrogen as the main component,
The load that reduces and removes the oxide film, such as the amount of hydrogen gas,
In order to reduce the dew point, temperature, time, etc., it was advantageous for the water atomized raw steel powder to have a lower oxygen content. On the other hand, the amount of carbon is unavoidably mixed in from raw materials and melting and refining processes. In addition, when actively alloying carbon for the purpose of reducing melting costs, the reduction annealing process is necessary to achieve a content that does not impede the compressibility and formability of pure iron powder or iron-based alloy steel powder after reduction annealing. The maximum content that can be decarburized is limited. However, in this case, there is no need to establish any relationship between the total oxygen content and the total carbon content of the water atomized raw steel powder, which is the raw material to be subjected to the reduction annealing process. On the other hand, in the case of a heat treatment method in which reduction decarburization is performed using pre-alloyed carbon by heating in a non-oxidizing atmosphere such as reduced pressure or inert gas, the pre-alloyed carbon and the oxygen in the water atomized raw steel powder are combined. This method performs deoxidation and decarburization through direct reaction, and recrystallization softening at the same time.The relationship between the amount of decarburization from water atomized raw steel powder and the amount of deoxidation is expressed by one or both of the following two equations. A relationship between chemical reaction amounts that satisfies the equation must be established. MO+C→M+CO↑ MO2+C→M+CO2↑ The purpose of the present invention is to provide a method for producing water-atomized raw steel powder of high quality (low density) by adjusting the amounts of oxygen and carbon. Summary of the present invention These steps include a step of melting molten steel adjusted to a predetermined composition, a step of storing the molten steel in a tundish to form a trickle, and injecting a high-speed water stream into it to water atomize it, and a step of producing the water atomized raw steel. The process includes dehydrating and drying the powder, and annealing the dried raw copper powder in a non-oxidizing atmosphere to reduce the retained oxygen by alloying and retained carbon to reduce the carbon content to 0.20% by weight or less and oxygen is 0
．． In the manufacturing method for obtaining copper powder of 25% by weight or less, the molar ratio ΔC between the amount of decarburization ΔC and the amount of deoxidation ΔO during the annealing
/△0 satisfies the range of 1.0 to 1.4, and the molten steel composition is adjusted so that the water atomized raw steel powder has oxygen of 0.80% by weight or less and carbon of 1.0% by weight or less. The method for producing water atomized raw steel powder is characterized in that the atmospheric oxygen concentration in each of the steps of trickle injection of molten steel, water atomization, and drying is set to 10% by volume or less. In order to achieve the above object, the present inventors produced water atomized steel powder that satisfied the predetermined total carbon content and total oxygen content and varied the type and content of alloying elements, and in particular, the theoretical oxygen content. The heating method →
1, when the molar ratio △C/△O of the amount of decarburization △C and the amount of deoxidation △O is 10 when induction heating is performed to 750 to 1400 ° C. for rapid reduction using alternating power of 50 cycles to 1 megacycle. It was confirmed through experiments that the value is in the range of ~1.4. Therefore, in the present invention, for the total oxygen amount of water atomized raw steel powder,
The amount of carbon remaining after deoxidizing and decarburizing annealing by heating to 750 to 1400 ° C. in a non-oxidizing atmosphere is 0.20% by weight or less, the amount of oxygen is 0.25% or less, and the amount of decarburization during the annealing is △
The molar ratio ΔC/Δ0 of C and the deoxidized amount Δ0 is 1.0 to 1.4
When adjusting the melting and refining components, a predetermined amount of carbon is alloyed in the molten steel in advance so that it falls within the range of . At this time, by limiting the total amount of oxygen after the drying step to 0.80% by weight or less, the maximum amount of carbon that can be alloyed in the molten steel in advance can be determined by the following equation. Carburizing molten steel has the effect of suppressing oxidation loss of alloy components and oxidation during water atomization, but when carburizing molten steel in an industrial melting furnace, the higher the carbon content, the more difficult it is to reach the target amount. becomes. However, if it is within about 1.0% by weight, 0.10% by weight in water atomization with a small diameter nozzle for a long time injection.
It is possible to produce raw copper powder with a permissible range of Particles that are mostly substantially dense can be produced. Furthermore, when the total oxygen content of the water atomized raw steel powder increases, the amount of carbon alloy corresponding to the amount of chemical reaction must be increased. Therefore, during annealing in a reduced pressure atmosphere, C is inevitably generated.
If the amount of gas mainly composed of O is increased and the total amount of oxygen in the raw copper powder exceeds 0.80% by weight, the phenomenon of copper powder blowing up becomes significant and causes troubles in the equipment. Now, in the present invention, the total oxygen amount remaining in the steel powder after decarburization and deoxidation annealing is 0.25% by weight or less, and the total carbon content is 0.2%.
The reason why it is limited to 0% by weight or less will be explained. First, the reason why the total amount of oxygen remaining in the copper powder was limited to 0.25% by weight or less is as follows. That is, since the alloyed C cleans the molten steel, the amount of oxide inclusions inside the steel powder can be extremely reduced. For this reason, most of the total oxygen content of the copper powder after annealing exists on the surface, and the steel powder base is not hardened much, but 0.2
If it exceeds 5% by weight, compressibility and moldability will be impaired. Furthermore, if copper powder with a high oxygen content exceeding 0.25% by weight is used as a raw material, the diffusion of alloying elements will be hindered during the sintering or forging heating process, resulting in the final products such as sintered materials and sintered forged materials. The mechanical strength and heat treatment properties such as quench hardenability and carburization properties of consolidated materials such as steel deteriorate. The reason for this is that oxides, mainly Mn, Cr, and V, generated on the surface of the copper powder increase, and the amount of elements that effectively affect hardenability decreases. In addition, for gas carburizing treatment, the inventors have confirmed that the higher the acidity of the material, the more O consumes C and inhibits diffusion, resulting in lower carburizing properties and shallower effective carburizing depth. . Therefore, there is no need to set a lower limit on the amount of residual oxygen in the copper powder. Next, the reason why the total residual carbon content of the steel powder was limited to 0.20% by weight or less is as follows. C is one of the seven most basic elements in steel, and forms a solid solution in the steel as an immersion type, influencing compressibility, formability, mechanical properties of compacted materials, quench hardenability, and the like. In powder metallurgy, it is common practice to mix graphite powder with raw steel powder to adjust the C content of compacted materials such as sintered materials and sintered forged materials. Therefore, the most important properties of raw steel powder are excellent compressibility and formability. There is a negative correlation between the amount of alloy carbon remaining in the copper powder and the density of the green powder, and the lower the amount of alloy carbon, the higher the density of the green powder, which is preferable. In this sense, considering the workability of handling the green compact, the amount of alloy carbon left in the alloy steel powder is limited to a maximum of 0.20% by weight. Further, for use as a raw material for consolidated parts corresponding to case hardened steel, a carbon content of 0.20% by weight in the copper powder alloy is sufficient. Furthermore, as mentioned above, the molar ratio △C/△O between the amount of decarburization △C and the amount of deoxidation △O is 1 during induction heating annealing in a reduced pressure atmosphere.
．． However, in order to efficiently deoxidize by main annealing, the C10 molar ratio between the amount of alloy carbon and the total amount of oxygen in the water atomized raw steel powder must be set at 1.0 to 1. It was confirmed through experiments that the C10 molar ratio of the water atomized raw steel powder should be made small in order to ensure sufficient decarburization. The amount of C to be alloyed is determined by the following formula. The present invention will be explained in further detail. First, the most fundamental thing in the present invention is to control the total oxygen amount of the produced water atomized raw steel powder. Water Oxidation of raw steel powder in the atomization process is mainly caused by atmospheric oxygen entrained by high-speed water flow, steam decomposition oxygen of high-speed water flow or cooling water, and atmospheric oxygen during dehydration and drying. Therefore, the total oxygen content of water atomized raw steel powder is It consists of dissolved oxygen, oxide inclusions, and surface oxides of the copper powder generated during the water atomization and drying process.Therefore, for each process, the total oxygen amount and atmospheric oxygen concentration of the water atomized raw steel powder and the atmospheric oxygen concentration are calculated. We confirmed the relationship between them through experiments, understood the manufacturing conditions, and completed the present invention. Each process is explained below. (a) Molten steel holding process Si and AI are easily oxidized during water atomization or reduction annealing (their oxidation Since these substances inhibit the compressibility and sinterability of alloyed steel powder, they are not used as alloying components of molten steel or as deoxidizers.Therefore, the amount of oxygen in molten steel is determined by the alloying elements C, Mn, and C.
It is determined by r, V, etc., and is most influenced by the carbon content. For example, under a CO gas atmosphere of 1 atm, the equilibrium relationship between [C] and (0) in molten steel at 1600°C is [%C]
[%0. It is known that l=o, o022, and there is almost no change even if the temperature is slightly shifted. However, in the actual operation of an industrial melting furnace, this concentration product is considerably higher than the equilibrium value, and when [C] exceeds 0.2% by weight, [O] remains almost constant, for example 0.02~
0.03% by weight, but as (C) becomes lower than this, (0) increases rapidly. For example, in peroxidized molten steel with C0,020% by weight and Mn 0.10% by weight,

[0] is 0
．． 06-0.10% by weight. Normally, in the water atomization method, it is better to have a larger molten steel injection port diameter from the viewpoint of productivity, utility costs, workability, etc., and also from the problem of nozzle clogging due to temperature drop, but it is better to From the viewpoint of powder properties such as apparent density, the applicable range is 5 to 30 iiφ. For this reason, Industrial Promise 1/ On a production scale, pouring molten steel takes a considerable amount of time, and during that time, changes in the alloy components within the molten holding vessel over time cannot be ignored. For example, in a high-frequency induction furnace lined with spinel refractories containing 065% Mg and 328% to 30% A120 with a dry stamp, the furnace volume is 200 kg of molten steel, and the surface of the molten steel is not coated with any film (in the atmosphere or with an oxygen concentration of 0. 5% by volume
C, Cr, M when Cr-Mn-■ molten steel is induction heated and held at 1600-1700℃ in the following nitrogen atmosphere.
Figure 1 shows the changes in n and V over time. In order to retain molten steel containing easily oxidized elements such as C, Mn, Cr, V, and Nb, the molten steel surface is covered with rice husks, a suitable slag material, or a heat insulating material, or N2
It is important to use an inert atmosphere such as , Ar, etc. to prevent oxidative consumption of the alloy components. (b) Molten steel injection process and water atomization process There is a pipe in the tundish between the tundish, which holds the molten steel and injects it as a trickle from the bottom, and the spray tank, which temporarily stores the water-atomized raw steel powder, spray water, cooling water, etc. Re-covering refractory materials, removing metal, repairing, burying molten metal nozzles,
A space is required for preheating, etc., and also for operations such as oxygen washing of nozzle blockages due to solidification of molten steel in the molten metal nozzle as the temperature drops, and observation and monitoring of molten steel injection status. When a high-speed water stream is sprayed, the surrounding atmosphere is engulfed by the ejector action. For this reason, the high-speed water flow becomes a mixed fluid with the surrounding atmosphere, and when the surrounding atmosphere is air, the oxygen further oxidizes the produced raw copper powder. Therefore, the space between the water nozzle and the spray tank should be sealed, or a means to suppress the amount of air entrained should be taken to connect the spray tank including the ladder installation space to the water nozzle with N2, A
The oxidation of the produced water atomized raw steel powder is controlled by substituting it with an inert gas such as r. In this way, the oxidation is performed essentially only by decomposition of water vapor, or, as described later, the oxygen concentration in the air involved is set to 10% by volume or less, thereby impeding the reduction annealing in the subsequent process and the properties of the reduction annealed steel powder. It is possible to control the total oxygen content of the water atomized raw steel powder within a range where there is no variation and with little variation. Figure 2 shows the height of the water surface in the spray tank and the water atomized raw steel in a nitrogen atmosphere with an oxygen concentration of 0.5% by volume or less, with the space between the tundish and the spray tank open to the atmosphere or sealed. This shows the relationship with the total oxygen content of the powder. The raw copper powder was immediately vacuum dried after water atomization, and the total oxygen content of the raw copper powder was analyzed using 160 meshes. As is clear from Figure 2, the total oxygen content of raw copper powder produced by water atomizing the molten steel injection flow in an open atmosphere is greatly affected by the distance to the water surface, but the oxygen concentration of the atmosphere during molten steel injection and spraying is The total oxygen content of water atomized raw steel powder produced by keeping the content below 0.5% by volume is not affected by the distance to the water surface. When water is atomized in an atmosphere with high oxygen concentration such as the atmosphere, the moment the molten steel injection stream is atomized with a high-speed water stream,
Since the oxygen concentration in the water vapor film becomes even higher, oxidation progresses further. In this case, by raising the water level as much as possible and submerging the water immediately after atomizing it with a high-speed water flow, contact with the atmosphere can be shortened and the cooling rate can be increased.
Oxidation of raw copper powder due to atmospheric oxygen can be suppressed. However, the water surface becomes violently rough due to the floating of the atmosphere that is struck by the high-speed water current, which disturbs the molten steel injection flow, contacts the water nozzle header, and solidifies, causing a blockage accident. I have no choice but to keep a certain distance. On the other hand, when water is atomized in an atmosphere with a low oxygen concentration, oxidation can occur substantially only by decomposition of water vapor. Next, Figure 3 shows the total oxygen content of the raw steel powder when it was atomized while keeping the water level constant and changing the atmospheric oxygen concentration. The total oxygen content of raw copper powder is also increasing in correlation with the increase in atmospheric oxygen, and in order to control the total oxygen content of raw copper powder to 0.80% by weight, it is necessary to reduce the atmospheric oxygen to 10% by volume or less. It shows. Specifically, in the water atomization process, the space required for work between the tundish and the spray tank, including the space for installing the water nozzle header, is made into a sealed structure, and a large area is constructed to prevent air from entering the spray tank. An inert atmosphere such as N2, Ar, etc. with an oxygen concentration of 10% by volume or less is created at a pressure higher than atmospheric pressure, and the water vapor, CO, CO2, SO2, etc. generated when molten steel injection flow is water atomized with a high-speed water stream is removed from the atmosphere outside the system. It is necessary to control the total amount of oxygen in the raw copper powder released to 0.80% by weight or less. (c) Drying process As mentioned above, the oxygen concentration in the molten steel injection atmosphere and spraying atmosphere is maintained at 10% by volume or less, water atomization is performed, and the total oxygen content of the water atomized raw steel powder produced by dehydration and drying is reduced to 0.
．． A feature of the present invention is the drying condition to reduce the carbon content to 80% by weight or less, and this determines the amount of carbon to be alloyed into molten steel in advance. That is, after dehydration, water vapor, an inert gas such as N2, Ar, etc. is introduced into a well-known dryer having a sealed structure or a structure with unavoidable gaps due to the structure, and the oxygen concentration in the atmosphere is reduced to 10% by volume or less, and the atmospheric pressure is reduced. Alternatively, dry under a positive pressure of about 100 mm of water column from atmospheric pressure. Figure 4 shows that after water atomization, the water is immediately added to 6 to 15% by weight.
The steam temperature is 1.
This figure shows the relationship between the atmospheric oxygen concentration after heating and drying with saturated steam at 70°C and the oxidation weight increase of 160 mesh raw steel powder after drying. When the oxygen concentration is 10% by volume, the oxidation weight gain is 0.2% by weight, and when the oxygen concentration is 21% by volume, the oxidation weight gain is 0.2 to 0.45% by weight.
It is. In order to keep the total oxygen content of the raw copper powder after drying to 0.80% by weight or less, it is necessary to limit the atmospheric oxygen concentration in the drying process to 10% or less. Since the drying temperature of the steam generated by drying is lower than its decomposition temperature, it does not oxidize the raw steel powder to increase its weight at all. When substantially dried, water-atomized raw steel powder with a moisture content of 0.10% by weight forms an oxide film, so pure iron powder does not substantially increase in weight due to oxidation even if held at 200°C for 4 hours in the atmosphere. Furthermore, it has been confirmed that there is no substantial oxidation increase in Cr-MO steel powder even when the powder is held at 300° C. for 4 hours in the atmosphere. Normally, dehydration is carried out immediately after water atomization, without any substantial oxidation increase in volume. It is important to control the oxygen concentration in the atmosphere when leaving it in the atmosphere or forcing the atmosphere through ventilation. It has been found that if water-atomized raw steel powder is completely submerged in water to cut off contact with the atmosphere, it will not substantially increase in weight by oxidation even after one week has passed. Next, if it becomes possible to suppress the total oxygen content of water-atomized raw steel powder produced by controlling the atmospheric oxygen concentration in each process of molten steel injection, water atomization, and drying, then In order to satisfy the oxygen content and total carbon content, a predetermined amount of carbon is alloyed in advance in the refining component adjustment process. It is necessary to know the relationship between the total oxygen content of the water atomized raw steel powder after the drying process. Figure 5 shows that Cr-Mo molten steel is water atomized in the air, immediately dehydrated to 6 to 15% by weight, and then heated to 200°C in the air.
, which shows the relationship between the total alloy carbon content and the total oxygen content of water-atomized raw steel powder held for 1 hour and dried, and the total oxygen content generally shows a high value. Figure 6 also shows that Cr-Mo molten steel alloyed with carbon in advance is water atomized in a nitrogen atmosphere with an oxygen concentration of 0.5% by volume or less, and immediately dehydrated to a water content of 6 to 15% by weight, followed by an oxygen concentration of 0.
．． 200℃ in a nitrogen atmosphere of 5% by volume or less or in the air
This figure shows the relationship between the alloy carbon content and the total oxygen content of water-atomized raw steel powder that was kept for 1 hour and dried. Regardless of the alloy carbon content, there is a large difference in the total oxygen content of raw copper powder when the drying process is performed in the air or in a nitrogen atmosphere. In this way, even if the molten steel injection process and the water atomization process are carried out in an atmosphere with an oxygen concentration of 0.5% by volume or less, and oxidation is limited to only due to the decomposition of water vapor, if the atmospheric oxygen in the drying process is high (and further oxidation occurs), The purpose of the present invention cannot be achieved. Therefore, the total oxygen content of water atomized raw steel powder is reduced to 0.680% by weight.
In order to achieve the following, it is necessary to suppress the atmospheric oxygen concentration in each step of molten steel injection, water atomization, and drying to 10% by volume or less, and if it exceeds 10% by volume, the total oxygen content of raw copper powder will decrease to If it exceeds .80% by weight, the quality deteriorates. (d) Decarburization and deoxidation annealing process Water atomized raw steel powder produced by alloying molten steel with a predetermined amount of C is heated with a theoretical oxygen partial pressure of 2. In a non-oxidizing atmosphere with a dew point of .1×10−1 Hg or less or a dew point of +5°C or less,
750 to 1400 using a known heating method at a heating rate of 10°C/7ni11 or more, preferably 20'c/min or more
The material is rapidly heated to .degree. C. and subjected to reduction annealing using C alloyed with a reducing agent. Therefore, in the main annealing process, the amount of decarburization ΔC and the amount of deoxidation △0
The understanding of the relationship between Figure 7 shows the relationship between the C10 molar ratio of various water atomized raw steel powders before annealing and the deoxidation rate after annealing, and Figure 8 shows the relationship between the C10 molar ratio of various water atomized raw steel powders before annealing, and the O
The relationship between the amount of decrease ΔO and the amount of C decrease ΔC is shown. Table 1 shows the chemical compositions of various water atomized raw steel powders used in the experiments shown in FIGS. 7 and 8. I mean here. The units for the amount of C and the amount of O are % by weight. From Figure 7, in order to obtain an efficient deoxidation rate of 60% or more, the C10 molar ratio of the raw steel powder should be in the range of 10 to 1.7, and the C10 molar ratio should be increased beyond 1.7. However, the deoxidation rate does not improve much (the amount of C remaining in the copper powder after annealing exceeds 0.20% by weight, increasing the hardness of the copper powder,
This is not preferable because the density of the green powder decreases. From Figure 8, the fact that the 66760 molar ratio is in the region greater than 10 indicates that the oxide is mainly directly reduced by the pre-alloyed C, and the 66760 molar ratio is in the region greater than 10.
A molar ratio of more than 1.4 is considered to indicate significant reoxidation. Therefore, the ΔC/Δ00C10 molar ratio should be limited to a range of 4. On the contrary, the amount of residual oxygen can be tolerated up to 0.25% by weight, and in order to ensure sufficient decarburization and improve the green density, the C10 molar ratio of the raw copper powder should be reduced. In this case as well, decarburization and deoxidation occur simultaneously during main annealing,
The 66760 molar ratio ranges from 1.0 to 1.4. Note that the total oxygen content is 0.80% by weight or less and the C10 molar ratio is 1.
By producing water atomized raw steel powder exceeding 7% by weight using the method of the present invention and treating it with the annealing process described above, the amount of residual C in the copper powder can be any amount exceeding 0.20% by weight, and all residual C can be reduced. Production of high C, low O steel powder with an oxygen content of 0.25% by weight or less and water atomized raw steel powder with a C10 molar ratio of less than 1.0, limiting the amount of gas generated during annealing and blowing up copper powder By preventing this, it is also possible to produce a low-C, high-O steel powder in which the total amount of oxygen remaining in the copper powder exceeds 0.25% by weight, and the amount of residual C is 0.20% by weight or less. EXAMPLE Taking into account melting temperature rise losses, each charging material was blended and melted in the atmosphere in a high frequency induction melting furnace. High temperature melting is performed for injection through a small diameter nozzle. For this reason, steelmaking pig iron is used as a C source at 0% relative to the target alloy content.
10 to 0.30% more by weight was charged to the hearth. Following the operating method of a general induction electric furnace, the ferroalloy is added, the smelting components are adjusted to achieve the target composition, the melting point is superheated to a predetermined temperature of 200℃, and the steel is poured into a tundish where the middle molecules are heated. At the same time, the molten metal was injected by gravity from a refractory nozzle with a diameter of 10 mrItφ provided at the bottom of the tundish, and the amount of water was 230,737 m1n, and the back pressure was 1.
Water was atomized at a constant distance of 2 m to the water surface using an inverted conical high-speed water jet with a pressure of 40 kg/caG. In this example, the time of tapping the steel from the melting furnace to the tundish corresponds to the molten steel holding process, but the time of pouring the molten steel is 10
Since the process was completed within minutes and the change in C over time was within 0.10% by weight, the molten steel surface was not protected at all and was left exposed to the atmosphere. After water atomization, it is allowed to settle naturally in the spray facility, the supernatant water is discharged, it is received in a vibration dehydrator as a concentrated slurry, it is dehydrated by applying vibrations at 25 cycles/second for 3 minutes, and then it is immediately placed in a rotary dryer with a steam pipe. It was dried with saturated steam at 170°C. Each device in each process after molten steel injection has a sealed structure.
By blowing in N2, the 02 concentration was set to an N2 atmosphere of 0.5% by volume or less, and by adjusting the amount of N2 and air blown, the 02 concentration was set to an atmosphere of 8% by volume. Note that these were made open to provide an atmospheric atmosphere. Various water atomized raw steel powders were heated at a frequency of 380 KHz, a heating atmosphere that was constantly evacuated by a rotary pump, a heating cycle, a heating rate of 50 to 80°C/m1yt, and 1300°C x 1.
Annealing was performed by a vacuum induction heating deoxidation method under the conditions of holding for 5 minutes and cooling in a cooling furnace. This sintered cake was crushed with an impact crusher and sieved to -60 mesh to obtain steel powder. Table 2 shows the production atmosphere of raw copper powder, powder characteristics of raw copper powder, O, C analysis values of copper powder annealed by vacuum induction heating method, and 6676
0 molar ratios are shown together. As explained above, the present invention aims to determine through experiments the upper limit of the atmospheric oxygen concentration due to air that inevitably enters the equipment during each process of molten steel injection, water atomization, and drying, and to The concentration is controlled and the molten metal is carburized in advance so that the final product satisfies a limited range of components, and in the decarburizing, deoxidizing annealing process, oxygen is reduced by this retained carbon and at the same time softened.
After that, it became possible to crush and sieve the reduction annealed cake to produce excellent copper powder in large quantities and at low cost on an industrial scale.

[Brief explanation of drawings]

Figure 1 shows the change in alloy composition over time when Cr-Mo-V molten steel is held at 1,600 to 1,700°C without coating the surface. Figure 2 shows the distance to the water surface during water atomization and the total amount of raw copper powder. Correlation diagram of oxygen content. Figure 3 is a correlation diagram between atmospheric oxygen concentration during water atomization and total oxygen content of raw steel powder. Figure 4 is a correlation diagram between atmospheric oxygen concentration during drying and oxidation increase in raw steel powder. figure,
Figure 5 is a correlation diagram between the total oxygen content and alloy carbon content of raw steel powder atomized in the atmosphere and dried in the atmosphere, and Figure 6 is a correlation diagram of raw steel powder atomized in nitrogen and dried in the atmosphere or in nitrogen. Figure 7 is a correlation diagram between the total oxygen content and alloy carbon content of copper powder, and Figure 7 is a relationship diagram between the C10 molar ratio of various water atomized raw steel powders shown in Table 1 and the deoxidation rate after annealing by vacuum induction heating method. , FIG. 8 is a diagram showing the relationship between the amount of deoxidation Δ0 and the amount of decarburization ΔC in annealing by the vacuum induction heating method.

Claims (1)

[Claims] 1 A step of melting molten steel adjusted to a predetermined composition, a step of storing the molten steel in a tundish to form a trickle, and a step of injecting a high-speed water stream into it to water atomize it, and dehydrating and drying the water atomized raw copper powder. The dried raw copper powder is annealed in a non-oxidizing atmosphere to alloy the retained oxygen and reduce the retained carbon to zero carbon.
In the manufacturing method for obtaining copper powder containing 20% by weight or less and 0.25% by weight or less of oxygen, the molar ratio ΔC/ΔO between the amount of decarburization λC and the amount of deoxidation ΔO during the annealing is 1.0 to 1.0. In addition to satisfying the range of 1.4, the oxygen content of water atomized raw steel powder is 0.
The molten steel composition is adjusted so that the content of carbon is 80% by weight or less, and the carbon content is 1.0% by weight or less, and the atmospheric oxygen concentration in each step of the molten steel trickle injection, water atomization, and drying is 10% by volume or less. A method for producing water atomized raw steel powder.