JPS5980702A - Production of alloy steel powder - Google Patents

Abstract

PURPOSE:To obtain low O- and low C alloy steel powder which prevents effectively the oxidation of easily oxidative elements by pulverizing a molten steel contg. the easily oxidative elements by a spray medium contg. a nonoxidative solvent to obtain the atomized steel powder regulated respectively of the contents of C and O then treating the same in an atmosphere contg. H2 and H2O under specific conditions. CONSTITUTION:A molten steel contg. >=1 kind among easily oxidative elements such as Cr, Mn, V or the like is prepd., then such molten steel is pulverized by a spray medium contg. a nonoxidative solvent selected from mineral oils, animal and vegetable oils, etc., whereby the atomized steel powder contg. <=0.2wt% O and >=0.1wt% C is obtd. Such high carbon atomized steel powder is treated under the condition A or B in a decarburization atmosphere contg. H2 and H2O to regulate the content of C. The atomized steel powder after the regulation of the content of C is cooled in an inert of reducing atmosphere, and the alloy steel powder of low oxygen and low carbon which contains respectively <=0.2wt% O and <=0.1wt% C and can prevent effectively the oxidation of the above-described easily oxidative elements is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing copper powder, and particularly to a method for producing low-oxygen, low-carbon alloy steel powder that can effectively prevent oxidation of easily oxidizable elements such as chromium and manganese.

As conventional methods for producing alloyed copper powder, water atomization reduction methods, gas atomization methods, and oil atomization methods are known. However, as a method for producing alloy copper powder containing easily oxidizable elements as in the present invention, the following problems were found in such conventional methods.

Water atomization-reduction method: Since water is used as the atomizing medium, this method inevitably oxidizes the resulting powder during water atomization. Moreover, the amount of oxidation is generally large, and the addition of easily oxidizable elements is restricted in terms of alloy component design.

In particular, when water atomizing molten steel containing easily oxidizable elements such as chromium (Cr), manganese (Mn), sodium (■), niobium (Nb), poron (B), and silicon (Si), these elements is easily oxidized, therefore the obtained copper powder must then be sent to a reduction process to reduce the amount of oxygen, but even with such treatment it is not possible to reduce the acid accumulation to the required level. is extremely difficult.

For example, even if the atomization conditions and atmosphere at that time are specially adjusted to suppress the oxygen content of the as-atomized powder to about 1.5% (1.5%
Powder with the desired amount of oxygen cannot be obtained unless the reduction treatment is performed at a high temperature for a long time of 5 hours or more.

When heated at such high temperatures and for long periods of time, even if powder with the desired amount of oxygen is obtained, it will already be sintered during processing, which requires an even more powerful crushing process. shall be. Moreover, when such a powerful crushing process is applied, the particle shape and particle size distribution change during crushing.
Problems also arise in terms of the quality of the resulting powder, such as compressibility, moldability, and sinterability.

In addition, as a special deoxidation method, prior to water atomization, carbon is intentionally added to the molten steel in large amounts, which results in LM
By obtaining atomized powder containing carbon as a reducing agent in Mn body and heating it at high temperature in vacuum, fic+0→
A method has been proposed in which oxygen and carbon are removed by a CO reaction. However, this method also requires heating at a high temperature of 51,100° C. or higher for a long time in order to avoid the amount of oxygen, and has the same problem as the above-mentioned method. Furthermore, a problem specific to this method is that in order to reduce the amount of oxygen by vacuum heating, it is necessary to maintain the carbon content remaining in the atomized copper powder obtained by atomization above a certain level, and the equipment for this purpose is required. and operations are becoming more complex.

Gas atomization method: A method for producing copper powder using an inert gas such as N2 + Ar as an atomizing medium. Although oxidation is small, the cooling rate is slow due to gas cooling, and the resulting product Ak.

The particle shape of the product tends to be spherical. Therefore, cold compaction of the obtained powder is difficult, and CIP.

Canning molding by HIP etc. is required.

However, these molding methods are subject to many restrictions, resulting in high costs, and are not generally used.

Furthermore, in this method, a large amount of gas is completely used during gas atomization, so the atomization processing cost is more than 10 times that of water atomization.

Therefore, although this method has been put into practical use for special purposes, it is rarely used as a method for producing copper powder for sintering or sinter-forging, which is also commonly used in powder metallurgy. Not adopted.

Oil atomization method: The oil atomization method is a method for producing copper powder using oil as a spray medium, and compared to the water atomization method described above, the resulting copper powder is not oxidized, that is, the oxidation of alloying elements is not caused. However, since carburization of the spray medium into the copper powder occurs during atomization, decarburization must be performed in the next step.

Cr, Mn + V + Nb, B, St
For copper powder containing easily oxidizable elements such as Moreover, an efficient decarburization treatment method has not been found.

The reason for this is that H2, H2-)hO is used as the decarburized gas.

COCO2/gas etc. can be considered, but the decarburization reaction using H2 gas is slow and is not practical.
Decarburization reactions involving oxidizing gases such as O and cow are fast, but under temperature and atmospheric conditions that satisfy decarburization, Cr+Mn, V, Nb, B, St, etc. are oxidized from the viewpoint of thermodynamic equilibrium conditions. This is because special controls are required when processing the atmosphere in the area.

Gatte, conventional, Cr l Mn, V I Nb
There has been no research at all into the decarburization conditions for copper powder, which contains elements that are oxidized in equilibrium terms, such as l B ISt , and which has an extremely high oxidation rate because it is a fine powder.

One object of the present invention is to provide a method for producing alloyed copper powder by oil atomization, in which Or v Mn + V r Nb , B + St during decarburization.
An object of the present invention is to provide a method for producing low-oxygen, low-carbon alloy steel powder, which is combined with a decarburization method that prevents oxidation of easily oxidizable elements such as fx as much as possible.

Yet another object of the present invention is to achieve a relatively low oxygen concentration of less than 12% by weight by using a blowing medium containing a non-oxidizing solvent such as mineral oil, animal oil or vegetable oil.
A copper powder having a relatively high carbon content is obtained, and then decarburization of the copper powder is completed before oxidation progresses, and Cr, Mn, with a carbon content of 1% by weight or less and an oxygen content of 0.2N or less are obtained.
It is an object of the present invention to provide a method for obtaining copper powder containing one or more types of easily oxidizable elements such as V, Nb, B, and St.

Here, the gist of the present invention is chromium.

Preparing a liquid steel containing at least one easily oxidizable element selected from the group consisting of manganese, panasium, niobium, boron and silica: preferably a non-oxidizing element selected from mineral oil, animal oil, vegetable oil and mixtures thereof. A step of pulverizing the molten steel using a spray medium containing a solvent to obtain as-atomized copper powder having a cumulative acid content of 2% by weight or less and a carbon content of 1% by weight or more: The as-atomized steel powder is At least i-h and H
A step of adjusting the carbon content by treating under the following conditions (A) or CB) in an atmosphere containing 2O; and cooling the carbon content-adjusted copper powder thus obtained under an inert or reducing atmosphere. A method for producing low-carbon, low-oxygen alloy steel powder consisting of the steps; Conditions (A): Temperature (t'C): 600°C≦t≦950°C Atmosphere (PH
2/PH, 0): 0.5≦PH27PH20≦10
00 treatment time (θ minutes) Conditions (B): Temperature (t°C): 950°C <t≦1250°C atmosphere 1211 atmospheres (””/PH, o): PH2/PH, o≧0.5
Processing time (θ minutes): The feature is that the copper powder obtained by the oil atomization method is 0 and H! After adjusting the carbon-containing needle to a desired degree under the above conditions (A) or CB) in an atmosphere containing the following conditions, the carbon-containing needle is cooled under an inert or reducing atmosphere. Note that PH2 is the hydrogen partial pressure in the atmosphere, and PH20 is the water vapor partial pressure.

Each step according to the present invention is not limited to the following sequential steps, and may be carried out by a conventional method.

However, in the present invention, such molten steel is made of Cr.
Since it contains at least one easily oxidizable element selected from I Mn r V + Nb HB and Si, it is preferable to prevent the oxidation of these elements as much as possible even during the melting stage of molten steel.

In the atomization process, as in the conventional oil atomization method, a spray medium containing oil selected from mineral oil, animal oil, and vegetable oil may be used, but in the present invention, due to its nature, Among these, those including non-oxidizing ones are used as spray media.

As long as it is essentially non-oxidizing as a whole, it may contain a small amount of oxidizing components such as water.

Non-oxidizing solvents used in the present invention include machine oil, quenching oil, and turbine oil in the form of mineral oil.

Whale oil as an animal oil and rapeseed oil as a vegetable oil.

There is soybean oil.

The oxygen content obtained in the atomization process according to the present invention (2) is limited to 2 weight yen or less, but it is preferable that the amount is as small as possible. The oxygen content can be adjusted to a low level by paying attention to preventing oxidation of the molten steel after deoxidizing, especially during atomization.

The carbon content at this time is 0.1% by weight or more, but such a large amount of carbon inevitably enters the cine due to carburization from the spray medium.

The high carbon atomized steel powder thus obtained is further sent to a decarburization step, where it is subjected to decarburization treatment under conditions (A) or (B), which will be explained in more detail below.

First, we consider the atmosphere in which alloyed copper powder containing 0.1 weight or more of carbon is decarburized to less than 1 weight of carbon. One possibility is to create an atmosphere in which as much reactive HzO as possible is added.

However, in an atmosphere containing H20e, Cr, which is the main component of copper powder, is less likely to oxidize than Fe or Fe.
This results in the oxidation of easily oxidizable elements such as , Mn, V, Nb, B, and Si. Therefore, it is important to select an atmosphere that does not cause oxidation while promoting decarburization.

By the way, dry pure hydrogen does not have much decarburizing property, but in a humid atmosphere, the decarburizing reaction is promoted by the action of water vapor. However, since water vapor is oxidizing, simply adding it will cause oxidation to proceed at the same time as decarburization.

Here, the present inventors have discovered that when water vapor is added to hydrogen, if the ratio of the partial pressure of water vapor to the partial pressure of hydrogen in the atmosphere is appropriately selected, Fe and the aforementioned easily oxidizable elements? :We obtained the knowledge that efficient decarburization can be performed without oxidation and at the same time can effectively reduce the oxygen content, and conducted a series of experiments to find the critical conditions.

FIG. 1 is a graph summarizing the experimental results regarding the influence of temperature. In these experiments, Cr-Mn-based low alloy steel powder (Cr 111
．． 0% by weight, Mn: 1.5% by weight) The container was made entirely of stainless steel, and the layer height was kept at 3 degrees, and the atmosphere inside the furnace was maintained at PH2/PH.
, O = 33.3, PH, = 70chi, the remaining tooth gas was used, and the atmospheric temperature was varied to investigate changes in the processing time and the content of carbon (C) and oxygen (9) in the copper powder. .

From the data shown in the graph of FIG. 1, it can be seen that decarburization is more effective as the ambient temperature is raised, but oxidation progresses as time passes. For example, in the illustrated example, it can be seen that the carbon content can be easily decarburized to less than 1% by weight in a short treatment time of 10 minutes or less, and that extreme oxidation can also be prevented. Furthermore, the data in Figure 1 shows that the higher the ambient temperature is, the less oxidation progresses, but the more rapidly decarburization progresses. It turns out that this is true.

Next, the sample steel powder whose composition and particle size distribution are shown in Table 1 was kept in a stainless steel container at a bed height of 20 m, heated in an H2 atmosphere, maintained at a predetermined temperature and atmosphere, decarburized, and then dried. Cooled with aX gas.

A series of experimental results are summarized in Figures 2 to 7 for each temperature.
This is shown graphically in the figure.

The horizontal axis shows I) H2/PH2o. The vertical axis shows the processing time to satisfy the target value. The ○ marks are C: 0.1 T & Quantity or less, and Oxygen: 0.2 Weight or less, all of which are satisfied (-),
An X mark indicates something that does not satisfy the target value.

As is clear from these series of graphs, PH2/PH
20' There is a critical region regarding temperature and processing time, and when it is expressed in the form of θ = f (PH2 / PH2o), temperature 111 (t °C), and processing time (θ, min), the following formula % formula % Temperature range 0.0 at 600°C to 950°C. Minimum treatment time (θmin) U required to decarburize to I N content or less: (1) The upper limit treatment time θmax required to suppress oxidation to 0.2% by weight or less is further expressed as: As is clear from the figure, the Pl(2/PH2o ratio is at least PH27,...).When <0.5, no region satisfying the condition is found, and when PH2/PH3
When it exceeds 1000, it takes several hours or more for decarburization even at high temperatures, and there is no advantage over the conventional method.

Therefore, the following conditions are determined to represent the critical region in the present invention.

Conditions (A): Temperature range (t°C): 600°C (t (950°C atmosphere 20
．． 5≦pH, / PH20≦1000 Processing time (θ minutes)
: Furthermore, at high temperatures exceeding 950''C, the following conditions are set as indicating the critical region of the present invention.

Atmosphere 2 PH27 PH20>0.5 Processing time (θ minutes): However, when the temperature becomes high, adhesion between particles becomes a problem, so there is a certain limit.

FIG. 8 is a graph showing the relationship between temperature and adhesion force.1.
This is not a good idea because if the temperature exceeds 1250° C., the mutual adhesion of the copper powders will rapidly become strong, making it difficult to crush them after deoxidizing treatment.

Therefore, the sweating conditions in the range exceeding 950° C. are determined to represent the critical region in the present invention.

Condition (B): Temperature range (t°C): 950°C < t < 1250°C
Atmosphere” Pa2/ PH20 > 0.5 Processing time (θ
The copper powder thus decarburized is then cooled to room temperature under an inert or reducing atmosphere.

There is no particular restriction on the type as long as reoxidation can be prevented, but
Preferably it is cooled under a dry atmosphere.

Now, to explain the apparatus for continuously carrying out the decarburization method in the method of the present invention, FIG. 9 is a schematic sectional view of the decarburization apparatus for carrying out the method of the present invention. Steel powder from the process is temporarily stored in a raw material supply water pipe 2, and then continuously supplied onto a steel belt 3 driven by a roller 4.

This steel belt 3 sequentially passes through a decarburization treatment furnace 5 consisting of a preheating chamber 6, a decarburization chamber 7, and a cooling chamber 8, during which the steel powder 1 is preheated, decarburized, and cooled. The treated steel powder 9 is discharged into a chute 10 from the end of the belt.

A non-oxidizing gas (eg H2 gas) is supplied to the preheating chamber 6 and the cooling chamber 8, creating a non-oxidizing atmosphere inside the chamber. In the figure, this non-oxidizing gas supply system is indicated by dots, and since the specific contents are thought to be already clear to those skilled in the art from this explanation, further explanation will be omitted.

In order to adjust the atmospheric gas, H is introduced into the decarburization chamber 7.
2O (steam) and H2 gas, and if necessary, υN2 gas are supplied through their respective supply paths (not shown), but once they are adjusted to a predetermined composition by a gas mixer (not shown), , and is supplied into the room via line 11. The exhausted gas passes through line 12 to dust separator 13
where the entrained solids are removed. Carbon monoxide generated during decarburization is passed from the gas separator 14 to the line 15.
It is then taken out of the system. The separated and purified decarburized gas is again supplied into the furnace via line 11.

The invention will now be further described in connection with examples.

Example 1 Cr obtained by atomizing using mineral oil
-Mn-based low alloy steel powder was decarburized using a decarburizer shown in FIG.

The chemical composition and particle size distribution of this atomized steel powder are shown in Table 2.

The treatment conditions at that time are shown in Table 3, and the chemical components and particle size distribution of the copper powder after the decarburization treatment are shown in Table 4.

As is clear from the results shown in Table 4, according to the present invention,
Carbon content is reduced by 0.5 without significantly increasing oxygen content.
We were able to decarburize up to 12 weight units in a short time.

Example 2 This example concerns a low-alloy steel powder containing easily oxidizable elements such as V, Nb, B+Si in addition to Cr and Mn, and 9j having the chemical composition and particle size distribution shown in Table 5. -9th powder
Decarburization was performed using the decarburization equipment shown in the figure. The treatment conditions at that time are shown in Table 6, and the chemical components and particle size distribution of the copper powder after decarburization are shown in Table 7.

As is clear from the data shown in Table 6, the amount of acid-purple-containing bait should be kept below 0.1 wt% without increasing too much, and what is more, it would not affect the other chemical components or particle size distribution in any way. It was possible to decarburize the carbon content to 0.1% or less.

Note that the as-atomized copper powder of this example was obtained by atomization using mineral oil.

=19- Example 3 This example concerns stainless steel copper powder.
Copper powder' having the chemical composition and particle size distribution shown in the table was decarburized using the decarburizer shown in FIG.

Note that this as-atomized steel powder was obtained by adding 5% water to mineral oil as a spray medium, and the carbon content in the as-atomized copper powder was higher than that in Example 1 and Example 2 described above. It is characterized by being lower than that of copper powder.

Table 9 summarizes the decarburization conditions, and Table 10 summarizes the chemical components and particle size distribution of the copper powder after decarburization.

As is clear from Table 10, even in stainless steel powder, it is possible to suppress the oxygen content to 1.2 wt% or less and decarburize the carbon content to 0.01% or less.

[Brief explanation of the drawing]

Figure 1 is a graph showing changes in carbon and oxygen-containing buds in copper powder over time for decarburization and decarburization. Figures 2 to 7 show decarburization treatment time and P at each temperature.
A graph showing the critical region of the method according to the present invention with respect to H2/PR,O; FIG. 8 is a graph showing the relationship between the atmospheric temperature during decarburization treatment and the adhesion force of each copper powder particle; and FIG. 1 is a schematic cross-sectional view of an apparatus for continuously carrying out decarburization treatment in the method of the present invention. l...Steel powder, 5...Decarburization treatment furnace, 6...Preheating chamber,
7... Decarburization chamber, 8... Cooling chamber. Applicant's agent Patent attorney Akira Hirose -21- Figure 2 PH2/PH20 Figure 3 PH2/PI-120 Figure 4 PH2/PH20 Figure 5 PH2/PH20 Pile 6121 PH2/PH20 Figure 7 PH2/PH20 Continued on page 1 0 Inventor: Masahide Unno No. 9, 5-1-10 Shimaya, Konohana-ku, Osaka City Sumitomo Metal Industries, Ltd. Steel Works Internal Procedures Amendment (Voluntary) September 13, 1980 Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office] Display of the case 1989 Patent Application No. 189238 2, Name of the invention Process for manufacturing alloy & VI powder 3, Person making the amendment Relationship to the case Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (211”) Sumitomo Metal Industry Co., Ltd. 4, Agent (Attachment) Contents of amendment (1) The claims are amended as follows: r At least one member selected from the group consisting of chromium, manganese, vanadium, niobium, boron, and silicon. A step of preparing molten steel containing an easily oxidizable element; atomizing the molten steel with a spray medium containing a non-oxidizing solvent to obtain an oxygen content of 0.2% by weight or less and a carbon content of 0.1% by weight or more. Step of obtaining azu atomized steel powder;
A step of adjusting the carbon content by treating under the following conditions (A) or (B) in an atmosphere containing 20; and cooling the carbon content-adjusted steel powder obtained in this way under an inert or reducing atmosphere. A method for producing low-oxygen, low-carbon, alloyed steel powder. Condition (A): Temperature (t°C) 2600°C≦t≦950°C Atmosphere (PHZ
/ PHzo): 0.5≦P Hz / PH
16≦1000 Processing time (0 minutes): Temperature (t'c): 950°C<t≦1250°C Atmosphere (
P4 /P+zo): P)1m /Pszo≧0
．． 5” (2) r on page 9, line 4 of the specification cylinder and page 17, line 13
o, 101 ÷ (1,0,-1,0038x 10-t
)J is rO, aLO÷(1,0-1,0038
xlO-3t) Correct as J. (4) Add the following statement between lines 12 and 13 on page 20 of the same book box. "In addition, although each of the following examples shows the case of a layer height of 4 mm, the case of a thin layer of 2 to 3 cranes, the case of a layer height of 20 fins,
Similarly, in the case of 30 mm, the carbon content could be reduced to 0.02% in a short time without increasing the oxygen content. ” Above 2

Claims (1)

[Claims] A process for preparing molten steel containing at least one oxidizable element selected from the group consisting of chromium, manganese, vanadium, niobium, arron and silicon; a spray medium containing a non-oxidizing solvent; Then, the molten steel is atomized to have an oxygen content of 0.2 weight or less and a carbon content of 0.
, a step of obtaining azu-atomized copper powder of 1% by weight or more;
1 under the following conditions (A) in an atmosphere containing! A low-oxygen, low-carbon alloy steel comprising a step of adjusting the carbon content by treatment under the conditions (B); and a step of cooling the carbon content-adjusted steel powder obtained in this way under an inert or reducing atmosphere. How to make powder. Condition (A): Temperature (t℃): 600℃≦t≦95 (1℃ atmosphere (P
H2/PH, O): 0.5≦pH2,/PH2o
≦10 (10 conditions (B): Temperature (t'C): 950°C <t≦1250°C Atmosphere (P
Hz/ ): ””/'PHzO≧0.5PR,
0