JPS589801B2 - Method for producing low oxygen, low carbon iron powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a low-carbon, low-oxygen iron-based powder that is particularly suitable as a powder raw material for powder metallurgy.

In the production of iron-based powder for powder metallurgy, it is very important to minimize the amount of oxygen and carbon contained, including nonmetallic inclusions.

In other words, if iron-based powder contains a large amount of oxides, it will not only prevent the density of green compacts and sintered compacts from improving when manufacturing sintered parts, but also damage the mold during molding and cause parts to deteriorate. When machining is performed, various problems such as a decrease in machinability occur.

In addition, in the case of iron-based powder for sintering and forging, even in high-density and high-strength parts, mechanical properties such as fatigue strength and impact toughness are significantly reduced due to the presence of this oxide.

On the other hand, if the iron-based powder contains a large amount of carbide, not only will the density of the green compact not improve when molding parts, but also the formability of the green compact will decrease significantly, similar to when the amount of oxygen contained is large.
In extreme cases, serious problems such as chipping of the corners of these green compacts occur.

Therefore, there is a need to develop a method for producing iron-based powders with low oxygen and carbon content.

Generally, conventionally known methods for producing iron-based powders for powder metallurgy include reduction methods, atomization methods, mechanical pulverization methods, and electrolytic methods.

In these manufacturing methods, in order to obtain iron-based powders with low oxygen and carbon contents, a final reduction step must be incorporated and deoxidation or decarburization, or both of these treatments must be performed.

However, in the production of pure iron powder that does not contain alloy components, the above-mentioned final reduction is relatively easy, but in the case of iron-based powders that contain alloy components such as Cr, Mn, Si, etc., depending on the manufacturing method, Since some oxides of these alloy components are contained in the raw material powder, finishing reduction becomes extremely difficult.

Therefore, in the final reduction process in the conventional technology, in order to obtain a low-oxygen powder, the raw material powder is heated in a reducing atmosphere containing hydrogen with a very low dew point (D.P.) (-50°C or less).
Alternatively, it was necessary to perform the final reduction within a temperature range of 750 to 1400° C. in a reducing atmosphere containing CO gas with a very low partial pressure of CO2 gas.

However, it is difficult to industrially obtain a reducing atmosphere with such a low dew point or CO2 gas partial pressure, and since these reducing atmospheres contain hydrogen gas or CO gas, the gas after reduction is It will necessarily contain some water vapor or CO2 gas, resulting in a reducing atmosphere that increases the dew point or CO2 gas partial pressure.

Therefore, industrially it is difficult to reduce oxides, especially Cr and Mn.
, Si, etc., or composite oxides of these metals, it is necessary to use a large amount of hydrogen gas or a reducing gas containing CO gas with a low dew point or CO2 gas partial pressure. .

It is also possible to deoxidize while keeping the dew point low by increasing the final reduction temperature, but this method is difficult because the high temperature reduction makes it difficult to crush the semi-sintered deoxidized cake in the subsequent process. cannot be adopted either.

Furthermore, in such a reducing atmosphere with a low dew point, it is difficult to decarburize the raw material powder, and with conventional methods, it is difficult to produce low-oxygen, low-carbon iron-based powder from raw material powder that contains particularly refractory oxides. is considered to be extremely difficult.

On the other hand, in order to obtain the above-mentioned low-oxygen, low-carbon iron-based powder, the raw material powder is alloyed with carbon in advance, or mixed with a carbon source material such as graphite powder, oil, or a hydrocarbon compound, and then neutralized. A method of deoxidizing and decarburizing by heating in an atmosphere or under reduced pressure is also considered.

In this case, in order to increase the deoxidation rate and decarburization rate, heating at high temperature and under high vacuum is necessary as estimated from thermodynamics, but in this case, the amount of added oxygen is greater than the molar amount of oxygen contained. The molar amount of carbon must be increased.

This is because only the direct reduction reaction with carbon is proceeding, so a large amount of carbon is consumed.

In this way, the carbon content and oxygen content required for the powder only by direct reduction reaction are less than 0.30% by weight and 0.00% by weight, respectively.
It has become clear from the results of various tests that in order to perform deoxidation that satisfies the constraint of less than 20% by weight, the molar ratio between the amount of carbon and oxygen contained in the raw material powder (C/O mol. ratio)
must exceed 2.0.

In an ideal direct reduction, this ratio is 1.0, but in reality, carbon added by the mixed powder method or master alloy method is liberated at the start of depressurization and during heating, resulting in carbon loss. .

In particular, the amount of loss increases as heating is performed under higher vacuum and higher temperatures.

In addition, as will be described later, when directly inductively heating powder with high frequency under high vacuum, arcs fly between iron-based powder particles, resulting in carbon loss as seen in the carbon deposition phenomenon. There are very many.

Therefore, it is not preferable to deoxidize only by a direct reduction reaction of carbon.

Furthermore, when deoxidizing only by direct reduction reaction,
The amount of carbon to be added needs to exceed 2.0 in C/O molar ratio, so when obtaining powder by the so-called master alloy method, in which carbon is added to the molten metal before water spraying, it is necessary to add carbon to the molten metal before water spraying. The powder becomes hollow spheres and is not suitable for powder metallurgy.

Then, it would be possible to mix carbon powder such as graphite powder using a mixing method, but if the C/O molar ratio exceeds 2.0, the amount of carbon powder to be mixed will increase and Uniform mixing of small carbon powder is extremely difficult.

In this case, even if the two appear to be mixed uniformly, they become microscopically nonuniform, and under high-temperature heating, the melting point of the raw material powder locally decreases due to this microscopic nonuniformity. The resulting deoxidized cake becomes a semi-molten state in which liquid phase sintering occurs, making subsequent pulverization difficult and therefore unsuitable for powder production.

Furthermore, since the C/O molar ratio is large, it becomes difficult to control the amount of residual carbon and oxygen in the deoxidized powder.

Therefore, carrying out deoxidation only by direct reduction of carbon as described above has various drawbacks.

Therefore, it is difficult to achieve the low oxygen content and low carbon content required for final reduction of iron-based powders for powder metallurgy.

On the other hand, when actually obtaining a reduced pressure state, an oil rotary pump,
This is usually done using a mechanical booster or a combination of these exhaust devices and an oil or mercury diffusion pump.

When exhausting with such a device, it is easy to achieve 0.05To
A high degree of vacuum of about rr can be obtained, and under such reduced pressure, the reduction of oxides is MxOy + ycO →
Indirect reduction with carbon in (1) is difficult to proceed, and MxOy+yC→xM+ycO (2)
direct reduction becomes dominant.

Here, M is a metal element.

Therefore, it becomes possible to reduce the refractory oxide, but in order to increase the reduction rate only by direct reduction, high temperature heating is of course necessary, and the C/O molar ratio in the raw material powder must be reduced to 2. Unless it exceeds .0, it is extremely difficult to improve the reduction rate, that is, to achieve the desired low oxygen level.

This direct reduction also reduces the amount of carbon contained, but
As mentioned above, it is difficult to control residual carbon and oxygen, so even if the amount of oxygen in the reduced powder satisfies the desired purpose, the amount of carbon does not decrease to the desired content and remains in the form of carbides. It often remains.

As a result, the hardness of the product powder obtained by these conventional methods increases, and the moldability of the powder decreases, as well as the density of the green compact. Not suitable.

The object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide an iron powder containing pure iron powder or iron alloy elements or oxides, particularly hard-to-reducible oxides such as Cr, Mn, and Si, or alloy oxides of these metals. The object of the present invention is to propose a manufacturing method that can obtain low-oxygen, low-carbon iron-based powder, which is particularly suitable for powder metallurgy, from iron-based raw material powder for alloy powder.

In order to solve the drawbacks of conventional methods, the inventors of the present invention have conducted various studies on deoxidation methods involving decarburization of pure iron powder and iron-based powder materials containing particularly refractory oxides. I discovered that.

That is, alloying elements and iron oxides are formed on the surface and inside of raw material powder such as sponge iron pulverized powder, sprayed powder, mechanically pulverized powder, etc.

In the reduction of these oxides, the raw material powders are either alloyed with carbon in advance (master alloy method), or a substance that becomes a carbon source is added to and mixed with the raw material powders (mixing method), and these raw material powders are directly reduced under reduced pressure. Alternatively, if a small amount of neutral gas or reducing gas is injected as a carrier gas and heated under reduced pressure, and the degree of vacuum during heating is adjusted within an appropriate range to allow the direct reduction and indirect reduction to proceed simultaneously, iron-based raw materials can be produced. This makes it possible to efficiently deoxidize and decarburize powder.

In other words, the method for producing a low-oxygen, low-carbon iron-based powder of the present invention can be applied to pure iron-based powder or oxides of iron alloy elements such as Si.
Iron-based raw material powder of iron alloy-based powder containing one or more of metal oxides that are thermodynamically more easily reduced than these, including oxides of The oxygen content of these raw material powders before final reduction is reduced to 4.0 by alloying carbon in advance or adding and mixing carbon sources such as graphite powder, oil, and other liquid or powdered hydrocarbons. C/ of raw material powder in parentheses below weight%
The O molar ratio is 0. 7-2. 0, and keep these raw material powders under a high degree of vacuum with an average pressure of 100 Torr or less (abbreviated herein as vacuum degree of 100 Torr or less), and the final reduction temperature is within the range of 750 to 1400 ° C. Decarburization and deoxidation are performed at the same time by heating at
It is characterized by obtaining iron-based powder of less than the weight factor.

In addition, when heating under the vacuum degree of 100 Torr or less, 80% of the reduction holding temperature is preheated in the air, neutral or reducing atmosphere, and then immediately heated under the above average vacuum degree and at the final reduction temperature etc. The method of final reduction under the conditions described above also belongs to the method of the present invention.

In the method of the present invention, the average degree of vacuum during the finishing reduction heating of the iron-based raw material powder is limited to a range of 100 Torr or less for the following reasons.

That is, the raw material powder cannot be sufficiently deoxidized and decarburized in a low vacuum of over 100 Torr.

This is because the indirect reduction that occurs after the direct reduction becomes active (see formula (I) (2) above), and the partial pressure of the generated CO2 gas becomes higher.As a result, the partial pressure of the CO gas becomes relatively lower. This is thought to be because the powder surface or internal oxides are no longer reduced.

In contrast, during heating in the present invention. Average degree of vacuum is 1
Under the degree of vacuum in the range of 00 Torr or less, direct and indirect reduction proceed simultaneously. It was found that the deoxidation rate and decarburization rate of the raw material powder were sufficient to be effective as an upper reduction process.

Here, the deoxidation rate and decarburization rate are defined by the following equations (3) and (4).

In addition, as mentioned above, a small amount of neutral gas or reducing gas is injected as carrier gas during heating, and the average degree of vacuum is increased to 100.
An explanation will be added that the method of the present invention can be effectively applied even if the temperature is maintained within a range of Torr or less.

First, as the neutral gas, gases such as helium (He), argon (Ar), and nitrogen (N2) having a purity of 99% or more can be considered.

It is thought that as a result of the CO gas partial pressure being kept low by the injection of these gases, deoxidation by direct reduction proceeds.

However, when these neutral gases are injected for reduction, the deoxidation rate and decarburization rate are not improved compared to when they are not injected.

However, if the capacity of the vacuum evacuation equipment is low or the volume of the evacuation system is large, neutral gas may be injected to reduce the average degree of vacuum during heating to 100 Torr or less within the range permitted by the capacity of the evacuation system. There is an advantage that direct reduction and indirect reduction can proceed simultaneously through adjustment.

The following injection of reducing gas is more effective than the case of neutral gas.

In this case, hydrogen gas having a dew point of −30° C. or lower is injected.

As a result, deoxidation proceeds efficiently due to the synergistic effects of direct reduction of carbon, indirect reduction, and reduction by hydrogen.

Here, it is important to note that the dew point of the injected hydrogen is -
The temperature should be kept below 30°C.

This is because, if this is not done, the dew point within the vacuum system will increase.

Next, the oxygen content of the raw material powder before finishing reduction was reduced to 4.0% by weight.
The basis for limiting the C/O molar ratio of this raw material powder to within the range of 0.7 to 2.0 will be explained in detail below.

First of all, regarding the lower limit of the C/O molar ratio of the raw material powder, one reason is that when starting depressurization and during heating, free carbon flies up and causes loss, and especially when using high frequency heating, powder particles The second problem is that the vapor deposition phenomenon of carbon occurs due to the arc discharge of comrades, resulting in a large loss of carbon.Secondly, the carbon (atoms) alloyed in the raw material powder by the master alloy method diffuses to the surface of the raw material powder particles during heating. , even though the degree of vacuum is below 100 Torr, there is some oxygen in the system, so
This is determined based on the fact that carbon powder reacts directly with this oxygen and is gasified, and that a similar phenomenon occurs with carbon powder obtained by mixing raw material powder with a carbon source using a mixing method, resulting in loss of carbon.

This situation causes the loss of carbon other than those involved in deoxidation, so the lower limit of the C/O molar ratio is 0.5 when the reduction of formulas (1) and (2) proceeds ideally. Must be greater than the value.

In this regard, the present inventors used iron-based raw material powders such as pulverized sponge iron powder, mechanically pulverized powder, and low-alloy and high-alloy atomized powders to obtain various results at an average vacuum degree of 100 Torr during heating. As a result of repeated tests, it was confirmed that the lower limit of the C/O molar ratio is 0.7, and that if it is less than this, the desired low-oxygen iron-based powder with an oxygen content of less than 0.20% by weight cannot be obtained.

Regarding the upper limit of the C/O molar ratio, the reduction of metal oxides present on the surface or inside of the iron-based raw material powder is explained in (2) above.
Proceeding only by direct reduction of the formula, i.e. CO
If this CO gas is exhausted at the same time as the gas is generated, the amount of carbon required for reduction is theoretically the number of moles equal to the amount of oxygen contained in the raw material powder.

That is, when the C/O molar ratio of the raw material powder becomes 1.0.

However, in reality, as mentioned above, carbon loss occurs, so in reality, when deoxidizing only by direct reduction of carbon, C/O
The molar ratio must also be larger than the theoretical value of 1.0, and the inventors have determined that the average vacuum degree is 0.05 Torr.
As a result of conducting various experiments, it was found that it is necessary to set the upper limit of the C/O molar ratio in an actual powder packed bed to 20.

In other words, when the C/O molar ratio exceeds 2.0, the amount of residual carbon in the product iron-based powder increases, and the desired amount of carbon content decreases to 0.3.
This is because a low carbon iron-based powder with a weight coefficient of less than 0 cannot be obtained.

Therefore, the average degree of vacuum during heating is 100 Torr.
In order to proceed with direct reduction and indirect reduction with carbon at the same time within the range of 0.7 to 2.
It must be within the range of 0.

Next, the reason for limiting the oxygen content of the raw material powder before deoxidation to 4.0 weight coefficient or less will be described in detail.

In reality, deoxidation and decarburization are possible even if the oxygen content exceeds 4.0% by weight, but the purpose of the method of the present invention is the final reduction, which can be called secondary reduction, of the iron-based raw material powder. , The specified low oxygen and low carbon iron-based powder can be produced at low cost and in small quantities, and if the oxygen content exceeds 4.0 weight factor, it should be added including carbon loss. The amount of carbon increases, requiring a longer reduction time, and the amount of oxygen and carbon remaining in the product powder is not constant, making it easier to maintain the amount of residual oxygen and carbon required for iron-based powder for powder metallurgy. Therefore, it is difficult to control the amount of oxygen content to 4.0% by weight or less, and therefore it is difficult to estimate the decarburization rate and deoxidation rate from the preset reduction conditions. It is limited to.

Here, the oxygen contained in the iron-based raw material powder refers to the oxides and hydroxide films on the surface of the powder particles, as well as the oxides and oxides and hydroxides of alloy metals interposed within the iron-based powder particles. Refers to everything that is.

In addition, the forms of iron oxide and iron hydroxide are FeO, Fe3O
4. Compounds and mixtures of Fe2O3, Fe(OH)2, Fe(OH)3, etc., and other alloy metal oxides and hydroxides are also included in the oxygen content range here. Enter Chuu.

Of course, the present invention is also applicable to iron-based raw material powder whose oxide film has been partially removed by pickling.

On the other hand, the carbon contained in the iron-based raw material powder may be in any form.

In other words, powdered materials such as graphite powder may be mixed.
A liquid such as oil may be added, or a carbon source such as a hydrocarbon or carbide may be added.

For example, powder produced by the spraying method is produced by alloying carbon in the molten metal before spraying, and then coarsely reducing iron oxide with alloyed carbon and coke, etc. Carbon, etc. obtained by carburizing sponge iron may also be used.

In short, in the method of the present invention, the molar ratio between the total amount of carbon contained by the mixing method, the master alloy method, or both methods and the amount of oxygen contained, that is, the C/O molar ratio is 0.7 to 2.
It is sufficient that it is within the range of 0.

Next, the heating holding temperature (reduction holding temperature) is 750
A range of ~1400°C is suitable.

That is, when the upper limit temperature exceeds 1400°C, a liquid phase is generated, especially when the amount of added carbon is large, and it becomes difficult to crush the cake after deoxidation.

In particular, when mixing graphite powder, etc., even if the carbon is mixed uniformly macroscopically, it is not uniform microscopically, and a liquid phase is generated from areas where carbon is highly polarized. As sintering progresses, pulverization in the subsequent process becomes extremely difficult.

Further, at a temperature below 750°C, long-term heating is required to obtain the desired deoxidation rate and decarburization rate, resulting in a significant decrease in production capacity.

In addition, for preheating, iron-based raw material powder with an oxygen content of 4.0 weight coefficient or less and a C/O molar ratio in the range of 0.7 to 2.0 is heated to a temperature of up to 80% of the reduction holding temperature. During this period, the exhaust system is closed and the temperature is raised in a neutral or reducing atmosphere at atmospheric pressure or 1 atm. Immediately thereafter, the average degree of vacuum at the finishing temperature is maintained within the range of 100 Torr or less under the specified finishing reducing conditions. Reduction with can also yield a low-oxygen, low-carbon powder product, which is the desired objective.

The reason for this is that the deoxidation and decarburization rates are high in the temperature range from the temperature range exceeding 80% of the reduction holding temperature to the remaining holding temperature, so that the influence of preheating is canceled out.

Therefore, heating should be started at an average degree of vacuum of 100 Torr.
There is no need to wait until the temperature is below r, and it is possible to immediately start evacuation and heating at the same time after charging the raw material powder, which shortens the time spent on the final reduction process. There are advantages.

The time for holding the reduction temperature in the range of 750 to 1,400°C may be set arbitrarily depending on the amount of oxygen in the powder, but the desired deoxidation can be achieved even though the holding time is shorter than in conventional methods. be exposed.

This is because, while conventional reduction methods involve gas reduction such as H2 and CO, the method of the present invention involves indirect reduction of CO gas, that is, gas reduction, and direct reduction with carbon also occurs. .

Furthermore, if a heating means based on high-frequency induction heating ζ is employed as a heating means, the time required to raise the temperature to the holding temperature can be shortened, rather than so-called electric furnace heating in which heating is performed from outside the vacuum system using a silicon carbide heating element or the like.

In this case, since self-heating occurs, it is more convenient to promote the diffusion of carbon within the particles when reducing the surface oxide.

In short, it is sufficient that the holding time is long enough not to make it difficult to crush the cake after deoxidation and to obtain the desired deoxidation rate and decarburization rate.

To do this, it is necessary to spend a relatively long time at a low temperature of about 750℃.
At a high temperature of about 1400°C, a short time is sufficient.

As a result of various tests regarding this heating holding time, 4
It was found that it was appropriate to set the time to less than 1 hour.

In the case of external electric furnace heating, the temperature rise time is long, so even if the holding time is about 4 hours, the overall heating time is relatively long.

On the other hand, in the case of high-frequency induction heating, the powder itself is heated, so the time required to raise the temperature to a predetermined temperature can be extremely short.

The heating means may be any method that can raise the temperature to 750 to 1400°C, and may be heated externally using thermal energy from electricity, gas, etc., or the above-mentioned high-frequency induction heating may be used to heat the iron-based raw material powder. Exactly the same result can be obtained by heating it.

As a carbon source to be added to the iron-based raw material powder, it is microscopically uniform because there are few components that are undesirable for iron-based powders for powder metallurgy, such as ash and sulfur, and the addition and mixing suppresses carbon segregation as much as possible. The more desirable it is.

Furthermore, when adding a hydrocarbon compound such as oil, it is preferable to wet the raw material powder evenly.

To describe the types of iron-based raw powder materials and the types and amounts of alloy components that can be used to achieve the purpose of the method of the present invention, first, the iron-based powder materials used in the method of the present invention include crushed sponge iron powder, cuttings, etc. All iron-based powders are covered, including mechanically crushed powder of chips generated in the process, sprayed powder, and commercially available iron-based powders if deoxidation is required.

In short, the oxygen content is 4.0% by weight or less and the C/O molar ratio is 0.7-2. It should be within the range of 0.

Regarding the types of alloy components, we manufacture various alloy steel powders,
As a result of deoxidation and decarburization tests, pure iron powder and Cu,
Iron alloy powder containing one or more alloying elements of Pb, Ni, Co, W, Mo and Nb, B, Cr, V, Mn, and Si constituting a refractory oxide is treated by the present invention. It can be done.

Furthermore, the order of difficulty in reducing these metal oxides is consistent with that predicted from thermodynamics.

Among these, since Si02, which is the most difficult to reduce, is partially reduced, the types of metal oxides that can be reduced by the method of the present invention include all metal oxides that are more easily reduced than Si02, including Si02, and these metals. It is effective for complex oxides.

The amounts of these alloying elements added range from low-alloy and high-alloy steel powders to ferroalloy powders, and a very wide range of iron-based metal powders can be targeted.

According to the method of the present invention that satisfies the above conditions, the deoxidation rate and decarburization rate of low alloy and high alloy steel powder containing SiO2 are both within the range of 64.0 to 99.4%, and the oxygen content is 4%.
．． Even when the content of carbon is at the highest level of 0% by weight and 6.0% by weight (C/O molar ratio is 2.0), the amount of oxygen and carbon contained in products commercially available as iron-based powders is less than the upper limit.

Therefore, it can be said that the method of the present invention is suitable for the final reduction of iron-based powder for powder metallurgy.

Hereinafter, how effective the method of the present invention is will be specifically explained using examples.

First, Table 1 shows the chemical composition and amount of nonmetallic inclusions of the iron-based powder materials (raw material powder) used for finishing reduction, and Table 2 shows the finishing results of these powder materials by the present invention method and the conventional method. This shows the reduction conditions.

Table 3 shows the amount of carbon (hereinafter abbreviated as C amount), oxygen amount (hereinafter abbreviated as O amount) remaining in the iron-based powder obtained by final reduction using the method of the present invention and the conventional method. It shows the amount of nonmetallic inclusions, decarburization rate, and deoxidation rate.

In Table 1, material A is a commercially available reduced iron powder manufactured using rimmed steel mill scale generated in the rolling of steel plates, and material B is sponge iron obtained by rough reduction with coke using killed steel mill scale as a raw material. It is pulverized to a particle size of 100 mesh or less.

Since B contains relatively large amounts of Si and Mn as alloy components,
Although analysis of nonmetallic inclusions was not performed, it is presumed that they contain a large amount of oxides of Si and Mn.

Material C is a coarsely reduced powder with a particle size of 100 mesh or less, which is made from by-product hematite produced by spray roasting waste acid from hydrochloric acid pickling of steel plates, and is coarsely reduced in the same way as B.

Of these, in A and B, graphite powder was mixed to set the C/O molar ratio to 0.76 and 1.62, respectively, and in C, rapeseed oil was added to set the C/O molar ratio to 0.94. .

Material D is a water-sprayed pure iron-based raw material powder, and Material E contains MnO. This is a water-sprayed low-alloy steel raw material powder containing 39% by weight, 2.09% by weight of Ni, and 0.50% by weight of Mo.

Material F is similarly a water spray raw material powder, and contains MnO. 23, NiO, 51, Cr0.54, Mo0.
It is a low-alloy steel raw material powder containing each weight factor of 53.

Material G is also a water spray powder and contains MnO. 73
, Cr1.08, Mo0.33 each weight%, and S1020.186, Mn00.33 as nonmetallic inclusions.
7, Cr2030.0503, Fe06.24 each weight%
It is a low-alloy steel raw material powder containing

Among these, D. E. In F, graphite powder was mixed to make the C/O molar ratio all 1.00, and in G, the same was made to 1.50.
And so.

Materials H and I are in the water-sprayed state, and no graphite powder is added by the mixing method, and approximately 1.
It is a low alloy steel raw material powder that has been alloyed with 0% by weight and sprayed with water, that is, carbon has been dissolved in solid solution in advance by the master alloy method.

H. I powder has a large amount of Mn as an alloy component at about 1.3% by weight, as well as about 0.5% by weight of Cr and about 0% of Mo.
．． 5% by weight, and in case (2), it further contains about 0.5% by weight of Ni.

These powders have relatively large amounts of nonmetallic inclusions such as MnO and FeO.

The C/O molar ratio of these powders is approximately 1.5.

Material J corresponds to a powder in which a large amount of Si is added to ■, and the carbon content according to the master alloy method is 0.228% by weight, and 0.8% by weight of rapeseed oil is added to this to adjust the C/O molar ratio. It is a low-alloy steel raw material powder with a ratio of 0.82.

Material K is a water-sprayed low-alloy steel raw material powder containing only Si as an alloy component, and like H and I, it is still water-sprayed.
The C/O molar ratio is 1.66.

Material L is high-speed steel S that is sprayed with a large amount of carbon in the molten metal.
It is high alloy steel raw material powder that is equivalent to KH-9 water spray,
In addition to Si, Mn, Cr, and Mo, W, ■
The C/O molar ratio is 1.64.

In this way, all C/O molar ratios were kept within the range of 0.7 to 2.0.

The materials A-L above were subjected to finishing reduction treatment under the conditions shown in Table 2, and a brief explanation of these conditions will be added below.

First, when materials B, G, H, I, J, K, and L are directly heated by high frequency, about 230 g of each is taken out and filled into a quartz tube with an inner diameter of 30 mmφ.

The filling height at this time was about 100 mm.

This packed bed tube is inserted into a vacuum system and the pressure is reduced using an oil rotary pump.

Thereafter, induction heating is gradually performed using a high frequency generator with a frequency of 380 KHz and an output of 5 KW.

However, for a part of the material H, the order of starting pressure reduction and starting heating was reversed, as will be described later.

In the case of high-frequency induction heating, the heating time to a predetermined reduction temperature was all within 40 minutes.

In addition, in order to obtain a predetermined average degree of vacuum during heating including temperature rise, the displacement of the oil rotary pump was adjusted using a cock.

Next, when materials A, C, D, E, and F are heated from the outside in an electric furnace, about 230 g of powder is taken from each powder and allowed to fall freely into a square quartz boat with a width of 50 mm, a height of 20 mm, and a length of 200 mm. These are charged into the refractory core tube, and the two oil rotary pumps and oil diffusion pumps
Reduce the pressure using the stage exhaust system.

Thereafter, the furnace core tube is heated from the outside in an electric furnace with a silicon carbide heating element having an output of 20 kW.

The heating time to the predetermined reduction temperature was approximately 3 hours in all cases.

In addition, in order to obtain a predetermined average degree of vacuum, the displacement was adjusted using a cock, just as in the case of high-frequency heating.

In the cooling after heating using high frequency waves and electric furnaces, after reaching a predetermined reduction holding time, the heating power was turned off, and the furnace was cooled to 100° C. while maintaining a predetermined average degree of vacuum.

In the conventional method of final reduction using hydrogen gas, approximately 230 g of the A-L material is filled into the quartz boat by free fall, and these are charged into a stainless steel furnace tube, and hydrogen gas from a commercially available cylinder is purified by a purification device. Purity and low dew point (D
．． P. -50℃) and the flow rate was 2l/min.
and relatively large.

In this case as well, heating was performed from the outside using a silicon carbide heating element electric furnace in the same manner as above.

The time for heating up to the predetermined reduction temperature was approximately 3 hours.

Cooling is performed by furnace cooling, and the reduction state is maintained until the temperature drops to below 100°C.D. P. A low hydrogen gas flow was continued.

The reduction conditions such as reduction temperature, reduction time, and heating atmosphere at this time are as shown in Table 2.

The semi-sintered powder cakes obtained by final reduction using these three methods were ground in a hammer mill and analyzed for carbon, oxygen and non-metallic inclusions.

The powder properties in Table 3, which shows the results after the final reduction of materials A-L according to the present invention and the conventional method, will be specifically explained with reference to Table 2.

In Table 2, Examples 1 and 2 are finished reduction examples of material A.
A-1 was obtained by the method of the present invention, and A-2 was obtained by hydrogen reduction using the conventional method.

A-1 is obtained by heating material A in an electric furnace under an average degree of vacuum of 8 to 10 Torr, and deoxidizing it under reducing conditions of 1100°C x 2 hours.

The amounts of C and O in the powder obtained in A-1 were 0.040 and 0.095% by weight, respectively, as shown in Table 3.

In addition, the decarburization rate and deoxidation rate were 93.3% and 64%, respectively.
．． It was 0%.

On the other hand, in conventional method A-2, the amounts of C and O are each 0.
065 and 0.102% by weight, which were higher than that of A-1.

In the conventional method, the hydrogen gas used is of high purity and its D. P. Since the temperature was as low as -50°C, decarburization was insufficient even after 5 hours of reduction, and the decarburization rate was only 53% at most.

However, the deoxidation rate is D. P. Although deoxidation did not progress as much as that of A-1 due to the low value, it was relatively high, reaching 61.4%.

The reason why temperatures exceeding 1100°C were not used in the conventional method is that using such high temperatures in pure iron powder systems causes sintering between powder particles, making it difficult to crush the cake in the subsequent process. It is.

Now, as in A-1 above, low oxygen and low carbon powder can be obtained by applying the method of the present invention, and the reason for this is that the mixed graphite acts as a deoxidizing agent.

In order to confirm this, material A except graphite powder was heated in the same manner as A-1 at an average vacuum level of 8 to 10 Torr, and the amount of O in the obtained powder was 0.30% by weight. The amount of O was greater than the amount before heating.

In this way, a powder material containing almost no carbon could not be deoxidized simply by heating in a vacuum.

The reason why the deoxidation rate of A-1 was higher than that of A-2 is that the average degree of vacuum during heating was maintained at 8 to 10 Torr and deoxidation was performed by direct reduction and indirect reduction of carbon.

However, in the case of A-2, the reduction was performed using hydrogen, so the amount of mixed carbon was consumed in a smaller amount than in A-1.

Examples 3 and 4 are cases where the coarse reduced powder B was subjected to final reduction, with B-1 using the method of the present invention and B-2 using the conventional hydrogen reduction method.

Compared to material A, the amount of O and the amount of C in B are larger, and the C/O molar ratio is 1.62, which is larger than that in A.

In B-1, heating was performed externally using an electric furnace, the average degree of vacuum during heating was 0.05 Torr, and the final reduction condition was 130 Torr.
The size was 0°C x 15mm.

In B-2, D. P. Reduction was carried out using a conventional method in a -50°C hydrogen atmosphere at 1100°C for 3 hours.

As a result, the amount of C and O in the powder was 0.0 for B-1, respectively.
202, 0.114% by weight each, 2.1% each in B-2
3.0.195% by weight, and both the decarburization rate and the deoxidation rate in the method of the present invention are greater than those in the conventional method.

Even when heated at a high temperature like B-1, the holding time was short, so sintering between the powder particles did not progress much, and the powder could be ground relatively easily.

Examples 5 and 6, like Material B, are examples of final reduction of coarsely reduced powder.

Material C has a carbon content of 0.21% by weight and O after rough reduction.
2% by weight of rapeseed oil was added to and mixed with powder having an amount of 1.72% by weight, and the C/O molar ratio was set to 0.94.

C-1 is a method of the present invention in which heating was performed externally using an electric furnace, the average degree of vacuum during heating was maintained at 8 to 10 Torr, and final reduction was performed at 1100° C. for 1 hr.

C-2 is hydrogen reduction (D.P. -50℃), which belongs to conventional method C.
) is an example.

The final reduction conditions for C-2 were 1100°C x 3hr.

The amounts of C and O in C-1 powder are 0.012 and 0.012, respectively.
198% by weight each, those of C-2 powder are 0.3% each
43 and 0.370% by weight.

As shown in this example, in the method of the present invention, a liquid reducing agent such as oil can also be used, and it can also be used in conjunction with a solid or gaseous reducing agent.In short, it is sufficient to add a substance to serve as a carbon source. There are many types of reducing agents.

Examples 7 and 8 are the final reduction of water-sprayed pure iron powder-based raw material powder D (mixed with graphite powder to have a C/O molar ratio of 1.00), and D-1 belongs to the method of the present invention. , D-2 were obtained by the conventional method.

D-1 is an example in which the average degree of vacuum is 8 to 10 Torr.

The reduction conditions were 1100'C x 2 hr by heating in an electric furnace.

In D-2, hydrogen (D.P. -50°G) was used, and 110
Reduction was performed at 0°C for 5 hours.

The amounts of C and O in the powder after reduction are as follows: D-1 is 0.
101 and 0.198% by weight, whereas in D-2, the amount of C and 0 is 0.969 and 0.390% by weight, respectively.Similar to the examples shown so far, the method of the present invention It can be seen that the charcoal rate and deoxidation rate were 95.7% and 93.7%, respectively, which were excellent.

Examples 9 and 10 are examples of application of the method of the present invention (E-1) and the conventional method (E-2) to Mn-Ni-Mo based low alloy steel raw material powder E with a large amount of Ni added.

The reduction conditions for E-1 are an average degree of vacuum of 8 to 10 Torr.
In E-2, it was heated at 1100°C x 2hr in an electric furnace at 110°C in hydrogen (D.P. -50°G).
Long-term reduction was performed at 0°C for 5 hours.

As a result, the C and O contents of E-1 powder were each 0.0
Values of 10 and 0.085% by weight were obtained for E-2 and 0.534 and 0.170% by weight, respectively, indicating that the method of the present invention is also excellent in deoxidizing low-alloy steel powder. I understand that.

In the case of this material E, it is assumed that other than the oxide of Mn, it is composed of oxides such as Fe, Ni, Mo, etc. that are relatively easy to reduce. It was obtained.

However, it is clear that the method of the present invention is superior in terms of decarburization.

If decarburization does not proceed with the conventional method, it may be unnecessary to mix carbon powder, but if an appropriate amount of carbon is added to the molten metal before water spraying, the melting temperature will be lowered, as is clear from the FeC system phase diagram. There is an advantage that the production of water spray raw powder can be carried out at relatively low temperatures.

As a result, water spray raw material powders with a large amount of C can be obtained, so the method of the present invention for decarburizing and deoxidizing these powders with a large amount of C is effective.

Next, in Examples 11 and 12, the method of the present invention (F-1) and the conventional method (F-1) for powder material F, in which graphite powder was mixed with water-sprayed powder and the C/O molar ratio was 1.0. This is an example of -2).

Material F is Material E with 0.54% by weight of Cr as an alloy component.
Mn-Ni-C with added Ni content of 0.51% by weight
This is r-Mo based low alloy steel raw material powder.

The reduction conditions for F-1 are an electric furnace with an average degree of vacuum of 0.
In F-2, the temperature was 1100°C x 2 hr in hydrogen (DP -50°C) at 1100°C x 3 hr in 05 Torr.

In powder F-1 after final reduction, the amount of C and O are each 0.
．． For F-2, these values were 0.870 and 0.399 weight %, respectively.

The amount of 0 in material F is the largest among the 12 types of materials A to L, at 3.56% by weight, and Cr is added as an alloy component constituting a refractory oxide. Nevertheless, the amount of O in the heather invention method (F-1) was smaller than that in the conventional method (F-2).

Further, since the amount of C in F was large, the amount of remaining C in F-2 was large.

Examples 13 to 19 are examples of application to material G in which graphite powder is mixed with the powder that has been sprayed with water, and the C/O molar ratio is made relatively large at 1.50.

G is Mn-Cr-Mo based low alloy steel raw material powder. As shown in Table 1, this material contains non-metallic inclusions St02, MnO,
Cr203 and FeO are 0.186 and 0.337 respectively
, 0.0503, and 6.24% by weight.

Conventional method G-7 was heated in an electric furnace, and the reduction conditions were 1100° C. x 5 hr in hydrogen (DP -50° C.).

Methods G-1 to G-6 of the present invention are heated at 1300°C x 15 m in an average vacuum degree of 8 to 10 Torr by high-frequency induction heating.
m reduction.

Among these, in G-1, the average degree of vacuum was set to 8 to 1 from before the start of temperature rise.
This is an example of heating while maintaining G
-2,G-3,. 400 each for G-4 and G-5,
It is set to exhaust up to 600, 800, and 1000 degrees Celsius, but without reducing the pressure, close the exhaust cock and keep it at 1 atm in the atmosphere, and after reaching these temperatures, maintain the average degree of vacuum at the 8 to 10 Torr mentioned above. However, the temperature continued to rise above these temperatures, and each reached 1300'C x 15
This is an example of thermal reduction at m.

G-6 is an example in which a small amount of (Ar + 3% H2) as a carrier gas was injected, the temperature was raised from room temperature to 1300° C. so that the average degree of vacuum was 80 to 100 Torr, and the temperature was maintained for 15 minutes for reduction.

In the methods G71 to G-6 of the present invention, the residual C and O amounts are 0.1% by weight or less and 0.06% by weight or less, respectively.
Decarburization and deoxidation are progressing.

However, in conventional method G-7, the amount of residual C and O is large.

From these examples, the degree of vacuum when starting temperature rise is not necessarily 1.
There is no need to maintain the temperature below 0.00 Torr, and once the pressure is set to a reduced pressure, start heating immediately to reach the reduction temperature of 8.0 Torr.
It is sufficient to evacuate the air until the vacuum level reaches a predetermined average degree of vacuum.

Therefore, there is no need to wait for the temperature to rise until a predetermined average degree of vacuum is obtained, and the final reduction time is shortened accordingly.

However, in this case, the temperature at which heating is possible under 1 atm is 8°C in the range of 750 to 1400°C at which final reduction is to be performed.
The temperature is below 10%.

If heated to a temperature higher than that under 1 atm, the desired amount of residual C and O cannot be obtained even with subsequent reduction at a higher temperature.

The reason why the desired objective can be achieved even if the temperature is maintained at 1 atm below 80% of the final reduction temperature is that the reduction ability is extremely large at temperatures above 80%.

Next, looking at the changes in the analysis values of nonmetallic inclusions in the powder before and after reduction in the G powder, we find that in the material G, SiO2, M
nO, Cr203, and FeO are 0.186 and 0.186, respectively.
337, 0.0503, and 6.24% by weight respectively, when the method of the present invention is carried out, the amounts of these inclusions in G-1 to G-5 are 0.0332 and 0.03, respectively, as shown in Table 3.
55, 0.0009, and 0.0686% by weight or less, which should show how great the reducing ability of the method of the present invention is.

In this way, in the method of the present invention, S, which is a hard-to-reducible metal oxide,
It has become clear that 102, MnO, Cr203, etc. are also rapidly reduced.

The reason that hard-to-reducible substances can be reduced in this way is that, as mentioned above, direct reduction with carbon is proceeding, and the fact that the amount of residual O is small means that reduction with CO gas (i.e. This is because indirect reduction) is also included.

In Examples 20 to 27, C/
This is an example of a low alloy steel material H having an O molar ratio of 1.46.

H is a Si-Mn-Cr-Mo iron-based raw material powder.

This material H is as shown in Table 1 <Si02, MnO, Cr
203, non-metallic inclusions such as FeO, 0.038 each
It contains 2, 0.298, 0.0064, and 3.45% by weight.

H-1 to H-7 are examples of induction heating using high frequency (H-1
~H-4 and H-7 are the methods of the present invention, H-5 and H-6
is the conventional method), and the reduction conditions are 1300°C x 15 min.
(However, only H-1 is 5 mm).

H-8 is a conventional method using hydrogen (DP -50°C), and the reduction conditions are 1100°C x 5 hr.

H-1 to H-7 were investigated for the influence of the average degree of vacuum during heating, and H-1 and H-2 were 8 to 10 Torr.
, H-3, H-4, H-5, H-6, H-7, the average degree of vacuum is 0.05, 30-50, and 200-300, respectively.
, 600 to 700. Finish reduction was performed at 80 to 100 Torr.

However, H-7 is an example in which neutral gas (Ar) is used as the carrier gas.

The final reduction time for H-2 is 15 minutes and that for H-1 is 5 minutes, so if the reduction time is longer like H-2, the decarburization rate and deoxidation rate will improve, and this The invention method becomes more effective.

Furthermore, as shown in Table 3, the amount of nonmetallic inclusions in the powder after final reduction by the method of the present invention is found to be lower than that of material H before reduction, and in particular, the reduction of MnO and FeO is remarkable.

Furthermore, reduction of SiO2 was also observed, albeit slightly.
The fact that Si02 can be reduced will become clearer when looking at the material temperature C and materials I and J, which will be described later.

Figure 1 shows the relationship between the decarburization rate, deoxidation rate, amount of residual C and residual O, and the average degree of vacuum during heating when material H is finished reduced by the method of the present invention and the conventional method (1300'C x 15mm FIG.

In this figure, the decarburization rate and deoxidation rate are determined by the average degree of vacuum being several + To
If the degree of vacuum is maintained at a low degree exceeding rr, it is recognized that the degree of vacuum decreases rapidly.

Further, the average degree of vacuum when the amount of residual C becomes less than the desired 0.30% by weight is a high degree of vacuum of 100 Torr or less.

On the other hand, the amount of residual O in the method of the present invention applied to material H and the conventional method was less than the desired value of 0.20% by weight.

Moreover, FIG. 2 is a graph showing the relationship between the amount of SiO2, the amount of MnO, the amount of FeO and the average degree of vacuum during heating (held at 1300° C. for 15 minutes) when material H is finished reduced by the method of the present invention.

Therefore, in order for the method of the present invention to be effectively carried out, 100 Torr is required.
A high degree of vacuum below r is required.

In Examples 28 to 34, C/
This is about low alloy steel powder material (2) with an O molar ratio of 1.48.

■ has the same type of alloy components as material F, but compared to F, it is a powder containing a larger amount of Mn.
This is Ni-Cr-Mo based low alloy steel raw material powder.

This material contains nonmetallic inclusions such as Si02, MnO, Cr203, and FeO at 0.0050 and 0.380, respectively.
It contains 0.0238 and 3.74% by weight, and I-
1 to I-6 belong to the method of the present invention, in which high frequency is used as the heating means, and the average degree of vacuum during heating is 8 to 1.
This is an example when the torque is set to 0 Torr.

These Examples are examples in which the reduction holding temperature and the reduction holding time are different.

For I-1 to I-4, the reduction holding temperature is 1300°C and the reduction holding time is 0, 5, and 15.60 min, respectively.

I-5 and I-6 are each 1250°C x 5min, 1
The final reduction was performed at 350°C for 5 minutes.

In the conventional method I-7, D. P. This is an example in which reduction was performed at 1100°C x 5 hours using hydrogen at -50°C.

In these methods of the present invention, the amounts of residual C and O are each 0.
0.075 and 0.130% by weight, respectively, which are lower than the conventional method's 0.624 and 0.176% by weight, respectively.

However, naturally, the method of the present invention provides high decarburization and deoxidation rates.

Moreover, MnO, Cr203, FeO in the powder of the method of the present invention
Even the non-metallic inclusions, such as, are lower than those for material (2).

Furthermore, Si02 is also 0.0050% by weight of the material.
After reduction, it becomes less than 0.0039% by weight, and SiO
It turns out that a 2-in-1 reduction is possible.

The amount of residual C and O and the amount of nonmetallic inclusions after reduction are determined by high temperature,
The longer the reduction, the lower the reduction, and it is recognized that the method of the present invention is extremely effective.

With high frequency heating, the temperature rises due to the heat generated by the powder itself, so a higher temperature can be obtained in a shorter time than with external heating using a silicon carbide heating element, and in such cases, the method of the present invention is particularly advantageous.

Since the reduction rate increases at high temperatures, deoxidation proceeds sufficiently even with a holding time of 60 minutes or less.

However, in the case of heating with an electric furnace, the reduction is performed at a relatively low temperature, so a reduction time of 2 to 5 hours is required.

If the heating time is longer than this, it will be difficult to crush the finished reduced cake, and this will not meet the purpose of obtaining a powder.

Examples 35 and 36 are examples of material J in which 0.8% by weight of vegetable oil was added as a carbon source to the powder as-sprayed with water, and the C/O molar ratio before heating was set to 0.82.

J is a Si-■-Ni-Cr-Mo based low alloy steel raw material powder, which contains less alloy components such as Si, Cr, and Mo than the material (2).

J-1 belongs to the method of the present invention in which final reduction was carried out at 1300°C for 15 minutes using high frequency, and J-2 belonged to the method of the present invention in which final reduction was carried out at 1100°C for 5 hours in hydrogen (DP - 50°C) using an electric furnace. This is the conventional method used.

Material J has nonmetallic inclusions of Si02, MnO, Cr203, and FeO at 0.1680.194, 0.0084, 1
．． 96% by weight, respectively, but in J-1 after final reduction by the method of the present invention, it contained 0.125, 0.030, and 0, respectively.
．． 0004 and 0.0054% by weight, respectively, and it is possible to reduce the hardly reducible oxides Si02, MnO, Cr203, etc.9.

The residual C and O amounts at this time were also lower than those of the conventional method, demonstrating the effectiveness of the method of the present invention.

Also, 1.3Mn-0.5Ni-0.5Cr-0.5M
O-type low alloy steel raw material powder (used as lees for materials H, I, and J).

However, H has no Ni component, and J has 0.38 Si.
As estimated from conventional methods such as H-8, 1-7, and J-2, in the final reduction with hydrogen gas, the conventional method with one reduction holding time of about 5 hours It can be seen that the amount of residual O is at most 0.15% by weight.

However, according to the present invention, as shown in I-4, the amount of residual C is about <0.055% by weight, and the current amount of residual C is also 0.007% by weight, and as far as powder is concerned, these values are the lowest values currently achievable. This kind of embodiment is not found in any other conventional method.

Examples 37 and 38 differ from the previous examples in that they are raw material powders with a high Si content as they have been sprayed with water, and the revised material K has a C/0 molar content of 1.66 using the master alloy method. is a Si-based low alloy steel raw material powder containing only 0.94% by weight of Si as an alloy component.

K-1 and K-2 were finished reduced by the method of the present invention and the conventional method, respectively.

K-1 has an average degree of vacuum during heating of 8 to 10 Torr,
By high frequency × 300℃ × 15 min, K-2 in hydrogen (D.P. -50℃) by electric furnace 1100℃ × 5
This is a product that has undergone hr finishing reduction.

Material K contained 0.0908% by weight of SiO2, but according to the method of the present invention (K-1), this value was reduced to 0.0201% by weight.
% by weight, and the residual C and O amounts are each 0.
0.076 and 0.045% by weight, indicating the remarkable effectiveness of the method of the present invention.

This is very significant, and confirms that deoxidation of alloy steel raw material powder alloyed with Si is possible only by the method of the present invention.

Examples 39 and 40 are examples of deoxidizing high-alloy steel raw material powder, in which water-sprayed raw material powder (C/O molar ratio 1.64) corresponding to high-speed steel SKH-9 was deoxidized by the method of the present invention (L-1). and conventional method (L-2
) was finished and returned.

For L=1, reduction was performed at 1300° C. for 15 minutes by heating with high frequency in an average vacuum degree of 0.05 Torr.

L-2 is heated at 1100°C in hydrogen (D.P. -50°C)
In the 3-hour reduction example, the C and O contents of powder L-1 were 0.271 and 0.105% by weight, respectively, whereas they were 1.18% by weight for powder L-2. ，
0.347% by weight, indicating that the method of the present invention is effective even in the case of high-alloy steel powder.

Table 4 shows the △C/△O molar ratio (the ratio of the weight loss (△C) of C mol before and after reduction to the weight loss (△O) of 0 mol before and after reduction) and the C/O mol of the powder material. It shows the relationship % with the ratio.

FIG. 3 shows the percentage relationship between the ΔC/ΔO molar ratio and the C/0 molar ratio of the powder material.

Table 5 shows the relationship between the average degree of vacuum during heating and the ratio of one-way reaction type that produces CO2.

The difference between the reduction mechanism of the present invention and the conventional method lies in the relationship between the ΔC/ΔO molar ratio and the C/O molar ratio of the powder material, as shown in Table 4.

In other words,. As can be seen from these tables, in the method of the present invention, △C/△O is always greater than 1.0 and △C
There is a positive correlation between /ΔO and C/O.

On the other hand, in the conventional method using hydrogen gas, △C/△O is always smaller than 1.0 and △C/△O and C/
There is a negative correlation with O.

However, in H-5 and H-6 of Example (conventional method), despite the large C/O molar ratio of 1.46,
The fact that △C/△O is 1.08 to 1.18 is the same as in the method of the present invention, except that this example was conducted under a low degree of vacuum with an average degree of vacuum of 200 Torr or more during heating. This is because it has been reduced to

If △C/△O exceeds 1.0, it means (1) and (2)
This means that carbon loss occurred in addition to the reduction reaction in the equation.

A possible cause of this loss is that free carbon adhering to the powder inevitably scatters at the start of depressurization, and this scattering is particularly severe when carbon powder is mixed.

In addition, even in a reduced pressure atmosphere, this atmosphere may contain a small amount of air, which may react with this oxygen and be lost. Especially when exhausting with a vacuum pump with a high pumping speed, even a small amount of vacuum may be present. Even if there is a difference, the desired pressure 10
Since 0 Torr or less can be obtained, this type of loss is large.

Furthermore, when the C/O molar ratio of the powder composite increases, the carbon alloyed with the powder diffuses to the surface during heating, and the free carbon that does not react with the oxide on the powder surface evaporates, i.e. under reduced pressure. There is loss due to the phenomenon of carbon deposition.

Particularly in the case of high-frequency heating, arcs fly between iron-based powder particles, which increases this loss.
1 to G-6, H-1 to H-4, H-7, I-1 to I-6
, K-1, and L-1, ΔC/ΔO becomes larger than 1.0 and falls within the range of 1.12 to 1.60, and the loss of carbon increases.

However, the embodiments of the method of the present invention (, A-1, C-1, D-1
, E-1, F-1), the above-mentioned arc generation is not observed, so the value of △C/△O is larger than 1.0, but within the range of 1.02 to 1.10. , carbon loss is small.

In contrast, an example of the conventional method of reducing with hydrogen gas (H-
5. In all conventional method examples except H-6), △C/
The value of ΔO is within the range of 0.44 to 0.77.

However, in H-5 and H-6, heating was done in a low degree of vacuum, and because high-frequency heating was performed, which is not the method of the present invention, △C/
ΔO is greater than 1.0 and ranges from 1.08 to 1.18.

In short, ΔC/ΔO becomes larger than 1.0 in reduced pressure heating, and smaller than 1.0 in gas reduction such as hydrogen.

However, even with reduced pressure heating, reduction at a low degree of vacuum exceeding 100 Torr is not included in the method of the present invention.

FIG. 3 shows the result, that is, the relationship between ΔC/ΔO and C/O of the powder material.

In the reduced pressure heating method of the present invention, when the C/O molar ratio becomes large, △
C/ΔO exceeds 1.0 and becomes larger.

Even with reduced pressure heating, C/
Even if the O molar ratio increases, H-5 and H-6 shown in Figure 3
As shown, ΔC/ΔO is at most 1.18, which deviates from the tendency of the method of the present invention.

Furthermore, using powder material H as an example, it will be explained how the deoxidation type (reduction type) changes when the average degree of vacuum during heating changes.

First, the method for determining the ratio of reduction methods that produce CO2 shown in Table 5 (details are given below).

Equation (5) is obtained from Equation (1) and Equation (2).

The rate at which the reactions in equations (2) and (5) proceed is m
, n%, then in a general reduction reaction, equation (2) and (5)
Equation (6) holds true because it proceeds by mixing with Eq.

m+n-=100 (6) The amount of change ΔC mole number of C lost in the reduction operation at this time is expressed by equation (7).

Using equation (6), equation (8) is obtained from equation (7).

Here, ΔCl is the molar amount of carbon content in the powder material that is lost without participating in the reduction reaction.

From equation (8), the n value is expressed as shown in equation (9).

When heating the material H with a vacuum pump while constantly evacuating, the degree of vacuum is 0.01 Torr or less, which is a height of 1.50.

Here, the C/O molar ratio of material H was about 1.50.

Furthermore, under such a high degree of vacuum, it is thought that the reaction of formula (1) does not proceed, and the reduction proceeds only by direct reduction of formula (2), so n=.

Therefore, n at low vacuum levels above 0.01 Torr.

is calculated using equation (10). It can be expressed as

Therefore, the ratio np that occurs at any average degree of vacuum can be found,
These are shown in Table 5.

According to this table, in the conventional method for H-5 and H-6, the rate at which the reaction of formula (5) proceeds is 50% or more, and indirect reduction in which CO2 gas is generated becomes dominant.

In such a case, the inside of the vacuum system will be filled with CO2 gas generated by the reaction of equation (5), and the CO2 partial pressure will become high, making it difficult for reduction to proceed.

In addition, the n value of conventional reduction using hydrogen gas was 168%.
However, the essence of this reduction is that hydrogen becomes larger than △C, suggesting that decarburization is difficult to occur.

Therefore, np at this time is an apparent value and is 100%
It exceeds.

In short, the method of the present invention differs from the conventional method in that the degree of vacuum during heating is always maintained at a certain value within the range of 100 Torr or less, including during temperature rise and temperature fall, so direct reduction of carbon according to equation (2) is performed. The reason is that the reduction in which CO2 is generated according to the formula (5) proceeds appropriately, and the reduction reaction according to the formula (5) does not exceed 50%.

In other words, in the method of the present invention, the reduction of CO gas or H2 gas in a near-equilibrium state is not dominant, and the reduction of CO gas or H2 gas in a non-equilibrium state is twice as much as the direct reduction of CO gas or H2 gas in a non-equilibrium state with carbon that has reducing ability.
This is because the reduction of O gas or H2 gas used as carrier gas is proceeding appropriately.

Looking at this from another perspective, in the method of the present invention in which equations (2) and (5) proceed simultaneously, a larger amount of oxygen is desorbed with the same amount of C than in the case of only direct reduction in a high vacuum. In other words, the amount of added C (including all methods such as the master alloy method and the mixing method) can be reduced to obtain powder with the same amount of O, and the method of the present invention does not require a direct reduction reaction of carbon. Compared to the conventional method of final reduction in a low vacuum of over 100 Torr and reduction in CO or H2 gas at 1 atm, the reduction of refractory metal oxides consisting of Cr, V, Mn, Si, etc. It has the characteristic that it can be reduced.

This is the point where the method of the present invention is superior to the conventional method.

As mentioned above, the scope of application of the method of the present invention extends to the finishing reduction of a very wide range of iron-based metal powders such as pure iron powder, low-alloy steel powder, high-alloy steel powder, and ferroalloy powder. You can get powder.

Now, from these examples, it is clear that the method of the present invention can be applied to iron-based powder materials (
It will be understood how powerful and effective this method is as a final reduction method for raw material powder (raw material powder), but this method is based solely on the direct reduction of iron-based powder materials with carbon, which has a very strong deoxidizing ability, and the use of CO gas. This is due to a synergistic effect caused by moderate overlap with indirect reduction.

As described above, the method of the present invention has made it possible to produce a low-oxygen, low-carbon iron-based powder for powder metallurgy.

Since this objective could not be achieved with the conventional technology, Cr,
It has been considered impossible to manufacture iron-based powder for powder metallurgy, especially for sintering and forging, which is alloyed with Mn, Si, etc. and has excellent hardenability and other mechanical properties.

Even if it were manufactured, the oxygen content would be 0.20% by weight or more, and the desired purpose could not be achieved.

However, when reduced in a reducing atmosphere with a very low dew point, 0
．． Although the oxygen content is less than 20% by weight, it has been extremely difficult to obtain this type of reducing atmosphere industrially.

Therefore, it is no exaggeration to say that in the past, only pure iron powder containing less than 0.3% by weight of Mn and low alloy steel powder mainly containing alloy components of Ni and Mo were manufactured and sold.

However, among these, iron-based powders containing Ni and Mo are not only expensive, but also sintered parts made from low-alloy steel powders mainly containing these alloy components do not have such excellent mechanical properties.

Therefore, if the method of the present invention is implemented, instead of low-alloy steel powder mainly composed of Ni and Mo, it will be possible to use powder metallurgy powder alloyed with Cr, Mn, Si, etc., which is relatively inexpensive and has excellent properties, especially for sintering. Low alloy steel powder for forging can be produced.

In addition, the method of the present invention can be applied not only to low-alloy steel powder but also to the final reduction of pure steel powder containing about 0.3% by weight of Mn, and deoxidation and decarburization proceed rapidly, and H2, CO This method has many advantages when put into practical use because it is inexpensive because it does not necessarily require reducing gases such as .

Furthermore, as shown in the examples, the present invention can be applied to finishing reduction of high alloy steel powder, and the applications of the present invention are truly wide-ranging.

In particular, when using a method using high-frequency induction heating, refractory oxides are deoxidized in a short time at high temperatures, and the amount of carbon in the powder can be reduced, making it suitable for the final reduction of any iron-based powder. There is.

[Brief explanation of drawings]

Figure 1 shows the decarburization rate, deoxidation rate, and residual C in an example of the present invention.
A graph showing the relationship between the amount of SiO2, the amount of residual O, and the average degree of vacuum during heating.
FIG. 3 is a graph showing the relationship between the amount and the average degree of vacuum during heating, and FIG. 3 is a graph showing the relationship between the ΔC/ΔO molar ratio and the C/O molar ratio of the powder material.

Claims (1)

[Claims] 1. Pure iron-based powder or iron-based raw material powder of iron alloy-based powder containing oxides of iron alloy elements is alloyed with carbon in advance, or a liquid or powdered carbon source is added and mixed. The oxygen content of the raw material powder is 4.0% by weight or less and the C/O molar ratio of this raw material powder is within the range of 0.7 to 2.0, and these raw material powders are heated under a degree of vacuum with an average pressure of 100 Torr or less. Deoxidation is performed at the same time as decarburization by heating within the final reduction temperature range of 750 to 1400°C,
Oxygen content is less than 0.20% by weight and carbon content is 0
．． A method for producing a low-oxygen, low-carbon iron-based powder, characterized in that less than 30% by weight of iron-based powder is obtained.