JP2016160469A - Method for producing sintered compact, and sintered compact obtained by the production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of obtaining a sintered compact having higher mechanical strength from raw material powder including atomized iron powder and reduced iron powder, and a sintered compact obtained by the production method.SOLUTION: Provided is a method for producing a ferrous sintered compact having improved mechanical strength characterized in that, in a method for producing a sintered compact by sintering a molded body obtained by subjecting raw material powder including atomized iron powder, reduced iron powder and graphite to compressive molding, the content of the reduced iron powder in the raw material powder is controlled to the range of 23 to 35 mass%, the content of the graphite is controlled to 0.2 to 1.2 mass%, the facial pressure upon the compressive molding is controlled to 6 t/cmor higher, and sintering temperature is controlled to 1,150°C or higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sintered body manufacturing method and a sintered body obtained by the manufacturing method.

  In this technical field, sintered bodies as powder metallurgy products obtained by compression molding and sintering iron-based raw material powders are used in various applications. Furthermore, it is known to use raw material powder containing atomized iron powder having good compressibility and reduced iron powder having good sinterability for the purpose of increasing the mechanical strength of such a sintered body. (For example, see Patent Document 1).

Japanese Patent Laid-Open No. 57-200501

  However, higher mechanical strength (for example, Young's modulus and rigidity) is required for the sintered body as described above. The present invention has been made to deal with such problems. That is, the present invention provides a production method capable of obtaining a sintered body having higher mechanical strength from a raw material powder containing atomized iron powder and reduced iron powder, and a sintered body obtained by the production method. One purpose is to do.

  Therefore, as a result of earnest research, the present inventor compression molded a raw material powder containing atomized iron powder, reduced iron powder and graphite at a predetermined content rate at a predetermined surface pressure, and obtained the molded body. It has been found that the above object can be achieved by sintering.

  More specifically, the present inventor is a manufacturing method for obtaining a sintered body by sintering a molded body obtained by compression molding a raw material powder containing atomized iron powder, reduced iron powder and graphite. It was found that the mechanical strength of the sintered body can be specifically improved by setting the content ratio of the reduced iron powder in the raw material powder to a specific range and the surface pressure during compression molding to a predetermined value or more. It is.

  In view of the above points, the method for manufacturing a sintered body according to the present invention is a method for obtaining a sintered body from a raw material powder containing atomized iron powder, reduced iron powder and graphite. This manufacturing method includes a raw material preparation step for preparing raw material powder, a molding step for compression molding the raw material powder to obtain a molded body having a desired shape, and sintering the obtained molded body at a predetermined sintering temperature. And a sintering step of obtaining a sintered body.

In the raw material preparation process, a raw material powder containing 23% by mass or more and 35% by mass or less of reduced iron powder is prepared. The raw material powder contains atomized iron powder, reduced iron powder and graphite as main components. However, the raw material powder can contain a small amount of subcomponents in addition to these main components. In the molding step, the raw material powder is compression molded at a surface pressure of 6 t / cm ² or more, and a molded body having a desired shape is obtained. In the sintering process, the molded body obtained in the molding process is sintered at a predetermined sintering temperature to obtain a sintered body.

A method for producing a sintered body according to one aspect of the present invention includes:
The raw material powder contains 0.2% by mass or more and 1.2% by mass or less of graphite,
It is a manufacturing method.

A method for producing a sintered body according to another aspect of the present invention includes:
The sintering temperature in the sintering step is 1150 ° C. or higher,
It is a manufacturing method.

  Furthermore, the sintered body according to the present invention is a sintered body obtained by various manufacturing methods including the above-described method for manufacturing a sintered body according to the present invention.

The sintered body according to one aspect of the present invention is:
In the sintered body, the average value of the circularity R represented by the following formula (1) is 0.61 or more when the area and the perimeter of the pores in the cross section of the sintered body are S and L, respectively. is there.

The sintered body according to another aspect of the present invention is:
The number of pores in the cross section of the sintered body is 2300 / mm ² or less,
It is a sintered body.

The sintered body according to yet another aspect of the present invention is:
The sintered body has a density of 6.98 g / cm ³ or more.
It is a sintered body.

  As described above, according to the present invention, in the manufacturing method of obtaining a sintered body by sintering a molded body obtained by compression molding a raw material powder containing atomized iron powder, reduced iron powder and graphite, The content rate of the reduced iron powder in the raw material powder is set to a specific range, and the surface pressure during compression molding is set to a predetermined value or more. Thereby, in the sintered compact obtained by compression-molding and sintering the raw material powder containing atomized iron powder, reduced iron powder, and graphite, higher mechanical strength can be achieved.

  Other objects, other features, and attendant advantages of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

It is a graph which shows the relationship between the Young's modulus of the sintered compact obtained by sintering the compression molding of the raw material powder containing atomized iron powder, reduced iron powder, and graphite, and the content of the reduced iron powder in the raw material powder . It is a graph which shows the difference in the circularity of the cross section of the pore inside a sintered compact by the presence or absence of the reduced iron powder in raw material powder, the surface pressure at the time of compression molding, and the difference in sintering temperature. It is a graph which shows the relationship between the density of the sintered compact obtained by sintering the compression molding of the raw material powder containing atomized iron powder, reduced iron powder, and graphite, and the content rate of the reduced iron powder in raw material powder.

<< First Embodiment >>
Hereinafter, the manufacturing method according to the first embodiment of the present invention (hereinafter sometimes referred to as “the method of the present invention”) will be described in detail with reference to the accompanying drawings as necessary.

(Constitution)
The method of the present invention
A manufacturing method for obtaining a sintered body from a raw material powder containing atomized iron powder, reduced iron powder and graphite,
A raw material preparation step of preparing the raw material powder containing 23% by mass or more and 35% by mass or less of the reduced iron powder;
A molding step of compression molding the raw material powder at a surface pressure of 6 t / cm ² or more to obtain a molded body having a desired shape;
A sintering step of obtaining the sintered body by sintering the molded body obtained in the molding step at a predetermined sintering temperature;
Is a manufacturing method.

  The raw material powder prepared in the raw material preparation step includes atomized iron powder, reduced iron powder, and carbon as main components. Carbon improves the mechanical strength of the sintered body. Specific examples of such carbon include graphite (graphite) and the like. The raw material powder can contain a small amount of subcomponents in addition to the main component. Specific examples of such subcomponents include a lubricant for developing lubricity with respect to a mold in the molding process. Specific examples of such a lubricant include zinc stearate.

  The content rate of the reduced iron powder in raw material powder is 23 mass% or more and 35 mass% or less. By keeping the content of the reduced iron powder in the raw material powder within the range, higher mechanical strength (for example, Young's modulus and rigidity) can be achieved as compared with the sintered body according to the prior art. On the other hand, if the content of the reduced iron powder in the raw material powder deviates from the range, the green body is sintered even if the surface pressure when the raw material powder is compression-molded into a green body in the molding process is a predetermined value or more. It becomes difficult to improve the mechanical strength of the sintered body obtained by bonding.

The surface pressure when the raw material powder is compression-molded into a molded body in the molding step is 6 t / cm ² or more. By setting the surface pressure to 6 t / cm ² or more, specifically high mechanical strength can be achieved in the sintered body obtained from the raw material powder containing the reduced iron powder at the above content. On the other hand, if the surface pressure is less than 6 t / cm ² , even if the raw material powder contains the reduced iron powder at the above-mentioned content rate, in the sintered body obtained from the raw material powder, a specifically high machine It is difficult to achieve the desired strength. On the other hand, the upper limit of the surface pressure can be appropriately set according to, for example, the strength of the mold used in the molding process, the mechanical strength and density required for the sintered body, and the like.

  In the sintering process, the molded body obtained in the molding process is sintered at a predetermined sintering temperature to obtain a sintered body. The sintering temperature is generally set to a temperature equal to or higher than the melting point of steel (1083 ° C.), but the higher the sintering temperature, the better. Preferably, the sintering temperature is 1150 ° C. or higher.

(Relationship between content of reduced iron powder in raw material powder and strength of sintered body)
Here, regarding the relationship between the mechanical strength of the sintered body obtained by sintering a compression molded body of raw material powder containing atomized iron powder, reduced iron powder and graphite, and the content of reduced iron powder in the raw material powder This will be described in detail below. First, various raw material powders A01 to A16 containing reduced iron powder were prepared at the contents listed in Table 1 below. The raw material powders A04 to A09 contain reduced iron powder at a content of 23% by mass or more and 35% by mass or less, and are raw material powders corresponding to the examples of the present invention. On the other hand, the content of the reduced iron powder in the raw material powders A01 to A03 is less than 23% by mass, and the content of the reduced iron powder in the raw material powders A10 to A16 exceeds 35% by mass. That is, these raw material powders are raw material powders corresponding to comparative examples, not examples of the present invention. In any sample, the graphite and lubricant (zinc stearate) content in the raw material powder was 0.8% by mass, and the rest was atomized iron powder.

Next, each raw material powder is compression-molded using a predetermined mold at a surface pressure of 5 t / cm ² , 6 t / cm ² and 7 t / cm ² , sintered at a temperature of 1150 ° C., and then reduced. Various sintered compact samples corresponding to the iron powder content and the surface pressure were manufactured. For each of these sintered body samples, Young's modulus was measured twice as a physical property value indicating mechanical strength, and an average value thereof was obtained. Further, the density of each sintered body sample was also measured, and the density will be described later.

The content and Young's modulus of the reduced iron powder in the raw material powders of the various sintered body samples are shown in the graph shown in FIG. The graph shows three cases where the surface pressure during compression molding of the raw material powder is 5 t / cm ² (dotted curve), 6 t / cm ² (dashed curve) and 7 t / cm ² (solid curve), respectively. It is shown for, but listed only two cases in which the surface pressure respectively 6t / cm ² and 7t / cm ² in Table 1.

As is clear from the graph of FIG. 1, when the surface pressure during compression molding is 5 t / cm ² (dotted line in the graph), the mechanical strength of the sintered body due to the addition of reduced iron powder to the raw material powder Almost no improvement effect was observed. On the contrary, in the region where the content of reduced iron powder in the raw material powder is about 30% by mass or more, a decrease in mechanical strength accompanying an increase in the content of reduced iron powder in the raw material powder was observed.

On the other hand, when the surface pressure at the time of compression molding is 6 t / cm ² (broken line in the graph), as is apparent from the graphs of Table 1 and FIG. In the region of less than mass%, an effect of improving the mechanical strength of the sintered body by adding reduced iron powder to the raw material powder was recognized. In addition, in the region where the content of the reduced iron powder is 23% by mass or more and 35% by mass or less, a remarkable improvement effect of the mechanical strength is recognized.

Furthermore, when the surface pressure at the time of compression molding is 7 t / cm ² (solid line in the graph), the reduced iron powder content in the raw material powder is within a region where the content of the reduced iron powder in the raw material powder is less than about 75 mass% The improvement effect of the mechanical strength of the sintered compact by addition was recognized. In addition, in the region where the content of the reduced iron powder is 23% by mass or more and 35% by mass or less, a remarkable improvement effect of the mechanical strength is recognized.

As described above, in the production method of obtaining a sintered body by sintering a molded body obtained by compression molding a raw material powder containing atomized iron powder and reduced iron powder, inclusion of reduced iron powder in the raw material powder The mechanical strength of the sintered body is specifically set to a specific range (23 mass% or more and 35 mass% or less) and the surface pressure during compression molding is set to a predetermined value (6 t / cm ² ) or more. Can be improved.

<Variation 1 of the method of the present invention>
Incidentally, as described above, it is known in the technical field that the mechanical strength of a sintered body obtained from the raw material powder is improved by adding carbon such as graphite to the iron-based raw material powder. Yes. From such a viewpoint, the raw material powder used in the method of the present invention also contains carbon such as graphite. However, when the content of graphite in the raw material powder is less than 0.2% by mass, the effect of improving the mechanical strength of the sintered body due to the addition of graphite to the raw material powder cannot be sufficiently obtained. On the other hand, when the content of graphite in the raw material powder exceeds 1.2% by mass or less, the toughness of the sintered body decreases and becomes brittle.

  Therefore, in the manufacturing method according to Modification 1 of the method of the present invention, the raw material powder contains 0.2% by mass or more and 1.2% by mass or less of graphite. Thereby, the mechanical strength (for example, Young's modulus, rigidity, toughness, etc.) of the sintered body obtained by the method of the present invention can be further improved.

<Modification 2 of the method of the present invention>
Furthermore, in this technical field, it is known to increase the mechanical strength of the sintered body by increasing the sintering temperature of the sintered body obtained from the iron-based raw material powder. However, the higher the sintering temperature, the higher the energy consumption in the manufacturing process for obtaining a sintered body.

  However, according to the method of the present invention, higher mechanical strength can be achieved as compared with the sintered body obtained by the manufacturing method according to the prior art. In other words, according to the method of the present invention, a sintered body having an equivalent mechanical strength can be obtained at a sintering temperature lower than that of the manufacturing method according to the prior art.

  Specifically, in the manufacturing method according to Modification 2 of the method of the present invention, the sintering temperature in the sintering step is 1150 ° C. or higher. Thus, according to the manufacturing method according to the modified example 2, a sintered body having mechanical strength equivalent to that of the sintered body obtained by the manufacturing method according to the prior art is obtained at a lower sintering temperature. be able to. Therefore, according to the manufacturing method which concerns on this modification 2, the energy consumption in the manufacturing process which obtains a sintered compact from iron-type raw material powder can be reduced.

<< Second Embodiment >>
As described above, the present invention relates not only to a method for producing a sintered body, but also to a sintered body obtained by the production method. The second embodiment of the present invention is a sintered body (hereinafter referred to as “invention of the present invention”) obtained by the manufacturing method according to various aspects of the present invention including the first embodiment of the present invention and its modifications. It may be referred to as a “combination”). As is clear from the above description regarding the method of the present invention and its modifications, the sintered body of the present invention has higher mechanical strength than the sintered body according to the prior art.

<Variation 1 of the sintered body of the present invention>
Incidentally, as described above, in the technical field, by increasing the sintering temperature of the sintered body obtained from the iron-based raw material powder, the mechanical strength of the sintered body obtained from the raw material powder is improved. It has been known. This is considered to be because as the sintering temperature rises, the contact area between the particles constituting the raw material powder increases and the sintering is promoted. Thus, when sintering is promoted as the sintering temperature rises, the shape of the pores inside the sintered body approaches a true sphere. That is, the closer the shape of the pores in the sintered body is to a true sphere, the higher the mechanical strength can be achieved.

  Here, the above will be described in detail below. First, various sintered body samples B1 to B4 were manufactured using various raw material powders containing reduced iron powder at the contents listed in Table 2 below, the surface pressure at the time of compression molding, and the sintering temperature. However, for any sample, the content of graphite and lubricant (zinc stearate) in the raw material powder was 0.8 mass%, and the rest was atomized iron powder.

  Next, the various samples were cut, and an image of a cross section of each sample was taken using an optical microscope at a magnification of 100 times. By analyzing the obtained image with image analysis software (Mitani Corporation, Win-ROOF (registered trademark)), the circularity R of the pores defined by the formula (1) described later was measured. The roundness R means that the closer the value is to 1, the closer the shape is to a perfect circle. The graph shown in FIG. 2 is a bar graph showing the circularity R of the various sintered body samples B1 to B4 shown in Table 2.

As shown in Table 2 and FIG. 2, the sintered body samples B1 and B2 according to the comparative examples in which the raw material powder does not contain reduced iron powder have the same sintering temperature (1150 ° C.) surface pressure is different (respectively 7t / cm ² and 8t / ^cm 2). However, these sintered body samples B1 and B2 exhibited equal circularity R (0.58).

The surface pressure during compression molding of the sintered body sample B3 according to the comparative example in which the raw material powder does not include reduced iron powder is equal to the surface pressure during compression molding of the sintered body sample B1 (7 t / cm ² ). However, the sintering temperature of the sintered body sample B3 is higher than the sintering temperature of the sintered body sample B1 (1250 ° C.). As a result, the sintered body sample B3 exhibited a greater circularity R than the sintered body sample B1 (0.62).

However, the sintered body sample B4 according to the example of the present invention in which the raw material powder contains 30% by mass of reduced iron powder has a surface pressure (7 t / cm) during compression molding equal to the sintered body sample B1 according to the comparative example. ² ) and a sintering temperature (1150 ° C.), the circularity R (0.65) was significantly higher than that of the sintered body sample B1. The circularity R of the sintered body sample B4 exceeds the circularity R of the sintered body sample B3 according to the comparative example manufactured at a higher sintering temperature (1250 ° C.). As a result, the sintered body sample B4 achieved a Young's modulus (161 GPa) significantly higher than the Young's modulus (154 GPa) of the sintered body sample B1.

  As a result of the study based on the above knowledge, the present inventor has found that the sintered body of the present invention achieves higher mechanical strength than the sintered body according to the prior art, the circularity R of the pores in the cross section is It has been found that it is desirable to be at least a predetermined lower limit.

Specifically, in the sintered body according to Modification 1 of the sintered body of the present invention,
The average value of the circularity R represented by the following formula (1) is 0.61 or more when the area and perimeter of the pores in the cross section of the sintered body are S and L, respectively.

  As described above, in the sintered body according to Modification 1 of the sintered body of the present invention, the average value of the circularity R of the pores in the cross section is 0.61 or more. Thereby, the sintered compact concerning this modification 1 can achieve higher mechanical strength. In order to accurately determine the average value of the circularity R, for example, depending on the measurement accuracy in the above-described image analysis and / or the variation in the shape of the pores in the cross section of the sintered body, etc. It is desirable to appropriately determine the cross-sectional area and / or the number of pores for calculating the circularity R of the sintered body.

<Modification 2 of the sintered body of the present invention>
Furthermore, the number of pores per unit area (the frequency of pores) in the cross section of the sintered body also affects the mechanical strength of the sintered body. As a result of diligent research, the inventor has found that the sintered body of the present invention achieves a mechanical strength greater than that of the sintered body according to the prior art, the presence frequency of pores in the cross section is below a predetermined upper limit value. I found it desirable.

Specifically, in the sintered body according to Modification 2 of the sintered body of the present invention, the number of pores in the cross section of the sintered body is 2300 / mm ² or less. Thereby, the sintered compact concerning this modification 2 can achieve higher mechanical strength.

<Modification 3 of the sintered body of the present invention>
In addition, the density of the sintered body also affects the mechanical strength of the sintered body. As a result of intensive studies, the inventor has found that the sintered body has a density equal to or higher than a predetermined lower limit in order to achieve greater mechanical strength than the sintered body according to the prior art. I found it desirable.

  Here, the above will be described in detail below with reference to Table 1 and the graph shown in FIG. FIG. 3 shows the relationship between the density of the sintered body obtained by sintering a compression molded body of raw material powder containing atomized iron powder, reduced iron powder and graphite, and the content of reduced iron powder in the raw material powder. It is a graph. First, various sintered body samples were manufactured with various raw material powders having the composition shown in the graph of FIG. 3 and the surface pressure at the time of compression molding. However, for any sample, the content of graphite and lubricant (zinc stearate) in the raw material powder was 0.8 mass%, and the rest was atomized iron powder. The sintering temperature was 1150 ° C. for all.

In the graph, the alternate long and short dash line curve, the dotted line curve, the broken line curve, and the solid line curve indicate that the surface pressure during compression molding is 4 t / cm ² , 5 t / cm ² , 6 t / cm ^2, and 7 t / cm ² , respectively. It shows that it is a density measurement result about the obtained sample. Next, the density of these various samples was measured by the Archimedes method. However, as mentioned above, in Table 1 listed only density in the two cases was the surface pressure respectively 6t / cm ² and 7t / cm ^2.

As shown by the circles in the graph, it was produced by the method of the present invention satisfying the content ratio of reduced iron powder in the raw material powder and the surface pressure at the time of compression molding in which the effect of improving the mechanical strength in the sintered body was recognized. The density of the sintered body is specifically increased. Specifically, as is clear from the graph of FIG. 3 and Table 1, raw material powder containing reduced iron powder of 23% by mass to 35% by mass is compressed at a surface pressure of 6 t / cm ² or more. The density of the sintered body obtained by molding and sintering is 6.98 g / cm ³ or more. As described above, the sintered body manufactured under such conditions can achieve higher mechanical strength (for example, Young's modulus and rigidity) than the sintered body according to the prior art. .

Therefore, in the sintered body according to Modification 3 of the sintered body of the present invention, the density of the sintered body is 6.98 g / cm ³ or more. Thereby, the sintered compact concerning this modification 3 can achieve higher mechanical strength.

<< Third Embodiment >>
Based on the above knowledge, a sintered body obtained from a raw material powder containing atomized iron powder, reduced iron powder, and graphite and having a reduced iron powder content of 23% by mass to 35% by mass is 6.98 g / Higher mechanical strength (for example, Young's modulus and rigidity) can be achieved by compression molding and sintering to a density of cm ³ or more.

That is, the sintered body according to the third embodiment of the present invention is a sintered body made of a raw material powder containing atomized iron powder, reduced iron powder, and graphite, and the raw material powder is 23% by mass or more and 35 It is a sintered body containing the reduced iron powder in an amount of mass% or less and having a density of the sintered body of 6.98 g / cm ³ or more.

  In the above, for the purpose of explaining the present invention, several embodiments and modifications having specific configurations have been described with reference to the accompanying drawings. However, the scope of the present invention is not limited to these illustrative examples. It should be understood that the present invention should not be construed as being limited to the embodiments and the modifications, and that appropriate modifications can be made within the scope of the matters described in the claims and the specification.

Claims (5)

A manufacturing method for obtaining a sintered body from a raw material powder containing atomized iron powder, reduced iron powder and graphite,
A raw material preparation step of preparing the raw material powder containing 23% by mass or more and 35% by mass or less of the reduced iron powder;
A molding step of compression molding the raw material powder at a surface pressure of 6 t / cm ² or more to obtain a molded body having a desired shape;
A sintering step of obtaining the sintered body by sintering the molded body obtained in the molding step at a predetermined sintering temperature;
Manufacturing method. The manufacturing method according to claim 1,
The raw material powder contains 0.2% by mass or more and 1.2% by mass or less of graphite,
Production method. The manufacturing method according to claim 1 or 2,
The sintering temperature in the sintering step is 1150 ° C. or higher,
Production method.   The sintered compact obtained by the manufacturing method of any one of Claims 1 thru | or 3. A sintered body made of a raw material powder containing atomized iron powder, reduced iron powder and graphite,
The raw material powder contains 23% by mass or more and 35% by mass or less of the reduced iron powder,
The sintered body has a density of 6.98 g / cm ³ or more.
Sintered body.

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