JP2002226901A - Stainless-steel short fiber, and sintered porous body using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless-steel short fiber in which the unevenness of an aspect ratio can be suppressed and to provide a sintered porous body in which the pore characteristics can be stabilized by using the short fibers. SOLUTION: The stainless-steel short fiber has a columnar shape free from round edge due to cutting at its ends, and fiber diameter (d) is made to <=10 μm and the average value of the aspect ratio between the diameter (d) and the length (L), L/d, is made to 2-20. The aspect ratio can be reduced by regulating the amount of N in the short fiber to 0.02-0.50 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel short fiber capable of suppressing variation in aspect ratio, and a sintered porous body capable of stabilizing pore characteristics by using the short fiber.

[0002]

2. Description of the Related Art Stainless steel short fibers are obtained, for example, by cutting stainless steel fibers into a predetermined length. Among them, the ratio of length L to diameter d (aspect ratio L /
In the short fibers having the adjusted range of d), when the short fibers are filled and formed into a predetermined shape, each short fiber can be oriented in a random direction, and three-dimensional fine pores are formed and formed therein. A sintered porous body can be obtained. Such a porous body has high porosity accuracy and porosity, and a three-dimensional complicated flow path can be formed in the inside thereof, so that pressure loss can be suppressed even though it is a fine porosity. . Therefore, when such a porous body is used as a filtering material for various fluids or an air buffering member, low pressure loss, clogging and the like can be suppressed, and a long life can be achieved.

The applicant of the present invention has reported that such short fibers have a fiber diameter of 2 to 20 according to Japanese Patent Publication No. 63-63645.
It has been proposed that a stainless steel short fiber of a predetermined length be obtained by subjecting a fiber material of stainless steel having a diameter of μm (so-called tow) as a starting material to a heat treatment for grain conditioning and a grain boundary corrosion treatment. I have. With this proposal, it is possible to produce columnar short fibers having no cutting sagging at the ends and having an aspect ratio of about 2 to 50.

The applicant of the present invention has proposed a sintered porous body using the above-mentioned proposed stainless steel short fiber, as disclosed in Japanese Patent Publication No. 3-33.
Japanese Patent Publication No. 370 proposes a filter material formed of the sintered porous body. The filter material has a porosity of 5%.
It can be 0% or more.

[0005]

Incidentally, the stainless steel short fiber according to the former publication is obtained by dividing the crystal of the long metal filament at each grain boundary. By adjusting the size of the crystals by controlling the conditions described above, short fibers having various aspect ratios can be obtained. However, when the diameter of the metal filament is small, the length based on the size of the crystal grains is large. Therefore, the aspect ratio is large as the diameter is small, and the variation tends to be large accordingly. There was found.

[0006] The reason for this is that, particularly in the case of fine stainless steel short fibers, heat absorption is faster and crystal grains grow more rapidly than in the case of large diameter fibers. It is presumed that it greatly affects the aspect ratio of the short fibers to be obtained.

By the way, the former proposal also has a fiber diameter of 12 to 4 μm, which
It is described that the aspect ratio is about 3 at the time of μm, about 7 at the fiber diameter of 8 μm, and the aspect ratio gradually increases to 9.5 at the fiber diameter of 4 μm. Further, the variation has increased about four times.

On the other hand, in recent years, ultrafine particles of 0.05 μm or less, which are required for, for example, semiconductor manufacturing gas, are used in 99.99.
In order to obtain a filter material that can be efficiently removed with a high accuracy of 99999% or more, it is theoretically considered that it is necessary to make the fiber extremely thin, for example, a fiber diameter of 2 μm or less. From the point of view, it is assumed that the aspect ratio further increases, and that the variation also increases.
It is required to suppress the variation.

That is, in a sintered porous body formed by sintering stainless steel short fibers having a large aspect ratio, the short fibers can be distributed only relatively flat inside the porous body, and the internal pores are accordingly increased. Are also planar and overlap, resulting in a low porosity. For this reason, such a filter medium has a large pressure loss and cannot be satisfactory in terms of service life.
It is hard to say that it is suitable as a filtering material that can be used in the above-mentioned applications.

According to the present invention, it is known that the aspect ratio of the stainless steel short fiber has a deep relationship with the crystal grain size of the fiber material, and it is effective to adjust the fine element in the fiber material as a control means. The stainless steel short fiber, which is a short fiber having a diameter as small as 10 μm or less and can be suppressed to a desired variation in the aspect ratio, and the use of the short fiber to form pores The purpose of the present invention is to provide a sintered porous body capable of stabilizing characteristics.

[0011]

Means for Solving the Problems The invention of claim 1 of the present application is
Column shape without cutting sagging at the end, and fiber diameter (d) of 1
A stainless steel short fiber having an average value of an aspect ratio (L / d) of a diameter (d) and a length (L) of 2 to 20 μm or less, wherein the N content in the short fiber is 0; .0
The average aspect ratio is suppressed to the predetermined range by adjusting the average aspect ratio to a range of 2 to 0.50 wt%.

According to a second aspect of the present invention, the fiber has a columnar shape with no cutting sag at the end, and has a fiber diameter (d) of 10 μm or less, and an aspect ratio between the diameter (d) and the length (L). A stainless steel short fiber having an average value of (L / d) of 2 to 20, wherein the amount of at least one element selected from Ti, Nb, Zr, B or V in the short fiber is 0.1%. 00
The average aspect ratio is suppressed to the predetermined range by adjusting the average aspect ratio to a range of 5 to 0.30 wt%.

The invention according to claim 3 is characterized in that the short fiber has a fiber diameter (d) of 0.1 to 5 μm, and the invention according to claim 4 is characterized in that the average aspect ratio is 5 to 5 μm.
12, and the variation coefficient of the variation (S) is 25% or less.

According to a fifth aspect of the present invention, there is provided a porous structure in which the stainless steel short fibers are made of austenitic stainless steel, and the stainless steel short fibers are randomly oriented. It is characterized by being a sintered porous body integrated by pressing and sintering.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Stainless steel short fiber 1 of the present invention
As shown schematically in FIG. 1, the fiber has a columnar shape having no cut sag at the end a. In particular, although the fiber diameter (d) is as thin as 10 μm or less, the diameter (d) and the length are small. The average value of the aspect ratio (L / d), which is the ratio to the length (L), is 2 to 20. In the invention of claim 1, the N content in the stainless steel short fiber is 0.02 to 2.0. 0.50
The amount of at least one element selected from the group consisting of Ti, Nb, Zr, B and V in the stainless steel short fiber is 0.005 to 0.30 wt% in the range of wt%.
And the aspect ratio is adjusted accordingly.

As the stainless steel short fiber 1, Ni-based, C
Various stainless steels such as r-based stainless steel can be used. Particularly, austenitic stainless steel can be formed by single crystal grains having a single transverse angle by recrystallization in heat treatment, and can be easily made into a short fiber, and has corrosion resistance and mechanical properties. It has excellent properties and heat resistance, and can be suitably used as a filtering material.
SUS2 along with US304, SUS316, etc.
01, SUS205, SUS302, SUS305, S
US310, SUS317, etc. can be used.

The stainless steel short fiber 1 has a "column shape in which no cut sag is formed at the end". Thereby, when filling in a predetermined mold, it is possible to prevent entanglement of each short fiber and to orientate in a free direction, thereby forming a porous body having high porosity with fine pores and a narrow pore diameter distribution. And can enhance filtration performance. In order to obtain short fibers having "columnar shape in which no cut sag is formed at the end", for example, the above-mentioned proposal, that is, JP-B-63-63645, is used.
The length of the grain boundary by heat treatment described in
It can be produced by a production method including a step of intergranular corrosion.

In the present invention, the reason why the fiber diameter (d) is set to 10 μm or less is that, for a thick short fiber exceeding the diameter, a fiber having a preferable aspect ratio and variation by a method such as condition adjustment in the prior art. For this reason, the present invention sets the upper limit to 10 μm, preferably 5 μm or less, more preferably less than 2 μm. The lower limit is not particularly limited. However, according to the recent technology for producing stainless steel fibers by the convergence drawing method, a fine fiber material of, for example, about 0.3 μm has been achieved. Even those that are fully applicable.

In the meantime, the fiber diameter can be indicated by the diameter when the short fiber is, for example, a columnar shape having a perfect circular cross section. Rather, it has an irregular cross-section with fine irregularities on the peripheral surface, and therefore, its measurement often involves difficulties. However, in the case of fine fibers as the object of the present invention, the degree of irregularities is extremely small and can be substantially ignored, and even at the time of the measurement, only one point is taken out and the cross-sectional shape and the average fiber diameter are determined. It is not easy. Further, the short fibers are usually used as a group thereof.

From the above, with respect to the fiber diameter in the case of such a short fiber having an irregular cross section, a group of a plurality of short fibers in a single lot was averaged, not an individual measurement value for each short fiber. The average fiber diameter can be used. For example, the average diameter of the transmission diameter measured for several short fibers randomly placed on the measurement surface of the projector is shown. Even by using such an averaging method, the difference between the maximum diameter and the minimum diameter of each short fiber can be canceled out and averaged.

In terms of the aspect ratio, it is ideal that all the short fibers are manufactured so as to have the same aspect ratio. Therefore, as for the aspect ratio in that case, the average value of a group is used as a substitute for the fiber diameter as in the case of the fiber diameter, and the calculation method is based on the measured fiber length (for example, about 100 points) for each short fiber (for example, about 100 points). The value obtained by dividing L) by the average fiber diameter (d) is defined as the aspect ratio of the short fiber, and the average value is 2 to 20 in the present invention.

The reason for setting the range to 2 to 20 is that if the value of the short fiber is larger than 20, the width of the pore diameter distribution becomes large when the porous body is made into a porous body, and the short fiber distribution becomes flat due to the pressing pressure. It is difficult to become a high-precision filter medium because it is easy to become a target. On the other hand, when the value is less than 2, the porosity cannot be increased because the shape is close to a general powder, and preferably 2 to 15, more preferably 5 to 5. ~ 12
Degree.

As described above, as for the aspect ratio, a certain degree of variation can be tolerated in a group of short fibers. It differs in various ways. For example, in applications in which ordinary filtration characteristics are to be obtained, the coefficient of variation (CV) of variation is preferably set to about 30% or less, and precision is required to filter the semiconductor gas, for example. For applications, for example, it is preferable that the average aspect ratio is 5 to 12 when the fiber diameter is less than 2 μm, and the variation coefficient of the variation is 25% or less.

The coefficient of variation (CV) is
It can be obtained by a coefficient obtained by dividing the standard deviation (S) by the following equation by the number of samples. Standard deviation (S) = √ {(A1 -A) 2 + (A2-A) 2 + ... + (An-A) 2} / n coefficient of variation (CV) = S / n × 100 (%) where, A1, A2, and An are measured values of the aspect ratio of each short fiber, A is the average value, and n is the number of measurement samples, and the size is, for example, about several tens to 100 points.

In the present invention, in order to observe the aspect ratio and the variation thereof in the stainless steel short fiber 1, the amount of N in the invention of claim 1 and the amount of Ti, Nb, Zr, The amount of at least one element selected from B or V is adjusted so as to be within the above-mentioned predetermined range.

Such an element makes the crystal grains fine in stainless steel, reduces the length as short fibers cut by intergranular corrosion, and obtains stainless steel short fibers 1 having a relatively small aspect ratio. But especially N
Can be easily used because it can easily penetrate into the crystal lattice and strengthen the dough to make the crystal grains finer. It should be noted that Ti, Nb, Zr, B or V also has a function similar to that of N for making the crystal fine.

Therefore, by adjusting such a fine element in a predetermined ratio range, even if the fiber has a fine diameter,
The length (L) of stainless steel short fiber is reduced, and as a result,
The aspect ratio (L / d) can be reduced, and the variation can be suppressed.

In order to exert such an effect, the content of N needs to be at least 0.02% or more. On the other hand, the amount that can be contained in stainless steel having a normal composition is at most 0.5%. Beyond that, N causes a new problem such as impairing the wire drawing processability and the productivity in the fiber production stage, so that the N content is in the range of 0.02 to 0.50 wt%.
More preferably, the content is 0.05 to 0.25 wt%. Note that N may infiltrate and increase during the manufacturing process, such as when the heat treatment furnace is set to a mixed atmosphere of nitrogen and argon. In such a case, the above value is set in consideration of the increasing amount of N. Is good.

For example, when the average aspect ratio of a short fiber having a fiber diameter of about 0.5 μm is about 2 to 8, the N content is slightly increased to 0.1 to 0.3 wt%, while the aspect ratio is increased. To obtain about 8 to 15 short fibers, for example, 0.08
It is preferable to reduce the amount to about wt% or less. However, since the crystal grain size changes depending on the heat treatment conditions, the above values are only guidelines and do not limit the scope of the present invention.

Also, Ti, Nb, Zr, B or V can be basically considered the same as in the case of N.
Since elements such as i and Nb also have an effect of increasing intergranular corrosion resistance, stainless steel short fibers 1
In the case where is obtained, there is a possibility that the cutting properties of the grain boundaries may be impaired and the workability thereof may be reduced, and it is difficult to add a large amount of other Zr, B, and V, so that production and specification thereof are performed. Slightly less than 0.005
0.30 wt%, preferably 0.02 to 0.20 wt%
Of the range.

In the case of using Ti, Nb or the like, in order to promote intergranular corrosion more efficiently and to shorten the fiber efficiently, for example, SUS304 or S
By using a high C material (0.05 wt% or more) such as US302, SUS316, or SUS201, Cr—C can be precipitated at the grain boundary to facilitate the division.

In the present invention, Ti, Nb, Zr, B
Alternatively, the amount of at least one element selected from V is adjusted to a range of 0.005 to 0.30 wt%, and a plurality of Ti, Nb, Zr, B or V including N are respectively added to the above. Each range can be used together.

On the other hand, the filament for producing the stainless steel short fiber 1, that is, the metal fiber material is, for example, a method of drawing a bundled composite wire (for example, JP-A-47-263).
No. 67) can be preferably used, and can be produced by drawing a wire to a target diameter and finally removing only the exterior material. In this method, for example, a tow of stainless steel fiber of about 0.1 μm can be obtained by repeatedly performing the wire drawing and the heat treatment while appropriately adjusting.

The metal fiber material obtained by such a convergence drawing method has a non-smooth outer surface b having an irregular cross-section due to the processing method, and the metal fiber material is subjected to intergranular corrosion. When the fibers are shortened, the ends a of each short fiber can have a columnar shape without cutting sagging or the like, and as described above, N, T
A person skilled in the art can easily produce the stainless steel short fiber 1 having a desired aspect ratio by adjusting the amount of i, Nb, Zr, B or V, setting heat treatment conditions, drawing conditions, and the like. The sintered porous body 3 obtained by sintering the porous body made of the short fibers having the non-smooth outer surface a has a high-precision filtering material having excellent particle trapping performance due to an increase in the specific surface area inside the porous body. can do.

The heat treatment is intended to eliminate the drawing strain of the stainless steel fiber used, to make the fiber cross section single crystal, and to grow the crystal grains to a predetermined size. For austenitic stainless steel of -8Ni, a temperature of 900 to 1400 ° C,
This is performed in a non-oxidizing atmosphere (for example, in an inert atmosphere such as argon gas) in which the time is about 0.5 to 2 hours. On the other hand, similarly to the case of the austenitic system, the Cr-based stainless steel is subjected to heat treatment conditions and crystallizing. The optimum conditions should be selected by making a connection with the grains.

Further, in the present invention, as described above, since stainless steel in which the above-mentioned refined elements such as N, Ti, and Nb are adjusted for the refinement of crystal grains is used, rapid crystal growth accompanying heat treatment is prevented. There is also the advantage that the processing conditions need not be strictly controlled, and the burden can be reduced by eliminating the labor of the operator. On the other hand, the subsequent selective corrosion treatment of the grain boundary can be carried out in the same manner as disclosed in the above-mentioned publication. The acidic solution used may be, for example, an inorganic acid such as nitric acid, hydrochloric acid, or hydrofluoric acid, or a metal salt such as copper sulfate, or a mixed solution thereof. The solution is relatively easy to use.

The processing conditions include, for example, a liquid temperature of 20 to
It is immersed in the above solution at 50 ° C., and the treatment is performed for about 5 to 30 minutes. The thus obtained short fibers are single crystal particles having substantially the same fiber diameter as the used fiber material, and are corroded. Has extremely stable characteristics with respect to In this way, it is possible to obtain a short fiber in which the fiber diameter (d) of the stainless short fiber is 10 μm or less, the average aspect ratio is 2 to 20, and the variation (S) thereof is suppressed.

FIG. 2 shows an example of the sintered porous body 3 made of the short fibers. The stainless steel short fibers 1 are pressed into a randomly oriented porous structure and sintered to be integrated. ing. It can also be seen that the short fibers 1 having a relatively small aspect ratio are distributed in a free direction to form three-dimensional voids 4.

In the present invention, the stainless steel short fiber 1 having a diameter of 10 μm or less is targeted. Even if an attempt is made to orient the particles in a random direction, the directionality is changed or pushed by pressurization at a predetermined pressure, and the filtration characteristics tend to be different from those initially expected. Therefore, the upper limit is set to 20 or less, and this aspect ratio is selected by correlating with the pressing force, the obtained porosity accuracy, the porosity, etc., so that the sintered porous body 3 can obtain the preferable filtration characteristics by ordinary trial. Obtainable.

The sintered porous body 3 can be formed into various shapes such as a disk shape, a block shape, and a column shape. Regarding the forming method, a certain amount of the short stainless steel fiber 1 is placed in a mold having the shape. At the same time as filling, press at a specified pressure with a stamping die, further sintering etc.
Various methods conventionally proposed according to products can be adopted.

As for the sintering conditions, since the stainless steel short fiber 1 is used, for example, the temperature is 800 to 1100 ° C.
The treatment is carried out by allowing the mixture to stand for about 10 minutes to 2 hours in an inert atmosphere at a low temperature. As a result, the short fibers are bonded to each other to form a strong sintered porous body 3. In this case, in addition to the short fibers, other powders or fibers may be mixed or laminated with other powders or fibers, and may be used as the filtering material, or as a buffer for reducing the flow rate, or as a heat insulating material. Various developments can be made without departing from the spirit of the present invention, for example, it can be used widely.

[0042]

Example 1 A plurality of stainless steel wires (wire diameter: 0.12 mm) each having the composition shown in Table 1 covered with an exterior material were prepared, and these were covered with a bundled exterior material to form a composite wire. The diameter was reduced by repeatedly performing wire drawing and heat treatment.

[0043]

[Table 1]

This linear body was treated with hydrofluoric acid to obtain 500 bundles of fibers, the surface of which was non-smooth and had an irregular cross section, and the average fiber diameter was about 2 to 2.5 μm. It was thin.

Next, the fiber was heat-treated at 1100 ° C. for 1 hour in an inert gas atmosphere, and then 3% hydrofluoric acid was added.
Grain boundary corrosion treatment was performed by immersion in a hydrofluoric acid solution containing 20% nitric acid. The average aspect ratio and the variation coefficient (CV), which is the variation, were determined for 100 short fiber powders obtained as a result. The results are as shown in Table 2, and the distribution histograms of Sample B and Sample F are shown in FIG.

[0046]

[Table 2]

[0047]

Embodiment 2 With respect to the composite wire of Samples A, C, and F of the above-described Embodiment 1, the wire drawing and the heat treatment are repeatedly performed to obtain ultra-fine fibers having a fiber diameter of 0.5 μm. It was set in an inert atmosphere at 1000 ° C. for 50 minutes and 100 minutes to perform a heat treatment. By this treatment, the crystal of the fiber grew slowly, and the next short fiber was obtained by performing intergranular corrosion treatment with the same solution as in Example 1 above.

[0048]

[Table 3]

[0049]

Example 3 The short fiber powder of the sample D was used for an outer diameter of 30 m.
m and a mold having a thickness of 2 mm were filled, and sintering was performed under the following conditions. Sintering temperature 1100 ° C Sintering time 1 hour Atmosphere Inert atmosphere with argon gas Pressurized pressure 100N / cm ²

When the obtained sintered porous body was observed with a microscope, it was found that each short fiber was oriented in a random direction and had a strong bond, and the pore characteristics were as follows.

Sample No. D (fiber diameter: 2 μm) Pore diameter 2.6 μm Porosity 63%

[0052]

As described above, according to the first aspect of the present invention, a columnar shape having no cutting sag at an end portion is formed, and by adding N,
Since the fiber diameter (d), the aspect ratio, and the variation thereof are adjusted, a porous body having excellent pore characteristics can be produced. Further, since an adjusting element having a function of refining crystal grains is used, there is an advantage that rapid crystal growth during the processing step can be suppressed, and a management load during operation can be reduced.

According to a second aspect of the present invention, the fiber diameter (d) is reduced by adding at least one element selected from Ti, Nb, Zr, B or V to form a column without cutting sag at the end. Since the aspect ratio and its variation are adjusted, rapid crystal growth during the processing step can be suppressed, so that the aspect ratio can be reduced even though the diameter is small, and the management burden during work can be reduced. There are advantages.

According to the third and fourth aspects of the present invention, by adopting the structure, a more uniform stainless steel short fiber can be obtained, and a sintered porous body having more improved filtration characteristics can be obtained.

Since austenitic stainless steel is used as the stainless steel short fiber, it has excellent corrosion resistance, mechanical properties, and heat resistance, and can be suitably used as a porous material such as a filter material.

The sintered porous material according to claim 6 is characterized in that:
Since the stainless steel short fibers according to any one of the above items 5 are formed by pressing the porous structure oriented in the random direction and sintering, a sintered porous body having excellent pore characteristics can be obtained.

Further, in the present invention, as described above, all of the adjusting elements have the function of refining the crystal grains, so that rapid crystal growth during the processing step can be suppressed. In addition, there is an advantage that the management burden during work can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing the appearance of a short fiber.

FIG. 2 is a perspective view illustrating a sintered porous body.

FIG. 3 is a histogram showing variation in aspect ratio of stainless steel short fibers according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Short fiber of stainless steel 3 Sintered porous material 4 Void

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B22F 5/10 B22F 5/10 C22C 33/02 C22C 33/02 C 38/00 302 38/00 302Z 38 / 14 38/14 // B21C 1/00 B21C 1/00 B D01F 9/08 D01F 9/08 DF term (reference) 4D019 AA01 AA03 BA02 BB07 BB13 BD01 CB06 DA01 DA03 4E096 EA03 EA13 4K018 AA33 BA17 BB02 CA14 GA07 4L037 AT07 AT05 CS13 FA02 FA05 FA12 FA20 PA29 PF56 UA15 UA20

Claims (6)

[Claims] 1. A fiber with no cut sag at the end and a fiber diameter (d) of 10 μm or less, and an average value of an aspect ratio (L / d) between the diameter (d) and the length (L). 2-20
The average aspect ratio is suppressed to the predetermined range by adjusting the N content in the short fibers to a range of 0.02 to 0.50 wt%. Stainless steel staple fiber. 2. A fiber having a columnar shape having no cutting sag at an end and having a fiber diameter (d) of 10 μm or less, and an aspect ratio (L / d) between the diameter (d) and the length (L). Is a stainless steel short fiber having an average value of 2 to 20, wherein the amount of at least one element selected from Ti, Nb, Zr, B or V in the short fiber is 0.005 to 0.30.
The stainless steel short fiber, wherein the average aspect ratio is controlled to the predetermined range by adjusting the average aspect ratio to the range of wt%. 3. The short fiber has a fiber diameter (d) of from 0.1 to 0.1.
The stainless steel short fiber according to claim 1 or 2, wherein the diameter is 5.0 µm. 4. The stainless steel short fiber according to claim 1, wherein the average aspect ratio is 5 to 12, and a coefficient of variation (CV) of the variation is 25% or less. 5. The stainless steel short fiber according to claim 1, wherein the stainless steel short fiber is made of austenitic stainless steel.
The stainless steel short fiber according to 2 or 4. 6. A sintered porous material, wherein the stainless steel short fibers according to any one of claims 1 to 5 are pressed into a porous structure oriented in a random direction and integrated by sintering. body.