JPH10194838A - Ceramic sintered material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic sintered material consisting essentially of silicon nitride and titanium nitride and having satisfactory strength and wear resistance as the constituent material of metallurgical iron working jigs, especially hot working jigs and to obtain metallurgical iron working jigs using the sintered material. SOLUTION: Metallurgical iron working jigs for hot working such as rolling rolls for wire rod 1, 2, guide rolls 3, 4 for wire rod or squeezing rolls for producing an electric resistance welded tube are made of a ceramic sintered material contg. 40-70wt.% TiN and 20-60wt.% Si3 N4 and having >=1,000MPa bending strength, >=4.5MPam<1/2> fracture toughness and >=98% relative density. The average grain diameter of the TiN grains in the sintered material is <=2μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic sintered material, and more specifically, to various hot workings such as a jig for processing iron metallurgy, for example, a rolling roll or guide roll for wire rod, a squeeze roll for manufacturing an electric resistance welded pipe, and the like. The present invention relates to a ceramic sintered material suitably used as a constituent material of a tool.

[0002]

2. Description of the Related Art Conventionally, the above-mentioned iron metallurgy hot working jig is mainly made of alloy steel or cemented carbide. For example, 90
At a high temperature of 0 ° C. to 1000 ° C., there is a problem that when used for processing an iron-based material, wear is severe, and the life is exhausted in a short time. Therefore, use of a jig made of a ceramic material having excellent abrasion characteristics instead of the above materials has been studied. For example, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silicon nitride (Si ₃ N) ₄ ), a jig made of sialon, silicon carbide (SiC), or the like has been proposed (Japanese Patent Publication No. 59-197307, Japanese Patent Publication No.
-48524).

However, among the materials of the jigs disclosed in the above publication, alumina tends to have insufficient strength, toughness and thermal shock, and is difficult to use under severe conditions such as processing at high temperatures. There are drawbacks. Further, zirconia has excellent strength at room temperature, but when heated to 300 ° C. or more, the strength is sharply reduced, and the thermal conductivity is poor and the thermal shock resistance is poor. Difficult to use. Further, silicon carbide also has a drawback that strength and toughness are not sufficient as a constituent material of a jig for hot working.

Therefore, attempts have been made to use silicon nitride-based materials which are excellent in both strength and thermal shock resistance.
For example, rolling rolls containing silicon nitride as a main component (60 wt% or more) (Japanese Patent Publication No. 59-21413), silicon oxide as a second phase, an oxide-based ceramic component such as MgO, Al ₂ O ₃ or AlN, TiN Hot rolling tools for iron alloys containing a total of 2 to 50% by weight of a nitride-based ceramic component (Japanese Patent Publication No. 59-21580), hot plastic working tools containing 60% by weight or more of silicon nitride ( JP 61
Various publications have been proposed.

[0005]

The materials used in the hot working jigs disclosed in each of the above publications have a silicon nitride content of 50% by weight or more, and have strength and thermal shock resistance. However, there is a disadvantage that the wear resistance when actually applied to the processing of iron-based materials is not always good. That is, when a hot plastic working jig is made of a ceramic material mainly composed of silicon nitride, a chemical reaction is likely to occur between the iron component in the workpiece and the silicon nitride component on the jig side. When it comes into contact with the workpiece under stress conditions, the silicon nitride component is consumed by the chemical reaction, which results in rapid wear of the jig.

In this case, it is known that it is effective to mix titanium nitride in the material in order to suppress the reaction between silicon nitride and the iron component. For example, JP-A-58-9
No. 5662 proposes a composite ceramic sintered body suitable for a cutting tool made of an iron-based material, which contains silicon nitride and 40 to 75% by weight of titanium nitride. However, since the ceramic sintered body disclosed in the above publication is premised on use as a cutting tool, the working temperature and stress at the time of sliding, etc., are much more severe than a cutting tool. Application to steel is not considered at all, and the material strength and the degree of chemical stability to iron components necessary for that purpose, as well as the material composition and organizational characteristics to achieve such strength and chemical stability, etc. about,
No disclosure or suggestion was made. Further, the ceramic sintered body disclosed in the publication is manufactured by a hot press method. However, the hot press method can be applied to a simple shape such as a tool, but a complicated shape such as a hot rolling jig. There is a problem that obtaining goods is difficult.

Further, the strength of a sintered material family containing 50% by weight or more of dispersed particles of TiN or the like in a conventional silicon nitride-titanium nitride-based material has a strength of at most 900 even using a hot press.
The limit was to obtain about MPa. However, hot working jigs such as guide rolls and rolling rolls are subjected to impact stress when the head of the material to be rolled such as a billet enters the roll, so that higher strength and toughness are required to ensure reliability. And specifically, the strength of the current silicon nitride-based material that does not contain titanium nitride is 10%.
A level of at least 00 MPa is required at least. However, the strength of the material disclosed in the above publication using MgO, Al ₂ O ₃ , and AlN as a sintering aid is about 900 MPa as described above, and does not reach the strength of a silicon nitride-based material of 1000 MPa, and has sufficient strength. It is hard to say that it is.

An object of the present invention is to provide a steel metallurgy processing jig, particularly a hot working jig, which is mainly composed of silicon nitride and titanium nitride, and has sufficient strength and chemical stability to ferrous metals. And to provide a ceramic sintered material having:

[0009]

In order to solve the above-mentioned problems, the ceramic sintered material of the present invention is
40-70 wt% of TiN and 20 to 60% by weight of Si ₃
N ₄ and a bending strength of 1000 MPa or more. The present inventors have conducted intensive studies and as a result,
The ceramic sintered material of the present invention, in which the composition of the material is adjusted within the above range and the bending strength is 1000 MPa or more, is iron-based on the assumption that high stress is applied at a high temperature of, for example, 900 to 1000 ° C. Even under conditions of hot working of the material, sufficient abrasion resistance is ensured, and furthermore, problems during working such as breakage hardly occur, and thus it is suitable for high performance and long life jigs for iron metal working. I found something. When the bending strength is less than 1000 MPa,
The durability required as a constituent material of an iron metal working jig, particularly a hot working jig, cannot be secured. Here, the bending strength is
More desirably, it is 1100 MPa or more, and further desirably, 1200 MPa or more. In addition, the bending strength referred to in this specification means a three-point bending strength measured at room temperature based on a method described in JISR1601 (Bending strength test method for ceramics).

The above-mentioned ceramic sintered material has a fracture toughness of 4.5 MPam ^1/2 from the viewpoint of ensuring reliability.
It is desirable that this is the case. Fracture toughness of 4.5 MPa
If it is less than m ^1/2 , when the material is applied to a hot working jig, depending on the conditions of use, problems such as breakage may easily occur. The fracture toughness value is more desirably 5.0 MPam ^1/2 or more. The fracture toughness value referred to in the present specification is JIS-R1607 (199
Of the fracture toughness test method described in “0 year”) measured by the indentation method (IF method: Indentation-Fracture method).

Next, when the total content of TiN and Si ₃ N ₄ is 6
If the content is less than 0% by weight, the bending strength of 1000 MPa or more cannot be ensured, and the fracture toughness value is also reduced, resulting in a reduction in the life of the jig. Note that the total content is more desirably 90% by weight or more. Also, TiN and S
Even if the total content of i ₃ N ₄ is 90% by weight or more, Si
₃ or the content of N ₄ is less than 20 wt%, or Ti
When the N content exceeds 70% by weight, the bending strength cannot be ensured similarly. On the other hand, when the content of Si ₃ N ₄ is 6
If the content exceeds 0% by weight or the content of TiN is less than 40% by weight, the effect of suppressing the reaction between silicon nitride and iron becomes insufficient, and for example, wear resistance when used as a hot working jig It leads to lack of sex. The content of TiN is more desirably 60% by weight or less, and the content of Si ₃ N ₄ is more desirably 24 to 55% by weight, and still more desirably 32 to 50% by weight. Is good.

That is, by adjusting the content of TiN to 40 to 70% by weight and considering the type and amount of the sintering aid to be added, a strength of 1000 MPa or more can be ensured, and the sintering conditions can be secured. 1300 by optimizing
In some cases, a strength of about MPa can be achieved. Note that Ti
When the amount of N increases and the amount of Si ₃ N ₄ decreases, the fracture toughness tends to decrease. However, from the viewpoint of reliability, the fracture toughness is 5 MPam, which is the level of the fracture toughness of the conventional silicon nitride material.
It can be said that it is desirable that at least ^1/2 is secured. From such a viewpoint, the content of TiN is set to 70% by weight or less (or 24% by weight or more of Si ₃ N ₄ ), more preferably 60% by weight or less (or 32% by weight or more of Si ₃ N ₄ ). Is good. If the amount of TiN is less than 40% by weight or the amount of Si ₃ N ₄ exceeds 60% by weight, the reactivity with iron increases, leading to deterioration of wear resistance. Therefore, in order to achieve both the mechanical strength and the chemical stability of the material, it is better to adjust the content of TiN in the range of 40 to 70% by weight.

The relative density of the ceramic sintered material having the above composition is desirably 98% or more. If the relative density is less than 98%, it may not be possible to secure a bending strength of 1000 MPa or more. When the surface of the ceramic sintered material is polished, the area ratio of the residual pores observed on the polished surface is desirably 1% or less. If the area ratio of the residual pores exceeds 1%, the bending strength of the material is reduced, and the open pores formed on the surface of the material are easily transferred to the material to be processed, and the finish of the processed surface is deteriorated. Occurs. The area ratio of the residual pores is more desirably less than 0.5%.

Next, in order for the sintered material to have the above-mentioned bending strength or fracture toughness value, it is also important to control the crystal grain size of the sintered body. In the ceramic sintered material of the present invention, the average particle size of the TiN particles in the sintered body is set to 2
It is desirable to set it to μm or less. Further, the standard deviation of the particle diameter is desirably 0.75 μm or less. If the average particle size of the TiN particles exceeds 2 μm or the standard deviation exceeds 0.75 μm, the amount of coarse TiN particles that easily become the starting point of fracture increases, so that the bending strength of the material can be maintained at 1000 MPa or more. In some cases, it may disappear, and the fracture toughness value may also decrease, leading to a reduction in the life of the jig. The average particle size of the TiN particles is more desirably set to 1.7 μm or less, and the standard deviation is preferably set to 0.1 μm.
It is desirable that the thickness be 7 μm or less.

When the ceramic material is assumed to be used as a hot working jig for iron metallurgy, a rectangular parallelepiped test piece having a length of 20 mm, a width of 8 mm and a height of 4 mm made of the material is used. Carbon content 0.45% by weight, temperature 1600 ° C
It is desirable that the residual ratio of the test piece when immersed in molten carbon steel for 5 hours is 80% by volume or more. If the residual ratio of the test piece is less than 80% by volume, the chemical stability of the material against iron is insufficient, and the wear resistance when used as a hot working jig for iron metallurgy is insufficient. , Leading to a reduction in the life of the jig. The residual ratio is desirably 90% by volume or more, and more desirably 95% by volume or more. In addition, the content of TiN is set to 40% by weight or more to make the residual ratio of the test piece 80% by volume or more, and 50% by weight or more to 90% by volume or more, and 95% by volume or more. For this purpose, the content is preferably 60% by weight or more. In addition, when the above test was performed, the residual ratio of the sample was 8%.
In addition to 0% by volume or more, if the unreacted portion that has not undergone a chemical reaction with the iron component remains in the sample at 5% by volume or more, desirably 10% by volume or more, the chemical stability of the material is increased. Is further improved, and the life of the hot working jig produced thereby can be further improved. In this case, in order to set the amount of the unreacted layer to 5% by volume or more, TiN
Is preferably 50% by weight or more, and in order to be 10% by volume or more, the content is preferably 60% by weight or more.

As is clear from the above description, the chemical stability of the ceramic sintered material in the reaction with iron (hereinafter referred to simply as “chemical stability” in the present specification,
In order to enhance the stability in the reaction with iron), it is desirable to increase the content of TiN. However, when the content of TiN increases, Si ₃ N ₄ is increased.
, The bending strength and the fracture toughness value decrease. Therefore, depending on the intended use of the material, TiN
It can be said that it is desirable to appropriately select the content of Si ₃ N ₄ and Si ₃ N ₄ and adjust the balance between chemical stability and strength or fracture toughness so as to be suitable for the intended use.

Next, in order to increase the relative density of the material to 98% or more, it is effective to add a predetermined sintering aid. As a sintering aid component, in addition to rare earth element oxides such as Y ₂ O ₃ and CeO ₂ , MgO, ZrO ₂ , Al ₂ O ₃ and CaO can be used, and one or more of them can be used in total. Is desirably 3.5% by weight or more. More specifically, MgO, ZrO ₂ , CeO ₂ , Al ₂ O ₃ and Y
It is preferred that two or more types of ₂ O ₃ be contained in a total of 3.5 to 10% by weight. If the content is less than 3.5% by weight, a relative density of 98% or more may not be obtained. On the other hand, if the content exceeds 10% by weight, the amount of the liquid phase generated during sintering becomes too large even if the relative density becomes a sufficient value, and for example, the average particle size of the TiN particles is maintained at 2 μm or less. In some cases, it may be difficult to obtain the required strength. In addition, MgO, ZrO ₂ , Ce as sintering aids
If three or more types of O ₂ and Al ₂ O ₃ are contained in an amount of 0.5% by weight or more each and a total of 3.5 to 10% by weight, densification of the material is suppressed while suppressing crystal grain growth. It is more desirable in aiming at.

[0018] The ceramic sintered material of the present invention is 1000
From the viewpoint of achieving a strength of not less than MPa or a fracture toughness of not less than 4.5 MPam ^1/2 , a hot isostatic press (H
It is desirable to manufacture by IP) method. The reason is as follows. Since the material can be densified at a relatively low temperature and crystal grain growth during processing can be suppressed, it is possible to easily obtain a sintered material in which the average density of TiN grains is 2 μm or less while the relative density is 98% or more. Can be. The micropores of the sintered body are crushed by the high-temperature and high-pressure treatment, and the portion that can be a starting point of destruction is reduced. The hot press method can easily obtain a complicated-shaped product which is difficult to manufacture.

The conditions for the HIP treatment are preferably such that the treatment temperature is 1600 ° C. or less and the pressure is 100 atm or more. If the processing temperature exceeds 1600 ° C., the crystal grains grow excessively during the processing, so that the required strength cannot be secured. On the other hand, when the pressure is less than 100 atm, the material is insufficiently densified, resulting in insufficient strength. On the other hand, in consideration of the durability of the device, the upper limit of the pressure is considered to be about 2000 atm for a generally used HIP device, but if a problem such as device durability does not occur, a higher pressure is set. Is also good. The processing temperature is more desirably set in the range of 1500 to 1600 ° C. The pressure is more desirably set to 1000 atm or more. In addition, after preliminarily forming the raw material powder, by preliminarily firing at a temperature of 1550 to 1650 ° C. and then performing HIP treatment, a sintered body having a desired shape can be efficiently manufactured. The pre-firing temperature is 1
If the temperature is lower than 550 ° C., open pores remain in the preformed body, and the effect of shrinking the open pores by the subsequent hydrostatic pressure treatment may be insufficient. On the other hand, when the preliminary firing temperature is 16
If the temperature exceeds 50 ° C., crystal grain growth occurs, leading to a decrease in the strength of the material.

Using the ceramic sintered material of the present invention, various hot working jigs for iron metallurgy can be constructed. Specific examples of the jig include a roll or guide roll for rolling a wire rod and a squeeze roll for manufacturing an electric resistance welded tube. Further, the ceramic sintered material of the present invention can of course be used as a constituent material of a jig for cold working having excellent durability.

[0021]

Embodiments of the present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 schematically shows a roll for rolling a wire rod and a guide roll as one embodiment of a processing jig for iron metallurgy according to the present invention. That is, the material W to be rolled is made of an iron-based material and
It is preheated to 00 to 1000 ° C. and is introduced between two rolling rolls 1 and 2 facing each other such that the roll rotation axis A1 is substantially parallel. Rolling roll 1,
A groove G1 is formed in the circumferential direction of each of the roll surfaces 2, and the groove G1 forms a roll hole C having a predetermined cross-sectional shape when the two rolls 1 and 2 are combined. Then, the material W to be rolled has its roll hole shape C
Is rolled into a wire W having a cross-sectional shape and dimensions defined by the die C.

On the other hand, the guide rolls 3 and 4 are arranged on the upstream side of the rolling rolls 1 and 2 with the material W to be sandwiched therebetween, and each of the guide rolls has a narrowed intermediate portion in the direction of the roll rotation axis A2. Shaped like a
The cross-sectional shape of the roll surface (outer peripheral surface) G2 is V-shaped. These guide rolls 3 and 4 rotate in opposite directions to each other in the transport direction of the rolled material W,
It serves to guide the rolled material W with respect to the rolling rolls 1 and 2 while positioning the rolled material W in the above-described roll die C. The feed speed of the material to be rolled W when introduced into the rolling rolls 1 and 2 varies depending on the material, temperature, wire diameter and reduction ratio of the material to be rolled W, but is about 30 to 100 m / sec.

The rolling rolls 1 and 2 and the guide rolls 3 and 4 have at least a portion including a contact surface with the rolled material W made of the ceramic sintered material of the present invention. The ceramic sintered material has a T-content of 40-70% by weight.
iN and 20 to 60% by weight of Si ₃ N ₄ are contained in a total of 90% by weight or more, the relative density is 98% or more, the TiN particles in the sintered body are 2 μm or less, and the bending strength is 1%.
000MPa or more (preferably 1200MPa or more),
The fracture toughness value is 4.5 MPam ^1/2 or more (preferably 5.
0 MPam ^1/2 ).

Rolls 1, 2 and guide rolls 3, 4
The component made of the ceramic material is manufactured by the following method. That is, Ti as a raw material powder
MgO as a sintering aid for N and Si ₃ N ₄ powders
Two or more of ZrO ₂ , CeO ₂ , Al ₂ O ₃ and Y ₂ O ₃ are mixed and mixed in a total amount of 5 to 10% by weight, and the mixture is prepared by a known powder molding method such as injection molding, slip casting, press molding and the like. Into the desired shape. Then, the molded body is pre-fired at a temperature of 1550 to 1650 ° C.
Hot isostatic pressing at 00-1600 ° C. and pressure 100-2000 atm.

Next, FIG. 2 shows an example of a squeeze roll for manufacturing an electric resistance welded tube. The electric resistance welded tube T is manufactured by, for example, bending a long plate material into a U-shape in the width direction, further bending it into an O-shape, and joining both end edges thereof by a seam welded portion S. The tube T 'formed after joining is heated by a furnace (not shown) and transported in the longitudinal direction, and is introduced between the squeeze rolls 5, 6 arranged so that the axes A3 are substantially parallel to each other. Is formed in a predetermined shape by being squeezed in the radial direction of the cross section.

The squeeze rolls 5 and 6 have a thread-wound form in which the middle part is narrowed in the direction of the axis A3, and the roll surface G3 which is in contact with the tube T 'has a cross-sectional shape of the formed tube. It is formed in an arc-shaped curved surface corresponding to the cross-sectional outer shape of T, and at least a portion including the roll surface is made of the above-described ceramic sintered material of the present invention.

The above-mentioned rolling rolls 1, 2 and guide rolls 3,
The squeeze roll 4 or the squeeze rolls 5 and 6 come into contact with and slide in a high stress state with respect to the material to be rolled W or the pipe T ′ heated to a high temperature. The material has sufficient strength to withstand the stress during sliding, and has low reactivity with the iron component of the material W to be rolled, so that it has excellent wear resistance and can maintain its life for a long time. it can.

[0028]

EXAMPLES Si ₃ N ₄ powder (specific surface area 12m ² / g, average particle size 0.6 .mu.m), TiN powder (specific surface area 2.6 m ² /
g, an average particle diameter of 1.3 μm) and a predetermined amount of a sintering aid having the composition shown in Table 1, and wet-mixed by a ball mill, followed by drying and granulation to obtain a raw material powder. this,
After the die press molding, cold isostatic pressing is performed, and then at a temperature of 1550 ° C. to 1950 ° C. in a nitrogen atmosphere of 10 atm.
For 4 hours, and further subjected to HIP treatment at a temperature of 1550 ° C. to 1,600 ° C. for 2 hours in a nitrogen atmosphere at 1000 atm to obtain a sintered body. Then, by grinding the sintered body using a diamond grindstone, a length of 40 mm,
A rectangular parallelepiped specimen having a width of 4 mm and a height of 3 mm was used. Tables 2 to 4 show the compositions and preparation conditions of the test pieces. Further, as a comparative example, a test piece composed of only Si ₃ N ₄ and a sintering aid without mixing TiN was similarly prepared. The composition is shown in Table 5.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

For each of the above test pieces, JISR1601
Based on the method described in (Ceramic bending strength test method), the three-point bending strength was measured at room temperature. Also,
JIS-R1607 (1990) Indenter press-fitting method (IF
Method: Indentation-Fracture method). Further, the relative density of each test piece was measured by the Archimedes method. Note that the relative density was obtained by dividing the sample density by the theoretical density, and the theoretical density was obtained by dividing Si ₃ N ₄ (3.
^{20g / cm 3), TiN (} 5.43g / cm 3), Al
₂ O ₃ (3.99 g / cm ³ ), ZrO ₂ (5.6 g / cm ³ )
³ ), MgO (3.65 g / cm ³ ), CeO ₂ (7.3
_{^{g / cm 3), Y 2}} O 3 (4.84g / cm 3 single density of each component) (or, a value) that describes in parentheses was calculated from the their blending ratio. The above results are shown in Tables 2 to 5.

That is, for a test piece prepared by the HIP method and having the composition described in the claims of the present invention, the type and amount of the sintering aid are appropriately selected, and the sintering conditions are appropriately adjusted. It can be seen that the setting achieves a bending strength of 1000 MPa or more and a fracture toughness value of 4.5 MPam ^1/2 or more. In particular, the sample in which the total amount of the sintering aid was set to 5% by volume and the content of Si ₃ N ₄ was 24 to 55% by weight was optimized by optimizing the sintering conditions.
It can be seen that a sample of 100 MPa or more, also in the range of 32 to 50% by weight, shows an extremely high strength of 1300 MPa or more. On the other hand, it can also be seen that setting the blending amount of TiN to 50 vol% (about 62 wt%) or less is effective in setting the fracture toughness value to 5 MPam ^1/2 or more.

The conditions of pre-firing and HIP for achieving the above relative density and average particle size vary depending on the composition. Further, it can be seen that when the sintering aid composition and the amount thereof are different, the ultimate level of the bending strength and the toughness value of the test piece changes. Specifically, when the total amount of the auxiliaries is 5% by weight or more,
Compared with the auxiliaries of composition A in Table 1 (comprising equal volumes of Al ₂ O ₃ and Y ₂ O ₃ ), the auxiliaries of the same B (MgO, ZrO ₂ , C
It can be seen that the case where eO ₂ and Al ₂ O ₃ are mixed in the same volume) has a higher effect of densifying the sintered body and improving the strength and toughness (Tables 2 and 3). On the other hand, even when the auxiliary agent of B is used, if the amount is less than 5% by weight, it is difficult to advance the densification of the sintered body, and it is found that the strength is also reduced (Table 4).

Next, Sample Nos. 4-2 to 4-5 and Sample Nos. 2-2, 3-1 and 4-2 and 5-2 (the latter corresponds to the one having the highest strength in the corresponding composition) For each sample of (1), the surface of the test piece was mirror-polished, and the structure photograph was taken at a magnification of 2000 and 5000 times with a scanning electron microscope. FIGS. 3 to 10 show the photographs of the structures (the figure numbers correspond to the order of the sample numbers described above, in which (a) shows a 2000 × photograph and (b) shows a 5000 × photograph). That is, Sample No. 2 shown in FIGS.
For each of the samples 2, 3-1, 4-2, and 5-2, Ti
As the N content increases, the area ratio of whitish particles in the photograph increases. Sample No. 4-
In the photograph of FIG. 2 (FIG. 9), the area ratio of the whitish portion obtained by performing the image processing is 48%, which substantially coincides with the volume content of 50% by volume of TiN of the sample.
In addition, analysis by an energy dispersive X-ray analyzer (EDS) was performed under observation with a scanning electron microscope, and it was confirmed that the whitish portions were TiN particles.

Next, sample numbers 4-2 to 4-2 shown in FIGS.
In each of the samples 4-5, it can be seen that the particle size of the TiN particles increases as the pre-firing temperature increases.
Therefore, using these photos, the following method
The average particle size of the TiN particles of these samples was determined. First, a visual field of 20 μm × 15 μm was set on the 5000 × photograph, and as shown in FIG. 11A, the maximum diameter d of all the TiN grains g observed in the visual field was measured. Since TiN has a cubic crystal structure and is presumed to show an equiaxed crystal structure in the sintered body, the particles having a distorted shape in the photograph include a plurality of small particles. It is considered that the particles are aggregated, and as shown in FIG.
g3 and the like, and their maximum diameters d1 to d3 were measured. From the particle size data of the particles thus obtained, the average value (that is, the average particle size) and the standard deviation were calculated.

Similarly, using a scanning electron micrograph,
The area fraction of each pore observed on the photograph was determined by circular approximation, and the sum of the areas was divided by the area of the observation visual field to determine the area fraction of the residual pores of each sample.

The average particle diameter and standard deviation of TiN and the residual porosity obtained for each of the samples Nos. 4-1 to 4-5 are compared with the relative density, strength and fracture toughness of the sample. Table 6 shows the correspondence. That is, in order to obtain a bending strength of 1000 MPa or more and a fracture toughness value of 4.5 MPam ^1/2 or more, the relative density is 98% or more, and
It can be seen that it is necessary that the average particle size of N is 2 μm or less and the area ratio of the residual pores is less than 1%. In addition, it can be seen that it is also effective to set the standard deviation of the TiN particle diameter to 0.70 μm or less in order to achieve particularly high strength.

[0041]

[Table 6]

Next, sample numbers 2-3 and 3 in Tables 2, 3 and 5
-3, 4-3, 5-3 and each sample of Comparative Example 2 were polished with a diamond grindstone to a length of 20 mm, a width of 8 mm,
A test piece having a height of 4 mm was prepared, and this was made of carbon steel (material JI
SS45C) and placed in an alumina crucible and heated to 1600 ° C in an argon atmosphere to completely melt the carbon steel and hold it for 5 hours. The sample was then cooled with molten carbon steel and cut with a solidified steel with a diamond cutter. Then, the reactivity between the sample and the molten carbon steel was evaluated by observing the cut surface. First, the residual ratio of the sample was determined by comparing the cross-sectional areas of the sample before and after the test. The area fraction of the unreacted portion in the area of the cut surface of the sample after the test was defined as the volume fraction of the unreacted layer. Table 7 shows the results. The test piece of Comparative Example 2 not containing TiN
Reacted with molten carbon steel and completely dissolved and disappeared. However, it can be seen that the reaction was suppressed as the TiN content in the test piece increased, and the volume of the unreacted portion increased. FIG. 12A shows an enlarged cross-sectional photograph (magnification: 7) of the sample of sample number 5-3. In the photograph, in the rectangular sample cross-section, it is observed that the gray band formed along the edge is a reaction part, and a slightly large reaction part is generated at the lower right corner. On the other hand, the portion that is slightly brighter than the inside of the reaction portion is the unreacted portion, and its proportion in the sample cross section is about 50%. On the other hand, FIG. 12B is a cross-sectional photograph of the sample of Comparative Example 2, in which the sample has almost completely melted and disappeared.

[0043]

[Table 7]

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an example of a rolling roll and a guide roll for manufacturing a wire rod.

FIG. 2 is a perspective view schematically showing an example of a squeeze roll for manufacturing an electric resistance welded tube.

FIG. 3 is a scanning electron micrograph of a ceramic sintered material of Sample No. 4-2 in Examples.

FIG. 4 is a scanning electron micrograph of the ceramic sintered material of Sample No. 4-3.

FIG. 5 is a scanning electron micrograph of the ceramic sintered material of Sample No. 4-4.

FIG. 6 is a scanning electron micrograph of the ceramic sintered material of Sample No. 4-5.

FIG. 7 is a scanning electron micrograph of the ceramic sintered material of Sample No. 2-2.

FIG. 8 is a scanning electron micrograph of the ceramic sintered material of Sample No. 3-1.

FIG. 9 is a scanning electron micrograph of another ceramic sintered material of Sample No. 4-2.

FIG. 10 is a scanning electron micrograph of the ceramic sintered material of Sample No. 5-2.

FIG. 11 is a diagram schematically showing a method for obtaining the maximum diameter of TiN particles in a sample.

FIG. 12 is a cross-sectional photograph showing an example of a state after a test of a sample used in an experiment for examining reactivity between molten carbon steel and the sample.

[Explanation of symbols]

 1,2 Rolling roll 3,4 Guide roll 5,6 Squeeze roll

Claims (9)

[Claims] 1. The method according to claim 1, wherein the TiN content is 40 to 70% by weight and
% By weight of Si ₃ N ₄ and a bending strength of 1000
A ceramic sintered material characterized by being at least MPa. 2. A composition comprising 40 to 70% by weight of TiN and 20 to 60% by weight.
% Of Si ₃ N ₄ , the relative density thereof is 98% or more, and the TiN particles in the sintered body are 2 μm
A ceramic sintered material characterized by the following. 3. The ceramic sintered material according to claim 2, wherein, when the surface of the ceramic sintered material is polished, an area ratio of residual pores observed on the polished surface is 1% or less. 4. The ceramic sintered material according to claim 2, which has a bending strength of 1000 MPa or more. 5. The ceramic sintered material according to claim 1, which has a fracture toughness value of 4.5 MPam ^1/2 or more. 6. A method of manufacturing the ceramic sintered body,
When a rectangular parallelepiped test piece having a length of 20 mm, a width of 8 mm and a height of 4 mm was immersed in molten carbon steel at a carbon content of 0.45% by weight and a temperature of 1600 ° C. for 5 hours, the residual ratio of the test piece was The ceramic sintered material according to any one of claims 1 to 5, which is 80% by volume or more. 7. As a sintering aid, MgO, ZrO ₂ , C
Two or more of eO ₂ , Al ₂ O ₃ and Y ₂ O ₃ are 3.5 in total.
The ceramic sintered material according to any one of claims 1 to 6, which contains 10 to 10% by weight. 8. As a sintering aid, MgO, ZrO ₂ , C
eO _2, Al ₂ 3 or more O _3, containing 3.5 to 10 wt%, respectively by 0.5 wt% or more and a total claim 1
8. The ceramic sintered material according to any one of items 7 to 7. 9. After molding the raw material powder, the temperature is 1550-16.
Preliminary firing at 50 ° C, and a temperature of 1500 to 1600 ° C
9. The ceramic sintered material according to claim 1, which is produced by hot isostatic pressing at a pressure of 100 to 2000 atm.