JP2000351671A - Particle-dispersed silicon carbide-based sintered product and guide roller which use the same and is used for rolling wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sintered article which has high hardness, high toughness, high thermal shock resistance and high oxidation resistance, by dispersing titanium boride-zirconium boride solid solution particles having a specific average diameter in a silicon carbide sintered product in a specific rate and specifying the relative density. SOLUTION: This sintered article is obtained by adding prescribed amounts of TiB2 and ZrB2 or ZrC to raw materials for the silicon carbide sintered product, kneading the mixture, molding the kneaded product, sintering the molded product under vacuum or in the flow of an inert gas without adding a pressure, and then subjecting the sintered product to a hot hydrostatic pressure press sintering treatment in an Ar gas atmosphere. The sintering treatment is preferably carried out at a highest temperature of 1,950 to 2,200 deg.C for 4 hr or longer, The titanium boride-zirconium boride solid solution particles expressed by the formula: Ti1-xZrxB2 [0.02<=(x)<=0.25] having an average particle diameter of 1 to 10 μm are dispersed in the silicon carbide(SiC) sintered product in a volume fraction of 20 to 70%, and the particle-dispersed silicon carbide-based sintered product has a relative density of >=99%. The sintered product is cut to obtain a guide roller which has excellent abrasion resistance and excellent lacking resistance and is used for rolling metal wire rods.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide sintered body excellent in high-temperature strength and fracture toughness, and further has an abrasion resistance, which is used when a metal wire such as iron is manufactured by hot rolling.
The present invention relates to a guide roller having excellent fracture resistance and heat resistance.

[0002]

2. Description of the Related Art Heretofore, although silicon carbide sintered bodies have excellent thermal shock resistance and hardness, they have hardly been applied to uses having low fracture toughness and large mechanical impact. Therefore, in order to increase the toughness of the silicon carbide sintered body, researches such as dispersing various particles and whiskers in the sintered body have been advanced.

[0003] By the way, hot wire rolling lines are generally
Thick prismatic billet heated to a high temperature of 1000 ° C or more,
Continuously passes between a number of roll stands to reduce the area,
It finishes to a predetermined shape and size, and a number of guide members are used between the roll stands to guide the wire being rolled to a predetermined position on the rolling roll. In general, the guide member is often a roller that can rotate in the traveling direction of the wire in order to reliably guide the wire at high temperature and high speed. In the rolling line, especially the guide roller used on the entry side of the finishing mill, which is the final stand,
Use of guide rollers with a small diameter is necessary because, in accordance with the reduction in the surface area of the wire, the threading speed may be extremely high, 60 m / sec or more, and it is necessary to move closer to the rolling rolls in order to increase the inductivity of the wire. And the use environment is extremely severe.

Heretofore, as a guide roller for a rolling machine for metal wires such as iron, those made of high-hardness carbon steel or cemented carbide such as tungsten carbide (WC) have been used. Cemented carbide rollers are less likely to react with the material to be rolled hot and have better wear resistance than those made of high-hardness carbon steel. Although the number of replacements is small, WC
Dropping of grains, chipping, macroscopic cracks, etc. may occur at the roller caliber part that contacts the wire,
This has been a cause of surface roughness and abrasions on the surface of the wire rod which is the material to be rolled. In addition, the dropped WC-containing hard grains adhered and pressed into the surface of the wire during rolling, which sometimes caused wire breakage during further wire drawing and thinning in a later step.

[0005] The guide roller is usually reused by grinding the worn area. However, since the remaining cracks cause chipping at the time of reuse, the area where chipping and cracks occur is completely removed. Need to be kept. If chipping or cracking occurs, the amount of grinding, including the depth of cracking, is generally required to be about three times the abrasion depth, increasing the cost of additional work and shortening the total life of repeated use as a roller. , It was disadvantageous in terms of economy. In addition, cemented carbides such as WC generally have a high specific gravity and a large moment of inertia of the roller, so they undergo severe wear before the roller rotation is accelerated during rolling, and the original high wear resistance is sufficiently high. There was a case that was not exhibited.

On the other hand, attempts have been made to apply a silicon carbide ceramic, which has a lower specific gravity and a higher hardness than a cemented carbide and is expected to have improved wear resistance, to a guide roller. In the gazette, a portion in contact with the wire is formed of silicon carbide ceramics, and an attempt is made to improve wear resistance and wire surface properties. Further, Japanese Patent Application Laid-Open No. 9-278523 proposes a guide roller having a significantly improved fracture toughness value of silicon carbide ceramics, and is reported to have improved roller life. Since a hafnium compound (HfB ₂ ) is used, there is a problem that the production cost is increased.

[0007]

However, the conventional guide roller made of monolithic silicon carbide ceramics has a sufficient function in terms of reducing the weight of the roller and has relatively high abrasion resistance. The occurrence of macroscopic chipping and cracking was observed in the final rolling mill of the rolling line because the fracture resistance has not been dramatically improved while maintaining the wear resistance almost equal to that of cemented carbide rollers. In a severe use environment where a high-temperature rolled steel passes at an extremely high speed, such as on the entry side, there is a problem of lack of reliability.

[0008] In the study of particle dispersion for the purpose of increasing the toughness of a silicon carbide sintered body, for example, in Japanese Patent Application Laid-Open No. 9-278523, expensive HfB ₂ is used as a raw material, Using the Ti-Hf-B solid solution produced by the reaction, the fracture toughness value of the sintered body was significantly improved. When this is processed and used as a guide roller, as the sliding wear characteristics during passing, cracks and chipping are suppressed and the amount of necessary removal when reused is reduced, but the wear itself during passing is the same as the current Carbide (WC)
It was not possible to significantly reduce the wear amount of the material. Further, the material disclosed in Japanese Patent Application Laid-Open No. 9-278523 lacks stability at the time of raw material preparation, and requires non-aqueous wet mixing. For this reason, there have been problems that the raw material cost is greatly increased as compared with the water-based mixing that is usually widely performed, and that safety must be ensured during production.

The present invention has been made to solve the above problems. An object of the present invention is to provide a low-cost sintered body having significantly improved wear resistance based on oxidation resistance and improved fracture resistance due to improved fracture toughness, and a wire rod guide roller using the same. It is in.

[0010]

In the present invention, a means for solving the problem is that Ti _1-x Zr _x B ₂ (0.02 ≦ x) having an average diameter of 1 to 10 μm in a silicon carbide (SiC) sintered body. ≦ 0.25), the titanium boride-zirconium boride solid solution particles are dispersed in a volume fraction range of 20 to 70%, and the relative density is 99%.
A particle-dispersed silicon carbide sintered body as described above, and a wire rolling guide roller formed by molding the sintered body.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies,
Wear of the ceramic wire rolling guide roller is caused by sliding with the wire passing at high speed, and for materials that are easily oxidized, the oxidized layer is formed during the passage of the high-temperature wire or during water cooling at the interval between the wires. It has been found that the formed oxide layer is very susceptible to wear. In addition, chipping and cracking around the worn part are mainly caused by mechanical shock when the tip of the wire enters the roller, heating by contact with a high temperature wire of 1000 to 1200 ° C, and water cooling from the surroundings. It has been found that these wears and defects are remarkable when the material of the roller has low hardness, low toughness, low thermal shock resistance, and low oxidation resistance.

Therefore, in order to simultaneously improve the wear resistance and the fracture resistance and achieve the object, it is necessary to increase the hardness, toughness, thermal shock resistance, and oxidation resistance of the roller material. is there. As a method for simultaneously improving these properties, it is effective to disperse hard and highly oxidation-resistant particles in a sufficiently dense sintered body, and in particular, Ti-Zr- having high hardness and high oxidation resistance. By dispersing the B solid solution particles in silicon carbide, compared to a conventional monolithic silicon carbide guide roller, while increasing the wear resistance,
It has been found that it is possible to impart an effect of significantly improving chipping resistance, cracking and other chipping resistance.

[0013] The Ti-Zr-B solid solution is a hard and oxidation-resistant high melting point compound having an hcp structure, remains as dispersed particles in a silicon carbide sintered body after sintering, and has a hardness of the entire sintered body. Has the effect of improving Then, a residual stress is generated in the vicinity of the dispersed particles due to a difference in thermal expansion coefficient between the silicon carbide phase and the solid solution phase or a difference in Young's modulus, and has an effect of improving fracture energy at the time of fracture, while significantly improving toughness. Has the effect of improving thermal shock resistance.

Ti-Z used for the guide roller of the present invention
rB solid solution, can be represented by _{Ti 1-x Zr x B 2} , as the range of the value of x is 0.02 to 0.25, more preferably 0.02
~ 0.10. When the predetermined amount of solid solution of ZrB ₂ in TiB _2, TiB ₂
Hardness can be significantly improved as compared with a single body, but when x is less than 0.02, the solid solution effect of Zr is poor and sufficient hardness cannot be achieved, and when x exceeds 0.25, the matrix carbonization The coefficient of thermal expansion is very different from that of silicon, so that when sintering a composite material, it is difficult to obtain a relative density of 99% or more in theoretical density and the fracture toughness value is lowered, which is not preferable.

The sintered body according to the present invention contains 20 to 70% by volume of the Ti _1-x Zr _x B ₂ solid solution. However, if it is added in an amount of more than 70% by volume, the residual stress due to the particle dispersion becomes excessive and the toughness value becomes low. It greatly decreases, and the fracture resistance decreases. On the other hand, if it is less than 20% by volume, sufficient contribution to improvement in hardness, toughness and thermal shock resistance cannot be recognized. More preferably, it is 40 to 60% by volume.

The particle diameter of the Ti _1-x Zr _x B ₂ solid solution phase to be dispersed is preferably in the range of an average crystal grain diameter of 1 to 10 μm, more preferably 3 to 5 μm. If it is smaller than 1 μm, it is difficult to obtain a contribution to toughness.
On the other hand, if it is larger than 10 μm, hardness and thermal shock resistance are reduced. Further, in the present invention, the relative density of the sintered body is set to 99% or more. However, when the relative density is less than 99%, the application of residual stress to the sintered body due to the dispersion of the Ti _1-x Zr _x B ₂ solid solution particles is not possible. It is not preferable because it becomes sufficient.

As a ceramic material, TiB
₂ , a predetermined amount of at least one of ZrB ₂ and ZrC may be added, and it is sufficient if Ti _1-x Zr _x B ₂ solid solution can be obtained as a final solid solution at the time of silicon carbide sintering, whether boride or carbide. . Silicon carbide (SiC) is a substance having a strong covalent bond, and it is difficult to sinter simply. Therefore, various additives may be added at the time of densification. As the sintering aid, boron carbide, metallic boron, carbon (such as carbon black), an organic carbon source, aluminum nitride, aluminum oxide, rare earth oxide, and the like can be used.

As the sintering method, any of a pressureless sintering method, a gas pressure sintering method, a hot isostatic press sintering method, and a hot press method can be used. It is also possible to combine a plurality of sintering methods. Pressureless sintering is performed in a vacuum or in the flow of an inert gas.
A dense sintered body is easily obtained. In order to achieve high density in a guide roller having a complicated shape, it is preferable to perform hot isostatic press sintering in an Ar gas atmosphere after sintering without pressure.

The maximum temperature range during sintering is 1950 to
The temperature is preferably 2200 ° C., and the holding time at the maximum temperature is preferably 4 hours or more. If the temperature is lower than 1950 ° C., a sufficiently high density cannot be obtained, it is difficult to generate a high residual stress in the vicinity of solid solution phase particles, and a high toughness cannot be obtained. On the other hand, if the temperature is higher than 2200 ° C., SiC is undesirably sublimated and decomposed.

The holding time during sintering is set in the above range of the sintering temperature so that the TiB ₂ powder used as a raw material and the ZrB ₂ powder react to form a stable Ti _1-x Zr _x B ₂ solid solution phase. At 4
Requires more than an hour of retention. Also used in the present invention
ZrC and ZrB ₂ are inexpensive raw materials as compared with HfB ₂ which is a ceramic raw material disclosed in Japanese Patent Application Laid-Open No. 9-278523, and can significantly reduce the raw material cost of the entire particle-dispersed silicon carbide system of the present invention. Will be possible. Moreover, since it has oxidation resistance, it is not limited to a non-aqueous dispersion medium such as alcohol or acetone as a dispersion medium at the time of powder preparation. It is easy to improve safety.

The wire rod guide roller made of the particle-dispersed silicon carbide sintered body of the present invention can be used for producing a Ti _1-x Zr _x B ₂ (0.02 ≦ _m ) having an average diameter of 1 to 10 μm in a silicon carbide (SiC) sintered body. x ≤0.2
5) Titanium boride-zirconium boride solid solution particles represented by the following formula are dispersed in a volume fraction range of 20 to 70%, and the relative density is
99% or more of the particle-dispersed silicon carbide-based sintered body, by a combination of these requirements, the guide roller obtained from the sintered body has high hardness, high toughness, high thermal shock resistance,
In addition, it has high wear resistance, chipping resistance, oxidation resistance, and long-term reliability.

[0022]

Next, examples of the present invention will be described together with comparative examples.
You. (Examples 1 to 5) Silicon carbide (SiC) powder (α type, purity 99%,
Titanium boride (TiB _Two) Powder (average particle size
4 μm), zirconium boride (ZrB_Two) Powder (average particle size 2 μm)
Or zirconium carbide (ZrC) powder (average particle size 2 μm),
Boron carbide (B_FourC) powder (average particle size 1.5 μm) and carbon
(C) Powder (average particle size 0.02 μm) was added to a specified amount (Table
Weight%), and acetone and purified water were used as dispersion media.
Kneading for 24 hours in a ball mill with silicon carbide
Was. The amount of acetone and purified water added is
The amount was 100 g with respect to 100 g of the raw material.

Next, the obtained mixed powder was molded and sintered. As the molding conditions, pressurization by cold hydrostatic pressure 150MPa
A donut-shaped molded body having an outer diameter of 70 mm, an inner hole diameter of 30 mm, and a thickness of 35 mm was obtained. The sintering conditions were as follows: During Ar gas circulation, after pressureless sintering at the temperature shown in Table 1 for 8 hours,
Similarly, at the temperature shown in Table 1 and in a high-pressure Ar gas atmosphere.
Hot isostatic pressing (HIP) sintering for 3 hours was performed.

From the obtained sintered body, a ball bearing having an outer diameter of about 56 mm, an inner diameter of about 28 mm, a thickness of about 25 mm, a caliber surface angle of 142 mm, and an outer diameter of 35 mm on the inner side of the guide roller can be arranged in the thickness direction. The various guide rollers were ground and subjected to a wire rolling test. Test pieces of various shapes were cut out from the obtained sintered body, and the mechanical properties were evaluated. Hardness was measured as Vickers hardness at an indentation load of 10 kg.
Regarding toughness, the fracture toughness value K _IC was measured at room temperature by the SEPB method of JIS R1607. The thermal shock resistance was evaluated by heating the bending test piece to a predetermined temperature in the atmosphere, then quenching it in water, and determining a quenching temperature difference ΔT at which the bending strength starts to deteriorate. The sintered body density was measured as a relative density by the Archimedes method.

The particle size and volume fraction of the Ti-Zr-B solid solution are as follows:
Optical microscope image of a mirror-polished surface of the sintered body (50 magnification)
(× 0), the particle diameter of 30 or more particles and the particle area fraction in the photographing surface were measured and expressed as an average value. Also,
The x value of Ti _1-x Zr _x B ₂ (hcp structure) was determined by high frequency plasma emission spectroscopy (ICP) analysis. Further, using X-ray diffraction, TiB ₂ , ZrC and ZrB ₂ in the raw material powder stage before mixing,
The solid solution in the sintered body was measured, and it was confirmed that Zr was dissolved in TiB ₂ after sintering.

Table 2 shows the properties of each of the obtained sintered bodies together with the particle size, volume fraction, x value, and relative density of the Ti-Zr-B solid solution. In the rolling test, ordinary steel was used as the material to be rolled, and the initial billet shape was about 120 mm □ × about 18 m in length and about 2 tons in weight, the wire temperature during rolling was about 1000 ° C, and the passing speed was about 60 m /
Rolling was performed under the conditions of seconds to produce a wire rod having a shape of φ5.5 mm and a length of about 12 km after rolling. As a guide roller before the final rolling roll, one set of two for each grade is arranged,
After passing a total of 160 tons (2 tons of billet x 80), the depth of the wear mark generated on the roller caliber part h
Was measured with a surface roughness meter. In addition, the presence or absence of damage around the wear mark, the chipping depth, and the crack depth were evaluated by fluorescence inspection and optical microscope observation of the polished cross-section surface. The required amount of grinding of the roller caliber surface during reuse is 1.2 times the wear mark depth h if no cracking or chipping damage is observed around the wear mark, and 1.2 times the chipping depth if chipping has occurred. Double and
If cracks have occurred, the crack depth shall be 1.2 times the crack depth.
2 Shown in the table. (Comparative Examples 6 to 11) Comparative Examples 6 to 8 were prepared with acetone using the same raw materials as in Examples 1 to 5, but each had a volume ratio of 70.
% (Comparative Example 6), when the sintering conditions were inappropriate and the relative density was less than 99% (Comparative Example 7), the dispersed particle diameter was 10 μm.
(Comparative Example 8). Comparative Examples 9 and 10
Is obtained by dispersing the same Ti-Hf-B solid solution particles as in JP-A-9-278523, Comparative Example 9 uses acetone as a non-aqueous dispersion medium, and Comparative Example 10 disperses water. This is an example in which the medium is used. Comparative Example 11 is a silicon carbide sintered body without particle dispersion. These are also shown in Table 1. The materials of these comparative examples were also subjected to a passing test under the same conditions as in Examples 1 to 5, and the results are shown in Table 2.

[0027]

[Table 1]

[0028]

[Table 2]

As shown in Table 2, according to the embodiments of the present invention, the wear trace depth was very small, 40 μm or less after passing 160 tons of wire, and the wear trace depth was around the wear trace. No crack or chipping loss is observed in any case, and the wear resistance and the chipping resistance are both excellent.However, each roller of the comparative example has a larger wear mark depth than the examples of the present invention, or It was confirmed that at least cracking and chipping occurred, and both abrasion resistance and chipping resistance were not achieved. As shown in Comparative Example 10, in the water preparation of a system in which the Ti-Hf-B solid solution is dispersed, an oxide is formed on the surface of the HfB ₂ layer during the preparation, and the oxide is decomposed and volatilized during firing, Fire cracking was caused.

Further, the required amount of grinding of the roller caliber surface when the guide roller is repeatedly reused is less than 48 μm according to the present invention, whereas each roller according to the comparative example has a smaller cracking / chipping area. The amount of grinding required for removal is as large as 87 μm or more. Considering the processing cost at the time of re-grinding and the total life of the product including repeated use, it was confirmed that the guide roller made of the sintered body of the present invention was advantageous.

[0031]

ZrC and ZrB ₂ to be used in the present invention exhibits, JP
Hf which is a ceramic raw material disclosed in JP-A-9-278523
Compared to B _2, inexpensive raw material of about 1/10, it becomes possible to suppress the material cost of the whole particles dispersed silicon carbide to less than 1/2. Further, it becomes possible to prepare an aqueous system which can significantly reduce the cost and danger at the time of preparing the powder, and the production cost can be further reduced.

The wire rolling guide roller made of the particle-dispersed silicon carbide sintered body obtained by the present invention has high hardness, high toughness, high thermal shock resistance, and high oxidation resistance, and has high wear resistance as described above. It has become possible to improve the fracture resistance while maintaining the properties. This makes it possible to produce a wire rolling guide roller having extremely excellent long-term reliability at low cost, and its industrial utility is very large.

[Brief description of the drawings]

FIG. 1 is an assembled side view of a wire rod guide roller used in a rolling test.

[Explanation of symbols]

 1… Wire rolling guide roller 2… Material to be rolled (metal wire such as iron) 3… Abrasion trace of roller caliber 4… Tipping 5… Crack

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Atsushi Aoyama 23-15 Suzukocho, Kamaishi City, Iwate Prefecture F-term in Kamaishi Works, Nippon Steel Corporation (reference) 4G001 BA22 BA23 BA26 BA44 BA45 BA60 BB22 BB43 BB44 BB45 BB60 BC12 BC13 BC43 BC56 BC57 BC73 BD04 BD12 BD16 BE11 BE22 BE33

Claims (2)

[Claims] 1. The method of claim 1, wherein the silicon carbide (SiC) sintered body has an average diameter of 1 to
Titanium boride-zirconium boride solid solution particles represented by 10 μm Ti _1-x Zr _x B ₂ (0.02 ≦ x ≦ 0.25) have a volume fraction of
A particle-dispersed silicon carbide-based sintered body dispersed in a range of 20 to 70% and having a relative density of 99% or more. 2. A wire rolling guide roller formed by molding and processing the particle-dispersed silicon carbide-based sintered body according to claim 1.