JPH09155415A - Ceramic roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic roller which consists of a sialon sintered compact and has excellent wear resistance. SOLUTION: This ceramic roller consists of the sialon sintered compact composed of sialon particles and grain boundary phase. The total amt. of the grain boundary phase of the sialon sintered compact is <=20wt.% and the Si, Al and Y converted to the oxides of the grain boundary phase exist within the limited regions of a triangular diagram (expressed by weight %) indicting the ternary component system of SiO2 -Al2 O3 -Y2 O3 . The porosity is <=10%, the crystal grain size is <=20μm and the surface roughness is 0.1 to 10μm. The fracture toughness value is >=5.0MPa.m<1/2> and the Vickers hardness at 800 deg.C is >=800.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling roll and a guide roller used in a hot rolling line for producing bar steel, wire rod, etc. More specifically, the present invention relates to a sialon firing having excellent hardness and high toughness. The present invention relates to a rolling roll and a guide roller (hereinafter referred to as "ceramics roller") formed of a unit.

[0002]

2. Description of the Related Art
The rolling rolls and guide rollers used in the hot rolling line for manufacturing bar steel and wire rods were mainly made of metal such as alloy steel and cemented carbide. There were problems such as short life. Therefore, as an alternative to a metal roll, a ceramic roll or roller utilizing excellent properties such as wear resistance, heat resistance, and light weight, for example, a silicon nitride ceramic roll is used or disclosed. There is.

For example, in Japanese Unexamined Patent Publication No. 62-104616, at least the contact surface with the material to be rolled has a porosity of 1
%, A guide roller for rolling is disclosed, which is formed of dense silicon nitride ceramics and has a surface roughness of the contact surface of 6 s or less. This roller limits the porosity of the roller material and the roughness of the contact surface with the material to be rolled, so that the material to be rolled adheres to the roller surface and the abrasion powder of the roller adheres to the material to be rolled, causing scratches. It is designed to prevent this. However, in the ceramic roller as described above, although the improvement in the point of preventing the material to be rolled from adhering to the roller is recognized, the strength of the roller itself, particularly the thermal shock resistance, can be considered sufficiently. Moreover, it cannot be said that the wear resistance is still sufficient, and there is room for further improvement especially in the high temperature wear resistance in consideration of the life of the roller.

Further, in Japanese Unexamined Patent Publication No. 6-277733, a ceramic roller used in a hot rolling line has a Vickers hardness of 9.0 at 800 ° C.
A hot-rolled ceramics roller made of a silicon nitride material having a GPa or higher, and a hot-rolled ceramics roller made of a silicon nitride material having a Vickers hardness of 10.0 GPa or higher at 1000 ° C. are disclosed. This technique addresses the problems of wear resistance and thermal shock resistance by using a silicon nitride material having a predetermined Vickers hardness for a roller used in a hot rolling line.

By the way, a silicon nitride (Si ₃ N ₄ ) sintered body, particularly a sialon sintered body, has attracted attention as a ceramic for high temperature, and its application to high temperature structural parts, such as automobile engine parts, has been advanced, and its toughness value has been increased. Attempts have been made to increase the However, since Si ₃ N ₄ is a compound with a strong covalent bond, it is difficult to sinter and mold Si ₃ N ₄ powder alone.
Oxides such as O, Y ₂ O ₃ and Al ₂ O ₃ are added as sintering aids for sintering, and at present, composite addition of Y ₂ O ₃ and Al ₂ O ₃ is the mainstream. SiO ₂ existing on the surface of Si ₃ N ₄ powder during sintering
And form a liquid phase in which Si ₃ N ₄ dissolves, from which S
i ₃ N ₄ is re-precipitated and densified to obtain a sintered body. The oxide added as a sintering aid partially forms a solid solution in the crystal lattice of Si ₃ N ₄ to form sialon, but since the amount of solid solution is very small, this oxide contains Si ₃ N ₄ grains. An amorphous grain boundary phase is formed in the boundary. For this reason, the obtained sintered body is columnar Si ₃ N ₄
It is composed of a two-phase mixed structure of grains or sialon grains and an amorphous grain boundary phase. Si ₃ N thus obtained
₄ The toughness value of the sintered body was not sufficient for use as a structural member.

[0006] Therefore, in increasing the toughness of this Si ₃ N ₄ sintered body, Lange et al. Have reported that the fracture toughness value increases as the amount of α-Si ₃ N ₄ in the primary raw material increases. Am.Cer
am.Soc.Bull., 62,1369,1983). Furthermore, Farber like Si ₃ N ₄
It has been reported that the larger the aspect ratio of the crystal lattice of, the higher the toughness value (Acta.Metall., 31,565-576,577-
584, 1983). Another method is to disperse hard particles such as carbides, silicides or borides of groups 4a, 5a and 6a of the periodic table in a sintered body in Si ₃ N ₄ and deflect cracks by the hard particles. The method is adopted.

However, in the method of increasing the toughness by making the Si ₃ N ₄ particles or the sialon particles themselves acicular, the toughness value is greatly affected by the characteristics of the grain boundary phase of the Si ₃ N ₄ particles as the base material. However, there was a limit in improving the toughness value. Further, even in the hard particle dispersion system, although the toughness is certainly confirmed to be improved as compared with the one which is not blended at all, for the same reason as described above, the original addition effect of the hard particles is not sufficiently exhibited, and it is defined in JIS-R1607. However, there is a problem that the fracture toughness value KIC obtained by the IF method does not exceed 5 MPa · m ^1/2 . Therefore, an object of the present invention is to optimize the composition of the grain boundary phase of the sialon sintered body and provide a ceramic roller made of the sialon sintered body having high toughness in addition to high hardness and excellent heat resistance which are the original properties of the sialon particles. To do.

[0008]

Means for Solving the Problems The present inventor has repeatedly studied the above problems from the viewpoint that the composition of the grain boundary phase and the total amount thereof are important for obtaining a high toughness sialon sintered body. As a result, in the sialon sintered body composed of sialon particles and the grain boundary phase, the total amount of the grain boundary phase is 20% by weight or less, and the sialon sintered body exhibits high toughness in a specific region of the grain boundary phase composition. I found a thing. That is, the ceramics roller of the present invention comprises a sialon sintered body composed of sialon particles and a grain boundary phase, and the total amount of the grain boundary phases is 20% by weight or less,
Si, Al, and Y converted into oxides of the grain boundary phase are SiO ₂ -Al ₂ O _3-
Point A (20,10,70), point B (20,25,55), point C (30,25,5) of the triangular diagram (shown by weight%) of Y ₂ O ₃ ternary system in FIG.
45), and is characterized by having a high fracture toughness value in addition to the high hardness of the sialon sintered body in the region surrounded by four points D (30, 10, 60). The ceramic roller of the present invention is characterized by having a porosity of 10% or less, a crystal grain size of 20 μm or less, and a surface roughness of 0.1 μm to 10 μm or less. And the ceramic roller is 5MP
It has a fracture toughness value of a · m ^1/2 or more and a Vickers hardness of 800 or more at 800 ° C.

The toughness of the sialon sintered body is greatly influenced by the properties of the main phase β'sialon and of course the second phase, the grain boundary phase. The ceramic roller of the present invention is
The sialon sintered body has a high density, high hardness, and high toughness in which the grain boundary phase composition of the sialon sintered body is limited to a specific region. In the ceramic roller of the present invention, the porosity is 10
% Or less, grain size 20 μm or less, surface roughness 0.1 μm
The reason for limiting the thickness to 10 μm or less is to impart thermal shock strength.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. The sialon sintered body forming the ceramic roller of the present invention is β
´ Sialon is the main component, and Si-Al-YO-
The grain boundary phase, which is considered to be composed of N, is present, and substantially consists of a two-phase mixed structure of sialon-grain boundary phase. Where β '
The composition of sialon is represented by the composition formula Si _6-z Al _z O _z N _8-z ,
The value of z can be in the range of 0 to 4.2, but preferably z = 0 to 1
Is appropriate. As the z value increases, the
This is because the amount of solid solution of Al and O increases, so that the sinterability decreases, and it becomes impossible to obtain a high-density sintered body that can withstand as a structural component.

According to the sialon sintered body forming the ceramics roller of the present invention, it is necessary that the total amount of the grain boundary phases is 20% by weight or less. This means that when the total amount of the grain boundary phases is 20% by weight or less. Since the grain boundary phase is dispersed and present between the sialon particles as the base material, when cracks occur, the cracks meander along the grain boundaries, whereas a sintered body having high toughness can be obtained. When it exceeds 20% by weight, a large lump of grain boundary phase with a diameter of 1 μm or more appears, and cracks do not meander at the grain boundary but go straight through the large grain boundary. Therefore, the grain boundary phase composition is optimized and the grain boundary phase is optimized. Even if the toughness is improved, the toughness is reduced.

According to the sialon sintered body forming the ceramics roller of the present invention, Si converted into oxide of the grain boundary phase,
Attached figure 1 showing Al and Y as a ternary system of SiO ₂ -Al ₂ O ₃ -Y ₂ O ₃
In the triangle diagram (expressed in% by weight) of point A (20,1)
0,70), point B (20,25,55), point C (30,25,45), point D (3
It must be in the area surrounded by 4 points (0, 10, 60). The oxide-converted Si, Al, and Y are the amounts of Si, Al, and Y contained in the grain boundary phase when present as an oxide, specifically, Si contained in the grain boundary phase, It can be determined by determining the amounts of Al and Y, and then calculating the amounts when each is an oxide.

In FIG. 1, the line segment AB indicates the position where the amount of SiO ₂ is 20%, and the line segment CD indicates the position where the amount of SiO ₂ is 30%. Also, the line segment
DA indicates an Al ₂ O ₃ amount of 10%, and line segment BC indicates an Al ₂ O ₃ amount of 25%. Line segment AB
In the lower region, the amount of SiO ₂ is small and the fracture toughness value is not improved. Further, the amount of SiO ₂ is decreased and the liquidus formation temperature is increased, which makes it difficult to densify. On the other hand, in the region above the line segment CD, the toughness value is hardly improved. Also, the line segment DA
In the region on the left side, the amount of Al ₂ O ₃ decreases, so
As in the case of iO ₂ , the liquidus formation temperature rises, making densification difficult, while the toughness value decreases in the region to the right of the line segment BC. From the above reason, it is understood that the area of the grain boundary phase composition obtained in the sialon sintered body having the sintered body density and the high toughness value that can be endured as the structural member is the area within the quadrangle surrounded by the points ABCD. It was

Next, in the production of the sialon sintered body forming the ceramics roller of the present invention, Si ₃ N is used as the raw material powder.
₄ powder, Al ₂ O ₃ powder, Y ₂ O ₃ powder, SiO ₂ powder, AlN solid solution powder or AlN powder is used. Si ₃ N ₄ powder itself α-Si ₃ N ₄
Both powder and β-Si ₃ N ₄ powder can be used, and their particle size is preferably 0.3 μm to 3.0 μm. Al
The N solid solution powder and the AlN powder are added in order to cause a synthesis reaction of β'sialon, and β'sialon is synthesized according to the reaction formula of Si ₃ N ₄ powder and a sintering aid.

[0015]

Embedded image

As described above, the synthesis reaction of sialon is carried out by the AlN powder, but the AlN solid solution powder, for example, 21R (6A
It is preferable to use AlN solid solution powder because the synthesis reaction of sialon is further promoted by using 1N · SiO ₂ ). In the ceramic roller of the present invention, using these powders, Si, Al, and Y converted into oxide of the grain boundary phase are SiO ₂ -Al ₂ O.
Point A (20,10,70), point B (20,25,5) in the triangular diagram (expressed by weight%) shown in the attached Figure 1 showing the _3- Y ₂ O ₃ ternary system.
5), point C (30, 25, 45), and point D (30, 10, 60) are weighed and mixed so that they fall within the area surrounded by 4 points, after adding an organic binder and mixing by wet method , To obtain a predetermined mixed powder. The mixed powder thus obtained is molded into a desired shape by a known molding method, for example, press molding, cold isostatic pressing or the like.

Next, the organic binder added at the time of mixing is removed from the molded body by a known degreasing method such as degreasing in the air or degreasing in the atmosphere. Next, the obtained degreased body is sintered by a known sintering method such as normal pressure sintering, gas pressure sintering, hot pressing or the like to obtain a dense sintered body. If the sintering temperature at this time is too high, a decomposition reaction of Si ₃ N ₄ occurs, so a nitrogen gas-containing non-oxidizing atmosphere at 1900 ° C. or lower, particularly 1700 to 1800 ° C. is desirable. According to this sintering, a part of the added AlN solid solution powder and Al ₂ O ₃ powder are dissolved in Si ₃ N ₄ to form β ′ sialon, but the remaining Al ₂ O ₃ and added Y ₂ O ₃ powder and SiO ₂ existing on the surface of Si ₃ N ₄ form a grain boundary phase. The grain boundary phase at this time is a composite oxide composed of SiO ₂ , Al ₂ O ₃ , and Y ₂ O _{3 as} the main components,
It is considered that a part of nitrogen also forms a solid solution and substantially forms a composite oxynitride composed of Si-Al-YON. At this time, the grain boundary phase composition is point A (20, 10, 70), point B (20, 10) in the triangular diagram (expressed by weight%) showing the ternary system of SiO ₂ —Al ₂ O ₃ —Y ₂ O ₃ twenty five,
5), point C (30, 25, 45), and point D (30, 10, 60). Nitrogen in the grain boundary phase is substituted and solid-dissolved with oxygen, but the amount is 0 to 40% by weight.

[0018]

Example 1 Si ₃ N ₄ powder (BETT specific surface area) as raw material powder
7.1m ² / g, α conversion rate 90.7%, impurity oxygen content 1.2% by weight) and Al
N solid solution powder (composition 6AlN ・ SiO ₂ , average particle size 2.5 μm), Y ₂ O
₃ powders (purity 99.9%, average particle size 1.2 μm), Al ₂ O ₃ powder (purity 99.9%, average particle size 0.6 μm), SiO ₂ powder (purity 99.8%,
Various sialon sintered bodies were obtained by using an average grain size of 1.0 μm). Sintered body is mixed with the above powder, and 16 × at a pressure of 1 ton / cm ^2.
Mold press-molded to a size of 16 x 5 mm, put the resulting molded body in a Si ₃ N ₄ crucible, and use a carbon heater in a normal pressure N ₂ gas stream at 1750 ° C for 5 hours It was obtained by sintering at.

The obtained sintered body was put in a crushing die made of cemented carbide and impact load was applied to obtain fine particles of 45 μm or less. After that, a solution in which only the grain boundary phase is selectively dissolved in 1N hydrochloric acid at 75 ° C. is analyzed by an ICP emission spectrometer SPS-1100 manufactured by Seiko Denshi Co., Ltd., and the amounts of Si, Al, and Y in the grain boundary phase are obtained. This was converted to oxide. Table 1 shows the composition of the grain boundary phase as SiO ₂ or Al.
The percentages of ₂ O ₃ and Y ₂ O ₃ and the total amount of grain boundary phases in the sintered body are shown. On the other hand, the density of the obtained sintered body was measured by the underwater substitution method, one surface of the sintered body was polished by lapping, and the fracture toughness value KIC was obtained by the indenter IF method specified in JIS-R1607. . The test load at this time was 30 kg. The results are shown in Table 1.

[0020]

Example 2 The ceramics roller of the present invention formed of a sialon sintered body was used as a copper rolling finish roll for rolling. As a result, wear resistance and skin are very good,
It was used for rolling for a long time without any problems. Further, it was also used for rolling a copper wire rod (the diameter of the wire rod is about 1 mm), and similarly, it was used for rolling without any problems. In particular, there is no problem that the wire material is damaged by the copper powder adhesion as in the case of using the chrome-plated steel roller.

[0021]

[Table 1]

According to the results shown in Table 1, all the sintered bodies within the grain boundary phase composition range (the area surrounded by ABCD in FIG. 1) have excellent fracture toughness values of 5 MPa · m ^1/2 or more. It was Further Al ₂
The region surrounded by O ₃ of 10 to 20% and SiO ₂ of 20 to 30% has a particularly excellent fracture toughness value, and both have a KIC of 6 MPa.
・ Products exceeding m ^1/2 were obtained. Since the sintered bodies of Nos. 11 to 18 are out of the range of the present invention, the fracture toughness value KIC or Vickers hardness is insufficient.

[0023]

As described in detail above, the ceramic roller of the present invention can effectively exhibit the mechanical properties of the sialon and the grain boundary phase, so that the sialon sintered body has high fracture toughness in addition to high density and high hardness. And has excellent wear resistance. For this reason, the reliability of the ceramics roller with further improved abrasion resistance is improved, and the practical use is greatly promoted.

[Brief description of the drawings]

FIG. 1 shows a composition range of a grain boundary phase in a sialon sintered body forming a ceramic roller of the present invention SiO ₂ —Y ₂ O ₃ —
FIG. ₃ is a triangular diagram of an Al ₂ O ₃ ternary system.

[Explanation of symbols]

 (None)

Claims (3)

[Claims] 1. A sialon sintered body composed of sialon particles and a grain boundary phase, wherein the total amount of the grain boundary phase is
Not more than 20% by weight and converted to oxides of the grain boundary phase
Point A (20,10,70), point B (20,25,55) in the triangular diagram of FIG. 1 in which Si, Al, and Y represent a ternary system of SiO ₂ -Al ₂ O ₃ -Y ₂ O ₂ , Point C
(30, 25, 45), D (30, 10, 60) A ceramic roller characterized by being made of a sialon sintered body in a region surrounded by four points. 2. A porosity of 10% or less and a crystal grain size of 20 μm.
The ceramic roller according to claim 1, which has a surface roughness of 0.1 μm to 10 μm. 3. A fracture toughness value of 5 MPa · m ^1/2 or more, 8
The Vickers hardness at 00 ° C. is 800 or more, and the ceramics roller according to claim 1 or 2.