JPH01140901A - Cutting tool made of ceramics - Google Patents

Abstract

PURPOSE:To enable application of the cutting tool in the caption to low speed cutting and high speed cutting of materials ranging from casting and steel to sintered hard alloy by forming the cutting tool with an alumina-silicon carbide-zirconia compound sintered compact comprising a specified percent by volume of silicon carbide and partially stabilized zirconia, and the residual percent of alumina. CONSTITUTION:A cutting tool made of ceramics is formed with an alumina- silicon carbide-zirconia compound sintered compact which comprises 5-50% by volume of silicon carbide with less than 3mum of an average particle size, 2-30% by volume of partially stabilized zirconia with 0.1-1.0mum of the average particle size (wherein the total of the zirconia and the abovementioned silicon carbide is less than 55% by volume), and a residual amount of alumina, substantially. The cutting tool made of ceramics has excellent tenacity, high hardness and abrasion resistance, and as well it exhibits excellent heat resistance and corrosion resistance, thereby enabling broad application to low speed cutting and high speed cutting of materials ranging form casting and steel to sintered hard alloy to be cut.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cutting tool, and more particularly to a throw-away tip made of ceramic that is resistant to impact and has high toughness, high strength, and high hardness.

(Prior art and problems) Conventionally, alumina (Aboz) has been used as a material for high-speed cutting tools for steel and cast iron because of its excellent wear resistance during high-speed cutting and its low coefficient of friction with iron. -Titanium carbide (Tie) ceramic cutting tools have been put into practical use and become mainstream. However, alumina-titanium carbide has poor toughness and insufficient impact resistance, so it is prone to breakage and cannot be used stably at present.

Therefore, in recent years, silicon nitride csxzNJ and alumina-silicon carbide (silicon carbide), which have excellent mechanical strength, hardness, and impact resistance, have been used as cutting tools.
SiC) whisker-zirconia (ZrO,) is attracting attention, but silicon nitride suffers from severe wear due to reaction with iron and has low versatility.
The use of the alumina-silicon carbide whisker-zirconia composite ceramics disclosed in No. 70266, which has high strength, high toughness, and high hardness, for cutting difficult-to-cut materials such as cemented carbide is being considered, and cemented carbide tools. It has also been confirmed that the cutting speed is 5 to 10 times faster than that of the conventional method.

However, when alumina-silicon carbide whisker-zirconia composite ceramics contain 15% by volume or more of silicon carbide whiskers, the presence of silicon carbide whiskers inhibits increasing the molding density, and methods other than hot pressing can easily reach a theoretical density ratio of 99. It has problems such as not being able to sinter to a high density of % or more.

Here, hot pressing is a type of accelerated sintering method in which powder is usually placed in a graphite mold and sintered while pressurized at high temperature for things that require relatively high temperatures, such as sintering ceramics. Because the pressure direction is uniaxial, products with relatively simple shapes are limited, and cutting tools require pressureless sintering/pressure sintering.
Even compared to the HIP (hot isostatic pressing, in which argon or other gas is used as a pressure medium to press isotropically at high temperature), there is a problem in that productivity is lower due to the addition of a cutting process.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems of cutting tools. Especially high strength.

As a result of extensive research and testing to improve the formability and sinterability of a highly tough alumina-silicon carbide whisker-zirconia composite sintered body, we have developed a high strength, resistant to impact.

It has been found that a highly tough alumina-granular silicon carbide-zirconia composite sintered body is suitable for this purpose.

The cutting tool of the present invention made of a high-strength, high-toughness alumina-granular silicon carbide-zirconia composite sintered body that is resistant to impact contains 5 to 50% by volume of granular silicon carbide with an average grain size of 3 μm or less; an average grain size of 0.1 ~1.0 μm partially stabilized zirconia 2-3
o volume % (however, the total of this zirconia and the granular silicon carbide is 55 volume % or less); The remainder is characterized in that it consists essentially of alumina.

Next, Kameyama will discuss limiting the range of components of a high-strength, high-toughness alumina-granular silicon carbide-zirconia composite sintered body that is resistant to impact.

When the particle size of granular silicon carbide exceeds 3 μm, the difference in thermal expansion coefficient from that of the alumina matrix (α5iC = 4
, 5 x 10-'/°C, αA1□0. =8X10-
'/'C) After sintering, microcracks are often introduced when the temperature is returned to room temperature, reducing the strength, so the thickness was set to 3 μm or less. If the amount is less than 5% by volume, the effect on cutting tool properties related to hardness and especially heat conduction will not be significant, while if it exceeds 50%, the matrix will become silicon carbide, which will cause wear due to reaction with iron-based materials. It is set in the range of 5 to 50% because it causes an increase in toughness and a decrease in toughness.

Partially stabilized zirconia is too stable if the particle size is less than 0.1 μm, whereas if it exceeds 1.0 μm, it becomes too unstable and neither contributes to strength improvement, so the particle size range is set to 0. The thickness was 1 to 1.0 μm.

If the amount is less than 2% by volume, the effect of increasing toughness will not be noticeable, and if it exceeds 30%, the hardness will decrease.
% range.

The total amount of the granular silicon carbide and zirconia is 5 by volume.
If it exceeds 5%, silicon carbide or zirconia will be added too much, and wear will increase due to reaction wear or insufficient hardness, so the total amount is set to 55% or less.

The product of this invention has excellent toughness, high hardness, and wear resistance, as well as excellent heat resistance and corrosion resistance, so it can be used in everything from castings and steels that require these properties to superalloys, which are the most difficult-to-cut materials. It can be widely applied as a cutting tool in a wide range of applications from low-speed cutting to high-speed cutting.Furthermore, the use of granular silicon carbide, which is a feature of the present invention, can increase the molding density, making it possible to use it instead of hot pressing. pressureless sintering/
HIP processing becomes possible, and manufacturing can be performed with sufficiently high productivity.

(Example) Examples of the present invention will be specifically described below.

A volume ratio of 60% alumina powder, 30% granular silicon carbide, and 10% partially stabilized zirconia was blended.

Alumina powder has a purity of 99% or more, an average particle size of 0°4 μm,
It is in α type crystal form. The granular silicon carbide is of α type crystal form and has an average particle size of 0.45 μm. The zirconia powder is partially stabilized zirconia with an average particle size of 0.2 μm stabilized with 2 mol % (3.5 wt %) ittria.

This raw material was mixed with ethyl alcohol in a ball mill using an alumina container and an alumina ball.
After 2 hours of mixing, these mixed powders were dried.

This mixed powder was molded into a disk with a diameter of 65 mm x thickness of 7 m+++ using a mold press, densified using a 2t/cm" rubber press, and then sintered at 1720°C for 3 hours in an argon gas atmosphere. 1600℃, 1.9t/Cm
HIP treatment was performed for 1 hour in an argon gas pressure of 1.

These sintered bodies were cut using a diamond grindstone and ground to JIS dimensions of 12.7 mm x 4° 76 mm.
A throw-away tip conforming to the R41215NGN433 type was created. A cutting test was conducted using this chip using a lathe under the following cutting conditions.

As a comparative product, a cutting test was conducted on a commercially available alumina-silicon carbide ceramic chip under the same conditions.

Cutting conditions Rigid material Strong cast iron (equivalent to FC30 material) H cylinder Dry inner diameter 95 + sm x length 150a + m Cutting speed 142 + * / win Feed 0, 35 am / r, p, a + depth of cut 0.25 mm Number of cuts 250 above Finish cutting was performed on the inner circumferential surface of the cylinder liner under cutting conditions, and the occurrence of chipping and changes in finished dimensions were measured to estimate the degree of chip wear and determine whether the chip life was good or bad.

The results of the cutting test are shown in Figure 1.

Furthermore, from these sintered bodies, a thickness of 2w++* x width of 3mm x
A bending test piece with a length of 13 mm was taken, the tension side surface was mirror-finished, and the following tests were conducted: (1) Bending test (2) Hardness test (3) Fracture toughness test The hardness test and fracture toughness test were performed using bending The test was carried out using the fractured material after the test.

As a comparative product, a test was conducted under the same conditions using a commercially available alumina-titanium carbide ceramic used in conventional cutting tips.

The test method was as follows.

(1) Bending test The test was conducted using a three-point bending test method based on JIS R1601 (bending strength test method for fine ceramics). Place the test piece on two points placed at a distance of 10 mm, and set the crosshead speed Q, 5H at one point in the center between the fulcrums.
A load of /a+in was applied and the maximum load until the test piece broke was measured.

(2) Hardness Test The hardness was measured using a Vickers hardness meter at a load of 20 kg.

(3) Fracture toughness test In this test, toughness was evaluated by the indentation method using a Vickers hardness meter. A load of 20 kg was used. The toughness was evaluated by determining the fracture toughness Kc. Fracture toughness Kc was calculated by Shinryo's formula.

The test results are shown in Table 1.

As a result of the cutting test in Table 1, the ceramic chips of the present invention showed no abnormality such as chipping of the four chips, and no change in dimensions.
, within 1 mm, with no problems and the finished surface was good, whereas the comparative alumina-titanium carbide ceramic chips had 3 out of 4 chips with 138 and 19 chips.
Chip defects occurred in the 6th and 248th chips. Only one piece had no damage, and the dimensional change was 0.13.
mm, which is larger than that of the inventive product, indicating that the inventive ceramic chip exhibits good impact resistance and abrasion resistance, whereas the comparative product has relatively low toughness, resulting in poor impact resistance and abrasion resistance. It is recognized that the wear resistance is poor, and the life of the ceramic chip of the present invention is significantly improved.

In addition, the test results using the test pieces are 1, as is clear from Table 1.
The bending strength is approximately the same as that of the comparative alumina-titanium carbide product, but the fracture toughness in particular is significantly improved to 6.2 MPa1 compared to the comparative product's Kc of 4.2 MPa.
It is recognized that it has excellent impact resistance. Hardness is Hv2
It has a hardness of 0.030, which is 230 higher than alumina-titanium carbide ceramics, which have excellent wear resistance.

(Effects) The ceramic cutting tool of the present invention has excellent impact resistance, high toughness, and wear resistance, and when applied to a cutting tool tip, etc., the performance was significantly improved.

Furthermore, the use of granular silicon carbide has a remarkable practical effect in that pressureless sintering/HIP processing, which can be expected to be highly productive, can be used in place of hot pressing.

[Brief explanation of the drawing]

Claims (1)

[Claims] 5-50% by volume of silicon carbide with an average particle size of 3 μm or less; 2-30% of partially stabilized zirconia with an average particle size of 0.1-1.0 μm
Volume % (However, the total of this zirconia and the silicon carbide is 55 volume % or less); A ceramic cutting tool characterized by being constructed of an alumina-silicon carbide-zirconia composite sintered body, the remainder of which is substantially alumina. .