KR20050110822A - Sintered body of wc-co alloys having high toughness and heat resistance - Google Patents

Abstract

The present invention relates to a cemented carbide sintered body in which the microstructure of the sintered body is controlled to have high toughness and high heat resistance to increase chipping resistance, fracture resistance, and high temperature wear resistance during cutting, and a coated cemented carbide cutting tool based on the sintered body. .

     According to the present invention, 7 to 20 containing at least one additive containing 68 to 88% of WC and 5 to 12% of Co-bonded phase and selected from carbides, nitrides and carbonitrides of Group 4a, 5a and 6a elements of the periodic table. Carbide alloy sintered body is provided, wherein the microstructure of the cemented carbide has a combined phase frequency of less than or equal to 10 times the size of the connective tissue is 1.5㎛ or more within a predetermined range and the size of the maximum connective tissue is less than 2.5㎛, It is controlled to have the characteristic that the pure Co content in the binding phase is 65% by weight or more to increase the heat resistance and high temperature wear resistance of the tool. In addition, by controlling the area ratio of the WC phase having a diameter of 3 μm or more in the microstructure to be 80% or more of the total WC area ratio, the fracture resistance and the chipping resistance may be improved. The coated cemented carbide cutting tool made of a thin film made of a material having a higher hardness than the base metal based on the cemented carbide sintered body thus produced shows excellent cutting performance in the interrupted and continuous cutting of steel.

Description

Sintered body of WC-Co alloys having high toughness and heat resistance}

The present invention relates to a cemented carbide sintered body, and more particularly, to a cemented carbide sintered body having high toughness and high heat resistance as a cemented carbide sintered body used for tools.

Since the development of tungsten carbide (WC) and cobalt (Co) based carbide alloys in 1929 by Schrter, Germany, various methods have been studied to obtain suitable properties for various applications. Currently, tungsten carbide (WC) has been studied. Carbide alloys based on Cobalt (Co) are widely used as cutting and wear resistant tools. Cutting tools are used to cut materials such as iron and steel (alloy steel), and various base material manufacturing methods with partial high toughness and hardness have been developed, and the tool base material has been developed to improve the wear resistance and toughness of the tool. Coating cutting tools having a coating layer formed on the surface of various ceramic oxides, carbides and the like by chemical vapor deposition (CVD) or physical vapor deposition (PVD) are widely used.

      Most of the coated cemented carbide tools used in recent years are designed to improve the thin film properties coated on the tool base material in manufacturing coated cemented carbide tools according to the trend of high cutting speed and heavy cutting, such as high cutting and high feed. Technology is being developed. However, the tool substrate is mainly responsible for overcoming the impact and high temperature that occur during the actual cutting operation, and the method of improving the material properties of the tool substrate known until now, such as hard phase particle size control, additive type and content control, and binder phase content control, etc. Increasing the toughness has a trade-off problem between toughness and abrasion resistance that the wear resistance is lowered and the wear resistance is improved when the wear resistance is improved.

An object of the present invention is to solve the problems of the prior art as described above, and to properly control the microstructure of the cemented carbide sintered body, which is a coated cutting tool base material, and to optimize the microstructure size and composition of the bonding phase, toughness required for intermittent cutting And a cemented carbide sintered body having high toughness and high heat resistance which can increase tool life by increasing heat resistance and high temperature wear resistance which are essential in continuous operation.

The purpose of the above is to properly select the type, particle size and blending amount of starting materials and to apply the appropriate sintering method to improve the toughness by controlling the coarse hard phase particle size distribution of the final microstructure of the final sintered body, and to control the size and composition of the bonding phase to control the heat resistance and It can be achieved by increasing the high temperature wear resistance.

In order to achieve the object of the present invention as described above, the present invention contains 68 to 88wt% WC and 5 to 12wt% Co-bonded phase, and selected from carbides, nitrides and carbonitrides of the elements of Groups 4a, 5a and 6a of the periodic table. The cemented carbide sintered body for cutting tools which consists of an alloy containing 7-20 wt% of 1 or more types of additives to be provided is provided.

In the above additives, 7-15 wt% of one or more of carbides, nitrides, and carbonitrides of Ti and Ta metals of Group 4a, 5a, and 6a elements are included, and Groups 4a, 5a, and 6a metals except Ti and Ta are included. At least one of the carbides, nitrides and carbonitrides of 0 to 5wt% is preferably a mixed composition.

The present inventors observed the correlation between the cutting characteristics of the coated cutting tool and the microstructure characteristics of the sintered base material in order to effectively improve the above-mentioned conventional problems, and the grain size of the WC determines the cutting toughness characteristics, and the composition of the bonding phase is high temperature heat resistance. On the other hand, it was found that the size and distribution of the connective phase tissue determined the abrasion resistance, and found the most ideal microstructure characteristics as the cutting tool substrate.

      In the present invention, in order to define the microstructural properties, it is necessary to define the size of the crystal phase and the measurement area. The measurement area is obtained by scanning electron microscopy (SEM) using the microstructure of any part of the inside of the sintered body (500 µm or more from the surface). When observed at 3000 magnification, the size of 30 μm × 25 μm is defined, and an actual analysis sample photograph is shown in FIG. 2. In addition, the size of the binding phase or WC crystal phase is defined as the diameter of the largest inscribed circle inside the phase form, an example of which is shown in FIG. 3. In the following description, the predetermined area means magnification and observation area in the above-described SEM observation, and means that the binding phase or the crystal phase size is also measured in the same manner as in FIG. 3.

The cemented carbide sintered body of the present invention as described above may be manufactured by vacuum sintering or isotropic pressure sintering (HIP) to have the following microstructural characteristics, thereby improving the toughness, heat resistance, and wear resistance of the cutting tool.

       In the microstructure of the cemented carbide sintered body, the WC area ratio of 3 μm or more is preferably controlled to 80% or more of the total WC area ratio, and the diameter (inscribed circle diameter) of the bonded phase structure of FIG. 1 is 1.5 μm or more. (3) It is preferable to control the frequency so that the frequency of the maximum connective phase tissue is less than 10 times within a predetermined area and is less than 2.5 μm.

The binding phase composition for determining the heat resistance and wear resistance of the cemented carbide sintered body is preferably controlled to maintain the Co content of 65% by weight or more as a result of analysis of the central EDS composition of the bonded phase having a diameter of 1.5 ~ 2.5㎛.

In addition, it is preferable to control the surface area of the sintered surface of the cemented carbide sintered body having a rich binding phase and no cubic carbide phase to 40 탆 or less.

In addition, as a thin film applied to the cemented carbide sintered body, at least one carbide, nitride, carbonate, carbonitride, and oxide containing a group 4a, 5a, and 6a element on the periodic table, which is harder than the base metal, is used. May be used.

The reasons for the composition and microstructure characteristics of the cemented carbide sintered body as described above are as follows.

In addition, the composition% in the present invention as described above means by weight unless otherwise specified.

 When the content of WC in the starting raw material combination is 68% or less, the hardness, which is an advantage of the cemented carbide, is remarkably lowered, and when it is 90% or more, the intrinsic toughness and heat resistance of the sintered body are very poor, so that it is difficult to simultaneously improve cutting toughness and wear resistance. In addition, when the iron group bonding phase is less than 5%, it is difficult to obtain a dense sintered body due to lack of a liquid volume ratio during liquid phase sintering, and when it exceeds 12%, a sharp decrease in wear resistance during cutting is caused. In addition, if the carbides, nitrides and carbonitrides of Group 4a, 5a and 6a elements used as additives are less than 7%, it is difficult to improve the heat resistance and abrasion resistance, and if it exceeds 20%, the physical properties of the entire sintered body are deteriorated due to the poor self-characteristics compared to WC. Let's go.

Herein, carbides, nitrides, and carbonitrides containing Ti and Ta among the 4a, 5a, and 6a elements are particularly excellent in improving heat resistance of cemented carbide, and a combination of carbides, nitrides, and carbonitrides containing Ti and Ta is 7 When added in an amount of ~ 15% by weight, the high temperature properties of the sintered body are the best, and carbides, nitrides and carbonitrides of 4-5, 5a and 6a group elements of 0-5% except Ti and Ta are included to improve the properties such as hardness. Can be.

The sintered body of the present invention is preferably manufactured by the vacuum sintering or isotropic pressure sintering (HIP) method to have the following microstructural characteristics using the blending composition as described above.

 In the microstructure of the cemented carbide sintered compact, the WC size is preferably 80% or more of the total WC area ratio of the crystal phase ratio of 3 µm or more, which results in a decrease in toughness of the sintered compact and fineness. This is because connective tissue in the tissue is difficult to control small and thin.

 Another large factor influencing cutting performance in the microstructure of the sintered body is the composition and size of the connective phase tissue, with the frequency of the combined phase in which the size of the bonded phase tissue is 1.5 µm or more frequently more than 10 times in the predetermined zone. If the lowering of the heat resistance characteristics, the high temperature wear resistance is lowered. In a similar context, it is important to control the size of the maximum connective phase tissue to not exceed 2.5 μm.

 The binding phase composition directly affects the high temperature properties of the sintered body.In the analysis of the binding phase with a diameter of 1.5 µm or more, when the Co content is less than 65% by weight, the melting point and softening point of the bonding phase are low, resulting in plastic deformation at the cutting temperature. It is difficult to achieve an improvement in cutting tool life. Therefore, as described above, elements that effectively increase the strength without lowering the melting point of the bonding phase are particularly suitable for Ti and Ta among Group 4a, 5a, and 6a elements, and the sum of carbides, nitrides, and carbonitrides containing them is 7 to 15% by weight. A case containing% is most suitable for maintaining high temperature characteristics and bonding phase strength.

 In vacuum and isostatic pressing sintering of cemented carbide containing nitride, a surface area (CFL: Cubic Phase Free Layer) is formed on the sintered surface of the sintered body with a rich binding phase and no cubic carbide phase. Its role is to improve the toughness, but if its thickness is more than 40 μm, the thick surface area is first deformed before being affected by internal tissue properties during cutting operations, leading to severe degradation of cutting tool wear resistance.

The thin film coated on the sintered body of the present invention as a base material is coated by a conventional CVD method. For example, as a first layer, Ti (C _x N _y ) (x + y = 1) having a thickness of 0.1 to 2.0 μm, and a second layer The layer is MT-Ti (CN) or MT-Ti (B _x C _y N _z ) with a thickness of 0.5 to 15 μm coated by medium temperature chemical vapor deposition (700 to 950 ° C.), and the upper layer is alumina with a thickness of 0.5 to 5 μm. (Al ₂ O ₃ ) thin film and outermost thin film, 0.1 to 2.0 μm thick, consisting of carbides, nitrides, carbonates, carbonitrides, and oxides of groups 4a, 5a, and 6a of the periodic table, or may include their solid solution It can be coated with a thin film.

EXAMPLE

The sintered body having the composition and the characteristics as described above was manufactured by sintering the sintered body having different microstructure characteristics and applied to the thin film prepared by the conventional CVD method as a base material was subjected to a cutting test. The first thin film is Ti (CN), 0.5μm thick, the second layer is MT-Ti (BCN), 8μm thick, coated by medium temperature chemical vapor deposition (700 ~ 950 ℃), and the third layer is 4μm thick alumina (Al ₂ O ₃ ) and the outermost shell used TiN having a thickness of 0.2 μm.

      After 500 micrometers or more of mirror polishing of the sintered compact was carried out, the microstructure of the surface part and the polishing surface was observed using the scanning electron microscope (SEM). The particle size and area ratio of WC, binding phase and added carbonitride in the microstructure were measured using an image analyzer, and the content of pure Co in the binding phase was analyzed using EDS.

      The cutting test was carried out in the following manner, the composition and the sintering method of the sintered body are summarized in Table 1, and the results of microstructure and cutting performance in Table 2.

(1) Cutting conditions (wear resistance)

 Workpiece: SCM440

 Cutting speed: 180 m / min.

 Feed (feed): 0.31 mm / rev

 Depth of cut: 2.0 mm

 Cutting tip shape: CNMG120408

 Dry cutting

Evaluation: Flank wear (V _B ) measurement after 20 min cutting

(2) cutting conditions (impact resistance)

 Workpiece: SCM440-4 grooves

 Cutting speed: 150 m / min.

 Feed (feed): 0.50 mm / rev.

 Depth of cut: 2.0 mm

 Cutting tip shape: CNMG120408

 Dry cutting

 Evaluation: Time (seconds) until end of life due to damage or deformation (average values performed five times are shown in Table 2)

Table 1. Composition and Sintering Conditions of Invention and Comparative Sample

Category / Number Composition (% by weight) Sintered WC Co TaC TaN NbC Mo ₂ C WTiCN WTiC TiCN Temperature (℃) Sintering Method invent One 80 10 3 One 2 4 1450 vacuum invent 2 76 10 5 5 4 1500 vacuum invent 3 75 10 5 3 3 One 3 1500 vacuum invent 4 75 10 5 5 4 One 1450 HIP invent 5 75 10 5 5 4 One 1450 vacuum invent 6 82 9 4 One 3 One 1450 HIP compare 7 90 5 One 4 1450 HIP compare 8 85 10 One 4 1450 vacuum compare 9 80 10 5 One 4 1450 vacuum compare 10 66 14 5 3 3 One 5 3 1500 vacuum compare 11 80 10 5 One 4 1450 vacuum compare 12 80 10 5 4 One 1450 HIP

Table 2. Evaluation results of microstructure and cutting performance of the invention and comparative samples

Category / Number Microstructural Characteristics Cutting performance  3㎛ or more WC Frequency of appearance by size of binding phase Binding Phase Component Analysis CFL Wear resistance Impact resistance Area ratio (%) 1.5 ~ 2.5㎛ Over 2.5㎛ Co content (%) Thickness (㎛) Abrasion amount (mm) Endurance time (seconds) invent One 85 3 0 72 30 0.12 126 invent 2 84 3 0 71 28 0.11 140 invent 3 83 5 0 68 30 0.14 132 invent 4 82 0 0 72 18 0.11 128 invent 5 90 5 0 72 20 0.15 186 invent 6 88 4 0 68 14 0.13 143 compare 7 25 20 5 55 6 0.33 5 compare 8 85 2 0 52 21 0.14 6 compare 9 40 18 4 75 21 0.36 2 compare 10 90 2 0 72 28 0.29 One compare 11 78 8 0 66 46 0.32 10 compare 12 90 0 0 50 5 0.15 8

As shown in the invention samples 1 to 6 of Tables 1 and 2, it can be seen that the composition and the microstructure of the present invention exhibit excellent wear resistance and impact resistance. On the other hand, samples 7 and 9 had a poor WC particle size, making it difficult to control the size of the bonding phase, resulting in inferior abrasion resistance and impact resistance. Lack of (nitride) content resulted in inferior impact resistance. In addition, it can be seen that sample No. 10 with too low WC content and sample No. 11 with too large CFL thickness in the starting composition showed poor cutting performance.

      As described above, according to the present invention, an insert for a cutting tool capable of significantly increasing chipping resistance, fracture resistance, and high temperature wear resistance during cutting by simultaneously increasing toughness and heat resistance through microstructured control of the cemented carbide sintered body Can provide.

      Those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit of the invention as defined in the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a microstructure diagram of a sintered compact of the present invention taken using a scanning electron microscope (SEM).

2 is an actual microstructure analysis area diagram defined in the present invention for analyzing microstructure characteristics.

FIG. 3 is a diagram showing that the size of an inscribed circle is to be measured by drawing a virtual inscribed circle of the maximum size inside a phase shape to be measured by using the WC phase and the combined phase size measurement example.

Claims (7)

In the cemented carbide sintered body, at least one additive containing 68 to 88% of WC and 5 to 12% of Co-bonded phase and selected from carbides, nitrides and carbonitrides of Group 4a, 5a and 6a elements of the periodic table Carbide alloy sintered body characterized in that the alloy containing 20% more than 90% of the size of the binding phase in the microstructure of the sintered body has a range of 1.5㎛ ~ 2.5㎛, the pure Co content in the binder phase is 65% by weight or more. The method of claim 1, wherein the additive is 7-15% of at least one of carbides, nitrides, and carbonitrides of Ti and Ta metals of Group 4a, 5a, and 6a elements of the periodic table, and 4a, 5a, and excluding Ti and Ta. A cemented carbide sintered body characterized by at least 0% to 5% of carbides, nitrides and carbonitrides of Group 6a metals. The method of claim 1, wherein the sintered body is vacuum or high temperature isostatic pressure sintered, and any partial microstructure of 500 micrometers or more from the surface is bonded phase structure in the size range of 30 micrometers x 25 micrometers when observed by the scanning electron microscope by x3000 magnification. Cemented carbide sintered body characterized in that the diameter of the bonded phase having a diameter of 1.5㎛ or more 10 times or less and composed of a microstructure having a maximum bonded phase size of less than 2.5㎛. The cemented carbide sintered body according to claim 3, wherein the pure Co content is 65% by weight or more as a result of the EDS composition analysis of the central portion of the bonded phase having a diameter of 1.5 µm or more. The cemented carbide sintered body according to claim 3, wherein the WC area ratio having a size of 3 μm or more is 80% or more of the total WC area ratio when the scanning electron microscope is observed. The cemented carbide sintered body according to claim 1 or 2, wherein the surface portion of the sintered body has a surface area of 40 µm or less with a rich binding phase and no cubic carbide phase.       The cemented carbide sintered body according to any one of claims 1 to 6, composed of carbides, nitrides, carbonates, carbonitrides, and oxides of Groups 4a, 5a, and 6a on the periodic table, using a cemented carbide sintered body as an insert (insert). A coated cutting tool coated with a chemical vapor deposition (CVD) thin film to be included.