JP5858363B2 - Substrate for cutting tool and surface-coated cutting tool including the same - Google Patents

Description

  The present invention relates to a substrate for a cutting tool and a surface-coated cutting tool including the same.

  Conventionally, a cutting tool made of a cemented carbide such as a WC-Co alloy or an alloy obtained by adding a carbonitride such as Ti, Ta, or Nb to a WC-Co alloy is used for cutting of general steel or cast iron. Has been. However, since the cutting edge of such a cutting tool becomes a high temperature of 800 ° C. or higher during the cutting process, there is a problem of plastic deformation. As a result, remarkable flank wear may occur.

Therefore, in order to solve such a problem, the carbide, nitride, or carbonitride (such as TiC, TiN, or TiCN) of Group 4 element of the periodic table, or Al ₂ is applied to the surface of the cutting tool. A surface-coated cutting tool in which a coating layer composed of a single layer of hard ceramics such as O ₃ or a composite layer thereof has been proposed and used. In general, these coating films are formed by a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method such as an ion plating method or an ion sputtering method. It has been.

  Among the coating films formed by these methods, especially the coating film formed by chemical vapor deposition has relatively high adhesion to the base material of the cutting tool made of cemented carbide, and has high wear resistance. It was excellent. However, the coating film tends to be thicker due to the recent demand for high-speed cutting and high efficiency, but the thickening of the coating film causes a decrease in adhesion to the substrate. This is the reason why the thickness of the coating layer of cutting tools generally used at present is in the range of about several μm to about several tens of μm. That is, as the thickness of the coating film increases, the wear resistance is expected to improve, but abnormal damage due to poor adhesion to the base material is feared.

  Under such circumstances, various techniques for improving the adhesion between the substrate and the coating film have been proposed. For example, in Japanese Patent Laid-Open No. 2000-212743 (Patent Document 1), the surface of a base material such as cemented carbide is subjected to electropolishing instead of mechanical polishing to machine the hard phase particles of the base material. Thus, the adhesion between the base material and the coating film is improved so as not to cause cracks.

  In JP 2008-238392 A (Patent Document 2), by performing shot blasting after brush polishing, the hard phase portion of the surface of the substrate is smoothed and the binder phase portion is removed. By forming the recess, the direction of crystal growth of the coating film is controlled. Thereby, the direction of crystal growth of the columnar structure of the coating film can be controlled, the toughness of the coating film is enhanced, and the adhesion between the substrate and the coating film is improved.

Japanese Patent Application Laid-Open No. 2000-212743 JP 2008-238392 A

  In Patent Document 1, although improvement in the adhesion between the base material and the coating film is expected to some extent, there is a problem that the adhesion is still low when cutting intermittently in high-speed machining and high-efficiency machining. . Further, in Patent Document 2, when cutting is performed intermittently by high-speed machining and high-efficiency machining, stress at the time of cutting is concentrated in a recess formed by removing a part of the binder phase, so that it is partially sudden. There was a problem that a deficiency was likely to occur.

  This invention is made | formed in view of such a situation, The place made into the objective is the base material for cutting tools excellent in adhesiveness with a coating film, and the surface coating cutting tool using the same. It is to provide.

  As a result of intensive studies to solve the above problems, the present inventor has improved the adhesion between the two by controlling the structure of the surface of the base material constituting the interface with the coating film. The knowledge that it has a great influence is obtained, and the present invention has been completed by further research based on this knowledge.

  That is, the present invention relates to a base material for a cutting tool, and the base material is made of a cemented carbide and includes a rake face and a flank face, and an arbitrary normal line on the rake face and the flank face. In a cross section obtained by cutting the base material along a plane including any normal line above, from a ridge where the rake face and the flank face intersect to a point 100 μm away from the rake face side and the flank face side, respectively. In the region near the edge of the blade edge that is the region, the first region from the surface of the base material to a depth of 0.5 μm toward the inside has a defect density of less than 0.05 / μm, and the surface of the base material The second region having a depth of 0.5 μm or more and 7 μm or less from the inside toward the inside has a defect density of 0.05 / μm or more and less than 1 / μm.

  Here, the second region preferably has a defect density of 0.07 / μm or more and less than 0.5 / μm. The cemented carbide preferably contains a hard phase and a binder phase.

  A surface-coated cutting tool according to the present invention includes the above-described base material for the cutting tool and a coating film formed on the base material. The coating film is composed of one or more layers, and the layers are composed of Group 4 elements (Ti, Zr, Hf, etc.), Group 5 elements (V, Nb, Ta, etc.), Group 6 of the periodic table. A compound of one or more elements selected from the group consisting of elements (Cr, Mo, W, etc.), Al, and Si and one or more elements selected from the group consisting of carbon, nitrogen, oxygen, and boron; Preferably, the coating film has a thickness of 2 μm or more and 30 μm or less.

  The base material for a cutting tool of the present invention has an extremely excellent effect of having excellent adhesion to the coating film formed on the surface thereof by having the above-described configuration. Therefore, the surface-coated cutting tool in which the coating film is formed on the surface of the substrate of the present invention achieves a long life in the cutting process.

Hereinafter, the present invention will be described in more detail.
<Base material for cutting tools>
The base material for a cutting tool of the present invention is made of a cemented carbide and includes a rake face and a flank face, and includes any normal line on the rake face and any normal line on the flank face. In the cross-section obtained by cutting the base material in a plane, in the vicinity of the edge of the cutting edge ridge line, which is a region from the ridge where the rake face and the flank face intersect each other to the rake face side and the flank face side by 100 μm, The first region having a depth of 0.5 μm from the surface of the substrate toward the inside has a defect density of less than 0.05 / μm, and has a depth of 0 from the surface of the substrate toward the inside. The second region of 5 μm or more and 7 μm or less has a defect density of 0.05 / μm or more and less than 1 / μm.

  As described above, by reducing the defect density in the first region which is the outermost surface portion of the base material, it is possible to dramatically reduce the damage to the coating film formed on the base material. The knowledge that damage to the coating film that occurs at the time of cutting, etc. occurs starting from defects on the outermost surface of the base material has been obtained by our study, and the defect density is reduced based on this knowledge. It has been made.

  Furthermore, by making the defect density in the second region higher than the defect density in the first region, even if damage such as a crack occurs in the coating film, the crack is prevented from propagating by the defect in the second region. It has become possible to prevent the crack from extending to the inside of the base material. Thereby, the fracture resistance is improved.

  That is, by controlling the defect density in the first region and the second region in this way, the adhesion between the substrate and the coating film is dramatically improved.

  Here, the reason why the region near the edge of the blade edge in the cross section is the region that is most involved in cutting during the cutting process, and the coating film is easily damaged or cracked. The reason why the depth of the first region is defined to be up to 0.5 μm (that is, less than 0.5 μm) is because the region is considered to be a starting point of damage occurring in the coating film. The reason why the depth of the second region is defined as 0.5 μm or more and 7 μm or less is to balance the region that is the starting point of damage generated in the coating film and the region that prevents the propagation of cracks in a well-balanced manner. .

  When the defect density in the first region is 0.05 pieces / μm or more, it is not possible to effectively prevent damage to the coating film starting from the defects. The defect density in the first region is more preferably less than 0.03 / μm, and the density is preferably as low as possible. For this reason, the defect density is ideally set to 0 / μm.

  Further, if the defect density in the second region is less than 0.05 / μm, the propagation of cracks cannot be sufficiently suppressed, and if it exceeds 1 / μm, the strength of the substrate itself is lowered. The defect density in the second region is more preferably 0.07 / μm or more and less than 0.5 / μm.

  In addition, it is preferable that the defect density in a region deeper than the second region (that is, the internal region of the base material) is less than 0.05 / μm. This is because if the defect density exceeds 0.05 / μm, the strength of the base material itself decreases.

  The plane including any normal on the rake face and any normal on the flank is normally a plane along the thickness direction of the coating film when the coating film is formed, It is a plane perpendicular to the substrate surface. The defect density of the base material targeted by the present invention is 100 μm away from the ridge where the rake face and the flank face intersect each other on the rake face side and the flank face side in the cross section cut by the plane. This is the defect density in the vicinity of the edge of the cutting edge, which is the area up to the point. This is because, as described above, the coating film is easily damaged or cracked in the vicinity of the edge of the blade edge.

  If the ridge where the rake face and the flank face intersect is honed or chamfered, and no clear ridge is formed, the rake face and flank face A virtual ridge formed by virtually extending each surface is regarded as “a ridge where a rake surface and a flank intersect”. In other words, even if the ridge where the rake face and the flank face intersect is subjected to a honing process or a chamfering process, a clear ridge is not formed. It does not depart from the scope of the invention.

  And the defect density in this invention can be calculated | required concretely as follows. That is, first, an ion etching process using an argon ion beam is performed on a cross section obtained by cutting the base material on the plane as described above, and then the cross section is processed at a magnification of 40000 times using a field emission scanning electron microscope. Observe in secondary electron image mode. This observation is performed over a length of 100 μm in the vicinity of the edge of the edge of the blade, and the number of defects in each of the first region and the second region is measured, and the number is divided by the length of 100 μm to obtain the defect density. Note that this observation may be performed at any one position in the vicinity of the edge of the blade edge on the surface portion of the substrate as long as the length of the observation region is 100 μm. This is because, by setting the observation region to 100 μm, the entire surface portion of the base material (region near the cutting edge ridge line) is usually reflected. In this regard, the above-mentioned planes exist innumerably per base material, but the section cut by any one of the planes satisfies the provisions of the present invention as long as the defect density is satisfied. To do.

  In addition, the defect in this invention means a cavity or a hole. The shape of the cavity or hole is not particularly limited. For example, the shape in which the diameter gradually increases from the surface of the base material toward the inside of the base material, or conversely, the diameter is narrowed, or the diameter is constant and the diameter is constant. Can be mentioned. Further, the size is not particularly limited, and examples thereof include a diameter (width, length in a direction substantially parallel to the substrate surface) of about 0.1 to 3 μm.

  In addition, when the cutting tool is a cutting edge replacement type cutting tip or the like, such a substrate includes those having a chip breaker and those having no chip breaker, and the cutting edge ridge line portion has a sharp edge ( Any of the ridges where the rake face and the flank face intersect), honing (sharp edges are given), negative lands (chamfered), and a combination of honing and negative lands.

<Cemented carbide>
The base material for a cutting tool of the present invention is composed of a cemented carbide. Any conventionally known cemented carbide can be used, but a cemented carbide containing a hard phase and a binder phase is preferred.

  Here, as the hard phase, one or more compounds selected from the group consisting of carbides, nitrides, and carbonitrides of group 4 elements, group 5 elements, or group 6 elements of the periodic table, tungsten carbide, It is preferable to contain. The hard phase is also preferably made of tungsten carbide.

  Examples of carbides, nitrides, and carbonitrides of Group 4 element, Group 5 element, or Group 6 element of the periodic table include TiC, TiN, TiCN, TaC, TaN, TaCN, NbC, NbN, NbCN, ZrC, ZrN, ZrCN, VC, VN, VCN, CrC, CrN, CrCN and the like can be mentioned.

  The binder phase preferably contains one or more elements selected from the group consisting of iron, cobalt, and nickel.

<Surface coated cutting tool>
The present invention also relates to a surface-coated cutting tool, and the surface-coated cutting tool of the present invention includes the above-described base material for a cutting tool and a coating film formed on the base material.

  Examples of such a surface-coated cutting tool include a cutting edge replacement type cutting tip for drill, a cutting edge replacement type cutting tip for end mill, a cutting edge replacement type cutting tip for milling, a cutting edge replacement type cutting tip for turning, and the like.

  In the surface-coated cutting tool of the present invention, it is preferable that the coating film covers the entire surface of the base material. However, a part of the base material is not coated with the coating film or the coating film is partially configured. Even if they are different, they do not depart from the scope of the present invention. Such a coating film can be formed of one or more layers.

<Coating film>
Said coating film is formed in order to improve various characteristics, such as abrasion resistance as a cutting tool, and chipping resistance, and to provide the discriminability of a used cutting edge. As such a coating film, a conventionally known coating film formed on the surface of the base material of this type of surface-coated cutting tool can be employed without any particular limitation, and it is composed of one or more layers. can do.

Such a layer is not particularly limited in its chemical composition, but one or more selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, Al, and Si in the periodic table And a compound of one or more elements selected from the group consisting of carbon, nitrogen, oxygen, and boron. Such compounds, for example TiC, TiN, TiCN, TiNO, TiCNO, TiB 2, TiO 2, TiBN, TiBNO, TiCBN, ZrC, ZrO 2, HfC, HfN, TiAlN, AlCrN, CrN, VN, TiSiN, TiSiCN AlTiCrN, TiAlCN, ZrCN, ZrCNO, Al ₂ O ₃ , AlN, AlCN, ZrN, TiAlC, NbC, NbN, NbCN, Mo ₂ C, WC, W ₂ C and the like.

  The thickness of such a coating film is not particularly limited, but can be 2 μm or more and 30 μm or less, more preferably 4 μm or more and 25 μm or less. In addition, such a coating film can employ a conventionally known formation method (film formation method) such as a physical vapor deposition (PVD) method or a chemical vapor deposition (CVD) method without any particular limitation. It is preferable to form by a method. This is because when the chemical vapor deposition method is employed, the film forming temperature is relatively high as 800 to 1050 ° C., and the adhesiveness to the substrate is excellent even when compared with the physical vapor deposition method.

<Manufacturing method>
The base material for a cutting tool of the present invention can be produced as follows.

  First, a base material made of a cemented carbide is prepared by sintering raw materials. Subsequently, a honing process is performed on a region including at least a region in the vicinity of the edge of the blade edge of the base material using a brush or a plastic medium. This honing process can be performed by a general method using a brush or the like.

  Next, a shot peening process in which fine particles collide is performed on the region subjected to the honing process. By this shot peening treatment, nuclei for forming defects in the region can be formed. The fine particles (media) used for the shot peening treatment preferably form defects nuclei and can reduce damage to the substrate as much as possible. preferable. As such fine particles, for example, fine particles of alumina or zirconia are suitable. In addition, as conditions for this shot peening treatment, it is preferable that the projection pressure is 0.05 to 0.30 MPa and the projection time is 1 to 10 seconds.

  Subsequently, the substrate that has been subjected to the above-described treatment is immersed in an alcoholic solution and subjected to ultrasonic treatment that irradiates ultrasonic waves. If this ultrasonic treatment is not performed, defects cannot be formed. Therefore, the defect density as described above cannot be obtained. The conditions for this ultrasonic treatment are preferably 10 to 30 minutes by immersing the base material in an alcohol solution, setting the ultrasonic frequency to 10 to 40 kHz, and setting the output to 500 to 1000 W. By the above processing, the defect density of the first region and the second region of the base material can be 0.05 / μm or more and less than 1 / μm.

Subsequently, the base material subjected to the above treatment is set in a sintering furnace, and 5 to 15 Pa in a mixed gas atmosphere (for example, Ar / CH ₄ = 9/1 volume ratio) in an atmosphere of 5 to 15 Pa. After holding for 20 minutes, a high-temperature quenching treatment is performed in which the temperature is cooled to room temperature at a rate faster than 30 ° C./min (preferably at a rate of 50 to 70 ° C./min). By this high-temperature rapid cooling treatment, the cobalt layer oozes out on the surface of the substrate, so that the defect density in the first region can be lowered and the defect density in the second region can be appropriately made higher than that in the first region. That is, by this high-temperature rapid cooling treatment, the defect density of the first region of the base material is set to less than 0.05 / μm, and the defect density of the second region is set to 0.05 / μm or more and less than 1 / μm. Therefore, the base material for the cutting tool of the present invention can be obtained. In addition, it replaces with this high temperature rapid cooling process, and also forms the cobalt layer on the base-material surface by PVD method, The defect density of the base material for cutting tool of this invention (namely, 1st area | region and 2nd area | region) Range).

  In addition, when setting it as the surface covering cutting tool using the base material for such a cutting tool, a coating film is formed on the surface of the base material which passed through said process. This coating film can be formed at a temperature of 800 ° C. or higher and 1050 ° C. or lower by using a chemical vapor deposition method, for example, by setting a substrate that has undergone each treatment in the chamber as described above.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
A raw material powder having a composition consisting of 88.5% by mass of WC, 8.5% by mass of Co, 2.0% by mass of TiC, and 1.0% by mass of TaC is sufficiently mixed and then desired. A cutting tip having a shape of “CNMG120408” (JIS B 4120 (1998)) was produced by press-molding to a shape and then sintering at 1500 ° C. for 0.5 hours in a vacuum atmosphere. Was used as a base material made of cemented carbide. A total of three substrates were prepared.

  And the honing process was performed with respect to the area | region including the blade edge ridgeline vicinity area | region of each base material on the conditions that rotation speed is 1500 rpm and incision is 3.0 mm using the brush which the SiC particle disperse | distributed.

  Next, shot peening treatment was performed on the region of each substrate subjected to the above honing treatment using an alumina medium having a diameter of 80 μm under the conditions of a projection pressure of 0.20 MPa and a projection time of 3 seconds.

  Subsequently, each substrate that had undergone the above treatment was immersed in an alcoholic solution, and was subjected to ultrasonic treatment under the conditions of a frequency of 25 kHz, an output of 700 W, and 20 minutes.

Subsequently, each base material that has undergone the above treatment is set in a sintering furnace and held in a mixed gas (Ar / CH ₄ = 9/1 volume ratio) atmosphere at 1400 ° C. and 10 Pa for 10 minutes. A base material for a cutting tool according to the present invention was obtained by performing a high-temperature rapid cooling treatment in which cooling was performed to room temperature at a cooling rate of ° C / min.

Subsequently, a 0.3 μm TiN layer, a 10.2 μm TiCN layer, a 4.2 μm Al ₂ O ₃ layer, and a 0.8 μm TiN layer are formed on the surface of each substrate thus obtained. Are formed in this order by a CVD method under a conventionally known condition to form a coating film on the substrate, thereby including the substrate and the coating film formed on the surface thereof. A cutting tool was produced.

<Examples 2-3 and Comparative Examples 1-4>
In Example 1, the same as in Example 1 except that the presence or absence of shot peening treatment, the presence or absence of ultrasonic treatment, and the cooling rate of high-temperature quenching treatment are the conditions described in Table 1 below. A base material for three cutting tools was obtained, and a surface-coated cutting tool using the base material was prepared.

  In Table 1, when the shot peening process is “present”, it indicates that the same shot peening process as in Example 1 was performed, and when “no”, the shot peening process was not performed.

  Similarly, “Yes” indicates that the same ultrasonic treatment as in Example 1 was performed, and “No” indicates that the ultrasonic treatment was not performed. The high temperature rapid cooling process indicates each cooling rate.

<Section observation>
Using each one of the surface-coated cutting tools of each Example and each Comparative Example obtained above, each in any plane including any normal on the rake face and any normal on the flank After cutting the surface-coated cutting tool (base material) and subjecting the cross section to ion etching using an argon ion beam, the processed cross section is subjected to a field emission scanning electron microscope (trade name: “SU6600”, Hitachi High-Technologies Corporation). In the secondary electron image mode at a magnification of 40000 times.

  The observation was performed over a length of 100 μm in the vicinity of the edge of the blade edge, and the number of defects in the first region and the second region was measured. Then, the defect density in the first region and the second region was calculated by dividing the number of measured defects by a length of 100 μm. The results are shown in Table 1 below.

<Evaluation>
The surface-coated cutting tools obtained in the above examples and comparative examples were evaluated by performing the following two types of cutting tests. The results are shown in Table 1 below. One surface-coated cutting tool was used for each cutting test.

<Cutting test 1: Abrasion resistance evaluation>
Work material = SCM435 (JIS), Cutting speed = 280 m / min. , Feed amount = 0.3 mm / rev. Cutting was performed under the cutting conditions of cutting depth = 1.5 mm and cutting oil = wet, and wear resistance was evaluated. The flank average wear width Vb (mm) was measured when the cutting time reached 15 minutes. The smaller the flank average wear width Vb, the better the wear resistance.

<Cutting Test 2: Fracture Resistance Evaluation>
Work material = SCM435 (JIS) grooved material, cutting speed = 150 m / min. , Feed amount = 0.25 mm / rev. Cutting was performed under the cutting conditions of cutting depth = 1.5 mm and cutting oil = wet, and the fracture resistance was evaluated. Cutting time (minutes) until chipping or chipping occurred in each surface-coated cutting tool was measured. The longer this time, the better the fracture resistance.

  As is apparent from Table 1, the surface-coated cutting tool of the example has improved wear resistance and fracture resistance compared to the surface-coated cutting tool of the comparative example, and the tool life is remarkably improved. Was confirmed. This confirmed that the surface-coated cutting tool of the present invention can sufficiently cope with high-speed machining. This is apparently due to the fact that the substrate for a cutting tool of the present invention has the configuration of the present invention, thereby improving the adhesion between the substrate and the coating film.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (6)

A substrate for a cutting tool,
The substrate is made of a cemented carbide and includes a rake face and a flank face;
The rake face side from a ridge where the rake face and the flank face intersect in a cross section obtained by cutting the base material at a plane including an arbitrary normal line on the rake face and an arbitrary normal line on the flank face. In the region near the edge of the cutting edge, which is a region up to a point 100 μm away from the flank side,
The first region from the surface of the base material to the depth of 0.5 μm toward the inner direction has a defect density of less than 0.05 / μm,
The base material for a cutting tool, wherein the second region having a depth of 0.5 μm or more and 7 μm or less from the surface of the substrate toward the inside has a defect density of 0.05 / μm or more and less than 1 / μm.   The base material for a cutting tool according to claim 1, wherein the second region has a defect density of 0.07 pieces / µm or more and less than 0.5 pieces / µm.   The base material for a cutting tool according to claim 1 or 2, wherein the cemented carbide includes a hard phase and a binder phase.   A surface-coated cutting tool comprising the base material for a cutting tool according to any one of claims 1 to 3 and a coating film formed on the base material.   The coating film is composed of one or more layers, and the layer includes at least one selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, Al, and Si in the periodic table. The surface-coated cutting tool according to claim 4, comprising a compound of an element and one or more elements selected from the group consisting of carbon, nitrogen, oxygen, and boron.   The surface-coated cutting tool according to claim 4, wherein the coating film has a thickness of 2 μm or more and 30 μm or less.