JP5597469B2 - Cutting tools - Google Patents

Description

  The present invention relates to a cutting tool, and more particularly, to a cutting tool that exhibits excellent wear resistance when processing gray cast iron.

  As a cutting tool, a coated cemented carbide in which a coating layer is formed on the surface of a substrate such as cemented carbide or cermet to improve wear resistance, slidability, and fracture resistance is widely used.

  For example, in Patent Document 1, a coating layer including a TiCN layer is formed on the surface of a cemented carbide substrate so that the average width of TiCN crystals located on the rake face is narrower than the average width of TiCN crystals located on the flank face. Even under severe cutting conditions such as intermittent cutting of cast iron, where the tool cutting edge is subjected to a strong impact, the TiCN layer has strong adhesion on the rake face side and the wear resistance of the TiCN layer on the flank face side. It is disclosed that it can be improved.

JP 2004-216488 A

  However, in the configuration of Patent Document 1, there has been a demand for a cutting tool that can withstand even severer cutting conditions although the adhesion of the TiCN layer on the rake face is improved. In particular, it has been required to improve the wear resistance and fracture resistance of the coating layer in both wet processing and dry processing.

  An object of the present invention is to provide a cutting tool capable of obtaining even better wear resistance and fracture resistance under severe cutting conditions such as gray cast iron cutting.

In the cutting tool of the present invention, a multi-layer coating layer including a TiCN layer is formed on the surface of the substrate. The TiCN layer is formed of streak crystals, and the substrate is disposed on the substrate side of the TiCN layer. The average crystal width of 1 μm height from the side is narrower than the rake face at the cutting edge, and the coating layer includes an Al ₂ O ₃ layer as an upper layer of the TiCN layer. The thickness of the TiCN layer and the Al ₂ O ₃ When the ratio to the layer thickness (Al ₂ O ₃ layer / TiCN layer) is R, the ratio Rc at the cutting edge is smaller than the ratio Rr at the rake face .

  Moreover, the total thickness of the coating layer on the cutting edge may be the same as the total thickness of the coating layer on the rake face.

Furthermore, the outermost layer of the coating layer is Ti (C _x N _y O _z ) _a (x + y + z = 1, 0 ≦ x ≦ 0.6, 0 ≦ y ≦ 0.6, 0.2 ≦ z ≦ 0.8, 1.0 ≦ a ≦ 1.7) layer.

  According to the cutting tool of the present invention, the crystal width at the cutting edge is narrower than the crystal width at the rake face, so that the chipping resistance at the cutting edge in wet machining is improved and the TiCN layer on the rake face in dry cutting is obtained. The heat resistance of the coating layer can be improved.

It is (a) schematic perspective view, (b) principal part expanded sectional view about an example of the throw away tip which is a suitable example of the cutting tool of this invention. 2 is a scanning electron micrograph of a fracture surface including a cutting edge of the throw-away tip in FIG. 1.

  An example of a throw-away tip that is a preferred example of the cutting tool of the present invention will be described based on a schematic perspective view of FIG. 1 and an enlarged sectional view of a main part, and a scanning electron micrograph of a fractured surface including a cutting blade of FIG. To do.

In the throw-away tip 1 of FIG. 1, the intersecting ridge line portion of the rake face 2 and the flank face 3 constitutes a cutting edge 4, and Ti carbide, nitride, charcoal containing a TiCN layer on the surface of the base 6. One or more layers of nitride, carbonate, nitride oxide and oxynitride, an Al ₂ O ₃ layer (hereinafter simply referred to as Al ₂ O ₃ layer) 12 having an α-type crystal structure, Ti ( C _x N _y O _z ) _a (x + y + z = 1, 0 ≦ x ≦ 0.6, 0 ≦ y ≦ 0.6, 0.2 ≦ z ≦ 0.8, 1.0 ≦ a ≦ 1.7) layer A covering layer is formed in which the outermost layer 14 is sequentially laminated.

According to FIG. 2, the TiCN layer 8 is composed of streak crystals, and the average crystal width of 1 μm height from the substrate 6 side in the TiCN layer 8 a on the most substrate side of the TiCN layer 8 is at the cutting edge 4. Since it is thinner than the rake face 2, it can improve the chipping resistance at the cutting edge 4 in wet machining, reduce the progress of wear due to boundary damage of the cutting edge 4, and the TiCN layer on the rake face 2 in dry cutting. 8 and the Al ₂ O ₃ layer 12 existing as an upper layer thereof can be improved to improve the heat resistance of the coating layer.

  The thickness of each layer and the properties of the crystals constituting each layer were observed in an electron micrograph (scanning electron microscope (SEM) photograph or transmission electron microscope (TEM) photograph) in the cross section of the cutting tool 1 as shown in FIG. By doing so, it is possible to measure. In the present invention, the average grain size of crystals constituting each layer (the average crystal width in the case of a streak crystal) is a layer that is half the thickness of the layer when the average thickness of the layer is 1 μm or less. A straight line parallel to the interface is drawn, and the number of grain boundaries crossing the line is counted and divided by the measured line segment length. When the average thickness of the layer exceeds 1 μm, a straight line length parallel to the interface of the layer is drawn at a position of 1 μm thickness from the beginning of the layer, and the line segment length measured by counting the number of grain boundaries crossing the line Calculate by dividing.

  Further, the fact that the total thickness of the coating layer in the cutting edge 4 is thinner than the total thickness of the coating layer in the rake face 2 can suppress the progress of wear on the rake face 2 in the dry machining, and at the flank face in the wet machining. This is desirable because it can prevent boundary damage.

Next, the coating layer formed on the substrate 6 side includes the TiCN layer 8, and in addition, one or more layers selected from the group of TiC, TiN, TiCNO, TiCO, and TiNO are preferably used. Improved fracture resistance. According to this embodiment, as a specific configuration, as shown in FIG. 2, a TiN layer 7 is formed as a first layer and a TiCN layer 8 is formed as a second layer immediately above the substrate 6. The TiCN layer 8 is composed of so-called MT-TiCN layers 8a and 8b made of streaky crystals formed at a relatively low film formation temperature of 780 to 900 ° C. using acetonitrile (CH ₃ CN) gas as a raw material. It is desirable that the so-called HT-TiCN layer 8c, which is formed at a high film temperature of 950 to 1100 ° C., is sequentially formed. Further, the MT-TiCN layers 8a and 8b are composed of a fine MT-TiCN layer 8a made of fine fine streak crystals having an average crystal width of less than 0.5 μm, and a relatively large coarse crystal having an average crystal width of 0.5 to 2 μm. It is desirable to consist of a lamination with a coarse-grained MT-TiCN layer 8b made of grain streak-like crystals. Thereby, the adhesive force with the Al ₂ O ₃ layer 12 is increased, and peeling and chipping of the coating layer can be suppressed. The streak TiCN layer may have a single layer configuration.

Further, the upper part of the HT-TiCN layer 8c is oxidized in the film forming step, so that Ti atoms are 40 to 55 atomic%, oxygen (O) is 15 to 25 atomic%, and carbon (C) is 25 to 40 atoms. It is desirable that the intermediate layer 11 having a thickness of 0.05 to 0.5 μm is formed by changing to a TiCNO layer of nitrogen and nitrogen (N). Thus, the α-type Al ₂ O ₃ layer 12 made of Al ₂ O ₃ crystals having an α-type crystal structure with an average particle size of 0.05 to 0.7 μm can be more easily produced.

Further, the Al ₂ O ₃ layer 12 formed as the upper layer of the TiCN layer 8 will be described. It is desirable _Al 2 _{O 3} crystals constituting the the Al ₂ O ₃ layer 12 is α-type crystal structure and an average crystal width as viewed from a direction perpendicular to the surface of the substrate 6 is 0.05~0.7μm It is desirable from the viewpoint of wear resistance. The ratio (d _Ar / d _Af ) of the average particle diameter d _{Ar on} the rake face 2 of the Al ₂ O ₃ layer 12 to the average particle diameter d _Af on the flank face 3 is 1.1 to 1.5. It is desirable in terms of improving heat resistance on the surface 2. In this configuration, it is desirable that the total thickness of the coating layer 5 in the cutting edge 4 is the same as the total thickness of the coating layer 5 in the rake face 2 in terms of a good balance between wear resistance and fracture resistance.

Further, the covering layer includes the Al ₂ O ₃ layer 12 as the upper layer of the TiCN layer 8, and the ratio of the thickness of the TiCN layer 8 to the thickness of the Al ₂ O ₃ layer 12 (Al ₂ O ₃ layer 12 / TiCN layer 8) When R is R, the ratio Rc in the cutting edge 4 is smaller than the ratio Rr in the rake face can suppress the progress of wear on the rake face 2 in dry machining, and boundary damage at the cutting edge in wet machining. This is important in that it can be prevented. That is, in the wet machining, local damage is generated at the boundary portion on the flank side of the cutting blade, and this is used to alleviate the loss caused by the progress of wear in the trigger. In dry processing, the rake face becomes hot, so the coating layer of the rake face tends to oxidize and deteriorate and wear tends to progress. According to the above configuration, the rake face 2 is not easily oxidized by Al ₂ O. _{Since the three} layers 12 are formed thick, the oxidation resistance is increased.

The outermost layer 14 is Ti (C _x N _y O _z ) _a (x + y + z = 1, 0 ≦ x ≦ 0.6, 0 ≦ y ≦ 0.6, 0.2 ≦ z ≦ 0.8, 1. 0 ≦ a ≦ 1.7), and the thickness of the central portion of the flank 3 of the outermost layer 14 is smaller than the surface roughness (Ra). With this configuration, since the TiCNO layer or TiCO layer as the outermost layer 14 is formed extremely thin on the uneven surface, the outermost layer 14 exists stably without being easily worn or peeled, and the structure of the gray cast iron The components Si, Mn, Al, Cr, Mo, etc. can be converted into oxides to promote the formation of belag, and the wear resistance can be improved in the machining of gray cast iron. The effect of generating the belarg is particularly significant at the stage where the outermost layer 14 is rubbed vigorously by the work material before the outermost layer 14 is removed by cutting. The outermost layer 14 is worn during cutting and does not exist as a continuous coating layer. However, the improvement of the cutting performance due to the effect of the belag is continued in the portion where the outermost layer remains.

  Here, the resistance of the outermost layer 14 is that the thickness of the outermost layer 14 at the center of the flank 3 is 0.01 to 0.1 μm and the surface roughness (Ra) is 0.1 to 0.5 μm. It is desirable in terms of enhancing wear resistance and chipping resistance. In addition, the ratio of the thickness / surface roughness (Ra) of the outermost layer 14 at the central portion of the flank 3 is preferably 0.2 to 0.3 from the viewpoint of improving the wear resistance due to the effect of generating a belag.

  Further, the surface roughness (Ra) of the outermost layer 14 at the center portion of the flank 3 is rougher than the surface roughness (Ra) of the outermost layer 14 at the rake face top surface (upper surface) portion 2a. It is desirable in that it can improve the chip dischargeability and promote the generation of belag on the flank 3. In addition, in the rake face 2, even if the surface roughness is small, it is in a state in which belag is likely to be generated due to contact of chips.

Furthermore, the thickness of the outermost layer 14 in the cutting edge 4 may be thinner than the thickness of the outermost layer 14 in the central portion of the flank 3 or the outermost layer 14 may not exist in the cutting edge 4. If so, in discontinuous cutting that is impacted such as cutting of the sprue peculiar to cast iron processing, the frequency of film breakage due to the cutting edge 4, that is, the portion subjected to honing processing or the outermost surface layer 14 near the land portion occurs. There is an effect of reducing.

  Further, since the outermost layer 14 shows white purple to gray purple, the surface of the cutting tool 1 is colored, and when the cutting tool 1 is used, it is easy to determine whether the outermost layer 14 is worn and used, The progress of wear can be easily confirmed.

On the other hand, the base 6 of the cutting tool 1 is made of tungsten carbide (WC) and, if desired, at least one selected from the group consisting of carbides, nitrides, and carbonitrides of Group 4, 5, and 6 metals of the periodic table. Cemented carbide, Ti-based cermet, or Si ₃ N ₄ , Al ₂ O ₃ , diamond, cubic crystal in which the hard phase is bonded with a binder phase made of an iron group metal such as cobalt (Co) or nickel (Ni) Any ceramic such as boron nitride (cBN) can be suitably used. In particular, when the cutting tool 1 is used as a cutting tool, the base 6 is preferably made of cemented carbide or cermet in terms of fracture resistance and wear resistance. Depending on the application, the substrate 6 may be made of a metal such as carbon steel, high-speed steel, or alloy steel.

(Production method)
An embodiment of a method for manufacturing the throw-away tip 1 of the present embodiment will be described.

  First, metal powder, carbon powder, etc. are appropriately added to and mixed with inorganic powders such as metal carbides, nitrides, carbonitrides, and oxides that can be formed by firing the hard alloy described above, press molding, cast molding, A predetermined tool shape is formed by a known forming method such as extrusion molding or cold isostatic pressing. Thereafter, the obtained molded body is fired in a vacuum or in a non-oxidizing atmosphere to produce the substrate 6 made of the hard alloy described above. Then, the surface of the base body is subjected to a polishing process such as a double-ended process or an outer peripheral process as desired, and then the honing process of the cutting edge part is performed. During honing of the cutting edge, the average crystal width of the streaky crystals that grow on the cutting edge by increasing the count of the abrasive grains at the final timing of processing and locally processing only the cutting edge with fine abrasive grains Can be made smaller than the average crystal width of the streaky crystal growing on the rake face.

  Next, a coating layer is formed on the surface of the obtained substrate 6 by chemical vapor deposition (CVD). First, the substrate is set in the chamber of the CVD apparatus. At this time, a coating formed on the rake face, the flank face and the cutting edge is formed by skewing a base with a screw hole in the center and adjusting the distance between the bases by reducing the distance between adjacent bases. The thickness of the layer can be varied. Moreover, the thickness of each coating layer can be adjusted by taking out the chip during polishing or after completion of the film formation and polishing it.

In film formation, first, a TiN layer is formed as a first layer directly on the substrate. The conditions for forming the TiN layer include, as a mixed gas composition, titanium tetrachloride (TiCl ₄ ) gas in a ratio of 0.5 to 10% by volume and nitrogen (N ₂ ) gas in a ratio of 10 to 60% by volume, with the remainder being hydrogen. Using a mixed gas composed of (H ₂ ) gas, the film is formed at a film formation temperature of 800 to 940 ° C. (chamber (furnace) temperature) and a pressure of 8 to 50 kPa.

  Next, a TiCN layer is formed as a second layer. Here, the TiCN layer has three layers of an MT-TiCN layer of a fine-grained streaky crystal layer having a small average crystal width, a coarse-grained streaky crystal layer having a larger average crystal width than this layer, and an HT-TiCN layer. The film-forming conditions in the case of configuring in FIG.

The film formation conditions of the fine streaky crystal layer in the MT-TiCN layer are as follows: titanium tetrachloride (TiCl ₄ ) gas is 0.5 to 10% by volume, nitrogen (N ₂ ) gas is 10 to 60% by volume, acetonitrile ( CH ₃ CN) gas is contained at a ratio of 0.1 to 0.4% by volume, and the remaining gas is a hydrogen (H ₂ ) gas mixture, the film forming temperature is 780 to 900 ° C., and the pressure is 5 to 25 kPa. To do. The film formation conditions of the coarse streak-like crystal layer in the MT-TiCN layer are as follows: titanium tetrachloride (TiCl ₄ ) gas is 0.5 to 4.0% by volume, nitrogen (N ₂ ) gas is 0 to 40% by volume, acetonitrile (CH ₃ CN) gas is contained at a ratio of 0.4 to 2.0% by volume, and the remaining gas is a hydrogen (H ₂ ) gas mixed gas, the film forming temperature is 780 to 900 ° C., and the pressure is 5 to 25 kPa. And

The film forming conditions of the HT-TiCN layer were 0.1 to 3% by volume of titanium tetrachloride (TiCl ₄ ) gas, 0.1 to 10% by volume of methane (CH ₄ ) gas, and 0 of nitrogen (N ₂ ) gas. The film is formed at a film forming temperature of 950 to 1100 ° C. and a pressure of 5 to 40 kPa, using a mixed gas containing hydrogen (H ₂ ) gas in a ratio of ˜15% by volume. The chamber is 950 to 1100 ° C. and 5 to 40 kPa, titanium tetrachloride (TiCl ₄ ) gas is 1 to 5% by volume, methane (CH ₄ ) gas is 4 to 10% by volume, and nitrogen (N ₂ ) gas is 10 to 30% by volume, carbon monoxide (CO) gas was 4 to 8% by volume, and the remaining mixed gas was hydrogen (H ₂ ) gas, which was introduced into the reaction chamber for 10 to 60 minutes to form a film. Subsequently, a mixed gas consisting of 0.5% to 4.0% by volume of carbon dioxide (CO ₂ ) gas and the remainder of nitrogen (N ₂ ) gas in a volume% is prepared and introduced into the reaction chamber to form a film. At a temperature of 950 to 1100 ° C. and 5 to 40 kPa, a mixed gas composed of 0.5 to 10% by volume of carbon dioxide (CO ₂ ) gas and the balance of nitrogen (N ₂ ) gas is placed in the reaction chamber for 10 to 60 minutes. Oxidizing the HT-TiCN layer by introducing Then, an intermediate layer is formed while changing to a TiCNO layer. Note that the intermediate layer can be formed without passing the mixed gas containing CO ₂ gas, but in order to make the crystals constituting the α-type Al ₂ O ₃ layer fine, CO ₂ It is desirable to go through a process of flowing a mixed gas containing gas.

Subsequently, a mixed gas consisting of 0.3 to 4.0% by volume of carbon dioxide (CO ₂ ) gas and the remainder of nitrogen (N ₂ ) gas in a volume% is prepared and introduced into the reaction chamber. The surface roughness of the coating layer surface is roughened by introducing it into the reaction chamber at 1000 to 1100 ° C. and 5 to 40 kPa for 5 to 30 minutes. Subsequently, an α-type Al ₂ O ₃ layer is formed. As the film forming conditions for the α-type Al ₂ O ₃ layer, aluminum trichloride (AlCl ₃ ) gas is 0.5 to 5.0% by volume, hydrogen chloride (HCl) gas is 0.5 to 3.5% by volume, A mixed gas consisting of 0.5 to 5.0% by volume of carbon dioxide (CO ₂ ) gas, 0 to 0.5% by volume of hydrogen sulfide (H ₂ S) gas, and the remaining hydrogen (H ₂ ) gas is contained in the chamber. It is desirable to form the film at a film forming temperature of 950 to 1100 ° C. and a pressure of 5 to 10 kPa.

Further, an outermost layer is formed on the α-type Al ₂ O ₃ layer. Titanium tetrachloride (TiCl ₄ ) gas is contained in an amount of 1 to 10% by volume, methane (CH ₄ ) gas is contained in an amount of 4 to 10% by volume, nitrogen (N ₂ ) gas is contained in an amount of 0 to 60% by volume, and the remainder is hydrogen (H ₂ ) Film thickness is obtained by introducing a mixed gas consisting of gas into the reaction chamber, setting the chamber temperature to 960 to 1100 ° C., and the pressure to 10 to 85 kPa, and forming the film formation time between 1 minute and 10 minutes. Then, a mixed gas consisting of 0.5 to 4.0% by volume of carbon dioxide (CO ₂ ) gas and the remainder of nitrogen (N ₂ ) gas is adjusted in volume% and introduced into the reaction chamber. The outermost layer is formed while the HT-TiCN layer is oxidized and changed into a TiCNO layer by introducing the film into the reaction chamber at 950 to 1100 ° C. and 5 to 40 kPa for 5 to 30 minutes. The ratio of oxygen to Ti is adjusted by the concentration of carbon dioxide (CO ₂ ) gas and the oxidation time.

  Then, at least the cutting edge portion, preferably the cutting edge portion and the rake face of the surface of the coating layer formed as desired is polished. By this polishing process, the cutting edge part and the rake face are processed smoothly, suppressing welding of the work material, and a cutting tool having further excellent fracture resistance is obtained.

  A metal cobalt (Co) powder with an average particle diameter of 1.2 μm is added to and mixed with tungsten carbide (WC) powder with an average particle diameter of 1.5 μm at a ratio of 6% by mass, and the cutting tool shape ( CNMG120412). The obtained compact was subjected to a binder removal treatment and fired at 1400 ° C. for 1 hour in a vacuum of 0.5 to 100 Pa to produce a cemented carbide. Furthermore, the cutting edge processing (R honing) was performed on the rake face side by brush processing on the manufactured cemented carbide.

  Next, various coating layers were formed on the cemented carbide by the CVD method under the film forming conditions shown in Table 1 and the layer configuration shown in Table 2. Then, the surface of the coating layer was brushed for 30 seconds from the rake face side, and sample No. 1 to 7 surface-coated cutting tools were prepared.

  The obtained tool was observed with a scanning electron microscope, and the shape, average particle diameter (or average crystal width), and thickness of the crystals constituting each layer were estimated. The results are shown in Table 2. Moreover, it showed in Table 3 about the total thickness of a coating layer, and measured the surface roughness of the coating layer using the contact-type surface roughness meter. Furthermore, the relationship between the surface roughness of the coating layer and the outermost layer thickness is shown in Table 3.

Next, a cutting test was performed using the throwaway tip under the following cutting conditions. The results are shown in Table 3.
(Condition 1)
Cutting method: End face machining (turning)
Work material: FC250
Cutting speed: 450 m / min Feed: 0.35 mm / rev
Cutting depth: 3.0mm
Cutting state: Dry evaluation method: Time for flank wear to be 0.3 mm or more (described as tool life in the table) and the state of the cutting edge at that time (Condition 2)
Cutting method: Planing (milling)
Work material: FC250
Cutting speed: 300 m / min Feed: 0.3 mm / tooth
Cutting depth: 2.0mm
Cutting state: wet evaluation method: number of impacts when abnormal damage such as chipping occurs. And the state of the cutting edge at that time

  From the results shown in Tables 1 to 3, sample Nos. 1 and 2 in which the average crystal width at the height of 1 μm from the substrate side of the streak-like TiCN crystal is the same for the rake face and the cutting edge. 7, and the average crystal width at a height of 1 μm from the substrate side of the streaky TiCN crystal is thicker than the rake face with a thicker cutting edge. In Nos. 5 and 6, the fracture resistance was poor in both turning and milling.

On the other hand, sample No. 1 whose average crystal width at a height of 1 μm from the substrate side of the streak-like TiCN crystal is thinner than the rake face with a cutting edge. 1 , 2 and 4 have high fracture resistance and extended tool life. Sample No. 3 shows a reference example.

1 cutting tool 2 rake face 3 flank 4 cutting edge 6 base 7 TiN layer 8 TiCN layer 8a fine MT-TiCN layer 8b coarse MT-TiCN layer 8c HT-TiCN layer 11 intermediate layer 12 _Al 2 _{O 3} layer 14 outermost layer

Claims (3)

A multi-layer coating layer including a TiCN layer is formed on the surface of the substrate. The TiCN layer is composed of streak crystals, and the average of the TiCN layer on the substrate side is 1 μm higher than the substrate side. The crystal width is narrower than the rake face at the cutting edge, and the coating layer includes an Al ₂ O ₃ layer as an upper layer of the TiCN layer, and a ratio between the thickness of the TiCN layer and the thickness of the Al ₂ O ₃ layer ( A cutting tool in which the ratio Rc at the cutting edge is smaller than the ratio Rr at the rake face, where R is ( Al ₂ O ₃ layer / TiCN layer) . Cutting tool according to claim 1, wherein the same as the total thickness of the coating layer total thickness of the covering layer in the cutting edge in the rake face. The outermost layer of the coating layer is Ti (C _x N _y O _z ) _a (x + y + z = 1, 0 ≦ x ≦ 0.6, 0 ≦ y ≦ 0.6, 0.2 ≦ z ≦ 0.8, 1. The cutting tool according to claim 1 or 2, comprising a layer of 0≤a≤1.7).