SURFACE-COATED CUTTING TOOL

Abstract

A surface-coated cutting tool has excellent welding resistance and fracturing resistance and comprises a hard coating layer, including at least a lower layer and an upper layer, formed on a surface of a cutting tool body. The lower layer is formed of one layer or two or more layers of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer. The upper layer is found as an Al.sub.2O.sub.3 layer on a surface of the lower layer. On at least an outermost surface of the upper layer of a rake face, a zirconium oxide layer is formed in an area ratio of 30% to 70%. The Al.sub.2O.sub.3 layer on the rake face has a tensile residual stress of 10 to 200 MPa and a surface roughness Ra is 0.25 m or less.

Claims

1. A surface-coated cutting tool comprising: a a cutting tool body made of WC-based cemented carbide or TiCN-based cermet; a rake face of the cutting tool body; a flank face of the cutting tool body; and a hard coating layer including at least a lower layer and an upper layer that is formed on a surface of the cutting tool body, wherein (a) the lower layer is formed of two or more layers selected from the group consisting of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer (hereinafter, collectively referred to as a Ti compound layer), (b) the upper layer is made of an Al.sub.2O.sub.3 layer, which is formed on a surface of the lower layer of which at least one layer is formed of the TiCN layer, (c) on an outermost surface of the upper layer formed on the rake face, a zirconium oxide layer is formed in an area ratio of 30% to 70%, and (d) the Al.sub.2O.sub.3 layer formed on the rake face has a tensile residual stress of 10 to 200 MPa and a surface roughness Ra is 0.25 m or less.

2. The surface-coated cutting tool according to claim 1, wherein a tensile residual stress of the TiCN layer on the rake face is 10 to 250 MPa.

3. The surface-coated cutting tool according to claim 1, wherein the flank face has an upper layer made of the Al.sub.2O.sub.3 layer, and the TiN layer, the TiC layer, the TiCN layer, or the TiNO layer is formed on an outermost surface of the upper layer of the flank face.

4. The surface-coated cutting tool according to claim 2, wherein the flank face has an upper layer made of the Al.sub.2O.sub.3 layer, and the TiN layer, the TiC layer, the TiCN layer, or the TiNO layer is formed on an outermost surface of the upper layer of the flank face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0055] Next, the coated tool of the invention will be described in detail with reference to examples.

[0056] Although an example using WC-based cemented carbide as a cutting tool body is described, the same is also applied to a case where TiCN-based cermet is used as a cutting tool body.

EXAMPLE 1

[0057] As raw material powders, a WC powder, a TiC powder, a TiN powder, a TaC powder, a NbC powder, a Cr.sub.3C.sub.2 powder, and a Co powder, all of which had an average particle diameter of 1 to 3 m, were prepared, and the raw material powders were mixed in mixing compositions shown in Table 1. Wax was further added thereto, and the mixture was blended in acetone by a ball mill for 24 hours and was decompressed and dried. Thereafter, the resultant was press-formed into compacts having predetermined shapes at a pressure of 98 MPa, and the compacts were sintered in a vacuum at 5 Pa under the condition that the compacts were held at a predetermined temperature in a range of 1370 C. to 1470 C. for one hour. After the sintering, cutting tool bodies A to C made of WC-based cemented carbide with insert shapes according to ISO CNMG 120408 were produced by performing honing with R: 0.05 mm on a cutting edge portion.

[0058] The cutting tool bodies were loaded in a typical chemical vapor deposition apparatus, and

[0059] first, under conditions shown in Table 2 (l-TiCN in Table 2 shows forming conditions of a TiCN layer having a longitudinally grown crystal structure described in JP-A-6-8010, and the others show forming conditions of a typical granular crystal structure), a Ti compound layer having a target layer thickness shown in Table 3 was deposited and formed as a lower layer of a hard coating layer.

[0060] Next, an Al.sub.2O.sub.3 layer and a TiN layer having target layer thicknesses shown in Table 3 were deposited on the surface of the lower layer under the conditions shown in Table 2.

[0061] Next, using ZrO.sub.2 grains as abrasive grains, a wet blasting process was performed on a rake face under conditions shown in Table 4, thereby producing present invention coated tools 1 to 3 having the Al.sub.2O.sub.3 layer and a zirconium oxide layer of the rake face shown in Table 5.

[0062] The thicknesses of the lower layer and the upper layer of the present invention coated tools 1 to 3 were measured (longitudinal section measurement) using a scanning electron microscope and were found to be substantially the same average layer thicknesses as the target layer thicknesses (average value of five points measured).

[0063] SEM observation and EDS analysis were performed on the outermost surfaces of the Al.sub.2O.sub.3 layers of the present invention coated tools 1 to 3 to measure the area ratios of the zirconium oxide layers present on the surfaces of the Al.sub.2O.sub.3 layers on the rake faces.

[0064] Table 5 shows the measured area ratios of the zirconium oxide layers.

[0065] In addition, the surface roughnesses Ra of the rake faces of the present invention coated tools 1 to 3 produced as described above were measured.

[0066] The surface roughness Ra was measured according to JIS B 0601:2001 using a stylus type surface roughness measuring instrument at a cut-off value of 0.08 mm, a reference length of 0.8 mm, and a scanning speed of 0.1 mm/sec.

[0067] Table 5 shows the results.

[0068] Furthermore, for the present invention coated tools 1 to 3 produced as described above, the residual stresses in the Al.sub.2O.sub.3 layers and the TiCN layers were measured.

[0069] The residual stress was measured by using an X-ray diffractometer using a sin.sup.2 method and Cu. For the measurement regarding -Al.sub.2O.sub.3, a calculation was performed using the diffraction peak of a (13_10) plane, a Young's modulus of 384 Gpa, and a Poisson's ratio of 0.232. Regarding TiCN, a calculation was performed using the diffraction peak of a (422) plane, a Young's modulus of 480 Gpa, and a Poisson's ratio of 0.2. Table 5 shows the results.

TABLE-US-00001 TABLE 1 Raw Mixing composition (mass %) material type Co TiC TiN TaC NbC WC A 7.5 Remainder B 8.0 1.7 2.9 Remainder C 9.0 2.2 2.0 2.4 Remainder

TABLE-US-00002 TABLE 2 Forming conditions (pressure of reaction atmosphere is expressed as kPa and temperature is expressed as C.) Hard coating layer Reaction Formation atmosphere Type symbol Reaction gas composition (vol %) Pressure Temperature TiC layer TiC TiCl.sub.4: 4.2%, CH.sub.4: 8.5%, H.sub.2: remainder 7 1020 TiN layer TiN TiCl.sub.4: 4.2%, N.sub.2: 30%, H.sub.2: remainder 30 900 (first layer) TiN layer TiN TiCl.sub.4: 4.2%, N.sub.2: 35%, H.sub.2: remainder 50 1040 (other layers) l-TiCN layer l-TiCN TiCl.sub.4: 4.2%, N.sub.2: 20%, CH.sub.3CN: 0.6%, 7 900 H.sub.2: remainder TiCO layer TiCO TiCl.sub.4: 4.2%, CO: 4%, H.sub.2: remainder 7 1020 TiCNO layer TiCNO TiCl.sub.4: 4.2%, CO: 4%, CH.sub.4: 3%, N.sub.2: 20%, 20 1020 H.sub.2: remainder -type AlCl.sub.3: 2.2%, CO.sub.2: 5.5%, HCl: 2.2%, 7 1000 Al.sub.2O.sub.3 layer H.sub.2S: 0.2%, H.sub.2: remainder

TABLE-US-00003 TABLE 3 Hard coating layer Lower layer (Ti compound layer) (target layer thickness: m is Average layer Wear indicated in parentheses) thickness recognition Chip body First Second Third Fourth of Al.sub.2O.sub.3 layer layer Type number layer layer layer layer (m) (m) Present 1 A TiN (0.2) l-TiCN (8.5) TiCO (0.5) 6 invention 2 B TiN (0.5) l-TiCN (7.5) TiCNO (0.5) 8 coated tool 3 C TiC (0.5) TiN (0.5) l-TiCN (7) TiCNO (0.5) 7.5 TiN (0.2)

TABLE-US-00004 TABLE 4 Processing conditions Abrasive Projection angle Wet Abrasive grain Blasting Blasting with respect to blasting Processing Abrasive grain size Mass ratio concentration pressure time normal to rake face type solution grain shape (grain size m) (mass %) (vol %) (MPa) (sec) (degrees) A Abrasive Spherical 150 to 210 75 15 0.20 15 0 grains + water Polygonal <125 25 B Abrasive Spherical 210 to 300 90 8 0.30 9 10 grains + water Polygonal <125 10 C Abrasive Spherical 300 to 425 80 10 0.25 11 5 grains + water Polygonal <125 20

TABLE-US-00005 TABLE 5 Hard coating layer (rake face) Wet Residual Residual blasting Area ratio Surface stress in stress in process of zirconium roughness TiCN layer Al.sub.2O.sub.3 Type type oxide layer (Ra) (MPa) (MPa) Present 1 A 62 0.23 88 110 invention 2 B 35 0.15 110 82 coated tool 3 C 51 0.17 98 55

[0070] For the purpose of comparison, a Ti compound layer having a target layer thickness shown in Table 6 was deposited as a lower layer of a hard coating layer on the cutting tool bodies A to C made of WC-based cemented carbide produced as described above under conditions shown in Table 2, and thereafter, an Al.sub.2O.sub.3 layer and a TiN layer having target layer thicknesses shown in Table 6 were deposited on the surface of the lower layer under the conditions shown in Table 2.

[0071] Next, a blasting process was performed on a rake face under conditions shown in Table 7, thereby producing comparative example coated tools 1 to 3 having an Al.sub.2O.sub.3 layer on the rake face shown in Table 8.

[0072] SEM observation and EDS analysis were performed on the outermost surfaces of the Al.sub.2O.sub.3 layers of the comparative example coated tools 1 to 3 to measure the area ratios of zirconium oxide layers present on the surfaces of the Al.sub.2O.sub.3 layers on the rake faces.

[0073] Table 8 shows the measured area ratios of the zirconium oxide layers.

[0074] In addition, for the comparative example coated tools 1 to 3 produced as described above, the surface roughness Ra of the rake face was measured in the same method as the present invention coated tools 1 to 3, and furthermore, the residual stresses in the Al.sub.2O.sub.3 layers and the TiCN layers were measured.

[0075] Table 8 shows the results.

TABLE-US-00006 TABLE 6 Hard coating layer Lower layer (Ti compound layer) (target layer thickness: m is Average layer Wear indicated in parentheses) thickness of recognition Chip body First Second Third Fourth Al.sub.2O.sub.3 layer layer Type number layer layer layer layer (m) (m) Comparative 1 Same as present invention coated tool 1 example 2 Same as present invention coated tool 2 coated tool 3 Same as present invention coated tool 3

TABLE-US-00007 TABLE 7 Processing conditions Abrasive Projection angle Abrasive grain Blasting Blasting with respect to Processing Abrasive grain size Mass ratio concentration pressure time normal to rake face solution grain shape (grain size m) (mass %) (vol %) (MPa) (sec) (degrees) a Abrasive Polygonal 125 to 250 100 12 0.15 18 0 grains + water b Abrasive Spherical 150 to 210 100 20 0.20 7 0 grains + water c Abrasive Spherical 210 to 300 80 15 0.25 12 60 grains + water Polygonal <125 20

TABLE-US-00008 TABLE 8 Hard coating layer (rake face) Residual Residual Wet Area ratio Surface stress in stress in blasting of zirconium roughness TiCN layer Al.sub.2O.sub.3 layer Type process type oxide layer (Ra) (MPa) (MPa) Comparative 1 a 23 0.27 310 280 example 2 b 9 0.35 180 162 coated tool 3 c 15 0.30 210 175

[0076] Next, in a state in which each of the present invention coated tools 1 to 3 and the comparative example coated tools 1 to 3 was screwed to a tip end portion of an insert holder made of tool steel by a fixing tool, a cutting test was conducted under the following cutting conditions A and cutting conditions B.

[0077] <<Cutting Conditions A>>

[0078] Work material: a round bar of JIS S45C

[0079] Cutting speed: 250 m/min

[0080] Depth of cut: 1.5 mm

[0081] Feed: 0.25 mm/rev

[0082] Cutting time: 10 minutes

[0083] A dry cutting test of carbon steel under above conditions.

[0084] <<Cutting Conditions B>>

[0085] Work material: a round bar with four straight grooves formed at equal intervals in the longitudinal direction according to JIS SNCM439

[0086] Cutting speed: 150 m/min

[0087] Depth of cut: 3.0 mm

[0088] Feed: 0.25 mm/rev

[0089] Cutting time: 6 minutes

[0090] A dry intermittent cutting test of alloy steel under above conditions.

[0091] In the above cutting tests, presence or absence of occurrence of welding, presence or absence of occurrence of chipping, and presence or absence of occurrence of fracturing were observed. Table 9 shows the results of the cutting tests.

TABLE-US-00009 TABLE 9 Cutting work test results Cutting work test results <<Cutting <<Cutting <<Cutting <<Cutting conditions A>> conditions B>> conditions A>> conditions B>> Presence or Presence or Presence or Presence or Presence or Presence or absence of absence of absence of absence of absence of absence of occurrence of occurrence of occurrence of occurrence of occurrence of occurrence of Type welding chipping fracturing Type welding chipping fracturing Present 1 Absent Absent Absent Comparative 1 Present Present Fractured within invention example 1.1 minutes coated tool 2 Absent Absent Absent coated tool 2 Present Present Fractured within 3.1 minutes 3 Absent Absent Absent 3 Present Present Fractured within 2.4 minutes

[0092] From the results shown in Tables 5, 8 and 9, it can be understood that the present invention coated tools have the zirconium oxide layer on the outermost surface of the Al.sub.2O.sub.3 layer as the upper layer of the rake face in an area ratio of 30% to 70% and thus have excellent welding resistance, chipping resistance, and fracturing resistance.

[0093] Contrary to this, in any of the comparative example coated tools, no zirconium oxide layer is formed on the outermost surface of the Al.sub.2O.sub.3 layer as the upper layer of the rake face, or even if the zirconium oxide layer is formed, the area ratio thereof is less than 30%. As a result, it cannot be said that sufficient cutting performance is exhibited regarding welding resistance, chipping resistance, and fracturing resistance.

INDUSTRIAL APPLICABILITY

[0094] As described above, the coated tool according to the present invention has excellent cutting performance, so that a reduction in costs and high workability can be realized by high performance of a cutting apparatus and power saving and energy saving during cutting work.