Surface-coated cutting tool

Abstract

To provide a cutting tool in which thermal conductivity of a titanium alloy, stainless steel or the like is low, and in which the hard film shows excellent deposition peeling resistance even when the cutting tool is used for high-speed cutting of material with high toughness, and further, which exhibits excellent cutting performance over a long period of use.SOLUTION: A surface-coated cutting tool with hard film on its tool substrate has compressive residual stress of -2000 to -300 MPa on both a rake face and a flank of the tool substrate. Further, in the surface-coated cutting tool, a ratio of the compressive residual stress of the flank relative to the compressive residual stress of the rake face exceeds 1.0 and is less than 1.5.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool) in which a hard coating layer has excellent resistance to adhesion and peeling, and which exhibits excellent cutting performance over long periods of use, particularly when used for high-speed cutting of titanium alloys, stainless steel, etc. [Background technology]

[0002] Conventionally, in the case of coated tools, from the viewpoint of improving adhesion between the tool base (substrate) and the coating, it has been proposed to perform a dry blasting treatment on the surface of the base and grind the surface to improve adhesion to the coating and thereby improve chipping resistance.

[0003] For example, Patent Document 1 describes a surface-coated tool in which an abrasive is collided with the surface of the tool base using pressure such as compressed air to make the surface of the tool base uniform and improve adhesion between the tool base and a hard coating.

[0004] Furthermore, for example, Patent Document 2 describes a surface-coated tool in which a residual stress of approximately the same magnitude as the residual stress present in the PVD coating layer is imparted to the tool substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-28854 [Patent Document 2] JP 2009-523618 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a strong demand for labor-saving and energy-saving cutting processes. Accordingly, cutting processes are becoming faster and more efficient. In intermittent cutting processes such as milling for workpieces prone to adhesion, such as Ti alloys and stainless steel alloys, excellent resistance to adhesion chipping is also required. However, there is no mention of the application of the coated tools described in Patent Documents 1 and 2 to high-speed cutting of titanium alloys, stainless steel, and the like.

[0007] The present invention aims to provide a cutting tool in which a hard coating exhibits excellent resistance to adhesion and peeling and exhibits excellent cutting performance over long periods of use, even when used for high-speed cutting of materials with low thermal conductivity and high toughness, such as titanium alloys, stainless steels, etc. Here, high-speed cutting refers to cutting at a cutting speed of 50 m / min or higher. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present inventors have thoroughly investigated the residual stress in a tool substrate (substrate) and have obtained the novel finding that, when predetermined compressive residual stresses exist on both the rake face and the flank face and a predetermined relationship exists between the compressive residual stresses on the rake face and the flank face, a hard coating exhibits excellent crack growth resistance and exhibits excellent cutting performance over long periods of use, even in cutting titanium alloys, stainless steel, and the like.

[0009] The present invention is based on this finding and is as follows. "(1) A surface-coated cutting tool having a tool substrate and a hard coating on the tool substrate, The tool body has a compressive residual stress of -2000 to -300 MPa on both the rake face and the flank face, A ratio of the compressive residual stress of the rake face to the compressive residual stress of the flank face is greater than 1.0 and is not greater than 1.5. Surface coated cutting tools. ” Effect of the Invention

[0010] The surface-coated cutting tool of the present invention has a tool base having a predetermined compressive residual stress, and therefore the hard coating has excellent crack propagation resistance even when used for high-speed cutting of titanium alloys, stainless steel, etc., and exhibits excellent cutting performance over long periods of use. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The coated tool of the present invention will be described in more detail below. In the present specification and claims, when a numerical range is expressed using "A to B" (A and B are both numerical values), the range includes the numerical values ​​of the upper limit (B) and the lower limit (A). The upper limit (B) and the lower limit (B) are expressed in the same unit.

[0012] Average hard coating thickness: The average thickness of the hard coating in the coated tool of the present invention is preferably 0.5 to 10.0 μm. The reason why this range is preferable is that if it is less than 0.5 μm, excellent wear resistance may not be exhibited over long-term use, while if it exceeds 10.0 μm, the crystal grains of the hard coating tend to become coarse, and the effect of improving chipping resistance may not be obtained.

[0013] Hard Coating Composition: The composition of the hard coating in the coated tool of the present invention is not limited to its composition or layer structure as long as it does not impair the object of the present invention. For example, a composite nitride of Ti and Al can be used. A specific composition is represented by the formula: (Ti 1-x Al x An example of such a hard coating is a composite nitride of Ti and Al, represented by (TiAl)N, where x is 0.35≦x≦0.80. In addition, (Ti (1-x) Al x ) and N do not have to be combined in a 1:1 ratio.

[0014] The average composition and average thickness of this (TiAl)N film can be determined by observing a cross section (a cross section perpendicular to the tool base surface: a longitudinal cross section) using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) equipped with an energy dispersive X-ray spectroscopy (EDS).

[0015] Compressive residual stress in tool substrate: It is preferable that both the rake face and flank face of the tool base have compressive residual stress of -2000 to -300 MPa, and the ratio (A / B) of the compressive residual stress (B) on the flank face to the compressive residual stress (A) on the rake face is greater than 1 and is 1.5 or less. When the compressive residual stress on the cutting face and flank face satisfies this range and ratio, the hard coating has excellent crack growth resistance even when used in high-speed cutting of titanium alloys, stainless steel, etc., and ensures excellent cutting performance over long-term use, while suppressing abnormal damage and flaking defects that are often observed during intermittent cutting.

[0016] Tool Base Material: Any known substrate containing WC as the hard phase of this type of tool substrate can be used as the tool substrate, so long as it does not impede the achievement of the object of the present invention.

[0017] Manufacturing method: After manufacturing the tool base, for example, a blasting treatment is performed using Al2O3 particles or ZrO2 particles to impart a predetermined compressive residual stress to the rake face and flank face, and then a hard coating is formed by ionizing a Ti-Al alloy target of a predetermined composition by an arc discharge method using an Arc Ion Plating (AIP) device, which is a type of PVD. The blasting process may be performed after the formation of the hard film, and may be performed by using a laser. EXAMPLES

[0018] Next, an embodiment will be described. Here, as a specific example of the coated tool of the present invention, the application to an insert cutting tool using a WC-based cemented carbide as the tool substrate will be described, but as described above, the tool substrate only needs to contain WC as the hard phase, and the same applies when applied to tools such as drills and end mills. Also, the hard coating is not limited to the above-mentioned (TiAl)N.

[0019] First, Co powder, TiC powder, VC powder, TaC powder, NbC powder, Cr3C2 powder, and WC powder were prepared as raw material powders. These raw material powders were mixed according to the composition shown in Table 1, and wax was added and wet mixed in a ball mill for 72 hours. The mixture was then dried under reduced pressure and pressed at a pressure of 100 MPa. These powder compacts were sintered and processed to the specified dimensions to produce tool bases 1 to 3 made of WC-based cemented carbide having an insert shape conforming to ISO standard SEEN1203AFTN1.

[0020] Next, in order to impart compressive residual stress to the tool substrate, Al2O3 particles with an average particle size of 10 to 100 μm were projected perpendicularly onto the rake face and flank face, as shown in Table 2. The projection pressure was 0.1 to 0.5 MPa, and the projection time was 5 to 180 seconds.

[0021] Next, in order to form a hard coating layer on the tool substrates 1 to 3 using a film-forming device having an AIP evaporation source, the substrates are ultrasonically cleaned in acetone and, in a dried state, are mounted along the outer periphery at a position radially away from the central axis on a rotating table in the AIP device by a predetermined distance. In addition, a Ti-Al alloy target for obtaining a hard coating of a predetermined composition is placed as a cathode electrode (evaporation source).

[0022] Next, the inside of the deposition apparatus was evacuated and -2While maintaining a vacuum of 100 Pa or less, the inside of the apparatus was heated to 400 to 1000°C using a heater, and then the Ar gas atmosphere was set to 0.1 to 2.0 Pa. A DC bias voltage of -200 to -1200 V was applied to the tool base rotating on the turntable, and a predetermined current in the range of 80 to 240 A was passed through the Ti target to cause an arc discharge, and the tool base surface was bombarded for 5 to 120 minutes.

[0023] The furnace temperature shown in Table 2 was maintained in the film-forming apparatus as a reactive gas, and nitrogen gas with a partial pressure in the range of 1 to 9 Pa shown in Table 2 was introduced for a predetermined time into the tool base rotating on the turntable, and an arc discharge was generated by gradually increasing the current flowing between the Ti-Al alloy target and the anode electrode, thereby producing coated tools 1 to 9 of the present invention (hereinafter referred to as "tools of the present invention") shown in Table 3.

[0024] On the other hand, for comparison, the tool bases 1 to 3 were subjected to blasting treatment and a hard coating was vapor-deposited on them using the same AIP equipment as above under the conditions shown in Table 2, to produce comparative coated tools 1 to 3 (hereinafter referred to as "comparative example tools") shown in Table 4.

[0025] The average thickness of each coating constituting the hard coating layer was determined by measuring five locations on a longitudinal section (longitudinal section) of the hard coating layer perpendicular to the surface of the tool base of the present invention tools 1 to 9 and comparative example tools 1 to 3 produced above, by cross-sectional observation using a scanning electron microscope (SEM) in a field of view set to include the entire thickness region of the hard coating layer and having a width of 10 μm in a direction parallel to the tool base surface.

[0026] In addition, the residual stress on the rake face and flank face was measured by X-ray stress measurement (sin 2 The diffraction peak of the (211) plane of WC was used, and the Young's modulus was 706 GPa, and the Poisson's ratio was 0.190. The constant K was calculated based on the material and the measurement wavelength, and 2θ-sin 2 It was calculated by multiplying the gradient determined from the ψ relational expression by the constant K.

[0027] [Table 1]

[0028] [Table 2]

[0029] [Table 3]

[0030] [Table 4]

[0031] Next, for the tools 1 to 9 of the present invention and the comparative tools 1 to 9, high-speed cutting tests were carried out on titanium alloys and nickel alloys under the following conditions.

[0032] Cutting test A: Workpiece: A round bar of Ni-based alloy with the composition, by mass, of Ni-19%Cr-18.5%Fe-5.2%Cd-5%Ta-3%Mo-0.9%Ti-0.5%Al-0.3%Si-0.2%Mn-0.05%Cu-0.04%C. Cutting speed: 55 m / min. Cutout: 1.5 mm Feed: 0.3 mm / rev. Cutting time: 6 minutes A wet continuous high-speed, high-feed cutting test was conducted on a Ni-based alloy under the above conditions (normal cutting speed and feed were 35 m / min. and 0.15 mm / rev., respectively). The results of cutting test A are shown in Table 5.

[0033] Cutting test B: Workpiece: A round bar of Ti-based alloy with the composition Ti-6%Al-4%V by mass. Cutting speed: 125 m / min. Cutout: 1.5 mm Feed: 0.32 mm / rev. Cutting time: 9 minutes A wet continuous high-speed, high-depth cutting test of a Ti-based alloy was conducted under the above conditions (normal cutting speed and feed were 100 m / min. and 0.2 mm / rev., respectively). The results of cutting test B are shown in Table 6.

[0034] [Table 5]

[0035] [Table 6]

[0036] The results in Tables 5 and 6 show that in the present invention tools 1 to 9, no abnormal damage such as chipping or peeling occurred under either cutting condition A or B, and that they have excellent resistance to adhesion and peeling. In contrast, it is clear that the comparative tools 1 to 3 reach the end of their life in a short period of time under both cutting conditions A and B due to the occurrence of chipping or the progression of flank wear. [Industrial Applicability]

[0037] The surface-coated cutting tool of the present invention exhibits excellent resistance to adhesion and peeling and shows excellent cutting performance over a long period of time, not only in cutting various steels under normal cutting conditions, but also in high-speed cutting of titanium alloys, nickel alloys, etc., which generates high heat and places a large load on the cutting edge. Therefore, it can fully meet the demands for high performance cutting equipment, labor-saving and energy-saving cutting, and cost reduction.

Claims

1. 1. A surface-coated cutting tool having a tool substrate and a hard coating on the tool substrate, The tool body has a compressive residual stress of −2000 to −300 MPa on both the rake face and the flank face, A ratio of the compressive residual stress of the rake face to the compressive residual stress of the flank face is greater than 1.0 and is not greater than 1.

5. Surface coated cutting tools.

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