Surface coated cutting tools

Abstract

To provide a surface coated cutting tool having high hardness and high toughness.SOLUTION: In the surface coated cutting tool, a coating layer has an average thickness of 1.0-20.0 μm, whose average composition is represented by the formula: (TiaX1bX2cX3dX4e)(CfNg)(X1, X2, X3 and X4 are different elements and respectively are any of Zr, Hf, V, Nb and Ta): 0.01≤a / (a+b+c+d+e)≤0.60 0.01≤b / (a+b+c+d+e)≤0.60 0.01≤c / (a+b+c+d+e)≤0.60 0.01≤d / (a+b+c+d+e)≤0.60 0.01≤e / (a+b+c+d+e)≤0.60 0.20≤f / (f+g)≤0.80 0.20≤g / (f+g)≤0.80 Sconfig≥0.85R (R is gas constant and In is natural logarithm), which includes crystal grain having a NaCl-type face-centered cubic structure.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool).

Background Art

[0002] Coated tools in which a coating layer is formed on the surface of a substrate such as tungsten carbide (hereinafter referred to as WC) - based cemented carbide are known, and it is known that they exhibit excellent wear resistance. And various proposals have been made for improving the coating layer in order to improve the durability of the coated tool.

[0003] For example, Patent Document 1 discloses a coated tool having a substrate and a coating layer on the substrate, wherein the coating layer has a face-centered cubic structure with a lattice constant of 0.403 to 0.455 nm (Ti x Zr 1-x )(C y N 1-y )(0.4 < x < 0.95, 0.2 < y < 0.9) or a face-centered cubic structure with a lattice constant of 0.430 to 0.450 (Ti x Hf 1-x )(C y N 1-y )(0.4 < x < 0.95, 0.2 < y < 0.9). The coating layer is said to be hard and have wear resistance.

[0004] Also, for example, Patent Document 2 describes a coated tool (insert) in which a nitride of Ti 1-x Me x having a lattice constant of 0.427 to 0.453 nm and an fcc structure (0.1 ≤ x ≤ 0.9, Me is one or more of Zr and Hf) is coated on a substrate. The coating layer of the coated tool is said to be hard and suitable for dry cutting of stainless steel.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] This invention has been made in view of the above circumstances and proposals, and aims to provide a coated tool having a coating layer that is highly hard and has improved toughness. [Means for solving the problem]

[0007] A surface-coated cutting tool according to an embodiment of the present invention is The substrate has a coating layer on its surface, The aforementioned coating layer has a composite nitride layer, The composite nitride layer has an average thickness of 1.0 μm or more and 20.0 μm or less. Its composition is given by the formula: (Ti a / (a+b+c+d+e) X1 b / (a+b+c+d+e) X2 c / (a+b+c+d+e) X3 d / (a+b+c+d+e) X4 e / (a+b+c+d+e) )(C f / (f+g) N gf / (f+g) (X1, X2, X3, and X4 are different elements, each being one of Zr, Hf, V, Nb, or Ta) The content of (Ti, X1, X2, X3, X4) and (C, N) is given by atomic ratio. When expressed as, 0.01 ≤ a / (a+b+c+d+e) ≤ 0.60 0.01 ≤ b / (a+b+c+d+e) ≤ 0.60 0.01 ≤ c / (a ​​+ b + c + d + e) ​​≤ 0.60 0.01 ≤ d / (a+b+c+d+e) ≤ 0.60 0.01 ≤ e / (a+b+c+d+e) ≤ 0.60 0.20 ≤ f / (f+g) ≤ 0.80 0.20 ≤ g / (f+g) ≤ 0.80 S config=-R / 2{[a / (a + b + c + d + e)]ln[a / (a + b + c + d + e)] + [b / (a + b + c + d + e)]ln[b / (a + b + c + d + e)] + [c / (a + b + c + d + e)]ln[c / (a + b + c + d + e)] + [d / (a + b + c + d + e)]ln[d / (a + b + c + d + e)] + [e / (a + b + c + d + e)]ln[e / (a + b + c + d + e)] + [f / (f + g)]ln[f / (f + g)] + [g / (f + g)]ln[g / (f + g)]} ≧ 0.85R (R is the gas constant, and ln is the natural logarithm) satisfies, and contains crystal grains having a face-centered cubic structure of the NaCl type.

[0008] Furthermore, the surface-coated cutting tool according to the embodiment may satisfy the following item (1).

[0009] (1) The composite nitride layer contains 0.50 atomic% or less of Cl. [Advantages of the Invention]

[0010] The surface-coated cutting tool has a coating layer with high hardness and high toughness. [Brief Description of the Drawings]

[0011] [Figure 1] Shows a schematic diagram of the crystal structure of TiN. [Figure 2] (TiX1X2X3X4)(CN) Shows a schematic diagram of the crystal structure. [Embodiments for Carrying Out the Invention]

[0012] The coating layer of the surface-coated cutting tool being high in hardness and high in toughness is in an antinomic relationship, and according to the conventional solid solution strengthening theory, it is considered difficult to make both compatible. On the other hand, in recent years, research has been conducted on solid solutions with increased mixing entropy, such as high-entropy alloys, which are alloys in which five or more elements are mixed in nearly equal atomic proportions, and multi-principal-element alloys, which are alloys composed of three or more elements, with at least two principal elements. However, there has been no research on increasing the mixing entropy of the coating layer.

[0013] The inventors of this invention have diligently studied how to achieve both high hardness and high toughness, which are contradictory properties that could not be achieved with conventional coating layers, by increasing the entropy of the mixture of the solid solution (alloy) constituting the coating layer.

[0014] As a result, when the mixing entropy is increased in a composite carbonitride layer of a specific composition that constitutes the coating layer, (i) A composite carbonitride layer of a specific composition is composed of multiple types of atoms with different atomic radii, which causes strain within the crystal grains and improves hardness and toughness. (ii) The thermal stability and oxidation resistance of the composite carbonitride layer at high temperatures will be improved. We gained this insight.

[0015] The following describes a surface-coated cutting tool according to an embodiment of the present invention. In this specification and in the claims, when a numerical range is expressed as "L~M" (where L and M are both numerical values), it is synonymous with "greater than or equal to L and less than or equal to M," and the range includes an upper limit (M) and a lower limit (L), with the units of the upper limit (M) and lower limit (L) being the same.

[0016] 1.Coating layer The following description will focus on the composite carbonitride layer that constitutes the coating layer according to this embodiment.

[0017] 1-1.(TiX1X2X3X4)(CN) layer (1) Crystal structure Figure 2 shows a schematic diagram of the crystal structure of (TiX1X2X3X4)(CN). As is clear from Figure 2, the crystal structure of (TiX1X2X3X4)(CN) is formed by atoms with different atomic radii (4 atoms at the cation sites: Ti, X1, X2, X3, X4; 2 atoms at the anion sites: N atoms; 3 atoms at the anion sites: C atoms) mixed randomly and without regularity within each cation and anion site to form a crystal lattice. Therefore, compared to the crystal structure of TiN schematically shown in Figure 1 (1 Ti atom, 2 N atoms), each atom is displaced from the ideal lattice point position. This creates strain within the crystal lattice (shown as deviation from the dotted line in Figure 2), and this strain improves hardness and toughness. The displacement of each atom is also schematically shown in Figure 2.

[0018] (2) Average thickness The average thickness of the composite carbonitride layer represented by the above formula (hereinafter sometimes referred to as TiX1X2X3X4CN) that constitutes the coating layer is preferably 1.0 μm or more and 20.0 μm or less. The reason for this is that if the average thickness is less than 1.0 μm, sufficient durability cannot be ensured due to the thin average thickness, while if the average thickness exceeds 20.0 μm, the crystal grains of the layer tend to coarseen, making chipping more likely. The average thickness of the composite carbonitride layer is more preferably 3.0 μm or more and 16.0 μm or less.

[0019] (3) Composition The TiX1X2X3X4CN layer has a composition formula: (Ti a / (a+b+c+d+e) X1 b / (a+b+c+d+e) X2 c / (a+b+c+d+e) X3 d / (a+b+c+d+e) X4 e / (a+b+c+d+e) )(C f / (f+g) N gf / (f+g) (X1, X2, X3, and X4 are different elements, each being one of Zr, Hf, V, Nb, or Ta) The content of (Ti, X1, X2, X3, X4) and (C, N) is given by atomic ratio. When expressed as, 0.01 ≤ a / (a+b+c+d+e) ≤ 0.60 0.01 ≤ b / (a+b+c+d+e) ≤ 0.60 0.01 ≤ c / (a ​​+ b + c + d + e) ​​≤ 0.60 0.01 ≤ d / (a+b+c+d+e) ≤ 0.60 0.01 ≤ e / (a+b+c+d+e) ≤ 0.60 0.20 ≤ f / (f+g) ≤ 0.80 0.20 ≤ g / (f+g) ≤ 0.80 S config =-R / 2{[a / (a+b+c+d+e)]ln[a / (a+b+c+d+e)]+[b / (a+b+c+d+e)]ln[b / (a+b+c+d+e)]+[c / (a+b+c+d+e)]ln[c / (a+b+c+d+e)]+[d / ( a+b+c+d+e)]ln[d / (a+b+c+d+e)]+[e / (a+b+c+d+e)]ln[e / (a+b+c+d+e)]+[f / (f+g)]ln[f / (f+g)]+[g / (f+g)]ln[g / (f+g)]}≧0.85R (R is the gas constant, and ln is the natural logarithm.) It is preferable that this be the case.

[0020] When the values ​​a, b, c, d, e, f, and g satisfy the above relationship, the entropy of the TiX1X2X3X4CN layer mixture is increased, and this TiX1X2X3X4CN layer has the physical properties (i) to (ii) obtained from the above findings.

[0021] (4) Cl content It may contain trace amounts of Cl. When a film is formed by the CVD method using chloride as the raw material gas, very small amounts of Cl (an amount that can be confirmed by single-element analysis) are present. Furthermore, if the Cl content is above the quantitative accuracy of the analytical instrument and is 0.50 atomic percent or less, the TiX1X2X3X4CN layer will have lubricity due to the Cl.

[0022] (5) NaCl type face-centered cubic structure The TiX1X2X3X4CN layer preferably has crystal grains with an NaCl-type face-centered cubic structure. However, it may contain crystal grains other than those with an NaCl-type face-centered cubic structure, but the presence of crystal grains other than those with an NaCl-type face-centered cubic structure is not intended. In this specification, "substantially having crystal grains with an NaCl-type face-centered cubic structure" means that in addition to the crystal grains with an NaCl-type face-centered cubic structure, there are also crystal grains other than those with an unintended NaCl-type face-centered cubic structure.

[0023] 1-2. Other layers (1) Lower layer When a lower layer consisting of one or more Ti compound (not limited to stoichiometric composition) layers, including Ti nitride, carbide, and carbonitride layers, with a total average thickness of 0.1 to 20.0 μm, is provided between the substrate and the TiX1X2X3X4CN layer, the adhesion between the substrate and the TiX1X2X3X4CN layer is improved, resulting in even greater durability. However, if the total average thickness of the lower layer is less than 0.1 μm, the improvement in adhesion by the lower layer is insufficient, while if it exceeds 20.0 μm, the crystal grains of the lower layer tend to coarseen, making chipping more likely.

[0024] (2) Upper layer It is preferable to provide an upper layer on top of the TiX1X2X3X4CN layer, which consists of one or more Ti compounds (not limited to stoichiometric composition) from among Ti nitride layers, carbide layers, carbonitride layers, and oxide layers, and / or an aluminum oxide layer (not limited to stoichiometric composition), with a total average thickness of 0.1 to 25.0 μm, to exhibit even better chipping resistance and wear resistance. However, if the total average thickness is less than 0.1 μm, even with the upper layer, further improvement in chipping resistance and wear resistance will not be achieved, while if it exceeds 25.0 μm, chipping caused by the upper layer is more likely to occur.

[0025] (3) Layers that occur unintentionally When the gas pressure or temperature inside the CVD furnace becomes unstable, a very small amount of a layer different from the TiX1X2X3X4CN layer, lower layer, and upper layer may be unintentionally produced.

[0026] 2.Base (1)Material Any conventionally known substrate material can be used, as long as it does not hinder the achievement of the objectives of the present invention. For example, it is preferable to use any of the following materials: cemented carbide (WC-based cemented carbide, including those containing WC and Co, and further containing carbides or nitrides such as Ti, Zr, Ta, Nb, Cr, etc.), cermet (mainly composed of TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), or cBN sintered body.

[0027] (2) Shape The shape of the base material is not particularly restricted as long as it is a shape that can be used as a cutting tool; examples include the shape of an insert and the shape of a solid tool.

[0028] 3.Measurement method The average thickness, elemental content, and average chlorine content of the TiX1X2X3X4CN layer in this embodiment are determined as follows.

[0029] (1) Average thickness The average thickness of the TiX1X2X3X4CN layer can be determined as follows: Using a cross-section polisher (CP) or similar device, a sample for observing the longitudinal section of the coating layer is prepared. The cross-section is observed using a scanning electron microscope (SEM), and the thickness of the layer is measured at multiple locations (e.g., 5 locations). These measurements are then simply averaged to obtain the average thickness of the TiX1X2X3X4CN layer. The definition of the substrate surface will be described later.

[0030] Here, the longitudinal section refers to the section perpendicular to the surface of the substrate when the surface of the insert is treated as a flat surface, ignoring minute irregularities on the substrate surface.

[0031] In this specification, the surface of the substrate is defined as the average line (straight line) of the interface roughness between the substrate and the coating layer in the observed image of the longitudinal section.

[0032] Specifically, the interface between the coating layer (or the lower layer if one exists) and the substrate is determined from the observed image of the longitudinal section. An average line is drawn for the roughness curve of the interface between the surface coating layer and the substrate, and this is considered the surface of the substrate. The direction perpendicular to this average line is defined as the direction perpendicular to the substrate (the thickness direction of the layer).

[0033] Furthermore, even if the substrate has a curved surface, if the radius of curvature of the curved surface is sufficiently large relative to the thickness of the coating layer, the interface between the surface coating layer and the substrate in the measurement area will be approximately flat, and the surface of the substrate can be determined using a similar method.

[0034] (2) Elemental proportions and chlorine content The elemental proportions and chlorine content of the TiX1X2X3X4CN layer are determined as follows. The elemental proportions of Ti, X1, X2, X3, and X4, a / (a+b+c+d+e), b / (a+b+c+d+e), c / (a+b+c+d+e), d / (a+b+c+d+e), and e / (a+b+c+d+e), as well as the elemental proportions of C and N, f / (f+g), g / (f+g), and chlorine content, are determined using an electron probe microanalyzer (EPMA). The electron beam is irradiated from the surface side of a polished sample, and the average of 10 characteristic X-ray analysis results obtained is taken.

[0035] (3) Identification of the crystal structure of the TiX1X2X3X4CN layer X-ray diffraction tests were performed on the TiX1X2X3X4CN layer using an X-ray diffractometer to confirm that it has a face-centered cubic structure of the NaCl type.

[0036] 4. Manufacturing method The manufacturing method for the TiX1X2X3X4CN layer of this embodiment can be carried out by CVD using, for example, the gases TiCl4, ZrCl4, HfCl4, VCl4, NbCl5, TaCl5, H2, HCl, N2, CH3CN, Ar, and H2. [Examples]

[0037] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Specifically, an insert cutting tool using a WC-based cemented carbide as the base material is given, but the material of the base material may be any of the aforementioned, and its shape may be that of a solid tool or the like as described above.

[0038] 1. Manufacturing of the substrate As raw material powders, WC powder, TiC powder, ZrC powder, TaC powder, NbC powder, Cr3C2 powder, TiN powder, and Co powder were prepared. These raw material powders were blended according to the formulation shown in Table 1, wax was added, and the mixture was ball-milled in acetone for 24 hours. After drying under reduced pressure, the mixture was press-molded into compacts of a predetermined shape at a pressure of 98 MPa.

[0039] Subsequently, this compacted powder was vacuum sintered, and after sintering, the cutting edge was honed to R:0.05mm to produce base bodies A to C made of WC-based cemented carbide with the insert shape of Mitsubishi Materials' CNMG120408-MA.

[0040] 2. Film formation TiX1X2X3X4CN layers were deposited on the surfaces of substrates A to C using a CVD apparatus to obtain Examples 1 to 10 shown in Table 5. The deposition conditions were as shown in Table 2, but were generally as follows.

[0041] Reaction gas composition (gas component content is in volume %): TiCl4: 0.02~0.10% *ZrCl4: 0.10~0.50% *HfCl4: 0.20~1.00% *VCl4: 0.02~0.10% *NbCl5: 0.02~0.10% *TaCl5: 0.02~0.10% CH3CN: 0.10~0.50%, HCl: 0.10~0.50% N2: 0.0~12.0% Ar: 10.0~50.0% H2: remaining *ZrCl4, HfCl4, VCl4, NbCl5, and TaCl5 are selected according to the composition of the TiX1X2X3X4CN layer. Reaction atmosphere pressure: 4.5~12.0 kPa Reaction atmosphere temperature: 800~950℃

[0042] For Examples 4 to 10, the lower and / or upper layers shown in Table 4 were formed under the conditions shown in Table 3.

[0043] For comparison, TiX1X2X3X4CN layers were deposited on the surfaces of substrates A to C under the deposition conditions shown in Table 2, yielding Comparative Examples 1 to 10 shown in Table 5. In the manufacturing process of the comparative example, the composition of the raw material gas was changed from that of the example. For Comparative Examples 4 to 10, the lower and / or upper layers shown in Table 4 were formed under the conditions shown in Table 3.

[0044] Furthermore, in order to compare with conventional technology, a TiCN layer and the lower layer, lower layer, and upper layer shown in Table 4 were deposited on the surfaces of substrates A and C under the conditions shown in Table 3, and conventional examples 1 and 2 shown in Table 5 were fabricated.

[0045] For Examples 1-10, Comparative Examples 1-10, and Conventional Examples 1-2, the average thickness of each layer, the content of each element, the average chlorine content, and whether or not they have an NaCl-type face-centered cubic structure were measured using the method described above. These results are summarized in Table 5.

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] [Table 4]

[0050] In Table 4, "-" indicates that it does not exist.

[0051] [Table 5]

[0052] In Table 5, Conventional Examples 1-2 do not contain Zr, Hf, V, Nb, or Ta (columns X1, X2, X3, and X4 are "-"), S config This is the result calculated from -R / 2{[f / (f+g)]ln[f / (f+g)]+[g / (f+g)]ln[g / (f+g)]}. "**" indicates that, because the content was below the quantitative accuracy of the analytical instrument, a trace amount of chlorine was confirmed by single-element detection analysis of chlorine, specifically by confirming the peak in the characteristic X-ray spectrum of chlorine. Furthermore, it was confirmed that all examples, comparative examples, and conventional examples substantially possess crystal grains with a face-centered cubic structure of NaCl type.

[0053] Next, for Examples 1-10, Comparative Examples 1-10, and Conventional Examples 1-2, wet end face cutting tests were performed on hollow round bars made of alloy steel SCM440 with two equally spaced grooves, with the tool steel cutting tool fixed to the tip of the bar using a fixing jig and screwed in place. The wear width of the flank surface of the cutting edge was then measured. This cutting test involves a process where flank wear is likely to progress, and because it includes intermittent machining, the cutting edge is prone to chipping. Therefore, since both wear resistance and chipping resistance are required in this process, it is suitable for evaluating hardness and toughness.

[0054] Cutting test Work material: JIS SCM440 Hollow round bar with two equally spaced grooves (20mm wide) (outer diameter Φ180, inner diameter Φ50) Cutting speed: 270m / min. Cutting depth: 2.0mm Feed rate: 0.3mm / rev. Number of cuts: 20 passes

[0055] Table 6 shows the results of the cutting tests. For Comparative Examples 1-10 and Conventional Examples 1-2, the number of cutting passes until the end of life due to chipping or flank wear (life determination criterion: flank wear width 0.4 mm) is shown.

[0056] [Table 6]

[0057] As is clear from the results shown in Table 6, all of the examples exhibited low wear, no chipping, improved hardness and toughness, and excellent cutting performance over the long term. In contrast, comparative examples 1-10 and conventional examples 1-2 all exhibited high levels of wear or chipping, leading to a short service life. [Explanation of Symbols]

[0058] 1 Ti atom 2 N atoms 3 C atoms 4. One of the following atoms: Ti, X1, X2, X3, or X4 (X1, X2, X3, and X4 are different elements, each being one of Zr, Hf, V, Nb, or Ta).

Claims

1. A surface-coated cutting tool having a substrate and a coating layer on the surface of the substrate, The aforementioned coating layer has a composite nitride layer, The composite nitride layer has an average thickness of 1.0 μm or more and 20.0 μm or less. When its composition is expressed by the formula: (Ti a / (a+b+c+d+e)X1b / (a+b+c+d+e)X2c / (a+b+c+d+e)X3d / (a+b+c+d+e)X4e / (a+b+c+d+e))(Cf / (f+g)Ngf / (f+g))(X1, X2, X3, X4 are different elements, each being one of Zr, Hf, V, Nb, or Ta, and the content of (Ti, X1, X2, X3, X4) and (C, N) is in atomic ratio), 0.01≦a / (a+b+c+d+e)≦0.60 0.01≦b / (a+b+c+d+e)≦0.60 0.01≦c / (a+b+c+d+e)≦0.60 0.01≦d / (a+b+c+d+e)≦0.60 0.01≦e / (a+b+c+d+e)≦0.60 0.20≦f / (f+g)≦0.80 0.20≦g / (f+g)≦0.80 S ｃｏｎｆｉｇ =-R / 2{[a / (a+b+c+d+e)]ln[a / (a+b+c+d+e)]+[b / (a+b+c+d+e)]ln[b / (a+b+c+d+e)]+[c / (a+b+c+d+e)]ln[c / (a+b+c+d+e)]+[d / (a+b+c+d+e)]ln[d / (a+b+c+d+e)]+[e / (a+b+c+d+e)]ln[e / (a+b+c+d+e)]+[f / (f+g)]ln[f / (f+g)]+[g / (f+g)]ln[g / (f+g)]}≧0.85R (R is the gas constant, and ln is the natural logarithm.) Satisfied, Contains crystal grains having a NaCl-type face-centered cubic structure A surface-coated cutting tool characterized by the following features.

2. The surface-coated cutting tool according to claim 1, characterized in that the composite nitride layer contains 0.50 atomic percent or less of Cl.

Images