JPH04300102A - Surface-coated cutting tool of cemented carbide - Google Patents

Abstract

PURPOSE:To obtain a surface-coated cutting tool of cemented carbide alloy excellent in durability. CONSTITUTION:A residual tensile stress in a TiN layer formed on the surface of a substrate by chemical deposition is alphaTiN and a value obtained by multiplying a coefficient of thermal expansion at the center of the substrate by 10<6> is x. Then the TiN layer which satisfies a relational expression 5x<2>-80x+315>=alphaTiN is charged on the WC-group cemented carbide substrate by chemical deposition as the outmost layer of a single or multiple layers.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is based on tungsten carbide (
This cutting tool has a cemented carbide base (hereinafter referred to as WC) and has a hard layer coated on the surface by chemical vapor deposition, and exhibits excellent fracture resistance especially when used in interrupted cutting. be.

0002

2. Description of the Related Art Conventionally, cutting tools have been widely used which have a WC-based cemented carbide as a base and coat the surface with a hard layer by chemical vapor deposition (hereinafter referred to as CVD).

[0003] Various materials are used for the hard layer, and among them, a titanium nitride (hereinafter referred to as TiN) layer has excellent wear resistance and welding resistance, and has a low coefficient of friction with chips. It is widely used because of its low carbon content and its golden color, which makes it look beautiful.

[0004] Using WC-based cemented carbide as a base, CVD
High tensile residual stress occurs in the TiN layer formed by this method, and the crystalline state tends to become columnar.
When a WC-based cemented carbide coated with a TiN layer is used as a cutting tool for interrupted cutting, cracks occur in the TiN layer, and chips are likely to occur from the cracks, which is a drawback. CVD as a way to improve
A method has also been proposed in which the TiN layer formed by the method is subjected to shot peening, sandblasting, etc. to impart compressive stress to the TiN layer, thereby improving the chipping resistance of the tool (Japanese Patent Application Laid-Open No. 1986-1999). (See Publication No. 31972).

[0005]

[Problem to be solved by the invention] However, the above C
TiN formed on the surface of WC-based cemented carbide by VD method
When the layer is subjected to shot peening or sandblasting by colliding metal balls, ceramic balls, metal powder, ceramic powder, etc., compressive stress is certainly applied, but the thin TiN layer is mechanically damaged. In addition, there is a problem that such scratches can lead to defects, and that applying shot peening, sandblasting, etc. after forming a TiN layer by CVD increases costs. Ta.

[0006]

[Means for solving the problem] Therefore, the present inventors
As a result of research to manufacture a TiN layer-coated cemented carbide cutting tool using the CVD method that has excellent fracture resistance without post-processing such as shot peening or sandblasting, we found that the surface of the WC-based cemented carbide substrate Even if the TiN layer is formed by the CVD method in Then, 5x2 −80x+315≧σTiN ……………
It was found that a cutting tool made of a TiN layer-coated WC-based cemented carbide formed by a CVD method that satisfies the relational expression (1) has sufficient fracture resistance.

[0007] The present invention was made based on this knowledge, and includes TiN on the surface of a WC-based cemented carbide substrate.
CVD of single layer or multilayer including TiN layer
A cutting tool made of a surface-coated cemented carbide coated by the method is characterized in that the residual stress of the TiN layer satisfies the above formula (1).

Generally, the thermal expansion coefficient of the WC-based cemented carbide substrate varies arbitrarily depending on the composition, and is practically about 4.5 to 6.
5×10-6/℃, but in this invention, Ti
Thermal expansion coefficient that tends to cause tensile residual stress in the N layer: 7.
It is particularly effective for WC-based cemented carbide substrates with temperatures below 0x10-6/°C. Furthermore, although the composition of the WC-based cemented carbide substrate may differ between the center and the surface, when the thickness of the surface is 200 μm or less, σTiN is largely controlled by the thermal expansion coefficient of the center of the substrate. It is hardly affected by the surface area.

In other words, in the present invention, the central portion of the WC-based cemented carbide substrate refers to a portion deeper than 200 μm from the surface of the substrate, and x is a value obtained by multiplying the thermal expansion coefficient of the center portion of the substrate by 10 6 .

[0010] Note that x may be determined by multiplying the actually measured coefficient of thermal expansion by 106, but the coefficient of thermal expansion is determined by calculation according to the mixing rule from the component composition constituting the WC-based cemented carbide substrate.
The coefficient of thermal expansion may be multiplied by 106.

[0011]

[Example] Example 1 A WC-based cemented carbide having the shape of ISO standard SNGN120408 and the composition shown in Table 1 was prepared.
The surface of the C-based cemented carbide was polished to a depth of at least 0.5 mm from the surface to produce WC-based cemented carbide substrates A to E that were uniform from the surface to the center.

The thermal expansion coefficients of these WC-based cemented carbide substrates A to E are determined by calculation according to the mixing rule, and the obtained thermal expansion coefficient is multiplied by 106 to determine the value of x. 2) The value of Y was obtained by substituting it into the equation, and the value of Y is shown in Table 1.

[0013] Y=5x2 -80x+315 (2
) A TiN layer was chemically deposited on the surface of these WC-based cemented carbide substrates A to E under the conditions shown in Tables 2 and 3, and the TiN layer was
Tensile residual stress of N layer σTiN (kgf/mm2)
was measured by X-ray diffraction using the 2θ-sin2ψ method, and the results are shown in Table 4. Note that the hard layers other than the TiN layer were formed by a normal chemical vapor deposition method.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

Under these conditions, the coating layer shown in Table 3 consisting of a single layer of TiN or multiple layers containing TiN was formed on the surface of the above-mentioned WC-based cemented carbide substrates A to E. After confirming whether the tools 1 to 5 and the conventional surface-coated cemented carbide cutting tools 1 to 5 satisfy the above formula (1), an interrupted cutting test was conducted using these cutting tools under the following conditions. The results are shown in Table 4.

Intermittent cutting conditions Work material: SNCM439 (HB 320) square material Cutting speed: 100 m/min Feed: 0.4 mm/rev Depth of cut: 3 mm Dry cutting The number of impacts until breakage was measured for 10 cutting edges,
The average value was calculated.

Example 2 Raw material powders include WC powder with an average particle size of 3.5 μm, TiC powder with an average particle size of 1.0 μm, NbC powder with an average particle size of 1.0 μm, and average particle size: 1.0 μm. A TaC powder, a TiN powder with an average particle size of 1.0 μm, and a Co powder with an average particle size of 1.2 μm were prepared, and these powders were blended in the proportions shown in Table 5, mixed, and press-molded. Later, ISO standard CN
A green compact having a shape corresponding to MG120408 was prepared, and this green compact was sintered under the conditions shown in Table 5, so that it had a surface layer with the composition and thickness shown in Table 5, and the composition of the center part was Table 1
WC-based cemented carbide substrates B' and D' that are substantially the same as the WC-based cemented carbide substrates B and D were prepared.

A TiN layer was chemically vapor deposited on the surfaces of the WC-based cemented carbide substrates B' and D' under the conditions shown in Table 6, and the tensile residual stress σTiN (kgf/mm
2) was measured by X-ray diffraction in the same manner as in Example 1, and the results are shown in Table 7.

[0022] The hard layers other than the TiN layer were formed by a conventional chemical vapor deposition method.

Surface-coated cemented carbide cutting tools 6 to 7 of the present invention, in which a coating layer shown in Table 6 consisting of a composite layer containing TiN is formed on the surface of the WC-based cemented carbide substrates B' and D'.
After confirming whether or not the above-mentioned formula (1) is satisfied for conventional surface-coated cemented carbide cutting tools 6 to 7, an interrupted cutting test was conducted using these cutting tools under the following conditions, and the results are shown in the table below. 7.

Intermittent cutting conditions Work material: SNCM439 (HB 290) square material Cutting speed: 100 m/min Feed: 0.3 mm/rev Depth of cut: 2 mm Dry cutting The number of impacts until breakage was measured for 10 cutting edges, and the average I found the value.

[0025]

[Table 5]

[0026]

[Table 6]

[0027]

[Table 7]

[0028]

Effects of the Invention The surface-coated cemented carbide cutting tool 1 of the present invention and the conventional surface-coated cemented carbide cutting tool 1 have the same composition of the WC-based cemented carbide substrate and the coating layer. Although both layers are given tensile residual stress, Ti satisfies the above equation (1).
The surface-coated cemented carbide cutting tool 1 of the present invention coated with an N layer has superior fracture resistance compared to the conventional surface-coated cemented carbide cutting tool 1 coated with a TiN layer that does not satisfy the above formula (1). Furthermore, cutting tools 2 to 7 made of surface-coated cemented carbide of the present invention
It can be seen that the same tendency is exhibited when comparing the conventional cutting tools 2 to 7 made of surface-coated cemented carbide.

As mentioned above, the surface-coated cemented carbide cutting tool of the present invention does not require post-treatment such as shot peening or sandblasting, so it can keep costs low and improve fracture resistance. It has the excellent effect of being able to

Claims (3)

[Claims] Claim 1: A tungsten carbide (hereinafter referred to as WC)-based cemented carbide is used as a base and a single layer of titanium nitride (hereinafter referred to as TiN) or multiple layers including a TiN layer are coated by chemical vapor deposition. In the surface-coated cemented carbide cutting tool, the tensile residual stress of the TiN layer is reduced to σTiN (kg
A cutting tool made of a surface-coated cemented carbide, characterized in that it is coated with at least one TiN layer that satisfies the relationship of the following formula (1) when f/mm2). 5x2 -80x+315≧σTiN
…………… (1) However, x is the value obtained by multiplying the coefficient of thermal expansion of the center of the WC-based cemented carbide by 106. 2. The surface of the WC-based cemented carbide substrate has a tensile residual stress that satisfies the relationship of equation (1) above.
The surface coated cemented carbide cutting tool according to claim 1, characterized in that an iN layer is coated as the outermost layer of the multilayer. 3. The surface-coated cemented carbide cutting machine according to claim 1 or 2, wherein the center portion of the WC-based cemented carbide substrate has a coefficient of thermal expansion of less than 7.0×10 −6 /°C. tool.