JP3021742B2 - Surface coated cemented carbide cutting tool - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool having a tungsten carbide (hereinafter abbreviated as WC) base cemented carbide as a base material and a hard layer coated on its surface by a chemical vapor deposition method. It shows excellent fracture resistance when used in.

[0002]

2. Description of the Related Art Conventionally, a cutting tool having a WC-based cemented carbide as a base material and a hard layer coated on the surface thereof by a chemical vapor deposition method (hereinafter referred to as a CVD method) has been widely used.

As the hard layer, various materials are used. Among them, a titanium nitride (hereinafter referred to as TiN) layer is excellent in wear resistance and welding resistance and has a coefficient of friction with chips. Is often used because of its advantages such as low appearance and beautiful appearance due to its golden color.

[0004] A WC-based cemented carbide is used as a base material and a CVD
Since a high tensile residual stress is generated in the TiN layer formed by the method and the crystal state is likely to be columnar,
When intermittent cutting or the like is performed using the WC-based cemented carbide coated with the TiN layer as a cutting tool, a crack is generated in the TiN layer, and a defect is easily generated from the crack as a starting point. To improve CVD
A method of applying a compressive stress to the TiN layer by applying a shot peening method, a sand blast method, or the like to the TiN layer formed by the method to improve the fracture resistance of the tool has been proposed (Japanese Patent Laid-Open No. 64-64). No. 3,1972).

[0005]

However, the above C
TiN formed on WC-based cemented carbide substrate surface by VD method
If a shot peening method or a sand blasting method is performed by colliding a metal ball, a ceramic ball, a metal powder, a ceramic powder, or the like with the layer, a compressive stress is certainly applied, but mechanical damage is caused on the thin TiN layer. In some cases, such scratches cause defects such as defects, and further, applying a shot peening method, a sand blasting method, or the like after forming a TiN layer by a CVD method leads to an increase in cost. Was.

[0006]

Means for Solving the Problems Accordingly, the present inventors have
As a result of researching to manufacture a cutting tool made of a cemented carbide coated with a TiN layer having excellent fracture resistance without performing post-processing such as the shot peening method and the sand blasting method, the surface of a WC-based cemented carbide substrate was obtained. even TiN layer formed by a CVD ^{_{method, σ TiN (kgf / mm 2}} ) to: tensile residual stress of the TiN layer, x: WC based on thermal expansion coefficient in the center of the cemented carbide substrate 10 ⁶
Assuming that the value is multiplied, 5x ² −80x + 315 ≧ σ _TiN (1) T formed by a CVD method that satisfies the relational expression:
It has been found that a cutting tool made of a WC-based cemented carbide coated with an iN layer has sufficient fracture resistance.

[0007] The present invention has been made based on such findings, and TiN is applied to the surface of a WC-based cemented carbide substrate.
CVD of single layer consisting of multiple layers or multiple layers including TiN layer
The 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).

In general, the coefficient of thermal expansion of a WC-based cemented carbide substrate varies arbitrarily depending on the composition, and is practically about 4.5-6.
Although it is 5 × 10 ⁻⁶ / ° C., in the present invention, TiN
Thermal expansion coefficient in which a layer tends to generate residual tensile stress: 7.0
It is particularly effective for a WC-based cemented carbide substrate having a density of less than × 10 ^-6 / ° C. Further, the composition of the WC-based cemented carbide substrate may be different between the central portion and the surface portion, but the thickness of the surface portion is 2 mm.
When the thickness is not more than 00 μm, σ _TiN is largely influenced by the thermal expansion coefficient at the center of the substrate, and is hardly affected by the surface.

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

Although x may be obtained by multiplying the measured thermal expansion coefficient by 10 ^{6, the} thermal expansion coefficient is calculated from the component composition of the WC-based cemented carbide substrate according to the mixing rule, and the thermal expansion coefficient is calculated. It may be obtained by multiplying the coefficient by 10 ⁶ .

[0011]

EXAMPLE 1 A WC-based cemented carbide having the shape of ISO standard SNGN120408 and having the component composition shown in Table 1 was prepared.
The surface of the C-base cemented carbide is polished to a depth of at least 0.5 mm from the surface.
C-base cemented carbide substrates A to E were produced.

The thermal expansion coefficients of the WC-based cemented carbide substrates A to E are calculated by the mixing rule, and the obtained thermal expansion coefficient is multiplied by 10 ⁶ to obtain the value of x. The value of Y was obtained by substituting into the equation (2), and the value of Y is shown in Table 1.

[0013] ^{Y = 5x 2 -80x + 315 ...............} (2) a TiN layer is chemically vapor deposited under the conditions shown in Table 2 and Table 3 the surface of WC-based cemented carbide substrate A-E, the TiN
The tensile residual stress σ _TiN (kgf / mm ² ) of the layer was measured by X-ray diffraction using the 2θ-sin ² ψ method, and the results are shown in Table 4.
It was shown to. 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 the above conditions, the surface coated cemented carbide alloy of the present invention in which a single layer of TiN layer or a coating layer of Table 3 consisting of multiple layers containing TiN is formed on the surfaces of the WC-based cemented carbide substrates AE. After confirming whether or not the tools 1 to 5 and the conventional surface-coated cemented carbide cutting tools 1 to 5 satisfy the above expression (1), an intermittent cutting test is performed using these cutting tools under the following conditions. Table 4 shows the results.

The intermittent cutting conditions Workpiece: square bar Cutting speed of _{SNCM439 (H B 320): 100m} / min Feed: 0.4 mm / rev Depth of cut: measuring the number of impacts until deficient for 3mm dry cutting 10 cutting edge,
The average was determined.

Example 2 As raw material powders, WC powder having an average particle size of 3.5 μm, TiC powder having an average particle size of 1.0 μm, NbC powder having an average particle size of 1.0 μm, and average particle size of 1.0 μm , A powder of TiN having an average particle size of 1.0 μm, and a powder of Co having an average particle size of 1.2 μm were prepared, and these powders were blended at a ratio shown in Table 5, mixed and press-molded. Later, ISO standard CN
A green compact having a shape corresponding to MG120408 was prepared, and the green compact was sintered under the conditions shown in Table 5 to have a surface layer having the composition and thickness shown in Table 5, and the composition at the center was Table 1
WC-based cemented carbide substrates B 'and D', which are almost the same as the WC-based cemented carbide substrates B and D, respectively, were produced.

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 σ _TiN (kgf / mm ² ) of this TiN layer was measured in Examples. The results were measured by X-ray diffraction in the same manner as in Example 1.
It was shown to.

The hard layers other than the TiN layer were formed by a usual chemical vapor deposition method.

The surface-coated cemented carbide cutting tools 6 to 7 of the present invention in which the coating layers shown in Table 6 consisting of a composite layer containing TiN are formed on the surfaces of the WC-based cemented carbide substrates B 'and D'.
After confirming whether or not the conventional surface-coated cemented carbide cutting tools 6 to 7 satisfy the above expression (1), an intermittent cutting test is performed using these cutting tools under the following conditions, and the results are shown in a table. 7 is shown.

The intermittent cutting conditions Workpiece: square bar Cutting speed of _{SNCM439 (H B 290): 100m} / min Feed: 0.3 mm / rev Depth of cut: measuring the number of impacts until deficient for 2mm dry cutting 10 cutting edge, its The average was determined.

[0025]

[Table 5]

[0026]

[Table 6]

[0027]

[Table 7]

[0028]

According to the present invention, the surface-coated cemented carbide cutting tool 1 and the conventional surface-coated cemented carbide cutting tool 1 have the same component composition of the WC-based cemented carbide substrate and the component composition of the coating layer. Although both layers are given a tensile residual stress, Ti satisfying the above formula (1)
Cutting tool 1 made of cemented carbide with surface coating of the present invention coated with N layer
Is superior in fracture resistance to the conventional surface-coated cemented carbide cutting tool 1 coated with a TiN layer that does not satisfy the above formula (1), and further has the surface-coated cemented carbide cutting tool 2 of the present invention.
It can be seen that the same tendency is shown by comparing 7 with conventional cutting tools 2 to 7 made of surface-coated cemented carbide.

As described above, the surface-coated cemented carbide cutting tool of the present invention does not require post-treatment such as shot peening or sandblasting, so that the cost can be kept low and the fracture resistance is also improved. It has an excellent effect that it can be performed.

Claims (3)

(57) [Claims] 1. Tungsten carbide (hereinafter referred to as WC)
In a surface-coated cemented carbide cutting tool obtained by coating a single layer made of titanium nitride (hereinafter referred to as TiN) or a multilayer containing a TiN layer by a chemical vapor deposition method using a base cemented carbide as a substrate, The residual tensile stress is σ _TiN (kgf / m
when the m ^2), the surface-coated cemented carbide cutting tool, wherein a TiN layer is coated at least one layer which satisfy the relationship of equation (1). 5x ² −80x + 315 ≧ σ _TiN (1) where x is the thermal expansion coefficient of the center of the WC-based cemented carbide substrate at 1
0 ⁶ times the value. 2. The surface of the WC-based cemented carbide substrate having Ti having a residual tensile stress that satisfies the relationship of the above equation (1).
The surface-coated cemented carbide cutting tool according to claim 1, wherein an N layer is coated as an outermost layer of the multilayer. 3. The cutting made of a surface-coated cemented carbide according to claim 1, wherein a thermal expansion coefficient of a central portion of the WC-based cemented carbide substrate is less than 7.0 × 10 ⁻⁶ / ° C. tool.