JP3027991B2 - Hard layer coated tungsten carbide based 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 has a hard layer which is excellent in wear resistance even when used in heavy cutting such as high feed and high depth of cut, and has excellent fracture resistance when used in interrupted cutting. And a tungsten carbide (hereinafter referred to as WC) based cemented carbide cutting tool.

[0002]

2. Description of the Related Art (1) Japanese Unexamined Patent Publication (Kokai) No. 2-197569 discloses that an extremely tough coated cemented carbide has a hardness of 2 to 5 μm just below the interface of the coating layer and a Vickers hardness of 500 g load. A coated cemented carbide substrate that is 700 to 1300 kg / mm ² and monotonically increases toward the interior of the cemented carbide matrix and becomes constant at about 50 to 100 μm below the coating layer interface.

(2) Japanese Unexamined Patent Publication (Kokai) No. 63-103071 discloses, as a tool material having remarkably improved wear resistance, that "the surface of a cemented carbide is composed of an iron group metal having an average of 4% or less and a β-solid solution. A low-pressure chemical vapor deposition comprising a 1-10 micron thick outer layer composed mainly of carbide and carbonitride, and a 2-40 micron thick inner layer composed of carbide, carbonitride and iron group metal and softer than the substrate. Of a hard-layer coated WC-based cemented carbide cutting tool. In addition, the cemented carbide substrate is composed of an outer layer rich in β solid solution with high hardness and reduced binding metal, and an inner layer low in hardness with rich binding metal in the middle of the cemented carbide. Is changing. "

[0004]

However, Japanese Patent Application Laid-Open No.
In the hard layer-coated cemented carbide described in 197569, cracks are hardly generated because the surface of the substrate is softened most, but once cracks are generated, the hardness increases as it goes inside, so that the cracks are easily propagated. And the above-mentioned JP-A-63
The hard layer-coated cemented carbide described in JP-A-10-3071 has a thickness of 4% or less of a carbide or carbonitride mainly composed of an iron group metal and β-solid solution of 4% or less in order to improve wear resistance. Since it is composed of an outer layer that is harder than the inside of the substrate of 1 to 10 microns, it is more likely to cause chipping, and any of the above hard layer coated cemented carbides is subjected to severe loads such as interrupted cutting with high impact force. When used for cutting, the reliability of the cutting edge was low because of the occurrence of chipping.

[0005]

Means for Solving the Problems Accordingly, the present inventors have
As a result of conducting research to obtain a hard layer coated cutting tool with high reliability even when used in intermittent cutting with high impact force and heavy cutting with severe wear, "substrate surface vicinity" was found to be within 5μm of the substrate surface and the substrate surface The following findings were obtained by defining the depth region, “the inside of the substrate” as a depth region exceeding 5 μm and within 50 μm from the substrate surface, and defining the “center portion of the substrate” as a depth region deeper than 50 μm from the substrate surface.

[0006] (a) The defect is caused by cracks generated on the surface of a cutting tool made of a hard layer-coated cemented carbide, which grow toward the inside of the substrate. For this reason, the hardness of the substrate of the conventional hard layer coated cemented carbide cutting tool is determined by the method disclosed in
Although the hardness of the base is lower than the center of the base near the surface of the base as in the cutting tool made of a hard layer-coated cemented carbide described in No. 7569, it contributes to an improvement in fracture resistance to some extent. However, in order to further improve the fracture resistance, the hardness in the vicinity of the substrate surface is softened more than the central portion of the substrate,
In addition, it can be achieved by making the minimum value of the hardness exist inside the substrate in the softened region excluding the vicinity of the substrate surface.

(B) The minimum value of the hardness is made to exist inside the substrate in a softened region excluding the vicinity of the surface of the substrate, and an inflection point where the gradient of the hardness changes from negative to positive besides the minimum value (hereinafter referred to as the inflection point) ,
It is called the minimum value. The minimum value is dH / dx <0 to dH, where H is the hardness, and x is the distance from the substrate surface toward the inside.
/ Dx> 0, that is, a point where dH / dx = 0) is present, the cracks generated on the surface are prevented from growing in the region of the minimum hardness, and At least one minimum value greatly suppresses crack propagation.

The present invention has been made based on these findings. (1) A first hard dispersed phase composed of tungsten carbide, and a bond mainly containing one or more of iron group metals. On the surface of a tungsten carbide-based cemented carbide substrate consisting of phases and unavoidable impurities, 4a, 5a and 6a of the periodic table
A compound of one or more metal elements selected from the group consisting of group metals, Al and Si, and one or more nonmetal elements selected from the group consisting of carbon, nitrogen, oxygen and boron; In a cutting tool coated with a hard layer composed of a single kind of layer or two or more kinds of layers (hereinafter, referred to as a hard layer), the hardness of the tungsten carbide-based cemented carbide substrate is as follows:
A hard layer coated tungsten carbide-based cemented carbide having at least one minimum value at which a minimum value and a hardness gradient other than the minimum value change from negative to positive inside the substrate and the hardness near the substrate surface is lower than the hardness at the center of the substrate. An alloy cutting tool, (2) a first hard dispersed phase composed of tungsten carbide, and a second hard composed of one or more carbides and / or charcoalized carbides of metals of groups 4a, 5a and 6a of the periodic table. Disperse phase, and a cutting tool formed by coating the hard layer on the surface of a tungsten carbide-based cemented carbide substrate comprising a binder phase containing one or more of iron group metals and unavoidable impurities, The hardness of the tungsten carbide-based cemented carbide substrate shows at least one minimum value where the hardness gradient other than the minimum value changes from negative to positive inside the substrate, and the hardness near the surface of the substrate is within the substrate. Hard layer coated tungsten carbide based cemented carbide cutting tool with lower hardness than the core,
It is characterized by:

In the present invention, "in the vicinity of the substrate surface" means the substrate surface and a depth region within 5 .mu.m from the substrate surface, and "inside the substrate" means 5 .mu.m from the substrate surface.
m and a depth region of not more than 50 μm, and “the center of the substrate” indicates a depth region deeper than 50 μm from the surface of the substrate.

[0010] The cemented carbide substrate used for producing the hard layer coated WC-based cemented carbide cutting tool of the present invention is mixed with a predetermined composition and the temperature of the pressed compact is raised to 1380 ° C. After vacuum sintering at a predetermined temperature within this temperature range, the atmosphere is switched to a carburizing atmosphere, sintered, and then gradually cooled at 0.3 to 3.0 ° C./min.

[0011] The cemented carbide substrate thus obtained is
When free carbon is contained, a desired hardness distribution is easily obtained. Further, the minimum value and the minimum value of the hardness are 5 from the substrate surface.
If it exists in the center of the substrate at a deep depth exceeding 0 μm, plastic deformation is likely to occur during cutting. Therefore, the minimum value and the minimum value of the hardness are 5 μm from the substrate surface.
Preferably, it is present inside the substrate in a depth region exceeding m and within 50 μm. Further, in the present invention, when the hardness in the vicinity of the substrate surface (the substrate surface and the depth region within 5 μm from the substrate surface) is larger than the center of the substrate, cracks are significantly increased from the substrate surface. Therefore, the hardness in the vicinity of the substrate surface is set lower than that in the center of the substrate.

[0012]

Next, a cutting tool made of a WC-base cemented carbide coated with a hard layer according to the present invention will be specifically described with reference to examples.

As raw material powders, all have an average particle size of 1 μm.
m of Ti (C _0.56 N _0.44 ) powder and TaC powder,
Furthermore, WC powder having an average particle size of 3.5 μm, and an average particle size:
1.2 μm Co powder was prepared, and these raw material powders were
C: 86.3%, Co: 5.6%, Ti (C
_0.56 N _0.44 ): 2.5%, TaC: 5.6%, and wet-mixed in a ball mill for 72 hours.
After drying, at the pressure of 10 kg / mm ² , the ISO standard SN
It was press-molded into a green compact having a shape conforming to MG120408.

The green compact is held at 1380 ° C. for 60 minutes in a vacuum atmosphere of 0.01 Torr, and then the atmosphere is changed to CH 3.
The mixture was kept at the same temperature for 30 minutes as a mixed gas of ₄ : H ₂ = 1: 2, and then cooled to 1300 ° C. at a cooling rate of 1 ° C./min at 128 ° C. without changing the atmosphere of the CH ₄ + H ₂ mixed gas.
Cooling to 0 ° C. was performed at a cooling rate of 20 ° C./min, cooling to 1260 ° C. was performed at a cooling rate of 1 ° C./min, and cooling to 1240 ° C. was performed at a cooling rate of 20 ° C./min. Then, the WC-based cemented carbide substrate of the present invention was produced.
FIG. 2 shows the sintering conditions and the subsequent cooling conditions.

The WC-based cemented carbide substrate of the present invention thus produced is subjected to a round honing of 0.06 mm, and thereafter, is subjected to acid cleaning, and is subjected to a conventional CVD method to obtain TiC (5 μm) -TiCN (1 μm)- A composite hard layer of Al ₂ O ₃ (2 μm) was coated to produce a hard layer-coated WC-based cemented carbide chip 1 of the present invention (hereinafter referred to as the present coated chip).

With respect to the coated chip 1 of the present invention, the vertical axis represents the micro Vickers hardness at a load of 200 g measured by a 10-degree polished slope, and the horizontal axis represents the distance from the substrate surface to the inside. As shown in FIG. The substrate inside the present invention cover the chip 1, as shown in FIG. 1, in addition to the two minimum values P of the minimum value P _m
There is ₁ and P _2, in order that, without defects to crater wear develops, it can be seen that very toughness is improved. Further, free carbon was contained in the center part at a depth of 200 μm or more from the surface of the cemented carbide substrate.

Further, using the coated tip 1 of the present invention, cutting test 1 work material: square material of SNCM439 (Brinell hardness 300), cutting speed: 200 m / min, feed: 0.5 mm / rev, cutting depth: 3 mm Intermittent cutting was performed under the following conditions, and the number of impacts until chipping occurred was measured. As a result, the coated chip 1 of the present invention has 24
It was damaged by the impact 205 times.

On the other hand, for comparison, the compact was heated to 1400 ° C.
Vacuum the temperature was raised to, after holding for 30 minutes in N ₂ atmosphere at 2 Torr, cooled to 1310 ° C. at a cooling rate of 10 ° C. / min, in a vacuum at 3 ° C. / min to 1200 ℃ (10 ^-3 Tor
r) to produce a conventional WC-based cemented carbide substrate,
Further, similarly, the green compact was sintered in vacuum at 1400 ° C., and after the sintering was completed, CH ₄ and N ₂ gases were introduced stepwise, and the resultant was gradually cooled to produce a conventional WC-based cemented carbide substrate.

After the surface of the conventional WC-based cemented carbide substrate is washed with an acid, the conventional WC-based cemented carbide substrate is subjected to ordinary chemical vapor deposition with a 0.06 mm round honing applied thereto. Each of them is coated with a composite hard layer of TiC (5 μm) -Al ₂ O ₃ (2 μm), and conventionally hard layer coated tips 1 and 2 made of WC-based cemented carbide (hereinafter referred to as conventional coated tips 1 and 2).
Was prepared. For the conventional coated chips 1-2, 10
The vertical axis represents the micro Vickers hardness at a load of 200 g measured by the degree-polishing slope, and the horizontal axis represents the distance from the substrate surface to the inside. The graph of the substrate hardness distribution is shown in FIG. As shown in FIG. 3, although the minimum value of the hardness of the substrate of the conventional coated chip 1 is near the surface of the substrate but not inside the substrate, and the conventional coated chip 2 has a minimum value inside the substrate, The hardness near the substrate surface was higher than the hardness at the center of the substrate.

Cutting test 2 Work material: Square steel material of SNCM439 (Brinell hardness 270), cutting speed: 100 m / min, feed: 0.4 mm / rev, cutting depth: As a result of intermittent cutting under the conditions of 3 mm and the number of impacts until the chip was broken, the conventional coated chip 1 was broken by 2747 times of impact and the conventional coated chip 2 was broken simultaneously with the cutting.

[0020]

According to the cutting test 1 of the coated tip 1 of the present invention, the cutting conditions are more severe than those of the cutting test 2 of the conventional coated tips 1 and 2, but the coated tip 1 of the present invention has defects. The coated tip 1 of the present invention shows excellent fracture resistance even when used for severe interrupted cutting, and is excellent when used for heavy cutting such as high feed and high cutting. It has excellent industrial effects because of its excellent wear resistance.

[Brief description of the drawings]

FIG. 1 is a graph showing the hardness distribution of a substrate of a WC-based cemented carbide tip coated with a hard layer according to the present invention.

FIG. 2 is a graph showing manufacturing conditions of a substrate used for manufacturing a hard layer coated WC-based cemented carbide chip of the present invention.

FIG. 3 is a graph showing the hardness distribution of a conventional hard layer-coated WC-based cemented carbide chip base.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B23B 27/14

Claims (2)

(57) [Claims] 1. A surface of a first hard dispersed phase composed of tungsten carbide, a binder phase mainly composed of one or more of iron group metals and a tungsten carbide-based cemented carbide substrate composed of unavoidable impurities, One or more metal elements selected from the group consisting of metals of groups 4a, 5a and 6a of the periodic table, Al and Si, and carbon,
One monolayer or two of a compound of one or more nonmetallic elements selected from the group consisting of nitrogen, oxygen and boron
Hard layer made of a kind or a plurality of layers (hereinafter, referred to as a hard layer) in the cutting tool comprising coating the hardness of the tungsten carbide based cemented carbide substrate, the group
Substrate in a depth region exceeding 5 μm and within 50 μm from the body surface
Internally the minimum and non-minimum hardness gradients go from negative to positive
Exhibit at least one changing local minimum and 5
Is the hardness near the substrate surface in the depth region within μm
Lower than the hardness at the center of the substrate in the depth region deeper than 50 μm
Hard layer coated tungsten carbide based cemented carbide cutting tool, characterized in that brewing. 2. A first hard dispersed phase consisting of tungsten carbide, a second hard dispersed phase consisting of one or more carbides and / or charcoalized compounds of metals of groups 4a, 5a and 6a of the periodic table; A cutting tool obtained by coating the surface of a tungsten carbide-based cemented carbide substrate comprising a binder phase containing one or more of iron group metals as main components and unavoidable impurities with the hard layer; hardness of the base cemented carbide substrate, the group
Substrate in a depth region exceeding 5 μm and within 50 μm from the body surface
Internally the minimum and non-minimum hardness gradients go from negative to positive
Exhibit at least one changing local minimum and 5
The hardness near the substrate surface in the depth region within μm
From the hardness of the center of the substrate in the depth region deeper than 50 μm from
A cutting tool made of a tungsten carbide-based cemented carbide based on a hard layer, characterized by a low hardness.