JPH0581366B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a cutting tool that is subjected to an impact load. [Prior Art and Problems to be Solved by the Invention] Cermet tools are widely used as tools for high-speed finishing cutting and milling. The chemical composition of cermet alloys is carbides with low wettability with steel;
Hard compounds such as nitrides and carbonitrides, and cobalt, nickel, etc. that bind these together.
Cermet tools are superior in terms of finished surface roughness because the hard compound that is their main component does not easily adhere to steel. Less defective. If this alloy is coated with ceramics by chemical vapor deposition, it is expected that the finished surface roughness and wear resistance will be further improved, but there is a problem in that the chipping resistance will deteriorate. In order to improve the fracture strength of as-deposited crystalline or amorphous ceramic films, various studies have been conducted, including film thickness, crystal grain size, film formation conditions that affect the crystal structure, and post-formation heat treatment methods. has not yet achieved sufficient effect. If the fracture strength of cermet alloys coated with ceramics can be increased, it will be possible to supply even better cutting tools, which will be used in applications such as milling, turning of grooved materials, and other high-speed cutting with intermittent loads. It is expected that it will spread. [Means for Solving the Problems] Therefore, the present inventors conducted research to develop a coated tool with even better fracture resistance. As a result, the wear resistance of cutting tools was improved by adding minute cracks to the coating. It has been found that fracture resistance can be significantly improved without impairing properties. This invention is based on the above knowledge, and
The target tool is a titanium carbonitride-based cermet alloy whose surface is coated with a chemical vapor deposition method.
Cutting of surface-coated cermet with excellent fracture resistance, characterized by having a coating of 2 μm or more and 10 μm or less, and having fine cracks as shown in A to C below that penetrate from the surface to the inside of the titanium carbonitride-based cermet. tool. (A) Average crack length: More than the coating thickness in the vertical direction from the coating surface, coating thickness + 5 μm or less, (B) Average crack width: 4 μm or less, (C) Average crack spacing: 10 μm or more, 200 μm
[Function] The film forming method is a chemical vapor deposition method. The coating is Tic,
It is a layer of any one of TiN, Ti (C, NF), and Al ₂ O ₃ or a stack of two or more of them. The thickness of the coating must be 2 μm or more to ensure wear resistance. Furthermore, as the coating thickness increases, the fracture resistance decreases, so the maximum thickness must be 10 μm. Usually, ceramics are applied to the surface of cermet alloy.
It is known that when coated using the CVD method, the mechanical strength of tools made of this coated alloy decreases, making them more likely to break. The cause is thought to be the difference in thermal expansion coefficient between the coating and the base material, and the tensile residual stress generated in the coating during the cooling process after CVD coating at high temperatures.This residual stress can be as high as 55Kgf/ ^mm2 . It has been confirmed that this can be achieved. When a tool with such tensile residual stress is used for interrupted cutting, additional tensile stress acts on the tool surface due to the cutting operation, and this is added to the tensile residual stress, which weakens the bending fracture strength and improves chipping resistance. This will lead to a decline in sexuality. The present invention provides fine cracks to the coating in order to improve this fracture resistance. These fine cracks whose length, width, and spacing are defined as described above release the tensile residual stress generated in the coating during the cooling process described above, and therefore, the total stress applied to the tool surface layer is: It is thought that the stress is reduced compared to the sum total of the stress that would occur when no microcracks are provided, and as a result, the propagation of cracks that lead to tool breakage is suppressed, and fracture resistance is improved. In other words, the fine cracks of the present invention are provided only to relieve the tensile stress remaining in the coating. The average crack length must be greater than the coating thickness and less than coating thickness + 5 μm in the vertical direction from the coating surface. This is because if the crack remains within the coating, the fracture resistance will not improve, and if the length within the cermet exceeds 5 μm, the fracture resistance will drop sharply. The average crack width is 4μm
Must be less than or equal to The reason for this is that as the crack width increases, fracture resistance improves, but wear resistance significantly decreases. The average value of crack spacing is 10 μm or more and 200 μm or less.
This is because if it is less than 200 μm, the crack density becomes too high and the wear resistance decreases, and if it exceeds 200 μm, the crack density becomes too small and a sufficient improvement in fracture resistance cannot be obtained. As a method for introducing such fine cracks, a method of injecting cast iron or the like onto the coating surface, a method of diamond grinding the coating surface, a method of applying mechanical or ultrasonic vibration pressure, etc. can be applied. The crack size and distribution were confirmed by breaking the tool and observing its cross section using an electron microscope (SEM). The average value of crack length, average value of crack width, and crack interval were measured from 10 photographs of the fracture surface taken at 10 fields of view and a magnification of 1000. Next, the surface-coated cermet cutting tool of the present invention having excellent fracture resistance will be specifically described with reference to Examples. [Example] Table 1 shows the crack dimensions and distribution of the test tools, as well as their cutting performance. The cermet alloy composition of the test tool is titanium carbonitride (Ti(C,N)): 47.0wt
%, molybdenum carbide ( _Mo2C ): 7.5wt%, tungsten carbide: 16.5wt%, tantalum carbide:
10.0wt%, niobium carbide: 5.0wt%, nickel (Ni): 5.0wt%, Co: 9.0wt%. A square cermet alloy with a side of 12.7 mm was manufactured through a process of crushing, mixing, granulation, sintering, and grinding. TiC/Ti(C,N)/TiC/Ti(C,N)/
The indexable tool was coated with Al ₂ O ₃ in this order to a thickness of 10 μm and 20 μm. A cast iron ball with an average grain size of 200 μm is inserted into this tool at a speed of 10 to 80 m/sec and at an angle of
Fine cracks were introduced by projecting at an angle of 70 to 90 degrees. The size and distribution of cracks were measured by breaking the tool and observing its cross section using an electron microscope (SEM). The average value of the crack length and the average value of the crack width were measured from 10 photographs taken of the fracture surface in 10 fields of view and at a magnification of 1000. The crack interval is the average value of adjacent crack intervals. The performance of the coated tool of the present invention and the comparative tool was evaluated by cutting. The conditions are as follows. (1) Intermittent cutting Work material: JIS S38C, a round bar with a diameter of 60 mm. Five grooves with a width of 10 mm were made at equal intervals parallel to the rolling direction. Cutting speed: 170m/min Feed: 0.15mm/rev Depth of cut: 1.0mm Tool life judgment criteria: Tool edge loss (2) Continuous cutting Work material: JIS S38C, round bar with a diameter of 60mm Cutting speed: 200m/min Feed: 0.15mm/rev Depth of cut: 1.0mm Tool life judgment criteria: Tool rake face wear depth Kt = 50μm The quality of tool fracture resistance is determined by the number of collisions with the groove until the tool breaks during interrupted cutting and reaches the end of its life. It was evaluated. The wear resistance of the tool was evaluated by the cutting time until the tool rake face wear depth Kt reached 50 μm in continuous cutting. The fracture resistance of the tool of the present invention is significantly superior to that of comparative tools. Tool life in interrupted cutting is more than 10 times longer. Also, the wear resistance is almost the same as that of the comparative tool. It can be seen that the effect of fine cracks is extremely significant.

[Table] [Effects of the Invention] The present invention improves fracture resistance, which is a drawback of conventional cermet tools, and has extremely significant industrial effects.

Claims (1)

[Scope of Claims] 1. A titanium carbonitride-based cermet alloy having a coating with a thickness of 2 μm or more and 10 μm or less coated by chemical vapor deposition on the surface of the titanium carbonitride-based cermet, and the coating penetrates from the surface to the inside of the titanium carbonitride-based cermet. A surface-coated cermet cutting tool with excellent fracture resistance characterized by having fine cracks as shown in A to C below. (A) Average crack length: Above the coating thickness in the vertical direction from the coating surface, coating thickness + 5 μm or less, (B) Average crack width: 4 μm or less, (C) Average crack spacing: 10 μm or more, 200 μm
below.