JPH04164504A - Surface coat high speed steel cutting tool excellent in wear resistance - Google Patents

Abstract

PURPOSE:To enhance wear resistance by forming minute cracks that reach from the surface of a coat until the inside of high speed steel in the coat having 2-8mum thickness coated on the surface of the high speed steel by means of physical vapor deposition method. CONSTITUTION:A coat having 2-8mum thickness is coated which 1 or not less than 2 kinds of TiC, TiN, Ti(C, N) on the surface of high speed steel by physical vapor deposition method. Minute cracks that penetrate from the surface till the inside of the high speed steel are formed with a width of not more than 0.8mum on this coat by a cloudburst process, etc., spacing the cracks with intervals of 5-50mum, thereby flaking of the coat is suppressed, and wear resistance of a cutting tool can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cutting tool with excellent wear resistance.

[Prior Art and Problems to be Solved by the Invention] A tool in which the surface of high-speed steel (base material) is coated with crystalline or amorphous titanium carbide or titanium nitride by physical vapor deposition (PVD) is The coating does not easily adhere to the steel material being cut, and because it is hard, it has excellent adhesive wear resistance and abrasive wear resistance, and is widely used industrially.

Since the processing temperature of physical vapor deposition is relatively low at around 500°C, there is almost no diffusion at the interface between the titanium compound film and the high-speed steel base material, so the adhesion is better than that of chemical vapor deposition. (CVD) coating. In addition, coated tools are manufactured through a process in which a titanium compound is vapor-deposited on a base material heated to approximately 500"C and then removed. During this process, due to the difference in thermal expansion coefficient between the coating and the base material, Because stress acts on the coating, microcracks with intervals of several hundred microns are usually observed in the coating.Stress is concentrated at the tips of the cracks during cutting, making the coating easy to peel off from the base material. PVD-coated tools are less wear-resistant than VDM-coated tools.

Improvements in adhesion strength are being made through various studies, including film thickness, crystal grain size, film formation conditions that affect the crystal structure, lamination method, and post-layer heat treatment method. However, no method has been found that can eliminate the stress concentration at the tip of the crack, which remains a problem in improving the wear resistance of the -layer.

[Means for Solving the Problems] Therefore, the present inventors conducted research to develop a PVD tool with excellent wear resistance, and found that by applying fine racks to the coating at high density, the coating could be improved. It has been found that peeling is suppressed and the wear resistance of cutting tools is significantly improved.

The present invention is based on the above knowledge, and the target tool is a Ti coated with a thickness of 2 μm or more and 8 uff1 or less on the surface of high-speed steel (
A resistant steel having a coating formed by laminating one or more of N, Ti ((:, N), and having microcracks shown below that penetrate from the surface to the inside of the high-speed steel. This is a surface-coated high-speed steel cutting tool with excellent wear resistance.

A) Average value of crack depth: At least the coating thickness in the vertical direction from the coating surface, but not more than coating thickness + 2 μm, B) Average value of crack width: 0.81.1 m or less, C)
Average value of crack spacing: 51 or more and 50 IJm or less [Function] The film forming method is a physical vapor deposition method. The coating is TiC, TiN, T
i(C,N) is a layer of one kind or a layer of two or more kinds. The lower limit of the thickness of the coating should be 2 μm or more from the viewpoint of wear resistance, and the upper limit of the coating should be 8 μm or less since the larger the thickness, the more easily the coating will be destroyed.

The average value of crack spacing must be greater than or equal to 5 μm and less than 50 μm. If the thickness exceeds 50 μm, the coating tends to peel off during cutting, so this value was set as the upper limit. It is thought that when the crack interval exceeds 501JI11, the stress concentration coefficient at the tip of the crack becomes large, making it easier for the crack to separate. As the crack interval becomes smaller than 50 μm, the coating becomes more difficult to peel off during cutting. This is thought to be because the stress concentration coefficient at the crack tip becomes smaller as the crack spacing becomes closer (H, Tada,
P, Paris and G, Irwin:
The 5tress Analysis o
f Cracks)landbook.

DEL RESEAR(:HC0RPORATION,
(1973)). Below 54 m, the ease of peeling remains constant. For this reason, the lower limit was set to 5 μm.

The average crack depth must be greater than the coating thickness and less than the coating thickness + 2 μm in the vertical direction from the coating surface. This is because if cracks remain within the coating, the coating is likely to peel off, and if the length within the high-speed steel exceeds 2 μm, the tool is likely to break during cutting.

The average crack width was 0.81. Must be 11 or less. The reason for this is that as the crack width increases, the coating becomes more likely to peel off. As a method for introducing such fine cracks, a method of injecting steel balls or the like onto the surface of the coating, a method of diamond grinding the surface of the coating, a method of applying mechanical or ultrasonic vibration pressure, etc. can be used.

The crack size was measured by polishing and corroding the surface of the tool coating and measuring the crack interval using an electron microscope (5EM). The crack intervals were measured from 10 photographs taken at 10 fields of view and a magnification of 10,000, and the average value was determined. The depth and width of the cracks were measured using an electron microscope (SEM) by measuring the cracks appearing in the cross section in the direction perpendicular to the film. The average value of the crack length and the average value of the crack width were determined from 10 photographs taken at 10 fields of view and a magnification of 10,000. Next, the surface-coated cemented carbide cutting tool of the present invention having excellent fracture resistance will be specifically explained with reference to Examples.

[Example] Table 1 shows the crack size and distribution of the test tool and its cutting performance. The high-speed steel used in the test tool meets Japanese Industrial Standards (JI).
5KH57 specified in S).

TiC/Ti(C,N) was added to this high-speed steel using the PVD method.
were coated with a thickness of 4 μm and 7 μm in this order to form an indexable tool. A steel ball having an average grain size of 300 .mu.m was projected onto this tool at a speed of 50 milliseconds and an angle of 70 to 90 degrees to introduce microcracks.

The crack interval was measured by polishing and corroding the surface of the tool coating and using an electron microscope (SEM). The crack intervals were measured from 10 photographs taken at a 1O field and a magnification of 10,000, and the average value was determined. The depth and width of the cracks were measured by using an electron microscope (SEM) to measure the cracks appearing in the cross section in the direction perpendicular to the film.

The average value of the crack length and the average value of the crack width were determined from 10 photographs taken with 10 fields of view and a magnification of 10,000.

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 workpiece material: JIS 548G, a round bar with a diameter of 60"m. Five grooves with a width of 10 mm were made at equal intervals parallel to the rolling direction.

Cutting speed: 100m/min Feed: 0.15ωm/rev Depth of cut: 1.5mm Tool life judgment criteria: Tool surface wear depth KT・50μ■ 2) Continuous cutting workpiece material: JIS 548G, round bar with a diameter of 60mm Cutting speed: room/min feed 0. ]5a+m/rev Depth of cut: 1.5mm Tool life evaluation criteria Tool surface wear depth KT・50im The wear resistance of the tool was comparatively evaluated based on the tool life.

Tool life is the cutting time until the tool rake face wear depth KT reaches 50 μm. The wear resistance of the tool of the present invention is significantly superior to that of comparative tools in both interrupted cutting and continuous cutting, and the tool life in interrupted cutting is 2.
~3 times longer, and the tool life in continuous cutting is 1.5~2
．． It is 0 times. It can be seen that the effect of microcracks is extremely significant.

[Effects of the Invention] The present invention improves the wear resistance, which is a drawback of conventional coated high-speed steel tools, and has extremely significant industrial effects.

Patent agent agent

Claims (1)

[Claims] 1. TiC, TiN, T coated on the surface of high-speed steel by physical vapor deposition (PVD) with a thickness of 2 μm or more and 8 μm or less
A wear-resistant steel having a coating formed by laminating one or two or more of i(C,N), and having microcracks shown below that penetrate from the surface to the inside of the high-speed steel. Excellent surface coated high speed steel cutting tool. A) Average value of crack depth: At least the coating thickness in the vertical direction from the coating surface, but not more than coating thickness + 2 μm B) Average value of crack width: 0.8 μm or less, C) Average value of crack spacing: 5 μm or more, and not more than 50 μm