JPH048409A - Coated cemented carbide tool excellent in shock resistance - Google Patents

Abstract

PURPOSE:To improve chipping resistance by generating a fine crack in the coating of a coated cemented carbide for which a coating comprising at least one layer of ceramic selected from carbide and the like such as Ti as a tungsten carbide base cemented carbide, is coated. CONSTITUTION:A fine crack is necessary for a coated cemented carbide comprising at least one layer of ceramic of at least one species selected from carbides, nitrides, nitride-carbides of Ti, Zr, Hf, Nb, Ta, Cr, Mo, and Al2O3, so as to improve chipping resistance. Since the chipping resistance is drastically deteriorated when the depth of crack penetration in the cemented carbide exceeds 5 micrometer, the coating depth of crack penetration is defined as not less than the thickness of coating in a vertical direction from the coated surface, and not more than the thickness of coating plus 5 micrometer. The average value of the crack width is not more than 2 micrometer, and when the value exceeds this level, the chipping resistance will be improved, however abrasion resistance will be drastically reduced. When the average crack distance is not less than 10 micrometer, the release of residual stress is insufficient, while, when it is less than 5 micrometer, since the abrasion resistance is reduced, the crack distance is defined as not less than 5 micrometer, and less than 10 micrometer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial 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] Conventional coated cemented carbide tools are coated with tungsten carbide-based cemented carbide on the surface by chemical vapor deposition or physical vapor deposition for the purpose of improving wear resistance. It is coated with crystalline or amorphous ceramics. In general, the performance of coated cemented carbide tools is superior to that of cemented carbide tools in terms of wear resistance, but inferior in chipping resistance. It is explained that this is because defects such as whites and clutter that occur in the film during film deposition act as fracture starting points, or because the fracture strength of the as-deposited ceramic film is low. In order to improve the film formation method that does not include defects such as holes and cracks, and the fracture strength of the film, we have been developing film thickness, crystal grain size, film formation conditions that affect the crystal structure, and heat treatment methods after film formation. Although various studies have been conducted on this topic, no sufficient results have been achieved.

The shapes of workpieces are becoming more and more complex year by year, and there are more and more opportunities for interrupted cutting to be performed under impact loads. Furthermore, there is a need for faster and heavier cutting, and the development of tools with excellent impact resistance is desired.

[Means for Solving the Problem] The present inventors believe that the reason that the fracture resistance of coated cemented carbide tools is inferior to that of cemented carbide tools is that the tensile stress generated during the formation of the ceramic layer remains in the coating. As a result of research, we found that the impact resistance of coated cemented carbide tools was significantly improved by creating cracks with appropriate shapes and distribution in the coating and releasing the residual stress within the coating. I found out.

The tool according to the present invention includes a tungsten carbide-based cemented carbide, one or more selected from carbides, nitrides, carbonitrides, and A1□03 of Ti, Zr, Hf, Nb, Ta, Cr, and Mo. A coated cemented carbide tool coated with a coating consisting of one or two or more layers of ceramic, characterized in that the coating has fine cracks with the following shapes and distributions: A coated cemented carbide tool with excellent impact resistance. be.

A) Average value of crack depth: At least the coating thickness in the vertical direction from the coating surface, 1,000 μm or more F, B) Average value of crack width: 2 layers or more F, C) Average value of crack spacing = 5 μJ or more , less than 10 μm [The cutting tool is made of Ti, Zr, Hf, Nb, Ta,
Cr, Mo carbides, nitrides, carbonitrides and Al2O
This coated cemented carbide tool has a coating made of one or more layers of one or more ceramics selected from the following.

Microcracks are necessary to improve fracture resistance. The cracks formed in this coating have a depth that reaches the interface between the coating and the cemented carbide base material or even slightly into the cemented carbide. However, when the depth of crack penetration into the cemented carbide exceeds 5 μm, the fracture resistance rapidly decreases. Therefore, the average value of the crack depth must be greater than the coating thickness and less than the coating thickness + 5 μm in the vertical direction from the coating surface.

Further, the average value of the crack width must be 2 layers or less. The reason for this is that when the crack width becomes larger than this value, the fracture resistance improves or the wear resistance significantly decreases.

The reason why the average value of the crack spacing was set to 51 or more and less than 109 m is because if the average spacing is larger than 10 μm, the release of residual stress will not be sufficient, and the effect will not be sufficient especially against severe impact loads under heavy cutting conditions. This is because the cracks do not appear, and on the other hand, when the crack interval becomes less than 5 μm, the wear resistance rapidly decreases. For the above reasons, the crack interval is 5.
It was set to be at least μm and less than IOμm.

As a method for introducing such fine cracks, a method of injecting cast iron or the like onto the surface of the coating, a method of applying tire pressure to the surface of the coating, a method of applying mechanical or ultrasonic vibration pressure, a method of rapid heating and cooling, etc. can be applied. The crack size and distribution were confirmed by observing the cross section of the fractured tool and the polished and etched surface using an electron microscope (SEM). The average value of the crack depth and the average value of the crack width were measured from 10 photographs taken of the fracture surface with a 1O view and a magnification of 1000. Also, 5 fields of view on the surface, 1000
The average value of the crack spacing was measured from five photographs taken at multiple times. Comparative tools include tools that are coated with ceramic but do not introduce cracks, and tools that have introduced cracks but whose depth, width, and spacing exceed the range specified by the present invention. There are two types.

Next, the coated cemented carbide tool of the present invention, which has excellent cracking resistance, will be specifically explained using examples.

[Example] WC: 88. Owt! li, TiC:2. Owt, *
, TiC/Tl(C,N)/Ah0 to the cemented carbide whose components are TaC: 3.0wt%, Conia, and 0wt96.
A cemented carbide tool (Model No. SNMA120408) coated with 3.3 and 3.8 and 15 μm thick in this order, and a tool of the present invention in which fine cracks were imparted to the coating by irradiating it with a laser, and the scope of the present invention. A cutting test was conducted under the following conditions using a tool that had cracks with a shape and distribution that exceeded the above.

The size of the crack was 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 views at a magnification of +000.

The crack interval was determined from five photographs taken of the ceramic coating surface in five fields of view and at a magnification of 1000.

1) Intermittent cutting work material: JIS 548C2 A round bar with a diameter of 50 mm was provided with five grooves each having a width of 10 mm at equal intervals in parallel to the rolling direction.

Cutting speed: 200 m/mi Feed rate: 0.4 mm/reν Depth of cut °2, On+m Tool life criterion Defective tool cutting edge 2) Continuous cutting work material: JIS 548G, round bar with a diameter of 60 mm Cutting speed: 300 rn/min Feed : 0.25mm/rev Depth of cut: 2.5mm Tool life criterion = tool rake face wear depth = 50μ
Fracture resistance of the tool was evaluated based on the number of collisions with the groove during interrupted cutting until the tool fractured and reached the end of its life. The wear resistance of the tool was evaluated by the cutting time until the tool rake face wear depth Kt reached 50 um in continuous cutting. Table 1 shows the test tools and their cutting test results. The fracture resistance of the tool of the present invention is significantly superior to that of the comparative tool. Furthermore, the wear resistance is almost the same as that of the comparative tool. It is clear that the effect of microcracks is quite significant.

[Effects of the Invention] The present invention improves the chipping resistance, which is a drawback of conventional coated cemented carbide, and has extremely significant industrial effects.

Claims (1)

[Claims] 1. Ti, Zr, Hf in tungsten carbide based cemented carbide
In a coated cemented carbide tool coated with a coating consisting of one or more layers of one or more ceramics selected from carbides, nitrides, carbonitrides of Nb, Ta, Cr, Mo, and Al_2O_3. A coated cemented carbide tool having excellent impact resistance, wherein the coating has microcracks having the following shape and distribution. A) Average value of crack depth: More than the coating thickness in the vertical direction from the coating surface, less than 5 μm + coating thickness, B) Average value of crack width: 2 μm or less, C) Average value of crack spacing: 5 μm or more, less than 10 μm