JPH05311313A - Wc-base sintered hard alloy - Google Patents

Abstract

PURPOSE:To obtain a WC-base sintered hard alloy for mining tool for which crack propagation is inhibited by specifying the grain size distribution of WC and carbon content in a WC-base sintered hard alloy consisting of specific percentages of WC and binding phase composed essentially of Co. CONSTITUTION:In a WC-base sintered hard alloy used for the mining tool, etc., and consisting of, by weight, 80-95% WC and the balance binding phase, composed essentially of Co, with inevitable impurities, the grain size of hard phase is regulated, from the microstructure at the grinding surface, so that the hard phase consists of, by area ratio, 10-30% coarse-grain WC (>7mu), 30-60% medium-grain WC (4-7mu), and the balance fine-grain WC (<7mu), and further, carbon content is regulated to a theoretical value or below, expressed in terms of WC in a two-phase region. Morover, a part of Co in the binding phase can be substituted by Ni and/or Cr by 0.1-50% and also a part of WC in the hard phase may be substituted by TaC and/or NbC by 0.1-3%. By this method, the WC-base sintered hard alloy where grain growth is prevented and crack propagation is inhibited can be obtained. By using this alloy, a high strength tool can be produced.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cemented carbide suitable for use in mining tools.

[0002]

[Problems to be Solved by the Prior Art and Problems] For cemented carbides used for mining tools, etc., E1 (Co amount 6%) to E6 (Same 20%) using coarse grain WC as JIS E type is used.
%), There are 6 types of materials. The characteristic of this system is that the WC is made coarse and the particle size is made uniform.
Characteristic is that particles of ~ 6 microns are uniformly dispersed.

Next, for mining, mainly E3, E4,
E5 equivalent products are used according to the purpose of use. However, looking at the grade of this system from the fracture toughness value, while the transverse rupture strength, which is one measure of strength, shows a value exceeding 300 kg / mm ² , crack propagation is the cause of fracture. In the fracture toughness value, its propagation depends on the Co content,
This tendency becomes remarkable especially in the case of a high hardness material having a small amount of Co.

[0004]

The cause of this is that the effect of stopping cracks becomes small due to the thinning of the mfp (mean free path) of the amount of Co, and the strength is not sufficiently improved. is there. Crack propagation is WC
Since it becomes difficult to propagate in the order of the boundary between the particles and Co, the grains of WC, and the inside of Co, it is necessary to increase the thickness of mfp and reduce the particle size distribution of WC, particularly the fine grains.

[0005]

Therefore, on the microstructure, the conventional E-type WC particles have a polygonal shape, the number of contacts between WC and WC particles increases, and crack propagation is likely to occur. Therefore, without growing the WC particles into a polygonal shape,
It was found that the boundary between WC particles and Co can be reduced by maintaining the shape with the particle edges dropped during the process of mixing and crushing even after sintering.

[0006]

Function: That is, 80 to 95% by weight of WC and the remaining Co
In a WC-based cemented carbide composed of a binder phase containing as a main component and unavoidable impurities, the WC grain size of the hard phase is a coarse grain WC (7 μm or more) in an area ratio from the microstructure on the polished surface.
30%, medium grain WC (4 to 7 μm) 30 to 60%, the rest fine grain WC (4 μm or less), and the carbon amount in the two-phase region in terms of WC converted to the theoretical value or less. First, coarse particles are used for WC to thicken mfp, and carbon is suppressed as much as possible to suppress grain growth and suppress crack propagation.

Further, in order to further enhance the effect, a small amount of Ni and / or Cr is added to the binder phase, spheroidization of grains is measured, and a small amount of TaC and / or NbC is added to the hard phase to form WC particles. Can have the effect of suppressing the growth of.

The reason for limiting the numerical values will be described below. Coarse-grained WC 7 μm is less than 10%, crack propagation is likely to occur, and if it exceeds 30%, hardness (HRA) decreases, so the content was made 10 to 30%. Medium grain WC4-7μm is 3
If it is less than 0%, crack propagation is large, and if it exceeds 60%, almost uniform grain size is obtained, so that it is 30 to 60%. The fine particles are left because they are observed on the polished surface and are caused by the positional relationship of the cutting. Also, the amount of carbon is specified to be 6.13% or less in terms of WC, because the higher the amount of carbon in the two-phase region, the more the particles grow,
Particles grow easily due to dissolution and precipitation in the sintering process,
When it is 6.13% or less in terms of WC, this tendency is suppressed, and the polygonal particle shape has slightly rounded corners. Hereinafter, detailed description will be given based on examples.

[0009]

EXAMPLES BalWC-8.0 to 12% Co as a composition
Coarse-grained WC for alloys to change the WC grain size
(Average particle size 8 micron) and Medium particle WC (5 micron same)
Was mixed with the remaining hard phase component and binder phase constituent powder, and wet mixed and pulverized. After that, in order to obtain fracture toughness, a test piece is formed, and 1350 to 1500 °
It was made by sintering at a temperature of C and grinding. The surface was lapped and finished into a mirror surface, and the microstructure was observed and classified according to the average grain size (major axis diameter + minor axis diameter) / 2, and the area was applied to each image processing device. Furthermore, as one of the methods of HRA measurement and fracture toughness, the Vickers indentation method (crack average length-cracks generated in squares of indentation by Vickers hardness meter) was measured. The results are also shown in Table 1.

[0010]

[Table 1]

From Table 1, it is possible to reduce the crack length by dispersing coarse particles WC, and this tendency is clearly shown especially in alloys containing a small amount of carbon and alloys containing Cr.

[0012]

As described above, in the cemented carbide used for mining tools and the like, as a result of various studies from the fracture toughness value,
It was possible to improve the fracture toughness by specifying the grain size of the coarse grains as the crack propagation property that causes fracture and making the WC grains into a rounded polygonal shape.

[Table 2]

Claims (2)

[Claims] 1. WC80-95 used for mining tools, etc.
In a WC-based cemented carbide containing a binder phase containing Co as a main component and an unavoidable impurity, the WC of the hard phase
Grain size WC in the area ratio from the microstructure on the polished surface
(7 μm or more) 10 to 30%, medium grain WC (4 to 7 μm)
A WC-based cemented carbide, wherein 30 to 60%, the rest is fine-grained WC (4 μm or less), and the carbon amount is not more than a theoretical value in terms of WC conversion in the two-phase region. 2. The WC-based cemented carbide according to claim 1, wherein a part of Co in the binder phase is replaced by Ni and / or Cr by 0.1 to 50%. 2. The method according to claim 1, wherein a part of WC in the hard phase is TaC and / or NbC of 0.1 to 0.1.
WC-based cemented carbide characterized by 3% replacement.