JPS61110758A - Method for carburizing wc-co sintered hard alloy at low temperature - Google Patents

Abstract

PURPOSE:To execute carburizing treatment suited for precision tools at a low temp., by subjecting the WC-Co sintered hard alloy to degreasing, to application of activated carbon-contg. carburizing paste, and to heat treatment. CONSTITUTION:The WC-Co sintered hard alloy is degreased with an adequate cleaning agent. The activated carbon-contg. carburizing paste is applied to the surface of the sintered hard alloy, which is dried and heated at a temp. as low as 500-600 deg.C by high-frequency heating or other methods to be carburized; the carburizing paste has a composition consisting of, for example, 60% activated carbon, 20% yellow prussiate of potash, and 20% barium carbonate. On this low-temp. treatment, the treated products are capable of minimizing their thermal stress as well as thermal deformation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a low-temperature carburizing method for a WC-Co layered hard alloy.

(Prior Art) Low-temperature nitriding is a well-known heat treatment method in which a material to be heat-treated is heated in a suitable medium to a temperature range of 500 to 500 °C to infiltrate nitrogen into its surface layer, but low-temperature carburization Until now, there have been almost no documents reporting this (temperatures of 910 to 1050°C are used for carburizing ordinary steel).

(Problem to be solved by the invention) It is known that low-temperature nitriding of steel materials has the following advantages, so if low-temperature carburizing of cemented carbide becomes possible, the following advantages of lIa are expected. and is very attractive industrially.

(2) The surface hardness reaches a certain high value when heated at about 400°C lower than the carburizing temperature of conventional steel materials, that is, 500 to 600°C.

■ Scratch resistance decreases and abrasion resistance increases.

■Fatigue limit and cavitane resistance increase.

■Thermal deformation and thermal stress of treated products are small.

■The permeation layer is finished by cutting, polishing, etc.

The present invention minimizes thermal deformation and thermal stress of the treated product, and is suitable for application to heat treatment for precision wood cutting A.
It is an object of the present invention to provide a low-temperature carburizing method for a C--Co layered hard alloy.

(Means and effects for solving the problems) The gist of the present invention is to degrease a W C-Co layered hard alloy with a suitable cleaning agent, and coat it with a carburized base containing activated carbon.
This is a low-temperature carburizing method for W C-Co cemented carbide, which comprises heat treatment at 0°C.

According to the present invention, the surface of the WC-Co cemented carbide to be subjected to low-temperature carburizing treatment is first degreased with, for example, ethyl alcohol.

Next, a carburizing paste containing activated carbon, for example 60% activated carbon + 20% activated carbon, is applied to the surface of the degreased W C-Co cemented carbide.
A carburizing paste with the composition of % yellow blood salt [K 4 Fe (CN ) si + 20% barium carbonate [13 aCOsl] is applied and dried.

Then, it is heat-treated at 500 to 600° C., for example, by high-frequency heating, and carburized.

In the method of the present invention, it is considered that the cleaning effect of a cleaning agent such as ethyl alcohol and the carburizing property of activated carbon blended in the paste should be evaluated.

<*Example) Cemented carbide high alloy Gl (WC-5%C) for wood cutting tools
o), G2 (WC-7%Co) and G3
(WC-9%Co) Standard 3 $1 test piece was used for low-temperature carburizing according to the method of the present invention.

First, these test pieces were degreased with ethyl alcohol,
Thereafter, the amount of ffl was measured using a direct scale. After this weighing operation, all test pieces were handled in a bottle set.

60% activated carbon + 20% yellow blood salt [K, Fe (C
N), ] + 20% barium carbonate [Bac Osi] composition was applied, and the carburizing paste was heated at a temperature of 100°C for 1 hour.
Dry in an electric dryer. Note that potato starch was used as the binder for the carburizing paste.

After drying, the test piece was heat-treated by high-frequency heating in the atmosphere.

The conditions were: processing temperature 500.550°C, processing time 2.5 and 10 minutes, paste thickness 1 and 21.
It is.

In order to compare and contrast with the test piece that was carburized as described above, a test piece that was given a thermal history under similar conditions (hereinafter referred to as untreated) was prepared. The untreated specimen was coated with artificial cryolite (N a3A IF) to prevent oxidation after degreasing.
g) was applied by caking with potato starch and heated at a temperature of 100℃ for 30 minutes.
Let dry for a minute. Furthermore, iron oxide (Fe) is added to prevent peeling.
20. ) was applied by caking it with a glass of water and then electrically dried at the same temperature for 1 hour.

Before and after treatment for carburized and untreated specimens!
11 Measurement of quantity change, microhardness test (test load 1 kg)
, a transverse rupture strength test (four samples were prepared under the same processing conditions and their average value was calculated), X-ray diffraction, and structure observation using a metallurgical microscope and a scanning electron microscope.

Table 1 shows the increase rate of surface hardness of cemented carbide, which is about 6 to
We were able to increase it by 16%. From Table 2, the rate of increase in hardness is the highest for alloy 01, and the rate is almost the same for alloys G2 and 03. This is a natural result since it is known that alloys with a low Co content have a large hardness. Conceivable.

21t Maximum value (%) of increase rate of hardness due to carburization According to Fig. 1, l! of the test piece! Weight increase approximately 0.8-4.5
It can be seen that the weight increase rate of each alloy G1, G2 and G3 is a function of processing temperature, processing time and paste thickness. The numbers listed in the upper column of Figure 1 indicate the processing conditions such as processing temperature, processing time, and paste thickness.
In this figure, (a) shows the effect of processing temperature on the weight increase of the test piece, (b) shows the effect of paste thickness, and (e) shows the effect of processing time. : Arrange each factor in order of magnitude, and then consider the product of the difference between that factor and the other two factors as the energy input to the sample, and sort them from smallest to largest. It is arranged as follows. From these figures, it is clear that the weight increase of the test piece is a function of the input energy, and it is recognized that the increase in weight of the test piece is a function of the input energy, and a slight curve of failure and failure is depicted as shown by the broken line.

The results of X-ray diffraction of the test piece after this treatment are shown in Figure 2.
According to this figure, the produced compound on the surface of the test piece is Co
, C, and no peak of the compound CosC was found. Therefore, this formation is considered to be the main cause of hardening and weight change of cemented carbide due to mainstream flow.

Next, Figure 3 shows the relationship between the hardness of the test piece after this treatment and the treatment time.According to this figure, the longer the treatment time, the more the hardness generally increases. is also related to the thickness of the paste, so the above-mentioned exceptions often occur.1 For example, when carburizing a test piece coated with paste to a thickness of 1, increasing the processing time from 5 to 10 minutes will actually increase the hardness. may also decrease. The cause of this should be attributed not only to the problem in measuring the hardness of the sintered material (due to porosity) but also to the amount of paste applied. In other words, since the amount of paste applied is small, the carbon supply does not reach the end, and even if the carbon has once diffused and penetrated, if the temperature is maintained at the carburizing temperature, it will not lose its activity and will diffuse toward a lower carbon concentration. This is thought to be due to the so-called decarburization phenomenon occurring. Therefore, an appropriate processing time must be selected depending on the base thickness.

Furthermore, the relationship between the transverse rupture strength of the carburized specimen and the treatment time is shown by the broken line in Figure 3. According to this, the longer the treatment time, the deeper the carbon diffusion layer becomes. (This is considered to be the reason why the transverse rupture strength value decreases as the processing time increases, which is the opposite trend to hardness.

Finally, FIG. 4 shows photographs of the fracture surfaces of carburized and untreated transverse rupture strength specimens observed with a scanning electron microscope. According to this, the treated material (G2, paste thickness 1 +s+*,
The depth of the carburized layer obtained under treatment conditions of 550°C for 5 minutes was found to be approximately 20μ from the hardness measurement results and microstructure observation results) and the difference in the surface condition of the untreated material was clearly seen. This confirmed the effectiveness of this method.

(Effect of the invention) By the method of the present invention, WC-Coi! It is possible to carburize at a low temperature of 500 to 600° C. using a carburizing paste in M1 hardening, and the surface of the alloy to be treated is lightened by forming a carbide layer with a composition similar to CO2C.

This low-temperature carburizing method is the lowest-temperature heat treatment method among all heat treatment techniques, and the thermal deformation and thermal stress of the treated product are minimized, making it ideal for application to precision tools and the like.

Finally, we will briefly discuss the application of this method to cemented carbide tools. In the conventionally well-known high-temperature carburizing method, after brazing the carbide tip with copper solder, the entire tool is coated with paste and carburized.
This operation is impracticable because the copper solder will melt. However, in this method, such processing is carried out using a light low-temperature carburizing method (carburizing paste is applied to the carbide chip part, and the paste used when no treatment is applied is applied to the substrate part to prevent oxidation). This makes it possible to improve hardness, longer life, and wear resistance by approximately 30% compared to conventional carbide tools.
It becomes possible to manufacture tools that are twice as improved. This is a remarkable effect with just 1 unit.

[Brief explanation of drawings]

Figure 1 shows the increase in fL'gk after carburizing the sample, (a) shows the effect of carburizing temperature on the weight increase of the sample, and (b) shows the effect of the carburizing temperature on the increase in the weight of the sample. FIG. 10(a) is a diagram showing the influence of the paste thickness on the increase in m wind of the sample. FIG. 2 is a diagram showing the X-ray diffraction pattern of the sample after carburization. FIG. 3 is a diagram showing the relationship between processing time, steepness, and transverse rupture strength value of a sample after carburization at each temperature. FIG. 4 is a photograph of the structure of the sample taken by SEM.

Claims (2)

[Claims] (1) A low-temperature carburizing method for WC-Co-based cemented carbide, which comprises degreasing WC-Co-based cemented carbide, applying a carburizing paste containing activated carbon, and heat-treating at 500 to 600°C. (2) Activated carbon content in carburizing paste is 10-90%
A low temperature carburizing method according to claim 1.