KR0178578B1 - Method for manufacturing cementer carbides sintered body - Google Patents

Abstract

The present invention has a higher Co concentration toward the outside than the average cobalt (Co) concentration of the cemented carbide sintered compact so as to contain both impact resistance and high compressive strength at the same time, and lower the Co concentration toward the center of the outer portion. The present invention relates to the production of a WC-Co-based cemented carbide sintered body which has a high compressive strength toward the center, wherein H ₂ , N is added to the WC-Co-based alloy powder by adding one or more of transition metals or transition metal carbides. ₂ , Ar is the first sintering step to increase the temperature to 1,000 ℃ at a temperature rising rate of 100 ~ 150 ℃ / hour at a temperature mixture of H ₂ O gas at 0.5 to 1 hour, 150 to 200 if the vacuum is maintained Cobalt (Co) content is higher than the average content from the center of the sintered body to the outside from the center of the sintered body to the second sintering step of raising the temperature to 1,350 to 1,500 ° C and maintaining the temperature for 1 to 2 hours at a heating rate of ℃ / hour. By increasing the technology relates to a process for the preparation of cemented carbide sintered body for impact resistance and high compression strength, characterized by a Co content lower joseongdoem the average Co content than the average content.

Description

Manufacturing method of cemented carbide sintered body for impact resistance and high compressive strength

1 is a state diagram showing an example of the use of parts of cemented carbide used in large belt type ultra high pressure generator.

Figure 2 is a graph showing the distribution of Co concentration in the core and outer diameter side.

3 is a graph showing the hardness distribution of the core and the outer diameter side.

4 is a graph showing the distribution of non-saturation degree in the deep and outer diameter side.

The present invention relates to a WC-Co-based cemented carbide sintered body having impact resistance and high pressure strength, and more specifically, the Co concentration is higher than the average Co concentration toward the outside from the sintered body, and the Co concentration is lower than the average Co concentration toward the center. In this regard, the outer portion has a high fracture toughness and a high tensile strength, and relates to a method for producing a cemented carbide sintered body which is adapted to have a high compressive strength toward a deeper portion.

Conventionally, tungsten carbide-cobalt (hereinafter referred to as WC-Co) based cemented carbide has high hardness and high oxidation resistance among Ni, Fe, Ni-Fe, Ti Zr, Hf, V, Nb, Ta, Cr, Mo. It is known to cemented carbides that have improved heat resistance and wear resistance by adding at least one kind.

When the cemented carbide is used as a cutting tool material, it has excellent flank wear resistance and crater wear resistance, thereby improving cutting durability.

However, in the case of the cemented carbide described above, the wear resistance and the heat resistance are improved, but the hardness and brittleness are poor, which results in a weak strength and impact resistance.

Therefore, there is a limit to the use of cemented carbide or the like used in dies or ultra-high pressure generators requiring high compressive strength including impact resistance.

FIG. 1 shows an example of a belt-type large ultra high pressure generator used in the synthesis of diamond or CBN or in the production of these fastening composites, and the pressure is synthesized by the anvil (1) above and below. The cylinder 2 is delivered to the sample 2 to be fastened with a sleeve 4 made of alloy steel or stainless steel to reinforce the internal pressure.

In such an apparatus, a WC-Co cemented carbide is used for the anvil 1, the cylinder 3, and the like.

This is used because cemented carbide has a higher compressive strength and excellent corrosion resistance and abrasion resistance than other materials.

However, as in one example of the device described above, the materials of cemented carbide parts, including impact-resistant die-pecking and other tools used in anvils, cylinders and other applications, are of high impact resistance (such as fracture toughness and breakout force) and high compression. Since the strength is not satisfied at the same time, there are many problems in service life.

Accordingly, the present invention has been made in order to solve the above-described problems, and the impact resistance and high compression to be used for various tools, dies or elvilles, cylinders, etc., which are subject to WC-Co-based cemented carbide sintered body, but are subjected to high impact, high pressure, etc. The purpose is to obtain a furnace alloy sintered body which can have strength simultaneously.

The present invention for achieving the above object is made by forming a WC-Co-based alloy powder by a conventional powder metallurgy method, while heating at a rate of 100 ~ 150 ℃ / hour from the initial stage of sintering to room temperature of 1,000 ℃ One or two or more of H ₂ , N ₂ and Ar are sintered in an atmosphere mixed with H ₂ O gas to gradually increase the oxygen content or decrease the carbon content from the center of the molding body to the outside. The Co content is higher than the average Co content of the alloy toward the outside from the core part of the sintered body as the step is sintered while heating at a rate of 150 to 200 ° C./hour to 1,350 to 1,600 ° C. while maintaining a vacuum, A WC-Co-based sintering agent is obtained by containing less than the average Co content of.

The present invention is applicable not only to the above-mentioned WC-Co system but also to all cemented carbide materials having Co of 3 to 25 wt% and having a particle size of 0.5 to 20 μm of WC used.

Some of the Co (Co) can be replaced with Ni or Fe or a mixed combined phase of Ni / Fe, and up to l5wt% of WC can be Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or their It can be replaced by one or more kinds of carbides.

The above composition and its composition ratio are merely to provide a conventional example, and the present invention is not intended to improve the properties by adjusting any specific composition ratio, and is not largely dependent on the magnitude of Co content in the WC-Co base alloy. As long as it contains Co, it is applicable, and is not limited to the specific composition and composition ratio containing Co.

More specifically, the WC-Co cemented carbide molded body of the present invention is manufactured according to the general powder metallurgical method.

That is, the alloy powder is milled and then molded into a desired material by general squeezing, such as atmospheric pressing, pressurized pressing, hot hydrostatic pressing, cold constant pressure pressing, or the like, followed by sintering. The amount of carbon in the powder is preferably set so that the degree of non-saturation of the alloy after sintering is 85% or more.

The molded article formed by the above method is heated to 1,000 ° C. at a heating rate of 100 to 150 ° C./hour in a gas atmosphere in which at least one of H ₂ N ₂ and Ar is mixed with H ₂ O gas from room temperature from 0.5 ° C. Hold for 1,0 hours.

At the temperature of about 1,000 ° C. above, gas is generated by the reaction of carbon and oxygen, and the generated gas must be sufficiently discharged.

At this time, if the temperature increase rate is less than 100 ℃ / hour, the speed is not helpful to improve the productivity, and if the temperature increase rate is 150 ℃ / hour or more it is likely to crack in the sintered body due to rapid heating.

If the holding time is 0.5 hours or less, the gas is not discharged enough, so that pores exist in the sintered body.

During this process, the oxygen flow rate is gradually increased on the outer side of the molded body, or the carbon content is gradually decreased.

The increase in the oxygen content to the outside is caused by the oxygen in the H ₂ O gas or the oxygen in the atmosphere, and the oxygen content increases in the outside as it is sintered in the mixed gas atmosphere. Due to action.

Following this initial sintering step. It sinters for 1 to 2 hours, heating up to the temperature range of 1,350-1,600 degreeC at the temperature increase rate of 150-200 degreeC / hour in a vacuum atmosphere.

When the sintering temperature is less than 1,350 ℃ and less than 1 hour, the sintering is insufficient, the alloy structure is uneven and the strength is also lowered. When the sintering temperature is more than 1,500 ℃ and more than 2A, the fluidity is increased to the excessive liquid shape and the sintered body weight The molded shape may be deformed and there is a fear that the tissue becomes coarse and the soil is degraded.

In the subsequent sintering process, the liquid phase temperature of Co phase is changed by the difference of oxygen concentration or carbon concentration difference between the outside and the deep side obtained during the low temperature sintering of the initial stage, and the liquid phase formed first inside the liquid phase during sintering moves to the outside Done.

Therefore, the Co concentration is formed inside and outside.

After such sintering, slow cooling is performed.

The following is described according to the embodiment.

Example 1

87% WC-13% Co-based alloy composition was targeted, and the particle size of WC was used in 2 ~ ㎛, after the alloy powder was prepared by the conventional powder metallurgy method by CIP (Cold Isostatic Pressing) method It was molded into a cylinder 3 type of ultra high pressure generator such as 1 degree.

Subsequently, the molded article was heated to 1,000 ° C. and maintained for 1 hour at a rate of 150 ° C./hour under the use of an H ₂ O / N ₂ atmosphere gas to increase the oxygen content of the molded article to 0.2% higher than the inner center, and then to 1370 ° C. while maintaining a vacuum. The temperature was raised at a rate of 100 ° C. per hour, vacuum sintered for 1 hour, and slow cooling (20 ° C. or less).

The difference in Co composition between the outside and inside of the sintered body thus obtained, the magnetic saturation of the bonding phase and the hardness of the alloy were shown in Figs.

It was attached to the ultra-high pressure generating device to compare the product lifespan having a general uniform composition and physical and mechanical properties generally produced as shown in Table 1 below.

Example 2

The molded article of the cemented carbide component as in Example 1 was heated to 1,000 ° C. and maintained at 1,000 ° C. at a rate of 100 ° C./hour from room temperature using a HO / H atmosphere gas from room temperature to maintain the carbon content of the outer part of the molded part in the center of the internal powder. After lowering 0,2%, the temperature was raised to 1370 ° C. at a rate of 100 ° C. per hour, followed by vacuum sintering at 1 hour, followed by slow cooling.

The difference between the Co composition, the saturation of the bonding phase, and the hardness of the alloy of the sintered body thus obtained were in accordance with FIGS. 2 to 4, respectively. As a result of the product and the life fertilizer having physical and mechanical properties were as shown in the following [Table 2].

As described above, the present invention provides more oxygen or less carbon as it sinters the WC-Co powder alloy or composite molded body thereof under low temperature and HO, N, Ar, HaO mixed gas atmosphere which is an initial stage in sintering. As the temperature is increased and sintered during the main sintering, the Co content is increased toward the outside of the sintered body, and the Co content decreases toward the inside, due to the above-described internal and external concentration differences.

Therefore, the outer side can be used as other cemented carbide members, such as dies or cylinders, for use in which the outer side has rich toughness and the inner side has a high compressive concentration so that it can simultaneously enjoy high toughness and compressive strength as a whole.

Claims (1)

In the molding and sintering by adding one or more of transition metals or transition metal carbides to a WC-Co-based alloy powder, 100 to 100 in an atmosphere in which at least one of H ₂ , N ₂ and Ar is mixed with H ₂ O gas. 1st sintering step to maintain 0.5 ~ 1 hour by heating up to 1,000 ℃ at 150 ℃ / hour heating rate, and 1 ~ 2 by heating up to 1,350 ~ 1,500 ℃ / hour at 150 ~ 200 ℃ / hour Cobalt (Co) content is higher than the average content as the secondary sintering step is maintained from the center of the sintered body to the outside, and the Co content is adjusted to be lower than the average content as the center toward the center. Method for producing cemented carbide sintered body for use.