JPH08134583A - Production of sintered hard alloy excellent in machinability - Google Patents

Abstract

PURPOSE: To produce a sintered hard alloy excellent in machinability by mixing specific amounts of carbide, nitride, and carbonitride grains with a matrix powder having a specific composition consisting of C, Si, Cr, W, Mo, V, Nb, Co, and Fe and also having specific grain size and sintering at a specified temperature. CONSTITUTION: A powder mixture is prepared by mixing, by weight, <=25% carbide grains and 2-25% of nitride or carbonitride grains with a matrix powder having a composition consisting of 1.0-4.5% C, <=1.5% Si, 3-6% Cr, <=30% W and/or <=20% Mo in the range satisfying W+2Mo<=45%, 2-10% of V or Nb, <=20% Co, and the balance Fe with inevitable impurities. At this time, the grain size of the matrix powder is regulated to <=7μm. Then, this powder mixture is bound by sintering. At this time, sintering temp. is regulated to a value in the range of -10 deg.C to +40 deg.C with respect to the melting temp. of eutectic carbide. Further, at this time, it is preferably to form a structure in which the average grain size of all the MC carbides is regulated to <=1.5μm and these are finely dispersed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to cutting tools such as drills, end mills and drill tips, dies for metal plastic working, tool jigs, dies and tools for resin molding, various blades, and industrial tools. The present invention relates to a method for producing a sintered cemented carbide used as a wear part or the like.

[0002]

2. Description of the Related Art A cutting tool made of high-speed tool steel is first considered as a method of improving its life by increasing its hardness. As an example of this means, Japanese Patent Publication Sho 55
No. 6096, Japanese Patent Publication No. 57-2142, Japanese Patent Laid-Open No. 57-1
HR in 81367 and JP-A-58-181848
High hardness alloys of C71 and above are disclosed. These are M
It contains a large amount of alloying elements such as W and Mo that form ₆ C carbides, and V that forms MC carbides, or contains a large amount of hard substances such as TiN, but increases the price and reduces toughness. A decrease in grindability is a serious problem in practical use. As a solution to this problem, the applicant of the present application has disclosed Japanese Patent Publication No. 5-75821 and Japanese Patent Publication No. 5-75822.
Proposed issue. Although these alloys have relatively low contents of alloying elements such as W, Mo, V, etc., or hard materials such as TiN, they are HR by ordinary quenching and tempering.
It is a sintered hard alloy having an excellent feature that it can obtain high hardness of C71 or higher.

[0003]

However, even the alloys described in Japanese Patent Publication No. 5-75821 and Japanese Patent Publication No. 5-75822 are used for cutting tools such as drills, end mills and drill tips, and for metal plastic working. In order to manufacture as molds, tools, jigs, molds for resin molding, tools, various kinds of blades, and industrial wear-resistant parts, etc. Since it is necessary to use a grindstone, the grinding cost is higher than that of the conventional powder high speed tool steel. As a result, it has become indispensable to improve the grindability of a so-called sintered cemented carbide, in which powdered high speed tool steel is used as a base powder and hard particles are added to the powder, for expanding applications.

On the other hand, the inventors of the present invention disclosed in Japanese Unexamined Patent Publication No. 2-125.
No. 848 proposes a hard alloy having a fine structure in which the average particle size of TiN particles or carbides is 5 μm or less and the average particle gap is 5 μm or less.
It is an alloy with improved grindability. However, as a result of further detailed studies after this, it was found that among the carbides, the grain size of MC type carbide represented by VC greatly affects the grindability. By controlling the diameter and the sintering temperature, M of the hard particles, which has a particularly large effect on the grindability,
The present inventors have found that it becomes possible to make the grain size of C carbides as fine as 2 μm or less, and as a result, an alloy with extremely excellent grindability can be obtained, and the present invention has been completed. That is, an object of the present invention is to provide a method for producing a sintered cemented carbide based on a powder high speed tool steel class capable of significantly improving grindability after heat treatment.

[0005]

[Means for Solving the Problems] Specifically, the present invention is% by weight.
C 1.0-4.5%, Si 1.5% or less, Cr 3-6%, W 30%
Hereinafter, one or two of Mo 20% or less has a composition of 45% or less in W + 2Mo, 2 to 10% of one or two of V and Nb, 20% or less of Co, and the balance Fe and inevitable impurities. Base powder, 25% or less of the carbide particles with respect to the total weight of the base powder, and 1 to 2 or more types of particles selected from 2 to 25% nitride or carbonitride are mixed and sintered. In the method for producing a sintered cemented carbide that is bonded, the grain size of the matrix powder is 7 μm or less, and the sintering temperature is in the range of −10 ° C. to + 40 ° C. with respect to the eutectic carbide melting temperature. It is a method for producing a sintered cemented carbide with excellent properties.

In the present invention, the particle size of the base powder is 7 μm.
It is necessary to make it extremely fine as follows. Further, the sintering temperature of the alloy is set to G. The melting temperature of eutectic carbides in high-speed steel proposed by Steven et al. (Trans AS
M, 57 (1964), 925. ) Te, Te = 1265.6-111.1C + 22.2V +
-1 based on the value obtained by 4.4W + 2.8Mo
By limiting the range to 0 to + 40 ° C., the grain size of MC carbide can be made extremely fine as 2 μm or less, whereby the grindability can be greatly improved. MC carbides of interest in the present invention are those added by sintering as carbides to be added separately,
It refers to two types, that is, finely precipitated in the matrix powder and present as carbides during sintering. In addition to this, MC carbides are precipitated as very fine secondary carbides in the heat treatment of the alloys of this system, but since these secondary carbides are extremely fine, the influence on the grindability is small.

[0007]

In order to obtain a sintered cemented carbide having excellent grindability in the present invention, it is extremely important to control the grain size of MC carbide, and the grain size should be 1.5 μm or less. Is important for obtaining excellent grindability. Further, MC carbide having a particle size of 2 μm or less is 80% or more in all MC carbide particles, more preferably MC carbide having a particle size of 2 μm or less is 80% or more in all MC carbide particles, and 1.5 μm or less It is desirable that the MC carbide particles of is 50% or more in all MC carbide particles. For this purpose, it is necessary to control the grain size of the matrix powder and the sintering temperature as described above. When the grain size of the matrix powder exceeds 7 μm, the sintering temperature is based on the eutectic carbide melting temperature. Then -1
Even in the range of 0 to + 40 ° C, it becomes difficult to densify the alloy by sintering.

As the eutectic carbide melting temperature (abbreviated as K), the one defined by the above formula for obtaining Te is used. C,
The values of V, W and Mo are calculated from the value of the matrix powder and the ratio of the compound of hard particles (carbide, nitride, carbonitride) added separately, and the value of the element of the matrix powder is added. do it. As a simple method, the final composition of the sintered body may be analyzed and obtained. When the relationship between the sintering temperature, the density of the sintered body, and the grain size of MC carbide is investigated in detail within the range of the components suitable for the present invention, both satisfy the conditions that the sintering temperature is K. On the other hand, it was found that the range of −10 to + 40 ° C. was good. That is, the sintering temperature is Te-
If it is less than 10, sintering will be insufficient and the density of the sintered body will decrease. On the contrary, when the sintering temperature exceeds Te + 40, MC carbides grow to have an average particle size of more than 1.5 μm, and MC carbides exceeding 2 μm increase with increasing temperature. For example, the sintering temperature is Te + 47 ℃
When it becomes approximately, the average grain size of MC carbide becomes 2 μm or more, and the grinding ratio decreases to 5.5 or less.

That is, by setting the particle size of the base powder to 7 μm or less, -10 to + 40 ° C., especially −
It enables low temperature sintering at 10 to + 30 ° C.
In the case of 8-9 μm powder that has been often used in the past, +3
It only densifies at 7 ° C, but M grows due to grain growth during sintering.
The average particle size of C carbides cannot be 1.5 μm or less.

The carbide particles added in the present invention are those which are bonded to the matrix by sintering. As a method of dispersing the carbide in the sintered cemented carbide, there is a method of increasing the amount of the carbide-forming element in the matrix. However, since the MC-type carbide-forming elements such as V and Nb in the present invention are easily oxidized, the matrix The resulting powder is oxidized and the sinterability is reduced, which is not preferable. In addition, when the amount of V, Nb, etc. in the matrix increases, the viscosity of the molten metal increases, and it becomes impossible to manufacture a powder serving as a matrix by the atomization method. Is desirable. If the amount of the added carbides exceeds 25% by weight based on the total weight, the toughness decreases, so the amount is set to 25% or less. Preferably 0.5 to 20% by weight, more preferably 0.5 to
15% by weight.

The action of each element and the reason for limiting the numerical values in the present invention will be described below. C has the effect of forming hard carbides by combining with W, Mo, V, etc., which are added at the same time, and has the effect of increasing wear resistance. In addition, a portion of C forms a solid solution in the matrix to increase the hardness of the matrix and It also has the effect of improving wear resistance.
Therefore, there is an optimum C content in consideration of the addition amounts of carbide forming elements such as W, Mo, and V. In the range of alloy elements of the present invention, if C is less than 1.0%, the hardness of the matrix is not sufficiently obtained, and the amount of carbide formed is small. On the other hand, if it exceeds 4.5%, the toughness deteriorates, so C must be 1.0 to 4.5%. Si has the effect of improving the steel quality as a deoxidizing element and the effect of forming a solid solution in the matrix to increase the hardness of the matrix. However, if it exceeds 1.5%, the toughness decreases, so Si is 1.
It is necessary to be 5% or less.

Cr has the effect of forming carbides and increasing wear resistance. Furthermore, it is solid-dissolved in the substrate to give hardenability,
It also improves the corrosion resistance of the base. If Cr is less than 3%, the above effect is small, and if it exceeds 6%, it is difficult to obtain hardness by heat treatment. Therefore, it is necessary that Cr is 3 to 6%. W and Mo are combined with C to form M ₆ C
It forms carbide of the mold and enhances wear resistance and seizure resistance.
Particularly, in the present invention, since the content of V described below is suppressed to a relatively low value from the viewpoint of workability and grindability, the effects of W and Mo are important for improving wear resistance and seizure resistance. Also,
Some of W and Mo are solid-solved in the matrix and then tempered to precipitate and harden, which also has the effect of increasing the hardness of the matrix. W 30% or less, M
o One or two of 20% or less has a W + 2Mo content, and if it exceeds 45%, the toughness is significantly reduced.
% Or less, preferably W + 2Mo amount of 1
It is 8-40%, more preferably 25-40%.

[0013] Co has the effect of forming a solid solution in the matrix to increase the hardness of the matrix. However, if it exceeds 20%, the toughness decreases, so Co is made 20% or less. V and Nb combine with C to form MC type carbides. By finely and uniformly dispersing this carbide, it is possible to greatly improve the wear resistance and seizure resistance together with the nitride and carbonitride particles described later. As a result of various studies on the addition amounts of V and Nb,
It has been found that when this is set to 2 to 10% and the amount of nitrides and carbonitrides is set to 2 to 30% as described later, good characteristics are obtained. Here, the content of V and Nb in the base is 2
If it is less than 10%, the effect is not sufficient, and if it exceeds 10%, the toughness decreases, so it is necessary to set it to 2 to 10%. The compositional limitation of the matrix powder in the present invention naturally determines the basic characteristics of the sintered cemented carbide, the grain size of the matrix powder is 7 μm or less, and the sintering temperature is −10 ° C. to + with respect to K.
It is important as a composition that balances the best use characteristics and grindability in the range of 40 ° C.

As described above, in the present invention, V, N
b is not only a method of preliminarily containing one or two of them in the base powder to form a carbide, but also one of carbides such as V and Nb and nitride particles of another element or the same element, carbonitride particles. Alternatively, a method of simultaneously adding two or more kinds is adopted. By selecting carbide particles, nitride particles, or carbonitride particles, or by adding them in combination, a high hardness of HRC71 or higher can be obtained. If the content is less than 2%, this effect is not sufficient, and if it exceeds 25%, the sinterability is deteriorated. Therefore, one or two or more of nitrides and carbonitrides have a total of 2%.
Must be -25%. As the nitride and carbonitride, Ti, Zr, V, Nb, and Hf nitrides and carbonitrides are easily available, and the cost is low, which is the most suitable.

Examples of suitable combinations of these hard particles include:
In the case of carbide alone, VC or NbC is added, in the case of combination of carbide and nitride, composite addition of VC and TiN, Mo ₂ C and T
iN composite addition, TaC / Mo ₂ C / TiN composite addition, (Ti, W) C / TiN composite addition, NbC / Ti
In the case of compounded addition of N, combination of carbide and carbonitride, VC and T
iCN composite addition, VC / TiCN / TaCN composite addition, and for nitride, TiN / TaN single or composite addition,
For carbonitride, TiCN and TaCN alone or in combination, in combination of nitride and carbonitride, in combination of TaN and TiCN, for combination of carbide, nitride and carbonitride, VC
And TiN and TiCN combined addition and VC, TiN and TaC
There is a composite addition of N.

[0016]

EXAMPLES The present invention will now be described in more detail with reference to examples. (Example 1) C 3.1%, Cr 4.1%, W 1
0.2%, Mo 7.8%, V 8.4%, Co 7.
A water atomized powder having a steel composition of 8% balance Fe and unavoidable impurities was pulverized by an attritor to obtain powders having various particle sizes. To this powder, 1% of VC having an average particle size of 1 to 3 μm and 10% of TiN were added, and a wet type attritor was used.
After being mixed in, dried and press-molded, a molded body was obtained. Further, this molded body was vacuum-sintered at 1800 to 1250 ° C. to produce a sintered body. After polishing each sintered body, the average grain size and grain size distribution of MC carbide were obtained by image analysis. In addition, after the sintered body was annealed, a test piece was manufactured, quenched at 1240 ° C, and tempered at 520 to 560 ° C (1 hour x 3 times) to measure hardness (HRC). A surface grinding test was performed using an alumina grindstone to evaluate the grindability of each sintered body. The results are shown in Table 1. In the final composition, the eutectic carbide melting temperature Te is 1188 ° C.

[0017]

[Table 1]

As seen in the examples of the present invention in Table 1, a matrix powder having a particle size of 3 μm or less is used and sintered at a sintering temperature in the range of −10 ° C. to + 40 ° C. with respect to the eutectic carbide melting temperature. As a result, it becomes possible to control the MC carbide grain size to 1.5 μm or less, and the grinding ratio (grinding amount / grinding wheel wear amount), which is the evaluation value of the grindability, is large. It turns out that an alloy can be obtained.

However, the particle size within the range of the present invention is 3 μm.
Even if a matrix powder of m or 6 μm is used, if the sintering temperature is made lower than the range of the present invention and sintering is performed at 1170 ° C. (Te-18 ° C.), a relative density of only about 94% is obtained, which is practically usable. It didn't look like that. Furthermore, when the sintering temperature was raised to 1235 ° C. (Te + 47 ° C.), the average grain size of MC carbides became 2.0 μm or more, the amount of fine carbides also decreased, and the grinding ratio fell to 5.5 or less. . Therefore, it is expected that the grinding cost will increase. When the matrix powder having a particle diameter of 8 μm or 12 μm is used, if the sintering temperature is lower than the value of Te, the relative density is 95% or less, so that the sinterability is low. Further, when the sintering temperature was raised above the value of Te, the carbides became coarse and the grinding ratio became 5.5 or less. The comparative examples in Table 1 are either particle size or sintering temperature,
Alternatively, both are out of the condition of the present invention.

[0020]

As described above, according to the present invention, in a method for producing a sintered cemented carbide containing a large amount of hard particles,
It is possible to control the particle size of MC carbide to 1.5 μm or less by setting the particle size of the matrix powder to 7 μm or less and the sintering temperature to the range of −10 ° C. to + 40 ° C. with respect to the eutectic carbide melting temperature. It will be possible. As a result, it became possible for the first time to significantly improve the grindability of a sintered cemented carbide containing hard particles, which is the object of the present invention. Therefore, the grinding process after the annealing after the sintering and the heat treatment of the quenching and tempering is extremely facilitated, and the working man-hour can be greatly reduced. This is an industrially very effective invention because the processing cost can be kept low when processing into various tools.

[Procedure amendment]

[Submission date] December 8, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

In the present invention, the particle size of the base powder is 7 μm.
It is necessary to make it extremely fine as follows. Further, the sintering temperature of the alloy is set to G. The melting temperature of eutectic carbides in high-speed steel proposed by Steven et al. (Trans AS
M, 57 (1964), 925. ) Is Te, T
e = 1265.6-111.1C + 22.2V + 4.4
Based on the value obtained by W + 2.8Mo, -10 to +
By limiting the range to 40 ° C., the grain size of MC carbide can be made extremely fine as 2 μm or less, whereby the grindability can be greatly improved. The MC carbides of interest in the present invention refer to two types, that is, carbides that are separately added and bonded by sintering, and those that are finely precipitated in the matrix powder and are present as carbides during sintering. In addition to this, in the alloys of this system, MC is generated as very fine secondary carbides during heat treatment.
Carbide precipitates, but this secondary carbide is so fine that it has little effect on the grindability.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

In order to obtain a sintered cemented carbide having excellent grindability in the present invention, it is very important to control the grain size of MC carbide, and the average grain size is 1.5 μm or less. Is important for obtaining excellent grindability.
Further, as a particle size distribution of MC carbides, MC carbides having a particle size of 2 μm or less account for 80% or more of all MC carbide particles, and more preferably MC carbides having a particle size of 2 μm or less are all MC particles.
It is desirable that 80% or more of the carbide particles and MC carbide particles of 1.5 μm or less account for 50% or more of all the MC carbide particles. For this purpose, it is necessary to control the grain size of the matrix powder and the sintering temperature as described above. When the grain size of the matrix powder exceeds 7 μm, the sintering temperature is based on the eutectic carbide melting temperature. Even in the range of -10 to + 40 ° C, it becomes difficult to densify the alloy by sintering.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

As the eutectic carbide melting temperature, the one defined by the above formula for obtaining Te is used. The values of C, V, W, and Mo are calculated from the ratio of the compound of hard particles (carbide, nitride, carbonitride) added separately and the value of the matrix powder, and the value added to the values of the elements of the matrix powder. It can be calculated from As a simple method, the final composition of the sintered body may be analyzed and obtained. When the relationship between the sintering temperature, the density of the sintered body, and the grain size of MC carbide is investigated in detail within the range of the components suitable for the present invention, the conditions satisfying both are that the sintering temperature is Te. On the other hand, it was found that the range of −10 to + 40 ° C. was good. That is, when the sintering temperature is lower than Te-10, the sintering becomes insufficient and the density of the sintered body decreases. On the contrary, when the sintering temperature exceeds Te + 40, MC carbides grow to have an average particle size of more than 1.5 μm, and MC carbides exceeding 2 μm increase with increasing temperature. For example, when the sintering temperature is about Te + 47 ° C., the average grain size of MC carbide becomes 2 μm or more, and the grinding ratio falls to 5.5 or less. ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 28, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

EXAMPLES The present invention will now be described in more detail with reference to examples. (Example 1) C 3.1%, Cr 4.1%, W 1
0.2%, Mo 7.8%, V 8.4%, Co 7.
A water atomized powder having a steel composition of 8% balance Fe and unavoidable impurities was pulverized by an attritor to obtain powders having various particle sizes. To this powder, 1% of VC having an average particle size of 1 to 3 μm and 10% of TiN were added, and a wet type attritor was used.
After being mixed in, dried and press-molded, a molded body was obtained. Further, this molded body was vacuum-sintered at 1180 to 1250 ° C. to prepare a sintered body. After polishing each sintered body, the average grain size and grain size distribution of MC carbide were obtained by image analysis. In addition, after the sintered body was annealed, a test piece was manufactured, quenched at 1240 ° C, and tempered at 520 to 560 ° C (1 hour x 3 times) to measure hardness (HRC). A surface grinding test was performed using an alumina grindstone to evaluate the grindability of each sintered body. The results are shown in Table 1. In the final composition, the eutectic carbide melting temperature Te is 1188 ° C.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C22C 38/30

Claims (4)

[Claims] 1. C 1.0 to 4.5% by weight, Si 1.5% or less,
One or two of Cr 3-6%, W 30% or less, Mo 20% or less
45% or less at W + 2Mo, 2 or 1 or 2 of V and Nb
˜10%, Co 20% or less, and a matrix powder having a composition consisting of the balance Fe and unavoidable impurities, 25% or less of carbide particles and 2 to 25% of nitride based on the total weight of the matrix powder. Alternatively, in a method for producing a sintered cemented carbide, which comprises mixing carbonitrides with one or more types of particles and combining them by sintering, the grain size of the matrix powder is 7 μm or less, and the sintering temperature is eutectic. -10 ° C to + 40 ° C for carbide melting temperature
The method for producing a sintered cemented carbide having excellent grindability, characterized in that 2. The average particle size of all MC carbide particles is 1.5.
The method for producing a sintered cemented carbide having excellent grindability according to claim 1, wherein a structure in which fine MC carbides having a size of not more than μm are dispersed is obtained. 3. As a particle size distribution of MC carbide, to obtain a structure in which MC carbide having a particle size of 2 μm or less out of all MC carbide particles has a fine MC carbide dispersed therein in an amount of 80% or more in all MC carbide particles. The method for producing a sintered cemented carbide having excellent grindability according to any one of claims 1 and 2. 4. As a particle size distribution of MC carbides, of all MC carbide particles, MC carbides having a particle size of 2 μm or less account for 80% or more of all MC carbide particles and all MC carbides having a particle size of 1.5 μm or less. Characterized by obtaining a structure in which 50% or more of fine MC carbides are dispersed in MC carbides,
The method for producing a sintered cemented carbide having excellent grindability according to claim 1.