JPH0835044A - Sintered hard alloy excellent in machinability - Google Patents

Abstract

PURPOSE:To produce a sintered hard alloy excellent in machinability suitable for various tools, wear resistant parts or the like and furthermore excellent in deflective strength. CONSTITUTION:The structure of a sintered hard allay is formed into the one in which a matrix in which Mn and S to be added are dispersed in the structure as fine MnS particles having <=3mum average particle and having a compsn. contg., by weight, 1.0 to 4.5% C, <=1.5% Si, 3 to 6% Cr, one or two kinds of <=30% W and <=20% Mo so as to satisfy <=45% W+2Mo, 2 to 10% of one or two kinds of V and Nb, <=20% Co, and the balance Fe with inevitable impurities is bonded with one or >= two kinds of particles selected from carbide particles by <=25% to the total weight and 2 to 25% nitrides or carbonitrides by sintering. Thus, the sintered superhard alloy excellent in machinability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to materials for cutting tools such as drills, end mills and drill tips, molds or tool materials and jigs for metal plastic working, molds and tool materials for resin molding, and various blades, and The present invention relates to a sintered cemented carbide used as an industrial wear resistant part or the like.

[0002]

2. Description of the Related Art As a method of improving the life of a high speed tool steel as a cutting tool, the first consideration is to improve the hardness. Therefore, in fact, Japanese Patent Publication Sho 55-6096
No. 57/142, JP-A-57-181367
JP-A-58-181848 and the like disclose high hardness alloys having a hardness of HRC71 or higher. 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.
In practical use, high price, low toughness, and poor grindability are major problems. To solve these problems, Japanese Patent Publication No. 5-75821 and Japanese Patent Publication No. 5-75
There is an alloy disclosed in No. 822. The alloys disclosed in these documents have a relatively high content of HRC71 or higher due to ordinary quenching and tempering, even though the content of alloying elements such as W, Mo, V, etc., or the content of hard materials such as TiN, etc., which are additionally added is relatively small. It is a sintered hard alloy having an excellent feature that is obtained.

[0003]

However, the alloys described in Japanese Patent Publication No. 5-75821 and Japanese Patent Publication No. 5-75822 are also used for cutting tools such as drills, end mills, drill tips, dies for metal plastic working, When used as tool materials, jigs, molds for resin molding, tool materials, various blades, industrial wear resistant parts, etc. Since it is necessary to use a borazon grindstone and the grinding cost is much higher than that of conventional powder high speed tool steel, improving the grindability of these alloys is an essential condition for expanding applications. Is coming. Therefore, in view of the above problems, an object of the present invention is to provide a sintered cemented carbide having significantly improved grindability after heat treatment without deteriorating the mechanical properties of the alloy.

[0004]

[Means for Solving the Problems] In order to improve the mechanical workability of steel, a method of adding a free-cutting substance is widely known for ordinary ingot materials, and MnS and the like are added. Free-cutting steel is widely used for machined parts. In this case, since MnS has a long elongated shape due to plastic working such as forging and rolling, it deteriorates mechanical properties especially in the direction parallel to the plastic working direction. Therefore, the addition amount is limited to about 0.2% in S amount. To be Also, for high speed tool steel, alloys containing S have been developed mainly in the United States. For example,
ORBIT, AIRKOOL-S, VIS as alloy name
COUNT20, 44, REX M3S-2 and TH
YRAPD3341 and the like are known, and 0.1 to 0.15% S is added to these. Furthermore, in powder high speed tool steel, the alloy name is C of Crucible Co.
PM REX M3S-2, CPM REX M3HCH
S and the like have been proposed, and 0.15 to 0.27% S is added.

However, in the case of these conventional alloys, MnS is longer in the plastic working because the hot plastic working step is indispensable as a post-step of HIP or hot extrusion not only in the molten material but also in the powder high speed tool steel. It becomes an elongated shape. As a result, the mechanical properties in the direction parallel to the plastic working direction deteriorate, and even in the case of fine powder high-speed tool steel with a fine structure, the S addition amount is 0.2 in the case of CPM REX M3HCHS.
The maximum value is 7%, and the MnS amount is 0.73% when all are supposed to form MnS. On the other hand, even in the case of powder-sintered products, there are increasing cases where workability becomes a problem as well as improvement of mechanical properties, and attempts have been made to add free-cutting elements to improve machinability. Metall
There is an M on page 245 of the document named Part Mater (published in 1992).
It has been shown that nS is effective. Furthermore, JP-A-6
No. 0-190553 and JP-A No. 62-167864 disclose that the amount of S added is about 0.15% or less.

[0006] In the case of a sintered product, a compound having high extensibility such as MnS, which imparts free-cutting property, is not plastically worked after sintering and therefore remains spherical or granular. Compared with this, it was found that there is an advantage that the deterioration of mechanical properties is small. However, in these conventional techniques, in order to improve the machinability of MnS,
However, there is no description about improving the grindability and there is a description about the amount of MnS added, but there is no mention of its particle size, distribution, etc.

The inventor of the present invention focuses on the above-mentioned problem, that is, the well-known method of adding MnS, which is conventionally used mainly for the purpose of improving the machinability in order to improve the grindability of a sintered alloy. As a result of various structural studies, it was found that by finely dispersing fine MnS particles, it is possible to significantly improve the grindability without deteriorating the mechanical properties of the alloy. And has reached the present invention. And, MnS has a great effect on the improvement of the machinability when it is elongated in the direction of plastic working, but it does not have a great effect on the improvement of the machinability, but rather has a shape close to a sphere. The invention was made based on the results of finding that it is better to have some. Therefore, in the present invention, MnS was added to a sintered alloy that was not subjected to plastic working such as forging or rolling, and an alloy having excellent grindability could be obtained.

That is, in the present invention, specifically, fine MnS having an average particle diameter of 3 μm or less is finely dispersed in the structure, and C 1.0 to 4.5% by weight and Si 1.5% or less by weight%. , Cr 3
-6%, W 30% or less and Mo 20% or less, 1 or 2 kinds, W + 2Mo, 45% or less, 1 or 2 kinds of V and Nb, 2 to 10%, Co, 20% or less, and the balance In a matrix having a composition of Fe and inevitable impurities, 25% or less of carbide particles based on the total weight and 2 to 25% of the total weight of one or more selected from nitrides or carbonitrides. It is a sintered cemented carbide with excellent grindability, characterized in that it has a structure in which the above-mentioned particles are bonded by sintering.

In the present invention, as the carbide particles, carbides of elements of the 4A and 5A groups in the periodic table can be used, but they are not carbides that react with the matrix to become M ₆ C type,
This is a carbide that is substantially MC type. In particular, the carbides of V and Nb are superior to the carbides of other elements in that they can be dispersed uniformly and finely in the matrix. In the present invention, the nitride particles or carbonitride particles are selected from the group consisting of Ti, Zr, Hf, V, Nb, and Ta, and these particles are particularly stable and difficult to form a solid solution in the matrix. It can be dispersed uniformly.

[0010]

The function of the sintered cemented carbide of the present invention is Mn.
It is characterized in that it is 80% or more with respect to that without S added, but this is achieved only by the fact that fine MnS having an average particle size of 3 μm or less is dispersed in the structure. The transverse rupture strength of the alloy is 8 compared to that without MnS added.
If it is 0% or more, even if the transverse rupture strength is lowered, there is practically no harm in use, but it is more preferably 90% or more.

The present invention is characterized in that fine MnS particles having an average particle size of 3 μm or less are dispersed in order to improve the grindability, and 80% or more of the MnS particles having a particle size of 2 μm or less are dispersed. In this case, particularly excellent grindability can be obtained. By dispersing fine MnS in this way, it becomes possible to significantly improve the grindability while minimizing the deterioration of the mechanical properties of the alloy.
It becomes possible to disperse a large amount of MnS in the structure, which was impossible in the past, and it becomes possible for the first time to significantly improve the grindability in the sintered cemented carbide as in the present invention. Is.

When MnS particles having a particle size of 2 μm or less are 80% or more of all particles and particles of 1.5 μm or less are 50% or more of all particles, the characteristics of the alloy are not deteriorated. Therefore, it is possible to obtain a material having further excellent grindability. Further, the amount of MnS is much larger than the amount well known in the related art, assuming that all of the added S forms MnS.
When it is 1.5%, excellent grindability can be obtained without deteriorating the mechanical properties of the alloy, but this is only possible by uniformly dispersing MnS. And more preferably the MnS content is 0.
It is 75 to 1.2%.

When the amount of MnS is less than 0.5%, MnS
In the case of finely dispersing, it is not possible to obtain sufficient grindability, and if the MnS content exceeds 1.5%, it is impossible to avoid a considerable deterioration of the mechanical properties of the alloy. In the sintered cemented carbide of the present invention, it is possible to obtain a high hardness of HRC71 or higher in the ordinary heat treatment. In applications requiring particularly high hardness, it is possible to obtain a hardness of HRC 72 or higher by optimizing the heat treatment conditions. The addition of MnS makes it possible to improve the machinability in the annealed state as well. In order to obtain such a large amount of MnS as 0.5 to 1.5%, the added Mn and S are each S0.1 in weight ratio.
6 to 0.60% and Mn 0.4 to 1.1% are required, but since MnS is bonded at Mn / S = 1.7, M
It is desirable that the ratio of n and S be Mn / S> 1.8.

In the present invention, the carbide particles are those which are bonded to the matrix by sintering. As a method of dispersing this carbide in the sintered cemented carbide of the present invention, there is also a method of increasing the amount of the carbide-forming element in the matrix.
Since Nb and the like are easily oxidized, the powder serving as a base is oxidized and the sinterability is lowered, which is not preferable. In addition, when the amount of V, Nb, etc. in the matrix increases, the viscosity of the molten metal increases, making it impossible to produce a powder serving as a matrix by the atomization method. It is preferable to tie it. 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-
It is 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 combines with W, Mo, V, etc. added at the same time to form a hard carbide, and has the effect of enhancing wear resistance. In addition, some of them have a solid solution in the matrix to increase the hardness of the matrix and also have 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 the present invention, if C is less than 1.0%, the hardness of the matrix cannot be sufficiently obtained,
The amount of carbide formed is also small. On the other hand, if it exceeds 4.5%, the toughness deteriorates, so the C content needs to be 1.0 to 4.5%. Si has the effect of improving the steel quality as a deoxidizing element. It also has the effect of increasing the hardness of the base by forming a solid solution in the base. However, if it exceeds 1.5%, the toughness decreases, so Si must be 1.5% or less.

Cr has the effect of forming carbides to enhance wear resistance, and further forms a solid solution with the substrate to impart hardenability,
It also improves the corrosion resistance of the base. If Cr is less than 3%,
Cr is required to be 3 to 6% for the reason that the above effect is small and conversely if it exceeds 6%, it becomes difficult to obtain hardness by heat treatment for quenching and tempering. W and Mo
Combines with C to form M ₆ C type carbides, which enhances wear resistance and seizure resistance. Particularly, in the present invention, since the content of V described below is suppressed from the viewpoint of workability, the effects of W and Mo are important for improving wear resistance and seizure resistance.
Further, 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 and Mo 20% or less in one or two types with a W + 2Mo content, and in excess of 45%, the toughness decreases significantly, so W +
The amount of 2Mo should be 45% or less. Preferably W +
2 Mo amount is 18 to 40%, more preferably 25 to 40
%.

Co has the effect of increasing the hardness of the matrix by forming a solid solution in the matrix. However, if Co exceeds 20%, the toughness decreases, so Co was set to 20% or less. V and Nb are 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 particles of nitride and carbonitride described later. As a result of various studies on the amounts of V and Nb added, it was found that good characteristics can be obtained when the amount is 2 to 10% and the amount of nitride and carbonitride particles described later is 2 to 30%. . If the content of V or Nb in the matrix is less than 2%, the effect is not sufficient, and if it exceeds 10%, the toughness decreases, so the content must be 2 to 10%.

As described above, in the present invention, V, N
One or two kinds of b are contained in advance in the base powder. Further, one or two kinds of carbide particles of V and Nb and one or more kinds of nitride particles or carbonitride particles of Ti, Zr, Hf, V, Nb and Ta are simultaneously added to the base powder. Mix and sinter. Dispersing the above-mentioned carbide, nitride, and carbonitride particles is one of the important structural requirements in the present invention. This is because by adding these, high hardness of HRC71 or higher can be obtained. If the amount of these particles is less than 2%, this effect is not sufficient, and if it exceeds 25%, the sinterability is reduced. Must be -25%. In addition, nitride,
As carbonitrides, compounds of Ti, Zr, V, Nb, and Hf are suitable because they are easily available and inexpensive.

[0019]

EXAMPLES The present invention will now be described in more detail with reference to examples. (Example 1) Water atomized powders A to I composed of nine kinds of steel compositions shown in Table 1 were prepared, and 2% of VC having an average particle diameter of 1 to 3 µm and 10% of TiN were added to the atomized powders in a weight ratio.
The mixture was added, mixed in a wet ball mill, dried, press-molded, and vacuum-sintered at 1180 to 1250 ° C to prepare a sintered body. For each sintered body, after polishing, the average particle size and particle size distribution of MnS were obtained by image analysis. Also,
After annealing the sintered body, it was quenched at 1180 to 1240 ° C. and tempered at 520 to 560 ° C. (1 hour × 3 times). Then, the hardness (HRC) and the transverse rupture strength of these samples were measured. Further, using the test pieces produced at the same time, a surface grinding test was performed using an alumina grindstone to evaluate the grindability of each sintered body. The grinding ratio is expressed by the ratio of (amount of grinding of sample) / (amount of wear of grindstone), and the larger the value, the better the grindability. The results are shown in Table 2. 1 to 4 show a structural photograph, an analytical photograph and a sketch drawing thereof when an image is analyzed. 1 to 4
According to the above, it can be seen that MnS of the alloy according to the present invention has a substantially spherical shape, unlike the conventional elongated shape obtained by plastic working.

[0020]

[Table 1]

[0021]

[Table 2]

According to Table 2, Mn having an average particle size of 3 μm or less
In the case of Samples 3 to 6 in which S is finely dispersed by 0.5 to 1.5%, high grindability (grinding ratio) 2-3 times higher than that of Sample 1 without MnS, and no MnS is obtained. 8 compared to
It can be seen that a high bending strength of 0% or more can be obtained. Further, regarding the particle size distribution of MnS, excellent properties are obtained when the particle size is 2 μm or less and 80% or more, particularly
It can be seen that in the case of Samples 3 to 5 in which m is 50% or more, a material in which grindability and transverse rupture strength are balanced can be obtained.

(Example 2) Water atomized powders J to N having five kinds of steel compositions shown in Table 3 were prepared, and carbide particles having an average particle diameter of 1 to 3 μm and nitrides or carbonitrides shown in Table 4 were prepared. The mixture was mixed in a wet ball mill in the ratios shown in the table, dried, press-molded, and vacuum-sintered at 1180 to 1250 ° C to produce a sintered body. For each sintered body, after polishing, the average particle size and particle size distribution of MnS were obtained by image analysis. Moreover, after annealing the obtained sintered body, 1180-1
Quenching was performed at 240 ° C., and tempering (1 hour × 3 times) was performed at 540 to 560 ° C. The hardness of these samples (H
RC) and the transverse rupture strength were measured. Further, using the test pieces produced at the same time, a surface grinding test was performed using an alumina grindstone to evaluate the grindability of each sintered body.

[0024]

[Table 3]

[0025]

[Table 4]

Even in the case of sintered bodies made of water atomized powder having various compositions shown in Table 3, when fine MnS having an average particle size of 3 μm or less is dispersed, excellent grinding results are obtained as shown in Table 4. It can be seen that good properties are obtained, and an excellent value is also obtained in transverse rupture strength, which is a typical mechanical property. That is, Samples 19 and 2 containing less than 0.5% MnS
In No. 0, only a grinding ratio of about 3 was obtained, and in Samples 22, 23, and 24 in which the MnS particle size exceeded 3 μm, the transverse rupture strength ratio decreased to 90% or less.

[0027]

According to the present invention, by dispersing fine MnS having an average particle size of 3 μm or less in the structure, a large amount of MnS which has been impossible in the past can be obtained while minimizing the deterioration of characteristics. It became possible to disperse, and it became possible for the first time to significantly improve the grindability of the sintered cemented carbide containing hard particles as in the present invention. As a result, the grinding process after the heat treatment becomes extremely easy, and the number of working steps can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a metallographic photograph showing an example of a microstructure of a sintered cemented carbide of the present invention.

FIG. 2 is a sketch diagram showing an example of a microstructure of a sintered cemented carbide of the present invention.

FIG. 3 is an X-ray photograph showing the analysis result of each phase of the sintered cemented carbide of the present invention.

FIG. 4 is a sketch diagram showing the analysis results of each phase of the sintered cemented carbide of the present invention.

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[Procedure amendment]

[Submission date] December 8, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Claims (12)

[Claims] 1. The added Mn and S are uniformly dispersed in the structure as MnS particles having an average particle size of 3 μm or less, and C in weight% is obtained.
1.0-4.5%, Si 1.5% or less, Cr 3-6%,
W 30% or less and Mo 20% or less 1 type or 2 types
45% or less at +2 Mo, 2 or 1 or 2 types of V and Nb
10%, Co 20% or less, with a composition having the composition of balance Fe and inevitable impurities, based on the total weight.
Excellent grindability, characterized by having a structure in which 25% or less of carbide particles and 1 to 2 or more kinds of particles selected from 2 to 25% of nitrides or carbonitrides are bonded by sintering. Sintered super hard alloy. 2. S 0.16 to 0.60% by weight, M
0.4 to 1.1% of n is added, The sintered superhard alloy excellent in grindability of Claim 1 characterized by the above-mentioned. 3. The sintered superhard alloy having excellent grindability according to claim 1, wherein the carbide particles are particles containing V or Nb as a main component. 4. The nitride or carbonitride particles are Ti, Z.
The sintered cemented carbide having excellent grindability according to any one of claims 1 to 3, which is selected from the group consisting of r, Hf, V, Nb, and Ta. 5. The transverse rupture strength is 80% or more of the sintered cemented carbide which does not disperse MnS.
A sintered cemented carbide having excellent grindability according to any one of 1 to 4. 6. The sintered super alloy having excellent grindability according to claim 1, wherein the transverse rupture strength is 90% or more of that of a sintered cemented carbide which does not disperse MnS. Hard alloy. 7. The burnt excellent in grindability according to claim 1, wherein the MnS particles have a particle size of 2 μm or less in an amount of 80% or more of all particles. Bonded super hard alloy. 8. The MnS particles have a particle size of 2 μm or less in 80% or more of all particles, and a particle size of 1.5 μm or less in 50% or more of all particles. A sintered cemented carbide having excellent grindability according to any one of claims 1 to 6. 9. The MnS content is 0.5 to 1.5% by weight, calculated as all of the added S forms MnS, and the MnS content is 0.5 to 1.5%. Sintered super hard alloy with excellent grindability. 10. The calculation according to claim 1, wherein all the added S forms MnS, and the amount of MnS is more than 0.75% by weight and 1.2% or less. A sintered cemented carbide having an excellent grindability according to Crab. 11. The sintered cemented carbide having excellent grindability according to claim 1, having a hardness of HRC71 or more after quenching and tempering. 12. The sintered superhard alloy having excellent grindability according to claim 1, which has a hardness of HRC 72 or more after quenching and tempering.