JPH04263038A - Sintered hard alloy - Google Patents

Abstract

PURPOSE:To obtain a WC-base sintered hard alloy excellent in impact toughness, thermal toughness, and wear resistance by specifying the composition consisting of WC, B1 type solid solution, and iron group metal and also specifying the composition of the above B1 type solid solution. CONSTITUTION:The WC-base sintered hard alloy can be obtained by providing a composition which consists of, by weight, 98-70% of WC and B1 type solid solution (where the weight ratio of WC to B1 type solid solution is regulated to 97/3 to 70/30), and 2-30% of iron group metal composed essentially of Co. In the above alloy, the above B1 type solid solution is constituted of WC, TiC, and a third hard material M (where M consists of one or more kinds among HfC, ZrC and VC, and HfN, ZrN or Vn is substituted for 5-30% of the above). At this time, the weight proportion of WC-TiC-M is regulated so that it is within the region enclosed with lines connecting four points in figure, that is, A (63.8WC-34.4TiC-1.8M), B (38.8WC-58.1TiC-3.1M), C (21.1WC-31.5TiC-47.4M), and D (42.6WC-23.0TiC-34.4M).

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a cemented carbide mainly composed of WC and B1 type solid solution, with the remainder being Fe metal such as Co. It relates to improving wear resistance and impact toughness.

[Prior art]

WC and B1 type solid solution (however, the weight ratio of WC and B1 type solid solution is in the range of WC/B1 type solid solution = 97/3 to 70/30) 98 to 70% by weight, and Fe group metal 2 mainly composed of Co. As is well known, cemented carbide consisting of ~30% by weight is rich in heat resistance, wear resistance, oxidation resistance, etc.
Widely used for cutting tools such as steel, cast steel, stainless steel, high manganese steel, tag tile cast steel, etc.

Conventionally, the B1 type solid solution in the hard phase of this type of cemented carbide is formed by: (1) using TiC and TaC as starting materials and dissolving them with a portion of WC during the sintering process;

■As a starting material, D. A solid solution of WC and TiC called C and TaC are used, and these are dissolved in solid solution during the sintering process.

(2) A method is known in which a ternary solid solution carbide of WC-TiC-TaC is used as a starting material.

In addition, the above D. As C or ternary solid solution carbide, usually,
The weight ratio of WC and TiC contained in it is WC/TiC.
=70/30 to 97/3 is used. This is T
This is to provide a good balance between iC's oxidation resistance and abrasion resistance and TaC's high-temperature toughness.

According to the phase diagram, WC is inevitably absorbed into a solid solution carbide consisting of TiC-TaC, and becomes a ternary solid solution carbide.

In addition, since TaC is very expensive, some of it is
Substitution with bC has also been proposed, but the conventionally known amount of NbC substitution is at most 30% by weight, and it is believed that if more than that is substituted, various properties of the alloy will deteriorate.

As mentioned above, WC-TiC-TaC solid solution has traditionally been mainly used as the B1 type solid solution in the hard phase, but recently there has been an attempt to utilize the excellent properties of HfC, VC, or ZrC as the B1 type solid solution. Attempts have also been made. However, there are not many examples in which a cemented carbide is actually used in a practical manner by incorporating a large amount of these carbides. The reason for this is not necessarily clear, but it is thought that the main reason is that the larger the content of these carbides, the more the mechanical toughness or thermal toughness deteriorates. That is, originally, the wettability between the B1 type solid solution and the Fe group metal is not as good as the wettability between WC and the Fe group metal. However, B
It is known from experience that when carbides or nitrides of Hf, Zr, or V are further contained in the type 1 solid solution, the wettability is further deteriorated and the toughness is reduced. This is thought to be the reason why it cannot be contained in large amounts.

[Problem that the invention seeks to solve]

It is an object of the present invention to provide a new cemented carbide having improved impact toughness, thermal toughness, and wear resistance by improving the above-mentioned drawbacks, that is, the wettability of B1 type solid solution and Fe group metal.

In order to achieve the above object, the present invention provides that, in weight %, WC
and B1 type solid solution in a total of 98 to 70% by weight (however,
The content of WC and B1 type solid solution is WC/B1 in weight ratio.
The weight ratio of the mold solid solution is within the range of 97/3 to 70/30)
and 2 to 30% by weight of Fe group metal mainly composed of Co, in which the B1 type solid solution contains WC and TiC as well as a third hard substance (however,
The third hard material M is composed of one or more of HfC, ZrC, or VC, and contains 5 to 30% by weight of the third hard material M.
is substituted with HfN, ZrN, or VN), and represents the weight ratio of WC-TiC-M.
．． 8M), point B (38.8WC-58, 1TiC-3.
1M), point C (21.1WC-31.5TiC-47.
4M), point D (42.6WC-23.0TiC-34.
4M) is characterized by being a solid solution within the area surrounded by the line connecting the four points.

The feature of the present invention is that by adjusting the weight ratio of WC and TiC in the B1 type solid solution as a starting material,
The reason is that the wettability of the B1 type solid solution has been improved. That is, the present inventors investigated the relationship between the composition of the raw material powder and various physical properties regarding the components constituting the B1 type solid solution in the hard phase;
After conducting a detailed study on the relationship between the raw material powder composition and the structure of the sintered body, we discovered the following surprising facts. ■As a raw material powder, D. Rather than forming a B1 type solid solution using C and other hard substances during the sintering process, a B1 type solid solution with a predetermined component composition is created in advance,
When this is used as a starting material, the resulting sintered body has higher hardness and excellent wear resistance. In this case the toughness is equivalent. (2) Toughness varies greatly depending on the content ratio of WC and TiC in the B1 type solid solution starting material, and there is an optimum range that improves toughness the most.

The details of the reason for ■ above are unknown, but it is probably D.
．． When D.C is used, other hard materials are mixed with D.D. during the sintering process. C
This is thought to be due to the fact that grain growth occurs due to solid solution.

The reason for the above (2) can be satisfactorily explained using FIG. That is, the sintering temperature range of normal cemented carbide is 1350°C to 1500°C, and as is well known, the phase boundary in this range is WC/TiC=70/3.
You can think of it as being on the 0 line.

If the WC/TiC ratio of the B1-type solid solution starting material deviates from this phase boundary, for example, if the composition is at point a or c in Fig. A driving force acts such that the composition of the B1 solid solution changes from point c to point b.

However, what is noteworthy is that W in the B1 solid solution
The diffusion rate is very slow at 1350°C to 1500°C, which is why the B1 type solid solution has a cored structure.

That is, when a B1 type solid solution having a composition at point a is used as a starting material, WC is released during the sintering process and the WC
Because it moves to the poor side, the surface layer is W compared to the inside.
C becomes poor. On the other hand, when a B1 type solid solution having a composition at point c is used as a starting material, WC is incorporated into the B1 type solid solution raw material particles from the phase boundary with the surrounding WC raw material powder particles during the sintering process, and the WC rich WC-rich solid solution is formed in front of the surface layer compared to the inside. FIG. 3 schematically shows the cored structure formed in this manner.

When a B1 type solid solution in which WC is poorer than the phase boundary is used as a starting material, the wettability with Fe group metals is significantly improved because the WC in the surface layer becomes very concentrated.

This is the most distinctive feature of the present invention. That is, the present invention precipitates WC on the surface of the B1 type solid solution to produce carbides such as ZrC, VC, and HfC, which have very poor sinterability but excellent properties as tool materials, or ZrN and VN. , B1 nitride such as HfN
This allows it to be contained in a large amount in the cemented carbide as a mold solid solution component.

In the present invention, in order to obtain preferable effects, it is desirable to pay attention to the content of WC and TiC, and the content of WC and TiC is preferably
It is preferable that the range is 65/35≧WC/TiC≧40/60. Also, to get even better properties, 60/40
It is desirable that the range be ≧WC/TiC≧50/50. When WC/TiC>65/35, not much WC precipitates on the surface of the B1 type solid solution and the toughness is not improved;
/TiC<40/60 is undesirable because the WC precipitated layer becomes too thick and the B1 type solid solution properties are lost.

Further, in the present invention, as the third hard material M, Zr
The reason for choosing C, HfC, and VC is that these carbides are T
This is because when a solid solution is formed with iC and WC, flank wear resistance and crater wear resistance are significantly improved. The same reason applies to ZrN, HfN, VN, etc. Particularly in the case of nitrides, their sinterability is much worse than that of carbides, so the present invention has made it possible for the first time to contain them in large amounts.

Further, the weight ratio of the third hard substance M to TiC is 95
The reason for setting /5≦TiC/third hard substance M≦40/60 is that when the content of the third hard substance M is as small as less than 95/5, the good properties due to the third hard substance contained are This is because it cannot be extracted, and on the other hand, if the content exceeds 40/60, the wettability with the Fe group metal deteriorates.

According to the experimental results of the present inventors, 80/20≦3rd
When the hard material M≦50/50, desirable improvement effects were obtained in toughness, wear resistance, and heat resistance.

In the present invention, the substitution amount of nitride in the third hard material M is set to 30% or less for the same reason as above.

In addition, in the present invention, the amount of TiN substitution is 50% of that of TiC.
The reason for this is that if more than that amount is substituted, the mechanical properties will deteriorate, which is undesirable.

Furthermore, when using a solid solution of TaC and NbC as the third hard material M, the weight ratio of TaC and NbC is 0.
．． It is desirable that the range is 3≦NbC/(TaC+NbC≦0.5.The reason is that if the added content is less than 0.3, the economic effect will be weak, while if the added content exceeds 0.5, the thermal shock resistance will be poor. This is because it cannot be put to practical use.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 In terms of weight ratio, 76WC-5TiC-3TiN-4TaC-
The raw material powders shown in Table 6 were blended to have a composition of 8Co.

Next, add 2 paraffin to this mixed powder as a press aid.
% by weight was added and mixed for 6 hours using an attritor in an organic solvent.

After drying, this was press-molded to a pressure of 1 t/cm 2 and vacuum sintered at 1425° C. to obtain a test piece. As shown in Table 2 of the obtained cemented carbide, Sample 2 according to the present invention using SS has far superior toughness compared to Comparative Sample 1.
It can also be seen that the hardness is high.

Example 2 In terms of weight ratio, 71WC-12TiC-7HfC-1HfN
-9Co was blended using the raw material powders shown in Table 3.

Sample 3 does not use a solid solution, and sample 4 uses D.
Sample 5 is a sample of the present invention using SS. However, SS in this example is WC-TiC-
It is a quaternary solid solution of HfC-HfN.

Samples were prepared from this blended powder using the same method as in Example 1, and various physical properties were investigated. The results are shown in Table 4.

As is clear from Table 4, Sample 5 according to the present invention using SS is superior to conventional materials in both hardness and transverse rupture strength.

Example 3 A sample was prepared in the same manner as in Example 1 by blending raw materials so as to form an alloy having the composition shown in Table 5 in terms of weight percent.

However, sample No. Nos. 6, 8, 10, and 12 were blended using solid solution carbonitrides having the compositions shown in Table 6. However, 6.
The solid solution carbonitrides used in Nos. 8, 10, and 12 were all WC/TiC=55/45 and TiC/M=60/40.
belongs to. In addition, all values in Table 6 are weight%.
However, the weight ratio is not converted to 100%. Table 7 also shows transverse rupture strength and hardness.

From this table, it can be seen that Samples 6, 8, 10, and 12 according to the present invention have superior transverse rupture strength compared to other conventional samples. It can thus be seen that the material of the present invention exhibits excellent toughness.

Example 4 A sample was prepared in the same manner as in Example 1 by blending raw materials so as to form an alloy having the composition shown in Table 8 in terms of weight percent. However, sample no. 14, 16, 18, 20 and 22 are the 9th
It is formulated using the solid solution carbonitride shown in the table.

However, the solid solution carbonitrides used in Nos. 14, 16, 18, 20, and 22 were all WC/TiC=50/50, Ti
C/M=60/40.

In addition, although all the values in Table 11 are weight %, the weight ratios are not converted to 100%.

Table 15 shows the transverse rupture strength and hardness of these samples.

From this table, samples 22, 24, 26, 28 according to the invention
It can be seen that specimens with 30 and 30 have superior transverse rupture strength compared to other conventional samples.

As detailed above, the present invention uses a B1 type solid solution as a starting material, and by particularly adjusting the ratio of WC and TiC in the solid solution, Fe group metals are formed on the surface of the B1 type solid solution during the sintering process. By depositing WC with good wettability, Zr, Hf, and V
By making it possible to add a large amount of carbides or carbonitrides, the toughness and wear resistance were significantly improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the weight ratio of WC-TiC-third hard material M, Figure 2 is a diagram showing changes in composition during the sintering process of B1 type solid solution, and Figure 3 is a diagram showing the composition change during the sintering process of B1 type solid solution. FIG. 4 is a diagram showing a cored structure and a diagram showing changes in the WC/TiC ratio of the starting material.

Claims (3)

[Claims] Claim 1: WC and B1 type solid solution (however, WC/B
The weight ratio of type 1 solid solution is 97/3 to 70/30) 98 to
In the WC-based cemented carbide composed of 70% by weight and 2 to 30% by weight of Fe group metal mainly composed of Co, the above B1
The type solid solution is composed of WC, TiC, and a third hard substance M (
However, the third hard material M is HfC, ZrC, or V
Consisting of one or more of C, 5 to 30 of them
Point A in FIG. 1 (63.8WC-34.4TiC
-1.8M), point B (38.8WC-58.1TiC-
3.1M), point C (21.1WC-31.5TiC-4
7.4M), point D (42.6WC-23.0TiC-3
A WC-based cemented carbide characterized by being a solid solution within a region surrounded by a line connecting four points of 4.4M). 2. The WC-based cemented carbide according to claim 1, wherein 5 to 50% of the TiC is replaced with TiN. 3. The third hard material M is TaC and NbC.
solid solution carbide, and the weight ratio of TaC and NbC is 0.
．． WC-based cemented carbide according to claim 1, characterized in that 3≦NbC/(TaC+NbC≦0.5).