JP3343747B2 - Powdered high speed steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to powdered high-speed steel, and more particularly, to cutting tools and dies manufactured using the powdered high-speed steel, which have excellent wear resistance and excellent grindability. Regarding powdered high-speed steel.

[0002]

2. Description of the Related Art Recently, cutting tools and dies are often manufactured by powder metallurgy. In that case, for example, the cutting tool is manufactured as follows. That is, first,
After a powdered high-speed steel having a predetermined particle size, for example, is filled in a mold having a predetermined shape, the powdered high-speed steel is sintered to produce a material having a shape similar to a target shape. Next, after roughing in an annealed state, the material is heated by using, for example, a vacuum quenching furnace, and then tempered by an atmosphere furnace to increase hardness. And finally, it is ground with a grinding wheel to obtain the desired shape.

[0003] In the case of this cutting tool, it is required that the cutting tool has excellent wear resistance in relation to the material to be cut, in view of its intended use. At the same time, as is evident from the above manufacturing process, the material itself, which is a sintered product, is ground in the final process, so it is a material excellent in grindability,
It is also required that the material has excellent hardenability. In response to such demands, measures have been taken to increase the total amount of carbides in the powdered high-speed steel, which is the raw material, to promote high alloying.

[0004] However, when such a treatment is performed,
Although the obtained material of the powdered high-speed steel certainly improves the wear resistance, on the other hand, the hardness becomes too high, which causes a problem of deterioration in grindability. Therefore, the time required to grind the cutting tool having the desired shape becomes longer, which causes a decrease in productivity and raises the cost of the final product.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the conventional powdered high-speed steel, and a product manufactured using the same has excellent wear resistance and excellent grindability. For example, an object of the present invention is to provide a powdered high-speed steel that is useful as a raw material when a cutting tool, a mold, or the like is manufactured by a powder metallurgy method.

[0006]

By the way, in powdered high-speed steel, various carbides are precipitated in its structure. Among these carbides, the size and hardness of MC type carbide such as VC and M ₆ C type carbide such as (Fe, W, Mo) ₆ C may affect the grindability of the high-speed steel. Are known.

Accordingly, the present inventors investigated the effect of the type and amount of carbide on the wear resistance and grindability of a steel type having the same hardness and bending strength as conventional powdered high-speed steel. did. As a result, the powdered high-speed steel in which the total amount of the MC type carbide and the M ₆ C type carbide and the mutual abundance are within a predetermined range has almost the same hardenability as JIS SKH51, and the hardness and the bending strength are the same as those of the conventional powdered high-speed steel. Although it was equivalent to steel, it was found that both wear resistance and grindability were superior to conventional powdered high-speed steel, and the powdered high-speed steel of the present invention was developed.

That is, the powdered high-speed steel of the present invention comprises:
1.5 to 2.5% by weight, Si: 0.1 to 1.0% by weight, Mn: 1.
0% by weight or less, Cr: 3.0 to 6.0% by weight, Mo: 2.0 to 2.0%
8.0% by weight, W: 5.0 to 20.0% by weight, V: 6.0 to 10%.
0% by weight, Co: 2.0% by weight or less, the balance being Fe, and when the carbide volume fractions of MC type carbide and M ₆ C type carbide are a volume% and b volume%, respectively, between a and b Then, the following equation: 15 ≦ a + b ≦ 30, 0.7 ≦ a / (a + b)
It is characterized in that a relationship of ≦ 1.0 is established.

[0009] In this powdered high-speed steel, carbides precipitated in the structure are MC-type carbides mainly composed of VC and M-type carbides.
_It is an M ₆ C-type carbide mainly composed of ₆ C and (Fe, W, Mo) ₆ C. Among these carbides, MC-type carbides function to improve the wear resistance of the material. Assuming that the ratio of the volume of the MC type carbide and the volume of the M ₆ C type carbide occupying in the structure (carbide volume ratio: volume%) is a and b, respectively, in the powdered high-speed steel of the present invention, , 1
The relationship of 5 ≦ a + b ≦ 30, 0.7 ≦ a / (a + b) ≦ 1.0 holds.

Here, (a + b) is an index indicating the total amount of precipitated carbide. When this value is smaller than 15, that is, when the total amount of MC type carbide and M ₆ C type carbide is If the content is less than 15% by volume, it is not possible to obtain a balanced improvement in wear resistance and grindability expected from conventional powdered high-speed steel. When (a + b) becomes a value larger than 30, that is, when the total amount of carbides is 30
If the content is higher than the volume percentage, mass production of such a structure of high-speed steel on an industrial scale becomes considerably difficult, and the production cost is increased.

From the above, (a + b) representing the total amount of carbides is set in the range of 15 to 30% by volume. Preferably, it is 15 to 25% by volume. On the other hand, a /
(A + b) is an index indicating the abundance ratio of MC type carbide which contributes to the improvement of wear resistance among the carbides precipitated in the structure, and the wear resistance of the high-speed steel increases as the value increases. I do. Since it is preferable that all carbides be MC-type carbides in terms of improvement of wear resistance, a / (a
+ B) has an upper limit of 1.0.

On the other hand, if a / (a + b) is smaller than 0.7, the effect of improving the wear resistance of the MC type carbide is not sufficiently exhibited, and the wear resistance of the obtained high-speed steel is insufficient. The preferred value of a / (a + b) is 0.8 to 1.0. Further, the MC type carbide and the M ₆ C type carbide described above are:
It is preferable that the equivalent circle diameter is 0.8 μm or more on average and the maximum value is 2 to 8 μm.

The reason for limiting the circle equivalent particle size to the above range is as follows.
When the average value is less than 0.8 μm, the grindability of the steel is improved, but the abrasion resistance tends to decrease. On the other hand, the larger the particle size of the largest carbide, the better the wear resistance. However, if the size exceeds 8 μm, the good grindability characteristic of powdered high-speed steel is impaired. Therefore, in order not to impair the characteristics of the powdered high-speed steel and to prevent a decrease in wear resistance, the maximum carbide particle size is 2 to 8 μm.
It is preferable to adjust to.

The grain size of the carbide can be adjusted by appropriately selecting the soaking temperature and soaking time of molten steel during the production of steel. In the powdered high-speed steel of the present invention, first, C mainly reacts with V to produce V
MC type carbide mainly composed of C, and W and M
It is an essential component for producing M ₆ C-type carbide mainly composed of W ₆ C and Mo ₆ C by reacting with o.

The content of C at this time is calculated, for example, as follows: The following formula reported by STEVEN et al: ΔC = C− (0.06Cr + 0.063Mo + 0.033W +
0.2V) is set as a value such that the ΔC value falls within the range of -0.3 to 0.1. Specifically, it is set to 1.5 to 2.5% by weight.

When the content is less than 1.5% by weight, predetermined amounts of MC type carbide and M ₆ C type carbide are not formed, and when the content is more than 2.5% by weight, the amount of C in the matrix becomes excessive. And the toughness is impaired. Si is a component that functions as a deoxidizing agent at the time of smelting, and its content is set to 0.1 to 1.0% by weight, similarly to ordinary high-speed steel.

Mn is also a component that functions as a deoxidizing agent like Si, and its content is set to 1.0% by weight or less. When this content is more than 1.0% by weight, residual austenite is generated in the structure and the whole becomes brittle,
It becomes unsuitable as a material for cutting tools. Cr is a component contributing to the improvement of hardenability, and its content is 3.0 to 6.0.
Set to% by weight.

When the content is less than 3.0% by weight
Is expected to improve hardness due to insufficient quenching of the material
become unable. If the content is more than 6.0% by weight, C
r_TwoC _ThreeAlso produces Cr-based carbides such as
MC type carbide and M₆Proper formation of C-type carbides is hindered
Become so. Mo is M₆To form C-type carbide
Is the essential component of ₆C is hardened
Contributes to secondary hardening of material by solid solution in matrix
The content is set to 2.0-8.0% by weight
Is done.

If the content is as low as 2.0% by weight, the secondary curing effect of the above functions will not be sufficiently exhibited, and if the content is more than 8.0% by weight, Mo will not be obtained.
_The amount of ₆ C generated increases, and M contributes to the improvement of wear resistance.
This leads to a reduction in the amount of C-type carbide produced. W is a component that functions in the same manner as Mo with twice the amount of Mo described above, and its content is set to 5.0 to 20% by weight.

When the content is less than 5.0% by weight, the secondary curing effect is not sufficiently exhibited as in the case of Mo. When the content is more than 20.0% by weight, the initial curing is not performed. The amount of M ₆ C-type carbide to be used increases, and the workability deteriorates due to an increase in the total amount of carbide (MC + M ₆ C). V is an essential component for producing MC-type carbide mainly composed of VC, and its content is set to 5.0 to 10.0% by weight.

If the content is less than 5.0% by weight, the value of a / (a + b) will not be 0.7. Further, when the content is 10.0% by weight, the a / (a + b) value becomes 1.0, that is, since the generated carbides are all MC-type carbides, the V content is in the above range. .
Preferably, the content is 6.0 to 10.0% by weight. Co functions to increase the hardness of the material and the strength of the matrix, but on the other hand, is a component that shifts the bainite transformation start time to a shorter time side and greatly affects the hardenability.

Therefore, the hardenability is determined according to JIS SKH5.
In the case where the purpose is to make it equal to 1, Co
Is preferably not contained. However, when melting steel, it is inevitable to mix it from outside the system such as scraps used, but even on the premise of this, in order to ensure the wear resistance and grindability of high-speed steel. The upper limit of the content of Co is 2.0% by weight.

The powdered high-speed steel of the present invention is prepared by melting an alloy consisting of a predetermined amount of each of the above-mentioned components, performing gas spraying, filling the HIP can, performing HIP treatment, and performing a diffusion treatment for increasing the particle size of the carbide. After that, hot forging is performed to obtain a predetermined material.

[0024]

【Example】

 Examples 1 to 13 and Comparative Examples 1 to 13 Steels of various compositions shown in Table 1 were melted.

[0025]

[Table 1]

Each of these steels was subjected to hot forging at a temperature of 1100 ° C. and a reduction of area of 50% or more, and annealed to obtain a test material. For each of these test materials, the hardness (HRC) in the state after annealing was measured. The results are shown in Tables 2 and 3. Thereafter, each steel is subjected to vacuum quenching in a temperature range of 1160 to 1200 ° C., and a temperature of 520 to 560 ° C. for 1 hour ×
The tempering was performed three times, and the hardness (HRC), bending strength, wear resistance, grindability, and carbide distribution at that time were measured. The results are also shown in Tables 2 and 3.

Measurement of carbide volume fraction (a) and equivalent circle particle size:
Using a sample subjected to electrolytic corrosion of Cr ₃ O ₃ , a SEM photograph was taken at a magnification of 2000 times, and measured as an area ratio (a) (= volume ratio) with a Luzex image analyzer. The circle equivalent particle diameter was obtained by changing the irregular shaped carbide to a circle equivalent particle diameter and calculating the average value.

Measurement of carbide volume fraction (b) and equivalent circle particle size:
Except for corrosion using KMnO ₄ as a corrosive liquid, the same as the measurement of the carbide volume fraction (a) and the circle equivalent particle size. The wear resistance index and the grindability index were calculated for each of the above steels according to the following specifications. Abrasion resistance index: Applied by the Ogoshi abrasion test method and expressed as a relative value when the result of Comparative Example 1 is set to 100. A material having a larger value indicates better wear resistance. Grindability index: Using a resin bond whetstone as the polishing whetstone,
Displayed as a relative value when the result of Comparative Example 1 is set to 100. A material having a larger value indicates better grindability. The above results are collectively shown in Tables 2 and 3. Table 2,
In No. 3, the ΔC value calculated for each steel is also shown.

[0029]

[Table 2]

[0030]

[Table 3]

In Tables 2 and 3, as is clear from comparison between Comparative Example 1 which is a conventional high-speed steel and Example 10 which is a high-speed steel of the present invention, the total amount of carbide (a + b) and the hardness after quenching are high. Example 1 in which the volume ratio (a) of the MC type carbide is about twice as large as Comparative Example 1
On the other hand, the wear resistance index increased by 20% and the grindability index increased by 90% or more, and both the wear resistance and the grindability were excellent.

[0032]

As is apparent from the above description, the powdered high-speed steel of the present invention has excellent wear resistance and excellent grindability. Moreover, the hardness after quenching is almost equal to that of the conventional high-speed steel. This is an effect brought about by increasing the total amount of carbides and increasing the proportion of MC-type carbides in the total amount of carbides.

Therefore, the powdered high-speed steel of the present invention has great industrial value as a raw material for cutting tools and dies manufactured by powder metallurgy.

Claims (3)

(57) [Claims] 1. C: 1.5 to 2.5% by weight, Si: 0.1 to 1.1%.
0% by weight, Mn: 1.0% by weight or less, Cr: 3.0 to 6.0% by weight, Mo: 2.0 to 8.0% by weight, W: 5.0 to 20.0% by weight, V : 5.0 to 10.0% by weight, Co: 2.0% by weight or less,
When the balance is made of Fe and the carbide volume ratios of the MC type carbide and the M ₆ C type carbide are a volume% and b volume%, respectively, between a and b, the following formula: 15 ≦ a + b ≦ 30,0. 7
A powdered high-speed steel characterized by satisfying a relationship of ≦ a / (a + b) ≦ 1.0. 2. The powdered high-speed steel according to claim 1, wherein the MC-type carbide and the M ₆ C-type carbide have a circle-equivalent average particle size of 0.8 μm or more and a circle-equivalent maximum particle size of 2 to 8 μm. 3. C: 1.5-2.5% by weight, Si: 0.1-1.0%.
0% by weight, Mn: 1.0% by weight or less, Cr: 3.0 to 6.0% by weight, Mo: 2.0 to 8.0% by weight, W: 5.0 to 15.0% by weight, V : 6.0 to 10.0% by weight, Co: 2.0% by weight, the balance being Fe, the volume fraction a (%) of MC type carbide and M ₆
Between the volume fractions b (%) of the C-type carbide, 15 ≦ a + b ≦
A relationship of 25, 0.8 ≦ a / (a + b) ≦ 1.0 is satisfied, and the MC-type carbide and the M ₆ C-type carbide have a circle-equivalent average particle diameter of 0.8 μm or more, and The equivalent maximum particle size is 2
The powdered high-speed steel according to claim 1, which is 8 µm.