JP3138958B2 - High speed tool steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plastic working tool, a roll, and a cutting tool, especially for processing a hard material which is difficult to cut, and a tool for processing a material which can be conventionally cut with higher efficiency. It relates to the high speed tool steel used.

[0002]

2. Description of the Related Art High-speed tool steels are required to have higher wear resistance in order to cope with difficult-to-machine materials.
The following method is used to improve the wear resistance. By increasing the amount of alloying elements, the room temperature hardness after the heat treatment is increased, and the wear resistance is improved. By increasing the equivalent amount of C and W (2Mo + W), W, Mo
Increase the amount of M ₆ C-type carbides mainly composed of steel, and improve the wear resistance by enriching the amount of carbides. By increasing the amounts of C and V, MC carbide having high hardness among carbides is increased, and the wear resistance is improved. As described above, a method of improving wear resistance by increasing the alloying element and increasing the room temperature hardness and the amount of carbide is mainly performed.

[0003]

However, when the above methods (1) to (3) are carried out by the conventional melting method, there are the following problems. Method challenge: The tool uses 600 parts due to frictional heat
° C or higher, and even if the room temperature hardness after the heat treatment is high, the tool-used portion rises to a high temperature of 600 ° C or higher due to frictional heat and the like, and the hardness decreases. Further, if the use at a high temperature is continued, the softening proceeds with time. Challenge method: crystallized reticulated huge M ₆ C type carbide cast state, significantly reduces the hot workability and toughness. Problems of method: MC type carbides become huge, and hot workability and toughness are reduced, and grinding to tool shape becomes impossible.

[0004] For these reasons, it is considered difficult to form a high alloy of high speed tool steel by the smelting method, and the production of high alloy high speed tool steel is carried out by powder metallurgy.

As a conventional high-speed tool steel produced by the powder metallurgy method, for example, a steel disclosed in Japanese Patent Publication No. 57-2142 is known. This is 0.8 to 3.95 by weight.
% Carbon, tungsten and twice as much molybdenum
0 to 50%, chromium is 3.0 to 5.0%, vanadium is 1.0 to 10.0%, cobalt is 5 to 15%, and the balance is composed of iron and unavoidable impurities. Although it was made, there was a problem that the cost would be high.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. In addition to maintaining high-temperature hardness even at a high temperature, the present invention restricts the particle size and area ratio of M ₆ C-type carbide so that M ₆ can be used even in a melting process. It is an object of the present invention to provide an inexpensive high-speed tool steel which increases the C-type carbide forming element (Mo, W), provides wear resistance higher than that of powder high-speed tool steel, and is excellent in grindability.

[0007]

The high-speed tool steel according to the first aspect of the present invention has a C content of 0.8 to 1.5% by weight,
i: 0.4% or less, Mn: 1% or less, Cr: 3 to 5%,
Mo: 0.5 to 15%, W: 2.5 to 12%, V: 1 to 1
2% Co: contains 5-10%, the balance being Fe
An alloy made by a melting method that satisfies the following relationships (a) and (b) . (B) 10 ≦ S ≦ 15, where S = 0.92 (2.0 [Mo%] + 2.5 [W%]) −
17.81 (b) 840 ≦ A ≦ 1020, where A = (S / 100 × 2300) + ((1−S / 100)
× H) S = 0.92 (2.0 [Mo%] + 2.5 [W%]) −
17.81 H = 26.14X + 531 X = −2.33 [Ceq] ² +5.73 [Ceq] +4
0.00 [ΔC%] ² −4.09 [ΔC%] − 0.02
[Co%] ² +0.29 [Co%] Ceq = 0.19 + 0.017 ([W%] + 2 [Mo
%]) + 0.22 [V%] ΔC% = [C%] − Ceq However, the range where the following relationship (c) or (d) is satisfied is
except. (C) F ≧ 7.30 where F = −0.90 [Mo%] [C%] − 0.45 [W%]
[C%] + 2.4 [C%] + 0.84 [Mo%] + 0.92 [W
%] + 2 [V% -1] ^1/2 +5.45 [Si%] + 32.7
[N%] (d) 2Mo + W: 12.0 to 22.0%, and
The ratio of 2Mo to 2Mo + W is 0.45 to 0.60.
In range.

In the high-speed tool steel according to the second aspect of the present invention, the area ratio of M ₆ C-type carbide mainly composed of Mo and W is 10 to 10%.
It is 15%.

The high-speed tool steel according to the third aspect of the present invention has an M ₆ C type carbide mainly composed of Mo and W having an average particle size of 1.
It is 4 to 2.0 μm.

[0010]

Hereinafter, an embodiment of the present invention will be described.

Generally, in applications to which high-speed tool steel is applied, the temperature of the tool-using portion reaches a high temperature of 600 ° C. or more due to frictional heat or the like. Therefore, high-speed tool steel is important in wear resistance at high temperatures, and factors such as the hardness (strength) of the material at high temperatures, temper softening resistance, and the size of primary carbides greatly affect the high-speed tool steel. The present invention provides a material that satisfies these factors contributing to wear resistance in an optimal balance.

The hardness (strength) of the raw material at high temperature, which is the first factor, largely depends on the proportion of the distributed primary carbide and the base material and their hardness at high temperature. When these relationships are expressed by an equation, high-temperature strength ∝ (primary carbide area ratio ×
(Hardness of carbide) + (base metal area ratio × high-temperature hardness of base metal).

The primary carbide of high speed tool steel contributes to wear resistance in the order of MC> M ₆ C, M ₂ C type carbide. However, MC-type carbide and significantly reduce the grindability of the material, M ₆ C type carbide has focused on feature that hardness decreases at high temperatures is slow, the amount of M ₆ C type carbide ( Examining the relationship between the area ratio), the high-temperature hardness of the base metal, and the alloy balance, as described above, the amount of primary carbide (M ₆ C) generated (area ratio) greatly contributes to the wear resistance of the material. As shown.

[0015] The M ₆ area ratio of C-type carbides (generation amount) result of obtaining correlation between the S and the alloy component, the area ratio of the alloy components of the M ₆ C type carbide, S = 0.92 (2.0 [Mo % ] +2.5 [W%])-17.
It was found to be represented by equation 81. This correlation is shown in FIG.
It is as shown in FIG.

The area ratio of the M ₆ C type carbide in the conventional high speed tool steel is about 6 to 7%, and at least 10% or more is required for remarkable improvement in wear resistance. However, 15
%, Hot working becomes difficult, so the upper limit is 15%.
And Therefore, when organized by parameter S, 10 ≦
S ≦ 15 (condition a).

The high temperature (600 ° C.) hardness H of the base metal is also determined by the alloy composition, H = 26.14X + 531, where X = −2.33 Ce
The formula q ² + 5.73Ceq + 40.00ΔC ² -4.09 ΔC-0.02Co ² + 0.29Co was found. The correlation between H and X is as shown in FIG.

The known hardness of M ₆ C type carbide is 1600-2300 HV
(Quoted from JIM Vol.7),
The relational expression that expresses the high temperature strength (A) is the above parameter and M ₆ C
Substituting the hardness of type carbide (2300 HV), A = (S / 100 × 23
00) + ((1-S / 100) × H).

The present inventors have found a correlation between the high-temperature strength and the wear resistance shown in FIG. 0.45 specific wear
When used as a tool at × 10 ^-4 mm ³ / kgfm or less,
Very good wear resistance has been obtained so far, and it is necessary to satisfy A ≧ 840 in order to realize this. Further, if A exceeds 1020, the toughness and hot workability will be significantly impaired, so the upper limit is set to 1020 (condition B).

As shown in FIG. 1, Co greatly contributes to the tempering softening resistance, which is the second factor, and the addition of Co imparts wear resistance. The effect of Co is remarkably recognized by adding at least 5% or more, but if added in a large amount, the toughness decreases, so the upper limit is made 10%.

Regarding the size of the primary carbide, which is the third factor, as shown in FIG. 5, there is a proportional relationship between the M ₆ C type carbide particle size and the wear resistance of the material. As described above, the specific wear amount is 0.
When it is 45 × 10 ^-4 mm ³ / Kgfm or less, since the tool shows extremely excellent wear resistance, the average particle size of the M ₆ C type carbide is
It is desirable that the thickness be 1.4 μm or more. However, when the grain size exceeds 2.0 μm, no remarkable improvement in wear resistance is observed, and rather the toughness and hot workability are impaired, so the upper limit is set to 2.0 μm.

V is necessary to satisfy the above condition (b), but when the content is large, coarse MC-type carbide is crystallized,
To significantly reduce the grindability, the upper limit is 2%.

The smaller the content of Si, the better the toughness. However, the refining is difficult if the content is too small because of the manufacturing convenience of use as a deoxidizing agent.

Cr combines with C to form double carbides, which contributes to wear resistance and improves hardenability. For this purpose, it is necessary to add at least 3% or more.
If no, a significant effect is not observed, so the upper limit is made 5%.

Mn is added as a deoxidizing and desulfurizing agent. However, if too much is added, the toughness is reduced.
% Or less.

Furthermore, the high-speed tool steel of the present invention is melted at a low speed of 130 to 170 kg / Hr by the electroslag melting method because the distribution of carbides is greatly affected by the melting conditions. This makes it possible to uniformly control the carbide particle size and distribution, and to maintain stable tool quality with less uneven wear.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Table 1 shows the chemical composition of a typical example of the high-speed tool steel of the present invention and comparative steels (known molten steel and powdered steel). The characteristics are as shown in FIGS.

[0028]

[Table 1]

The wear test is based on the friction speed obtained by the Ogoshi-type wear test.
The test was performed under the conditions of 1.37 m / sec, friction distance of 200 m, and final load of 18.9 kg, and SCr420 (149 HB) was used as the mating material. Also, M ₆ C
The average particle size of the type carbide was determined by subjecting a sample to electrolytic corrosion using a 10% oxalic acid aqueous solution, performing image analysis on the M ₆ C type carbide, and calculating the average. From these results, it is recognized that the steel of the present invention exhibits excellent wear resistance more than powdered high-speed steel, which is a high alloy.

Furthermore, 13
FIG. 6 shows a microstructure photograph of the steel of the present invention dissolved at a dissolution rate of 8 kg / Hr. Here, it is recognized that the white grains are M ₆ C-type carbides and are uniformly distributed.

[0031]

As is evident from the foregoing description, according to the present invention the alloy content and high-temperature hardness, the relationship of M ₆ C type carbide area ratio and M ₆ C type carbide revealed, high-temperature hardness of requesting an alloy balance , M ₆ C type carbide area ratio, and particle size are obtained.

[0032] Accordingly, the upper limit of the amount of crystallization and the grain size are limited while enriching the M ₆ C-type carbide, not the MC-type carbide, which significantly impairs the grindability, so that it can be produced within the range that can be produced by the melting method. Thus, a method for producing a high alloy high-speed steel with which the maximum adhesive wear characteristics can be obtained.

These adhesive wear characteristics show a performance higher than that of powdered high-speed steel, and there is a merit of a lower cost when applied to a field where powdered high-speed steel has been used conventionally. Furthermore, since the addition amount of V, which is an MC type carbide forming element that significantly reduces the grindability, is minimized, the grindability is excellent. Therefore, the high-speed tool steel of the present invention is suitable for various tools such as cutting tools, plastic working tools, and rolls.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between an area ratio of a primary carbide of a high-speed tool steel according to the present invention and an amount of specific friction.

FIG. 2 is a characteristic diagram showing a relationship between an alloy component of the present invention and an area ratio of M ₆ C-type carbide.

FIG. 3 is a characteristic diagram showing a relationship between a parameter X of the present invention and a high-temperature hardness of a base material.

FIG. 4 is a characteristic diagram showing a relationship between a specific wear amount and a parameter A according to the present invention.

FIG. 5 is a characteristic diagram showing the relationship between the specific wear amount and the M ₆ C-type carbide particle size of the present invention.

FIG. 6 is a photograph showing a microstructure of a high-speed tool steel according to an embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuji Machida 3-10-15, Yawatacho, Shinminato-shi, Toyama Japan High Frequency Steel Industry Co., Ltd. 3-10-15, Yawata-cho, Japan Toyama Works, Japan High Frequency Steel Industry Co., Ltd. (72) Inventor Masahiro Machida 179 Kanegasaki Nishi-Oike, Uozumi-cho, Akashi-shi, Hyogo Pref. Document JP-A-5-33102 (JP, A) JP-A-1-165748 (JP, A) JP-A-60-12211 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 302 C22B 9/18 B22P 23/10

Claims (3)

(57) [Claims] C. 0.8% to 1.5% by weight of S
i: 0.4% or less, Mn: 1% or less, Cr: 3 to 5%,
Mo: 0.5 to 15%, W: 2.5 to 12%, V: 1 to 1
2% Co: contains 5-10%, the balance being Fe
A high-speed tool steel made of an alloy by a melting method satisfying the following relations (a) and (b) . (B) 10 ≦ S ≦ 15, where S = 0.92 (2.0 [Mo%] + 2.5 [W%]) −
17.81 (b) 840 ≦ A ≦ 1020, where A = (S / 100 × 2300) + ((1−S / 100)
× H) S = 0.92 (2.0 [Mo%] + 2.5 [W%]) −
17.81 H = 26.14X + 531 X = −2.33 [Ceq] ² +5.73 [Ceq] +4
0.00 [ΔC%] ² −4.09 [ΔC%] − 0.02
[Co%] ² +0.29 [Co%] Ceq = 0.19 + 0.017 ([W%] + 2 [Mo
%]) + 0.22 [V%] ΔC% = [C%] − Ceq However, the range where the following relationship (c) or (d) is satisfied is
except. (C) F ≧ 7.30 where F = −0.90 [Mo%] [C%] − 0.45 [W%]
[C%] + 2.4 [C%] + 0.84 [Mo%] + 0.92 [W
%] + 2 [V% -1] ^1/2 +5.45 [Si%] + 32.7
[N%] (d) 2Mo + W: 12.0 to 22.0%, and
When the ratio of 2Mo to 2Mo + W is 0.45 to 0.60
In range. 2. The M ₆ C-type carbide mainly composed of Mo and W has an area ratio of 10 to 15%.
High speed tool steel as described. 3. The high-speed tool steel according to claim 1, wherein the M ₆ C-type carbide mainly composed of Mo and W has an average particle diameter of 1.4 to 2.0 μm.