JPH07173581A - Powdery high speed tool steel excellent in toughness - Google Patents

Abstract

PURPOSE:To produce a powdery high speed tool steel having toughness equivalent to that of a melted material. CONSTITUTION:This powdery high speed tool steel excellent in toughness is a one having a compsn-contg. 1.0 to 1.5% C, 0.1 to 1.0% Si, <=0.5% Mn, <=0.5% Ni, 2.0 to 6.0% Cr, 7.0 to 9.0% Mo, 1.0 to 5.0% W, 2.0 to 4.0% V and 5.0 to 10.0% Co, furthermore satisfying 18%<=2Mo+W <=22%, and the balance substantial Fe with inevitable impurities, and in which the shape of carbides is formed of a planar one. By forging or rolling, planar carbides are oriented parallelly to the working direction. It is suitable particularly for a cold forging die tool or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder high speed tool steel having excellent toughness, and is particularly suitable for cold forging die tools and the like.

[0002]

BACKGROUND OF THE INVENTION High speed tool steel is a tool steel in which a large amount of Cr, Mo, W, V, etc. is added to further improve hardness and wear resistance at high temperatures. Widely used as a material for cutting tools and cold working dies. Further, in the high-speed steel produced by the usual melting method, since carbides are easily segregated, powder high-speed steel with a uniform and fine structure has come to be used in the fields where particularly high performance is required. Came.

Conventionally, molten high speed tool steel, so-called molten high speed steel has been used for cold forging dies. However, in the molten metal, the addition amount of an alloying element (for example, V) that improves wear resistance is used. There is a limit. Therefore, it has not been possible to sufficiently meet the needs of users who want to improve wear resistance. In order to meet such requirements, powder high speed tool steel (powder high speed steel) capable of adding a large amount of alloy elements such as V is used.

However, in the case of the powder high speed steel, although the wear resistance is improved, there is a problem that the fracture toughness value of the material becomes worse than that of the molten high speed steel. Therefore, in a special cold forging punch field in which generation of microcracks during use is unavoidable, there is a problem that the powder high speed steel has a shorter life than the molten high speed steel.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a powder high speed tool steel having a toughness equivalent to that of an ingot.

[0006]

Means for Solving the Problems As means for solving the above problems, the present invention is C: 1.0 to 1.5%, Si:
0.1-1.0%, Mn: 0.5% or less, Ni: 0.5% or less, Cr: 2.0-6.0%, Mo: 7.0-9.0%, W:
1.0-5.0%, V: 2.0-4.0%, Co: 5.0-1
Excellent toughness characterized by containing 0.0% and satisfying 18% ≦ 2Mo + W ≦ 22%, the balance consisting essentially of Fe and unavoidable impurities, and having a carbide-like plate shape. The main point is powder high speed tool steel.

[0007]

The present invention will be described in more detail below. First, the reason for limiting the chemical composition of the powder high speed steel in the present invention will be explained.

C: 1.0-1.5% C combines with carbide forming elements such as Cr, Mo, W and V to form a hard double carbide, which improves the wear resistance of the material and at the same time the matrix. It is an important element to form a solid solution in the material and obtain the hardness of the material. At least 1.0 to obtain the desired hardness
%, But the addition of more than 1.5% causes a decrease in toughness, so the C content is made 1.0 to 1.5%.

Si: 0.1-1.0% Si has the effect of adding as a deoxidizer and at the same time strengthening the matrix. In order to obtain these effects, it is necessary to add at least 0.1%, but addition of a large amount exceeding 1.0% causes a decrease in toughness, so the Si content is 0.1-1.0%. To do.

Mn: 0.5% or less Mn is an element to be added as a deoxidizing agent as well as Si, and at the same time is an element to improve hardenability. However, excessive addition leads to a decrease in toughness, so the Mn content is made 0.5% or less.

Ni: 0.5% or less Ni is an element that greatly contributes to improvement of hardenability and toughness due to grain refinement. However, addition of a large amount adversely affects toughness, so the Ni content is 0.5. % Or less.

Cr: 2.0-6.0% Cr is an element that combines with C to form a double carbide, which improves wear resistance and at the same time forms a solid solution in the matrix to improve the hardenability of steel. Is. To obtain these effects, it is necessary to add at least 2.0%, but excessive addition exceeding 6.0% is a factor that greatly impairs hot workability and toughness, so the Cr content is 2.0. ~ 6.0%.

V: 2.0-4.0% V, like Mo and W, combines with C to form a very hard and hard to dissolve solid carbide, and therefore has the effect of greatly improving the wear resistance. Further, in forming the plate-shaped carbide, the V content and M
The key point is the balance of o and W, but V content of 2.0-4.0% is essential in this component system. That is, if V is less or more than this range, the shape of the carbide will be spherical.

On the other hand, V also has the effect of improving the toughness by making the crystal grains finer. It is necessary to add at least 2.0% in order to exert this effect effectively, but 4.0%
On the contrary, excessive addition exceeding 5 hinders toughness and grindability. Therefore, the amount of V is set to 2.0 to 4.0%.

Co: 5.0 to 10.0% Co is an element that forms a solid solution in the matrix to strengthen the matrix and greatly improve the hardness and yield strength at high temperatures. In order to exert this effect effectively, it is necessary to add at least 5.0%, but if it is added excessively in excess of 10.0%, it becomes a factor that hinders the toughness, so that Co is 5.0 to 5.0. It is set to 10.0%.

Mo: 7.0-9.0%, W: 1.0-5.0
% Mo and W both combine with C and Fe to form a double carbide, but in order to form a plate-like carbide, Mo is 7.0 to 7.0.
It is indispensable to set the range of 9.0% and W to 1.0 to 5.0%.

Further, in order to obtain a good balance between hardness and toughness, it is necessary to satisfy 18% ≤2Mo + W≤22%.

The powder high speed tool steel of the present invention is characterized in that the carbide has a plate shape. Since conventional powder high-speed tool steel has spherical spherical carbides, its fracture toughness is inferior to that of ingots, but by making the shape of carbides plate-like, it is possible to obtain fracture toughness equivalent to that of ingots You can

Since the powder high-speed tool steel of the present invention is manufactured by a conventional method and has a plate-shaped carbide, the fracture toughness is remarkably improved as compared with the conventional powder high-speed tool steel, and the fracture equivalent to that of the ingot is obtained. Toughness can be obtained. Moreover, since this plate-shaped carbide is evenly distributed and is oriented parallel to the processing direction by processing such as forging and rolling, micro cracks are prevented from occurring during use even under severe operating conditions. it can.

Next, examples of the present invention will be described.

【Example】

With respect to the steel having the chemical composition shown in Table 1, the alloy powder produced by gas atomization was filled in a mild steel capsule, degassed, sealed, and then solid-formed by hot isostatic pressing (HIP), and further forged. Then, rolling was performed to manufacture a test material.

Each test material was subjected to heat treatment under the conditions shown in Table 2, and the hardness, specific wear amount and fracture toughness value were examined. The results are shown in Table 2. A vacuum furnace was used for the heat treatment. The measurement of the specific wear amount was carried out by the Ogoshi-type wear tester under the following conditions. Abrasion amount: 1.96 m / sec Final load: 6.3 kgf Abrasion distance: 400 m Counterpart material: SUS304 (Hv: 176)

As is clear from Table 2, the steels A and B of the present invention have the same fracture toughness and improved wear resistance as compared with the conventional steel D (molten material). Further, it can be seen that the comparative steel C has considerably improved wear resistance as compared with the conventional steel D, but has a low fracture toughness value.

The figures show the microstructures of the respective steels after heat treatment. The structure (a) of the invention steel A and the structure of the invention steel B are shown.
In (b), the shape of the carbide is plate-like, whereas in Comparative Steel C
The structure (c) and the structure (d) of the comparative steel D are spherical carbides.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

As described above, according to the present invention,
Since it is possible to provide a powder high-speed tool steel that has better toughness than conventional powder high-speed tool steels, has the same toughness as ingots, and has excellent wear resistance, especially when applied to cold forging die tools, etc. It can be significantly improved.

[Brief description of drawings]

FIG. 1 is a photograph showing a microstructure (metal structure) of each steel type after heat treatment, wherein (a) is the steel A of the present invention, (b) is the steel B of the present invention, and (c) is the present invention.
Shows the case of comparative steel C, and (d) shows the case of conventional steel D (molten material).

Claims (2)

[Claims] 1. C .: 1.0 to 1.5 in% by weight (hereinafter the same)
%, Si: 0.1 to 1.0%, Mn: 0.5% or less, Ni:
0.5% or less, Cr: 2.0 to 6.0%, Mo: 7.0 to 9.
0%, W: 1.0 to 5.0%, V: 2.0 to 4.0%, C
o: Includes 5.0 to 10.0%, and 18% ≤ 2Mo + W
A powder high-speed tool steel excellent in toughness, characterized by satisfying ≦ 22%, the balance consisting essentially of Fe and unavoidable impurities, and having a carbide-like plate shape. 2. The powder high speed tool steel according to claim 1, wherein the plate-shaped carbide is oriented parallel to the processing direction by forging or rolling.