JPH0959748A - P/m high speed tool steel excellent in wear resistance and chipping resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a P/M high speed tool steel-excellent in chipping resistance as well as in wear resistance. SOLUTION: This steel is an Mo type high speed tool steel containing Ni and Co, and further, Nb is contained by 0.5-2.0wt.% and the average grain size and the maximum grain size of carbides are regulated to 0.40-0.80μm and <=5μm, respectively. Moreover, at the time of producing the P/M high speed tool steel, it is recommened that the grain size regulation of carbides is performed by soaking treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a powder high speed tool steel having excellent wear resistance and chipping resistance, and a method for producing the same.

[0002]

2. Description of the Related Art In order to increase the hardness of cutting tools, C
High-speed tool steel in which a large amount of r, W, Mo, V, etc. is added to crystallize carbide is widely used. However, when the high-speed tool steel is manufactured by an ordinary melting method, carbides are easily segregated, which adversely affects the toughness. Therefore, the rapidly solidified powder is taken out by gas spraying the molten metal and then sintered by the HIP method. A powdered high speed tool steel has been developed.

Further, in Japanese Unexamined Patent Publication (Kokai) No. Hei 5-163551, fine NbC is added by containing 2 to 7% of Nb.
A high-speed tool steel powder for high-speed tool steel, which is intended to improve the wear resistance by containing a hard carbide of 1 to 5 μm containing Nb as a main component, while suppressing the coarsening of crystal grains to improve the toughness. It is disclosed. However, when cutting is performed using a tool made of the powder high-speed tool steel, there is a problem that chipping may occur during use, resulting in poor chipping resistance.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has a high powder speed which exhibits not only excellent wear resistance but also excellent chipping resistance. It is intended to provide tool steel.

[0005]

The present invention, which has solved the above-mentioned problems, is a Mo-based high-speed tool steel containing Ni and Co, in which Nb is 0.5 to 2.0% (weight%, the same applies hereinafter. ) And the average particle size of the carbide is 0.40 to 0.80 μ
The gist is that the particle size is m and the maximum particle size is 5 μm or less. Further, in producing the above powder high speed tool steel, it is recommended to adjust the grain size of the carbide by soaking.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In order to improve the wear resistance of a cutting tool, it is considered to increase the hardness of the tool, increase the carbide grain size of the tool material, increase the amount of carbide of the tool material, etc. To be However, the above-mentioned means (1) to improve the wear resistance, on the contrary, impede the chipping resistance of the tool.In the conventional powder high speed tool steel, the wear resistance and the chipping resistance are simultaneously balanced at a high level. I have not obtained anything.

According to the present invention, fine carbides are crystallized by adding an appropriate amount of Nb, and the subsequent soaking treatment, etc.
This problem is solved by controlling the grain size of carbides to an appropriate size. That is, the present inventors
By combining addition and grain size control of carbide, it became possible to balance wear resistance and chipping resistance after cutting at a high level.

In the present invention, Nb is one of the most important elements, and by combining with C like V, which will be described later, to form a hard carbide and a finer carbide than VC, which is a high speed tool. Greatly improves the chipping resistance of steel. In order to exert such an effect, it is necessary to add at least 0.5% or more, but if added excessively, a huge NbC (or a carbide mainly composed of Nb) exceeding 5 μm is crystallized and chipping resistance is improved. Because it will greatly hinder
The upper limit was 2.0%. The preferable Nb content is 1.0 to 2.0%.

The average grain size and maximum grain size of the carbides have a great influence on the cutting performance of the tool, and are extremely important factors in the present invention. If the average particle size of the carbide is less than 0.40 μm, the wear resistance becomes insufficient,
On the other hand, if it exceeds 0.80 μm, the chipping resistance is greatly impaired, so the average grain size of the carbide is 0.40 to 0.40.
It is essential to control in the range of 0.80 μm. However, even if the average grain size of carbides is within this range, if the maximum grain size of carbides exceeds 5 μm, chipping resistance is also impaired, so it is necessary to set the maximum grain size of carbides to 5 μm or less. And it is preferable to control in the range of 3 to 5 μm.

As described above, it is extremely important in the present invention to adjust the grain size of carbides. JP-A 5-163
The powder high-speed tool steel of No. 551 forms fine carbides of 5 μm or less by containing 2 to 7% of Nb, but at the same time, carbides exceeding 5 μm are also dispersed and chipping occurs. Was there. In the present invention, the amount of Nb added is limited to a small amount, the grain size of the carbide is adjusted by soaking, etc., and the average grain size and the maximum grain size of the carbide are controlled within a specific range, whereby wear resistance and chipping resistance are improved. It balances sex at a high level at the same time.

The present invention is a Mo-based high speed tool steel containing Ni and Co, and the components other than Nb are not particularly limited, but the preferred contents of chemical components other than Nb are shown below. .

C: 1.0 to 2.0% C combines with carbide forming elements such as Cr, W, Mo, V and Nb to form a hard composite carbide to improve the wear resistance of the material. , Is an important element for ensuring the hardness of the material by forming a solid solution in the matrix. However, if too much is added, the amount of C that forms a solid solution in the matrix increases, which causes cracking during hot forging and a decrease in toughness. Therefore, it is necessary to determine the C content in consideration of the content of the carbide forming element,
It is limited to 1.0% or more and 2.0% or less, and the carbon equivalent Ceq = 0.017 (W + 2Mo) + 0.22V + 0.11Nb + 0.
It is preferable to adjust the value of 19 to be 0.05 to 0.30.

Si: 0.1 to 1.0% Si is an element that is added as a deoxidizing agent for steel and is effective for strengthening the matrix. In order to exert such an effect, it is necessary to add at least 0.1% or more, but if it is too much, the toughness is rather lowered, so 1.0
% Is preferable.

Mn: 0.5% or less Mn acts effectively as a deoxidizer like Si and has the effect of enhancing the hardenability of steel. However, if added excessively, the toughness is lowered, so 0.5% is preferably made the upper limit.

Ni: 0.5% or less Ni contributes to the improvement of the hardenability and is an element effective for improving the toughness by refining the crystal grains. However, if the amount is too large, the toughness is rather impaired, so the upper limit is preferably 0.5%.

Cr: 2.0 to 6.0% Cr is an element that combines with C to form a carbide, which improves wear resistance and also forms a solid solution in the matrix to improve the hardenability of steel. . In order to exert such an effect, it is necessary to add at least 2.0% or more, but if added excessively, it becomes a factor that greatly impairs hot workability and toughness, so the upper limit is 6.0. It is desirable to set it as%.

V: 4.0% or less V, like W and Mo described later, combines with C to form a very hard and hardly solid-solved carbide, which greatly improves wear resistance. V has the effect of refining the crystal grains and increasing the toughness. However, if added excessively, the toughness and the abradability are largely impaired, so the upper limit is preferably made 4.0%.

Co: 12% or less Co is an element that forms a solid solution in the matrix to strengthen the matrix, and at the same time, greatly improves hardness and proof stress at high temperatures. However, if added excessively, it becomes a factor that hinders the toughness, so the upper limit is preferably made 12%.

W, Mo: 16% to 20% in W + 2Mo W and Mo combine with C to form a composite carbide and, at the same time, form a solid solution in the matrix to strengthen the matrix, resulting in wear resistance and temper softening. It is an element that increases resistance. In order to fully exert such effects, the value of W + 2Mo is 16%
The above is necessary. On the other hand, if it is too large, it will impede hot workability and reduce toughness. Therefore, it is recommended to set the upper limit to 20%.

In the present invention, in order to adjust the grain size of the carbide, a soaking treatment may be adopted, and the treatment conditions vary depending on the steel type. Heat treatment may be performed for a time.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification of the design of the present invention can be made without departing from the gist of the preceding and the following. It is included in the technical scope.

[0022]

EXAMPLES Alloy powders having the composition shown in Table 1 were produced by the gas atomizing method. Each powder obtained was filled in a mild steel capsule, deaerated and sealed, and then hot isostatic pressing (HI
P), solidified and molded, then subjected to soaking treatment at 1180 ° C for 10 hours to adjust the grain size of the carbide, and then forged and rolled at a forging ratio of about 100, and heat treated (1210 ° C quenching, 550 ° C 3 times return). The test piece of the present invention (No.
1, 2). Test pieces of comparative examples (No. 3 to 10)
Was produced without adjusting the grain size of the carbide by the soaking treatment. After polishing each obtained test piece, SEM
A photograph was taken, the average particle size and the maximum particle size of the carbide were measured by an image processing device, and the hardness was measured by HRC.

Further, a cutting test was conducted under the following conditions to examine the wear resistance and chipping resistance of each test piece. [Cutting Test] After manufacturing the cutting tip shown in FIG. 1 and subjecting it to the heat treatment, using the tip holder shown in FIG.
A cutting test was performed on each of D11 (raw material, about HRC18) and SKD61 (tempered material, about HRC40) work materials under the following conditions. Rotation speed: 128 rpm Feed: 24 mm / min Depth of cut: Rd35 mm, Ad2 mm Cutting direction: Down However, SKD11 is dry cutting by air blow, SK
D61 was performed by wet cutting with a water-soluble lubricant.

The wear resistance of each work material is the outer circumference 2 of the tip.
The evaluation was made by the cutting distance until the second wear amount reached 0.2 mm or the time when an uncuttable chip occurred. In addition, the chipping resistance was judged to be poor in chipping resistance (evaluation: x), and the chipping resistance was judged to be good in chipping resistance (evaluation: ◯). The results are shown in Table 2.

[0025]

[Table 1]

[0026]

[Table 2]

From these results, the present invention example No. which satisfies all the conditions of the present invention. 1 and No. 1 No. 2 is in the high hardness region of HRC68 or higher, and it is clear that the wear resistance and the chipping resistance are balanced at a high level.

On the other hand, the comparative examples (Nos. 3 to 10) which do not satisfy any of the conditions of the present invention do not have sufficient wear resistance or chipping resistance. In particular, No. 1 has the same composition and differs only with or without particle size adjustment. 2 and No. Comparing three, N
o. It can be seen that No. 3 is inferior in wear resistance because the average grain size of carbides is too small, less than 0.40. In addition, No. 5 is N
Comparative example in which the content of b exceeds 2%
It corresponds to the powder high speed tool steel of Japanese Patent No. 163551), the maximum grain size of carbides exceeds 5 μm, and it is understood that the chipping resistance is poor.

As described above, the present inventors set the Nb content to 2
% Or less, the maximum grain size of the carbide is controlled to be small and grain size adjustment such as soaking treatment is performed to appropriately grow the average grain size that is too small from the viewpoint of wear resistance. It has succeeded in obtaining a powder high speed tool in which wear resistance and chipping resistance are balanced at a high level.

[0030]

EFFECTS OF THE INVENTION Since the present invention is constituted as described above, it has become possible to provide a powder high speed tool steel which exhibits excellent wear resistance and chipping resistance at the same time, and a manufacturing method thereof.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the shape of a cutting tip used in an example.

FIG. 2 is an explanatory view showing a holder of the cutting tip.

Claims (2)

[Claims] 1. A Mo-based high-speed tool steel containing Ni and Co, containing 0.5 to 2.0% by weight of Nb, and having an average grain size of carbide of 0.40 to 0.80 μm. A powder high-speed tool steel having excellent wear resistance and chipping resistance, which is characterized by having a maximum grain size of 5 μm or less. 2. The method for producing a powder high speed tool steel according to claim 1, wherein the grain size of the carbide is adjusted by a soaking treatment.