JPS6289843A - Sintered tool steel - Google Patents

Abstract

PURPOSE:To obtain sintered tool steel excellent particularly in hardness, wear resistance and toughness by adding proper amounts of BN powder to a fine- grained tool steel powder and by sintering the resulting mixture. CONSTITUTION:The BN powder is added by 0.3-25% to the tool steel powder which is fine-grained to such an extent that the grain size is about 350 mesh or below and also average grain size comes to about 30mum or below, and they are blended. At this time, any of c-BN powder, w-BN powder and two-phase sintered powder of c-BN and w-BN powders may be used as the above BN. Subsequently, above-mentioned powder mixture is sintered, so that the desired sintered tool steel can be obtained. Further, the above tool steel may contain C, Cr, W, Mo, V, Co, etc., and the preferred content of each component is shown below: C, 0.5-3%; Cr, 2-30%; W, 0 or 0.1-30%; Mo, 0 or 0.1-20%; V, 0.5-7.5%; and Co, 0 or 0.1-20%.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a sintered tool steel used as a tool material for cutting tools and the like, particularly a sintered high-speed steel having excellent hardness, wear resistance, and toughness. .

(Prior art and its problems) Conventionally, the Al5I M40 series has been developed as a high-speed steel with high hardness (IrR065-70). The M4
In order to improve the hardness of the 0 series high-speed steel, 5% by weight or more of CO (hereinafter referred to as %) is added to increase the amount of C and prevent a decrease in toughness. Speed steel is manufactured by melting method, so
Segregation of carbides is likely to occur, and the heat treatment conditions become harsh. Furthermore, since the amount of V is small, there is also the problem that abrasion resistance is reduced.

Conventionally, high-speed steel manufactured by powder metallurgy,
In order to avoid improving hardness and wear resistance, MOLW, Co5C
It is known that high-speed copper powder is created by atomizing a highly alloyed molten metal by increasing the amount of additives such as , N, etc. using the gas atomization method, and then solidifying the resulting powder by hot isostatic pressure treatment. .

However, in high-speed steel manufactured by the above-mentioned gas atomization method, there is a limit to the adjustment of the amount of each component added, and if the limit is exceeded, there is a problem that good atomization cannot be performed. For example, when adding Ti to high-speed steel, the maximum amount of Ti added is 2%; if it exceeds 2%, even if vacuum melting is performed, bubbling occurs due to the C○ reaction and the viscosity of the molten metal decreases. and atomization becomes impossible. or,
Regarding ■, [if 5% or more is added, it will be 1+ if it dissolves in the atmosphere.]
U = 1-? N Ma kzu) F1hzekogu〒1 ninsu? 1 ゛City゛ and ■7
．． If more than 5% is added, the carbide in the powder becomes huge even though atomization can be performed. On the other hand, if the amount of V is reduced to such an extent that the above problems do not occur, sufficient hardness and wear resistance cannot be obtained.

In order to solve this problem, a product is produced by co-reducing oxide powder with H7 and C, mixing carbide powder and nitride powder, pulverizing the mixture, molding and sintering the resulting powder. Are known. This sintered high-speed steel has the advantage that the content of each component can be adjusted relatively easily. However, the sintered high-speed steel produced by the co-reduction method has a problem in that when Mo, W, Cr, V, etc. added as oxide powders are carbonized, the carbides agglomerate and the toughness decreases.

(Means and Effects for Solving the Problems) As a result of intensive research, the present inventor has found that by incorporating an appropriate amount of boron nitride (BN) into tool steel, the above problems can be solved and the hardness and wear resistance can be improved. found that the scales had improved toughness.

Based on the above knowledge, the tool steel according to the present invention is manufactured by adding 13N powder to atomized steel plate powder and mixing the mixture, and then sintering the mixture. The density ratio of this sintered tool steel is preferably 99% or more.

In order to obtain good hardness, wear resistance, and toughness, the above BN
The amount of powder added is preferably in the range of 0.3 to 25%. If the amount of BN powder added is increased within this range, the hardness and wear resistance will improve, but on the contrary, the toughness will decrease. Therefore, the amount of BN powder to be added may be selected so as to obtain hardness, wear resistance, and toughness depending on the application.

In addition, the tool steel powder obtained by atomization has a particle size of about 3
If the particle size is reduced to 50 mesh or less and the average particle size is approximately 30 μm or less, no matter which value from the above range is selected as the amount of BN powder added, BN will always be added to the tool steel powder.
The powder can be dispersed sufficiently uniformly, thereby providing a high-performance tool steel.

The above BN has h-BN (hexagonal BN) due to its crystal structure.
), U-BN (wurtzite type BN) and C-BN
(cubic system BN), but in the present invention, as the BN added to the tool copper powder, either cBN powder, wBN powder, or two-phase sintered powder of c-B'N and w-BN is used. can do.

In addition, the said tool steel can contain C, Cr, WSMo, (1), Go, etc., and the preferable content of each component in that case is shown below.

C: 0.5-3% Cr.2-30$ W: 0 or 0.1-30% Mo: 0 or 0.1-20% V: 0.5-7.5% Co: 0 or 0. 1-20% (Example) C1.3%, Mn0.31%, Sio, 29%, Po
, 023%, SO, 014%, Cr3.93%, Mo
5.14%, W6.30%, V 2.95%, Co7.
A molten metal with 99% balance Fe is gas atomized to have an average particle size of 1.
A 9.0 μm high speed steel powder was prepared. C-BN powder having an average particle size of 20 μm was added in an amount of 0 to 27% to the high speed steel powder and mixed. Subsequently, temperature 1111111'f' - mouth: -h Qnna+m-ys k-th mouth a% + and E
bn n ■ (TJ T D S L applied and sintered,
A sample material was created.

Figure 1 shows the microscopic structure (x100x) of the sample material when the amount of cBN powder added was 5%. As is clear from the figure, by atomizing the high-speed steel powder, BN
are evenly distributed within the tissue.

After oil quenching at 1190℃ for 3 minutes on the above sample material, 540℃
C-1. The heat treatment of air cooling for 5 hours was repeated three times, and the hardness of the sample material was measured after such heat treatment.

Figure 2 shows the results. As is clear from the figure, c
- The hardness improves as the amount of BN powder added increases.

Further, the results of measuring the transverse rupture strength of the sample material after the above-mentioned heat treatment are shown in FIG. As is clear from the figure, as the amount of c-BN powder added increases, the transverse rupture strength, that is, the toughness decreases. Especially when the amount of c-13N powder added is 25% or more,
The aggregation of BN becomes significant and the transverse rupture strength rapidly decreases.

After the above heat treatment, the wear resistance of the sample material was investigated using the Ohkoshi abrasion test method, and the results are shown in FIG. However, the test material was 90M415, the final load was 6.3 kg, the wear distance was 400 m, the wear rate was OJm/sec, and the test was conducted without lubrication. As is clear from the figure, as the amount of c-BN powder added increases, the specific wear amount decreases, and therefore the wear resistance improves. In particular, the amount of c-BN powder added is 0.3%.
When the amount exceeds this level, the wear resistance increases rapidly.

The above described the measurement results when c-BN powder was added, but 5% vt-BN powder with an average particle size of 19 μm was
The measurement results of each characteristic when added are shown with x marks in FIGS. 2 to 4. As can be seen from Figures 2 to 4, w-B
The characteristics when 5% of N powder is added are almost the same as those when the same amount of c-BN powder is added. In the above embodiments, the high-speed steel powder was produced by gas atomization, but it may be produced by ultra-high pressure water atomization instead.

[Brief explanation of drawings]

FIG. 1 is a photograph substituted for a drawing showing the metal structure of the sintered high-speed steel according to the present invention, FIG. 2 is a graph showing the relationship between the hardness after heat treatment and the amount of BN powder added in the sintered high-speed steel according to the present invention, Figure 3 is a graph showing the relationship between the bending horn after heat treatment in the sintered high-speed steel according to the present invention and the amount of BN powder added. Figure 4 is the specific wear amount after heat treatment in the sintered high-speed steel according to the present invention. It is a graph which shows the relationship between and the amount of BN powder added. Patent Applicant: Kobe Steel Co., Ltd., Agent Patent Attorney: 1 person, above.

Claims (1)

[Claims] (1) Particle size of approximately 350 mesh or less, and average particle size of approximately 3
A sintered tool steel characterized in that 0.3 to 25.0% by weight of boron nitride powder is added to tool steel powder atomized to 0 μm or less, and the mixture is sintered.