JPS6115142B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to nitrogen-containing high-speed steel produced by powder metallurgy, and by specifying the content of C and N in the steel, it is possible to improve the mechanical properties of high-speed steel, including thermal distortion caused by heat treatment, toughness, etc. The cutting performance has been significantly improved without deteriorating the mechanical properties. It is generally known that by adding nitrogen to high-speed steel containing alloying elements such as Cr, W, and V, various performances of the high-speed steel can be improved. This can be confirmed by nitriding treatment.
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This is due to the effects of easy heat treatment management, high secondary hardening ability, fine austenite crystal structure, improved mechanical properties, and improved cutting performance. Conventionally, such nitrogen-containing high-speed steels have been mainly produced by a melting method. However, this melting method requires complicated processes such as melting the molten steel in a high-pressure nitrogen atmosphere for nitriding treatment or adding nitrides to the molten steel. Since the amount is small and it is difficult to form and distribute carbonitrides finely and uniformly in steel, the desired performance cannot be significantly improved. As a means to avoid the limitations associated with such melting methods, attempts have recently been made to develop nitrogen-containing high-speed steels using powder metallurgy or powder forging methods. This takes advantage of the large specific surface area of the powder and the porous nature of the powder sintered body. For example, by adding nitrogen to the raw material powder in advance, or by changing the heating temperature, heating time, and nitrogen atmosphere during sintering This method attempts to enrich the steel with a desired amount of nitrogen using relatively easy-to-operate means such as adjusting partial pressure, and this method can be expected to form fine, uniformly dispersed nitrides. It is. However, the cutting performance of nitrogen-containing high-speed steels conventionally produced by powder metallurgy is not necessarily improved as much as expected, but is rather inferior, or there are doubts about the value of such high-speed steels. In addition, the reason why nitrogen-containing high-speed steel produced by powder metallurgy, which has been put into practical use for a few years, has both machinability and wear resistance is unknown. This is partly due to the fact that the relationship between alloying elements and nitrogen enrichment, which imparts high cutting performance, has not been clarified. Speed steels are limited to steel types with specific compositions. For example, Kobe Steel Technical Report Vol. 24, No. 3, P10 describes Mo-based high-speed steel (JIS SKH9 and
It has been reported that cutting performance was significantly improved by adding 0.4 to 0.5% nitrogen to JIS SKH55 (improved type). However, although adding a large amount of nitrogen to high-speed steel whose alloy components have already been standardized is effective in improving wear resistance and heat resistance, on the other hand, the stoichiometry of high-speed steel This results in an imbalance of the alloy components, which increases the amount of retained austenite during quenching, requires an increase in the number of tempering cycles, increases heat treatment distortion, and reduces toughness, making it difficult to use as a cutting tool. This causes problems such as a limited range. The purpose of the present invention is to solve the above-mentioned heat treatment problems,
without adversely affecting mechanical properties such as toughness.
The objective is to provide high-speed steel with excellent cutting performance. By the way, among the main alloying elements of high-speed steel, C
has a close relationship with carbide-forming elements such as W, V, Mo, and Cr, and has a great influence on the properties of high-speed steel. For example,
"Iron and Steel" (Volume 45, No. 5, P.511-516) has C.
% = 0.19 + 0.017 (W% + 2Mo%) + 0.22V%, and it is more strictly regulated than other alloying elements. On the other hand, N generally has properties similar to C, and both have small atomic weights of 12 and 14, respectively, and are interstitial atoms in steel, forming stable alloy compounds. It has the property of being easy to use. Therefore, when attempting to improve the cutting performance or mechanical properties of high-speed steel containing a large amount of N, it is necessary to
It is considered that this should be done in relation to the quantity. The present inventors took advantage of the fact that the powder metallurgy method is an advantageous means for enriching any amount of nitrogen and forming fine and uniform carbonitrides, as described above.
In order to improve the performance of high-speed steel, in particular the cutting performance, which corresponds to the chemical composition of SKH52 (AISI M3-1) melted material, we have conducted various studies based on the above opinion regarding C and N, and as a result, we have developed these high-speed steels. The present inventors have discovered that the above object can be achieved by specifying the C content and C+N content within a certain range for the speed steel composition, and have completed the present invention. That is, the gist of the present invention is that Cr3.8 to 4.5%,
Mo4.8~6.2%, W5.5~6.7%, V2.8~3.3%, Co0
Contains ~20% and C0.9% or less, C+N1.0~
By setting it to 1.4%, heat treatment distortion is reduced,
It significantly improves the cutting performance of high-speed steel while maintaining a high level of mechanical properties such as toughness. Hereinafter, the nitrogen-containing powder metallurgy high speed steel of the present invention will be explained. The basic components of the nitrogen-containing powder metallurgy high-speed steel of the present invention, excluding C and N, correspond to the composition standardized by SKH52 type (AISI M3-1), that is,
Cr3.8~4.5%, Mo4.8~6.2%, W5.5~6.7%,
V2.8~3.3%, Si0.4% or less, Mn0.4% or less, P0.03
% or less, S0.03% or less, or steel types with a composition in which Co is added in a range of 20% or less to the above components. In addition, C is added to the chemical composition equivalent to each steel type above.
By setting the C+N content to 0.9% or less and setting the amount of C+N to 1.0 to 1.4%, a significant improvement in cutting performance can be brought about, as will be shown in Examples below. In order to produce the nitrogen-containing powder metallurgy high speed steel according to the present invention, alloying elements such as Cr, Mo, W, V, Co, etc.
Steel powder containing different amounts of C (for example, gas atomized steel powder) depending on the desired equivalent steel type,
After blending so that the amount of C+N is 0.9% or less and filling it into a mild steel capsule and degassing, the amount of C + N is 1.0.
The steel may be nitrided to a concentration of ~1.4%, then compressed using a hot isostatic press to form a steel ingot, and then subjected to an appropriate heat treatment depending on the component composition. As described above, the present invention is applied to high-speed steel containing an alloying element corresponding to SKH52 or a steel type having a composition obtained by adding Co to the same. Even if these steel types have different amounts of Co, Co has a weak affinity for C and N and hardly contributes to the formation of carbonitrides. According to the regulations on the amount of C and C+N,
Equivalent effects can be obtained with each steel type. Therefore, Co
It is used in combination with W, Mo, V, etc., and is appropriately added within a range of about 20% or less for the purpose of improving high-temperature hardness. Next, the cutting performance of the nitrogen-containing powder metallurgy high speed steel according to the present invention will be specifically explained by giving examples. Steel powders with different amounts of C (80 mesh or less) are produced by gas atomization, each powder is mixed in an appropriate ratio, filled into a mild steel capsule, degassed, nitrided, and then hot isostated. A steel ingot was formed by compression molding using an ice press, and this was subjected to heat treatment to obtain a product. The manufacturing conditions and cutting performance of the product are shown below. As a comparison material, a melt-sawn material according to the specifications was produced, and the cutting performance of the product obtained by heat treatment was measured and compared. (1) Manufacturing conditions (a) Chemical composition of raw material powder: Tables 1 and 2 show the chemical composition of raw material steel powder equivalent to SKH52 and Co added thereto.

【table】

[Table] (b) Nitriding treatment Nitriding was performed by heating at 1000 to 1150°C for 2 hours in a nitrogen atmosphere. However, the content of the product was adjusted by appropriately controlling the atmospheric pressure and temperature. (c) Heat treatment Quenching: 1200-1300℃ x 3 minutes, oil cooling. Tempering: 560℃ x 1.5Hr (repeat 2 to 4 times). (2) Cutting performance Interrupted cutting tests were conducted on powder metallurgy high-speed steels and ingots with different amounts of C and N obtained under the above conditions under the following conditions. Cutting speed: 25m/min, depth of cut: 1.5mm, feed: 0.2mm/rev, cutting oil: not used, tool shape: 0°, 15°, 6°, 6°, 15°, 15°,
0.4 ^R , work material: SNCM8 ( _HB 300-320), 4 lots. Fig. 1 shows the cutting life time (cutting time until flank wear width V _B =0.6 mm) obtained in the above-mentioned interrupted cutting test. In the figure, A, B, C, D, and E indicate those obtained using the steel powders shown in Tables 1 and 2, respectively, and M ₁ and M ₂ indicate ingot materials. As is clear from the figure, C0.9% or less, C+
In the range of approximately 1.0 to 1.4% N, compared to conventional melted lumber,
It is recognized that a cutting life of about 2 to 2.5 times is guaranteed. Furthermore, the results of measurements conducted separately confirmed that there were no problems with respect to heat treatment distortion and transverse rupture strength.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between cutting performance and C+N amount using C amount as a parameter.

Claims (1)

[Claims] 1 Cr3.8~4.5%, Mo4.8~6.2%, W5.5~6.7
%, V2.8~3.3%, and C0.9% or less, C
Nitrogen-containing high-speed steel manufactured by a powder metallurgy method characterized by +N1.0 to 1.4%. 2 Cr3.8~4.5%, Mo4.8~6.2%, W5.5~6.7
%, V2.8~3.3%, Co20% or less, and
A nitrogen-containing high-speed steel manufactured by a powder metallurgy method characterized by a C+N content of 0.9% or less and a C+N content of 1.0 to 1.4%.