JPS6117901B2 - - 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 means that MX or M ₆
M ₆ It is more stable than C-type carbide, has a wide range of suitable quenching temperatures, is easy to manage heat treatment, has high secondary hardening ability, and has a fine austenite crystal structure, which improves mechanical properties. This is due to effects such as 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 the partial pressure, and this method can be expected to form fine, uniformly dispersed nitrides. be. 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 for imparting high cutting performance has not been clarified. Steel is 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 SKH ₉ and JIS
It has been reported that cutting performance was significantly improved by adding 0.4 to 0.5% nitrogen to 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 will upset the balance of alloy components, increase the amount of retained austenite during quenching, require an increase in the number of temperings, and increase heat treatment distortion.
Furthermore, problems such as a decrease in toughness and a limited range of application as a cutting tool arise. 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.
C
As a result of various studies based on the above-mentioned views regarding N and N, it was discovered that the above object can be achieved by specifying the C content and C+N content within a certain range for these high-speed steel compositions, and the present invention has been made based on this research. It was completed. That is, the gist of the present invention is that Cr3.5-4.0%,
Mo9.0~10.0%, W1.4~2.1%, V1.0~1.35%,
Contains Co7.75-8.75% and C0.7% or less, C+
By setting N0.8 to 1.2%, heat treatment distortion is reduced and mechanical properties such as toughness are maintained at a high level.
This greatly improves the cutting performance of high-speed steel. 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 AISI M33, that is, Cr3.5 to 4.0%,
Mo9.0~10.0%, W1.4~2.1%, V1.0~1.35%,
Co7.75~8.75%, Si0.2~0.45%, Mn0.15~0.40
%, P0.03% or less, and S0.03% or less. In addition, C is added to the chemical composition equivalent to each steel type above.
By setting the amount of C+N to 0.7% or less and setting the amount of C+N to 0.8 to 1.2%, a significant improvement in cutting performance can be brought about, as 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 mixing the mixture so that the amount of C+N is 0.7% or less and filling it into a mild steel capsule and degassing it, the amount of C+N is 0.8%.
The steel is nitrided to a concentration of ~1.2%, then compression-formed using a hot isostatic press to form a steel ingot, which is then subjected to an appropriate heat treatment depending on the component composition. Next, the cutting performance of the nitrogen-containing powder metallurgy high speed steel according to the present invention will be specifically explained with reference to Examples. Example For high-speed steel equivalent to AISI M33, steel powders with different amounts of C (80 mesh or less) were produced using a gas atomization method, each powder was mixed in an appropriate ratio, filled into a mild steel capsule, and degassed. Thereafter, the steel was subjected to nitriding treatment and compression molded using a hot isostatic press to obtain a steel ingot, which was then subjected to heat treatment to obtain a product. The manufacturing conditions and cutting performance of the product are shown below. In addition, as a comparative 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: The chemical composition of raw steel powder equivalent to AISI M33 is shown in Table 1.

[Table] (b) Nitriding treatment Nitriding was performed by heating at 1000 to 1150°C for 2 hours in a nitrogen atmosphere. However, the nitrogen 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 2-4 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. The cutting life time (cutting time until the flank wear width V _B =0.6 mm is reached) in the above-mentioned interrupted cutting test is shown in FIG. In the figure, A, B, C, and D are obtained using the steel powder shown in Table 1, respectively, and M is a melted material. As is clear from the figure, C0.7%
Hereinafter, it was confirmed that a cutting life approximately twice as long as that of conventional ingot material is guaranteed within the range of about 0.8 to 1.2% C+N. Furthermore, the results of measurements conducted separately confirmed that there were no problems with regard to heat treatment distortion and resistance.

[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 Cr3.5~4.0%, Mo9.0~10.0%, W1.4~2.1
%, V1.0~1.35%, Co7.75~8.75%, and is produced by a powder metallurgy method characterized by C0.7% or less and C+N0.8~1.2%. steel.