JPS6115140B2 - - 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 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 SKH9 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, and Cr, and has a great influence on the properties of high-speed steel. For example, in "Iron and Steel" (Volume 45, No. 5, P.511-516), C%
=0.19+0.017(W%+2Mo%)+0.22V%, and 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 utilized 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. Performance of high speed steel equivalent to
In order to improve the cutting performance in particular, as a result of various studies based on the above opinion regarding C and N,
For these high-speed steel compositions, the present inventors have discovered that the above objects can be achieved by specifying the amount of C and the amount of C+N within a certain range, and have completed the present invention. That is, the gist of the present invention is that Cr3.8 to 4.5%,
By containing W17.0~22.0%, V0.8~1.5%, Co00~17%, and C0.6% or less and C+N0.7~1.1%, heat treatment distortion is reduced and mechanical properties such as toughness are improved. This material significantly improves the cutting performance of high-speed steel while maintaining a high level of mechanical properties. 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 are SKH4A, SKH4B, SKH2,
Compositions equivalent to those standardized by SKH3, SKH5, etc. are applied. That is, Cr3.8~4.5%, W17.0~19.0%,
V1.0~1.5%, Co9.0~11.0%, Si0.4% or less,
Equivalent to SKH4A type defined as Mn 0.4% or less, P 0.03% or less, S 0.03% or less, Cr3.8-4.5%, W18.0-20.0%, V1.0-1.5%,
Co14.0~16.0%, Si0.4% or less, Mn0.4% or less,
SKH4B defined as P0.03% or less, S0.03% or less
Seed equivalent, Cr3.8~4.5%, W17.0~19.0%, V0.8~1.2%,
Si0.4% or less, Mn0.4% or less, P0.03% or less, S0.03
Equivalent to SKH2 type specified below %, Cr3.8~4.5%, W17.0~19.0%, V0.8~1.2%,
Si0.4 or less, Mn0.4% or less, P0.03% or less, S0.03%
Equivalent to 3 types of SKH specified below, Cr3.8~4.5%, W17.0~22.0%, V1.0~1.5%,
Co16.0~17.0%, Si0.4% or less, Mn0.4% or less,
Applicable to steel types equivalent to SKH class 5, defined as P0.03% or less and S0.03% or less. In addition, C is added to the chemical composition equivalent to each of the above steel types.
By setting the amount of C+N to 0.6% or less and setting the amount of C+N to 0.7 to 1.1%, a significant improvement in cutting performance is brought about, as shown in the examples below. In order to produce the nitrogen-containing powder metallurgy high-speed steel according to the present invention, alloying elements such as Cr, W, V, and Co are contained in accordance with the desired equivalent steel type, and steel powder with a different amount of C (for example, gas atomized steel powder), the amount of C is
After mixing the mixture so that it is 0.6% or less, filling it into a mild steel capsule and degassing it, the amount of C + N is 0.7 to 1.1.
%, followed by compression molding using a hot isostatic press to form a steel ingot, which is then subjected to an appropriate heat treatment depending on the component composition. As mentioned above, the present invention provides SKH4A, SKH4B,
Applicable to high-speed steels containing alloying elements equivalent to SKH2, SKH3, etc. Each of these steel types is
Although there is a difference in the amount of Co, Co has a weak affinity for C and N and hardly contributes to the formation of carbonitrides, so it is not directly related to the amount of Co, and the amount of C and C+N is specified as described above. Therefore, the same effect can be obtained for each steel type. Therefore, the amount of Co is approximately 17% when used in combination with W, V, etc. for the purpose of improving high-temperature hardness.
It can be added as appropriate within the range of % or less. 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 JIS, SKH4A, SKH2, and SKH5, steel powders with different amounts of C (80 mesh or less) are manufactured using the gas atomization method, and each powder is mixed in an appropriate ratio and filled into a mild steel capsule. death,
After degassing, it was subjected to nitriding treatment, and then compression molded using a hot isostatic press to obtain a steel ingot, which was then heat treated 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 is shown in Tables 1, 2, and 3.

【table】

【table】

[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, D, E and F
are those obtained using the steel powders shown in Tables 1, 2, and 3, respectively, and M ₁ to M ₃ indicate ingot materials. As is clear from the figure, C0.6% or less, C+
In the range of approximately 0.7 to 1.1% N, compared to conventional melted lumber,
It has been observed that a cutting life of approximately 3 to 4 times longer 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%, W17.0-22.0%, V0.8-1.5%
A nitrogen-containing high-speed steel manufactured by a powder metallurgy method, characterized in that it contains 0.6% or less of C and 0.7 to 1.1% of C+N. 2 Cr3.8~4.5%, W17.0~22.0%, V0.8~1.5
%, contains 17% or less of Co, and 0.6% or less of C, C
Nitrogen-containing high-speed steel manufactured by a powder metallurgy method characterized by +N0.7 to 1.1%.