JPS61159557A - Powdery high-speed steel - Google Patents

Abstract

PURPOSE:To obtain a powdery high-speed steel inhibiting the coarsening of carbide grains during hot working and hardening, undergoing no reduction in the toughness, and giving superior wear resistance and superior hardness at high temp. by providing an alloy composition having a lower Mo content and a higher W content than a conventional composition. CONSTITUTION:Alloy steel powder consisting of 1.65-1.80% C, <=0.40% Si, <=0.40% Mn, 3.80-4.50% Cr, 4.50-5.50% Mo, 7.3-8.5% W, 4.50-5.50% V, 7.00-9.00% Co, <=0.030% P, <=0.030% S, <=0.25% Cu, <=0.25% Ni and the balance Fe in the composition range of 8% Co tool steel is molded and sintered to obtain a high-speed tool steel making good use of advantages of a sintered steel and having further increased wear resistance and further increased hardness at high temp. without reducing the toughness.

Description

[Detailed description of the invention]

Purpose of invention

[Industrial application field]

The present invention relates to improvements in powdered high speed tool steel. [Prior Art] In order to improve wear resistance and hardness, which are important properties in high-speed tool steel, it is generally advantageous to select a high alloy composition. However, if a material with a high alloy composition is manufactured by melting and casting, the carbide particles tend to become coarse and the toughness decreases, so it is advisable to use a powder metallurgy method. However, even in sintered steel, coarsening of carbides occurs to some extent during quenching, so there is a limit to the improvement of the above-mentioned properties, and in order to take advantage of the advantages of powder metallurgy, it is necessary to It is necessary to carefully consider the relationship with the amount added and select a well-balanced composition.

[Problems to be solved by the invention]

An object of the present invention is to provide a powdered high-speed steel having further improved wear resistance and hardness, with no reduction in toughness or other properties, based on careful alloy design carried out from the above viewpoints. It is in. Structure of the Invention [Means for Solving the Problems] The improved powder high speed tool steel of the present invention has the following composition in the area of 8-Go tool steel: C: 1.65
~1.80%, Si: 0.40% or less, Mn: Q
, 40% or less, Cr: 3.80-4.50%, Mo
:4.50~5.50%, W:7.3~8.5%, V:
4.50-5.50% and 'Co: 7.00-9
．． 00%, P: 0.030% or less, S: 0.0
30% or less, Cu: 0.25% or less, Ni: 0.2
Selecting an alloy composition in which the content is 5% or less and the balance is Fe,
It is made by molding and sintering the powder of this alloy.

[For use]

The above composition was determined by examining the balance of each alloy component as described above, but the most important feature lies in the balance between relatively low MO and high W. In the formula for tungsten equivalent, W% + 2MO%, which is well known as an index of wear resistance, MO has twice the influence of W, so to increase the equivalent value, increase the Mo content. It is effective to increase it. However, it has been found that hot workability and the coarsening tendency of carbides during quenching are smaller in W carbides than in MO carbides, so in the present invention, we take advantage of this fact by increasing the W content. This improves wear resistance and high-temperature hardness while avoiding a decrease in toughness. The effects of each alloying element and the reasons for limiting the composition are as follows. Mo: 4.50-5.50% Forms MeC type carbide together with W, contributing to machinability and wear resistance. To obtain this effect, 4.50%
On the other hand, in order to suppress the damage caused by coarsening of carbides during hot working and quenching, the addition amount is limited to no more than 5.50%. W near. In conjunction with 3-8.5% 1v1o, carbides provide machinability and wear resistance. Taking advantage of the fact that carbides are difficult to coarsen, 7.5% or more of MO is added in order to work in place of MO, which is kept at a low level. The upper limit was determined in consideration of the decrease in toughness and material price. Cr: 3.80 to 4.50% The lower limit is necessary to ensure hardenability, and the upper limit was determined in consideration of the decrease in toughness. There are many things. V: 4.50 to 5.50% Added to maintain wear resistance in low friction areas. If it becomes too large, huge carbide particles will precipitate, impairing toughness, so it should be within the above range. Co:7. OO~9.00% Helps solid solution of W and MO into the matrix and improves heat resistance. If it is not added in an amount of 7.00% or more, the tempering hardness will be insufficient, while if it is added in an amount exceeding 9.00%, the effect will not be enhanced and the toughness will decrease. C: 1.65-1.80% Essential for the formation of W, MO, Cr and V carbides,
In addition, it dissolves itself in the matrix to provide high tempering hardness. The ideal amount can be calculated as the "carbon equivalent" of the following formula. C%=0.06Cr +0.033W +0.063Mo +0.20V The other elements mentioned above are deoxidizing agents or impurities normally contained in the raw materials, and the upper limit number is the allowable amount thereof. ,

【Example】

Steel having the following composition was melted, sprayed with a nitrogen gas jet stream, and sieved to prepare alloy powders of various particle sizes. The comparative example is a conventional product. Nα 1 2 3 Comparative example C1,681
,711,661,2&S i O,310,290,310,22Na
1 2 3 Comparative example Mn
O, 280, 300, 330, 24P O,
0150,0120,0090,009SO,
0130,0100,0110,010CIJ
O,0B 0.0B 0.09 0.04
N i O,090,070,080,06Cr
4.33 4.17 4.06 4.
llMo 4.58 5.39 4.67
4.98W 8.41 7.88 7.
49 6.40V 4.52 5.24
4.88 3.12Co 8.01 7
．． 44 8.72 8.44 Blending alloy powder,
It was filled into a soft m capsule with a diameter of 120 mm, degassed, sealed, and hot forged. Subsequently, the forged material was subjected to the following heat treatment. Quenching: 1,210'CXa minutes → Oil-cooled tempering: 5
When the microstructure of the material after heat treatment at 50° C. for 1 hour → air cooling (3 times) was examined, it was found to be sufficiently fine and no formation of coarse or giant products was observed. In addition, the carbide content was measured by electrolytic extraction, and the following results were obtained for 1 q. Invention Nα1-3 19.5-22.4% Comparative example
The measurement results of 12.4% hardness and toughness are as follows. NQ 1 2 3 Comparative example hard
Sa 68.2 67.8 68.0
66.7 (HRc) Transverse rupture strength 417 420 422 37B<
Kyf/lNn2) The specific wear amount was determined by a human wear test under the following conditions. Rotating disk: 30M21 (SA) Final load: 6.5 to 9 Friction speed: 2.86m/sec Friction distance: 200m The results are as follows, and the specific wear amount is generally small, especially in the low friction speed region It can be seen that this high-speed steel is excellent. No. 1 2 3 Amount of wear compared to the toe at rest 0.96 0.98 1.02 1.8
Second, specific grindability was tested under the following conditions. Grinding wheel: WA#120 Depth of cut ~0.5 feed Re: 0.02 m/stroke Grinding wheel circumferential speed: 1370 TrL/min The grinding ratio, that is, (amount to be ground/amount of grinding wheel wear) is as follows. Shark drawing ratio up to NQ 1 2 3 6
．． 91 7.51 7.98 5.42 Finally, a cutting tool was made from the powdered high-speed steel of the present invention, and an interrupted cutting test was conducted under the following conditions to examine its practical performance. Feedback: 0.05s/rev. Depth of cut: 5ffill+ Cutting speed: 6C)~52m/min Cutting material: 80M420 (N> Gear m=2.5 2=31 φ=82.5 The following data were obtained. NQ 1 2 3 Comparative example maximum flank 0
．． 55 0.51 0.47 0.63 Wear (s
) Effects of the Invention By carefully selecting the powder high-speed tool steel of the present invention, and in particular selecting an alloy composition with a lower MO content and higher W content than conventional products, the powder high-speed tool steel has improved performance during hot working and quenching. We succeeded in suppressing the coarsening of carbide particles. This makes full use of the advantages of sintered steel, providing a tool steel with even higher wear resistance and high-temperature hardness without deterioration in toughness.

Claims (1)

[Claims] C: 1.65-1.80%, Si: 0.40% or less, M
n: 0.40% or less, Cr: 3.80-4.50%, M
o: 4.50-5.50%, W: 7.3-8.5%, V
:4.50~5.50% and Co:7.00~9.0
Contains 0%, P: 0.030% or less, S: 0.030
% or less, Cu: 0.25% or less, Ni: 0.25% or less, and the balance is Fe.