JP6410515B2 - Nitride powder high-speed tool steel excellent in wear resistance and method for producing the same - Google Patents

Description

  The present invention relates to powder high-speed tool steel used for cutting tools, dies, and the like, and a method for producing the same.

  Conventionally, powder high-speed tool steel has a feature that it has better toughness than molten high-speed tool steel because fine carbides precipitate. Further, N is further added to precipitate carbonitride to further improve the performance (seizure resistance) of the powder high-speed tool steel, for example, disclosed in Japanese Patent Application Laid-Open No. 61-6255 (Patent Document 1). As shown, the chemical composition is mass%, C: an amount satisfying the following formula (%), Ceq + 0.15 ≦ C + 12 / 14N ≦ Ceq + 0.35, where Ceq = 0.19 + 0.017 (W + 2Mo) +0 .22V, in the above formula, N, W, Mo and V are the contents (%) in steel, Cr: 3-5%, Mo: 8-12%, W: 8-14%, V: 4- 6%, Co: 5 to 15%, N: 0.2 to 1.2%, the balance being substantially Fe, and (W + 2Mo) of 27 to 32% is proposed. ing.

  Further, as disclosed in JP2013-60617A (Patent Document 2), in mass%, C: 0.85 to 1.20%, Si ≦ 0.5%, Mn: ≦ 0.5 %, Cr: 3.8 to 6.0%, Mo: 5.6 to 8.0%, W: 5.1 to 8.0%, V: 3.0 to 6.0%, N: 0.00. 4 to 1.5%, these are C + N: 1.25 to 2.50%, Mo + W / 2: 8.3 to 11.0%, and 4.7 (Mo + W / 2) + 1.4N-Cr -2.1Mn: A steel alloy that satisfies ≧ 32.5%, the balance being Fe and inevitable impurities, and has high toughness characterized by a hardness of 65 HRC or more, and excellent in corrosion resistance and seizure resistance Nitride powder high speed steel has been proposed.

  On the other hand, when more advanced characteristics required for cutting tools in recent years (for example, characteristics when cutting at high speed) are required, wear resistance and toughness are still insufficient, and further improvements are possible. It has been demanded. Since the above-mentioned wear resistance is generally better as the hard carbide precipitated in the structure is larger, the powder high-speed tool steel having fine carbide may be inferior in wear resistance to the molten high-speed tool steel. In particular, the difference in the life becomes significant when a tool requiring a high cutting speed such as a hob or broach is applied.

  Nitride powder high-speed tool steel has an effect of improving seizure resistance due to carbonitride precipitation, and the life when applying a high-speed cutting tool is improved compared to powder high-speed tool steel. Still life is inferior. Furthermore, as a method for improving the wear resistance of powder high-speed tool steel, Electric Steel Manufacturing, Vol. 58, No. 4, pages 251 to 259, Hitachi Mina, Matsuda Yuki (non-patent document 1), a large amount of carbide in the structure. It has been reported that it is precipitated or increased, but if it is excessively performed, the toughness is lowered, and there is a problem from the viewpoint of chipping resistance.

Japanese Patent Laid-Open No. 61-6255 JP2013-60617A

Electric Steelmaking, Vol.58, No.4, pp.251-259 by Hitachi Minasa and Yuki Matsuda

  As described above, Patent Document 1 improves the seizure resistance by controlling components (C, N, Cr, Mo, W, V) and containing nitrogen to precipitate carbonitride, but the carbonitride is fine. Therefore, it is inferior in wear resistance when high-speed cutting is applied. Patent Document 2 obtains a high-toughness nitrided powder high-speed steel with excellent corrosion resistance and seizure resistance by controlling the components. However, since the average grain size of the nitride is as fine as 1 μm or less, it is resistant to high-speed cutting tools. Inferior to wear. Non-Patent Document 1 examines changes in wear resistance and toughness due to coarsening of carbide in powder high-speed steel. However, although the wear resistance is improved by the coarsening of the carbide, there is a problem that the toughness is lowered.

  As a result of diligent development to solve the above-mentioned problems, nitride powder high-speed steel with toughness that does not cause chipping while exhibiting excellent wear resistance and seizure resistance when applying high-speed cutting tools Is to provide.

The gist of the invention is that
(1) By mass%, C: 0.8 to 2.5%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Cr: 3.0 to 5.0% , Mo: 2.0 to 8.0%, W: 3.0 to 14.0%, V: 2.0 to 10.0%, Co: 0 to 10%, N: 0.3 to 1.5 %, And a Ceq value: 0.1 to 0.8, a nitrided powder high-speed tool steel in a quenched and tempered state consisting of Fe and unavoidable impurities, wherein the carbide in the metal structure has an average grain size A nitride powder having excellent wear resistance, characterized in that the diameter is 4 to 20 μm, the average particle size of carbonitride is in the range of 2 μm or less, and the average interparticle distance of precipitates is 10 μm or less. High speed tool steel.
However, Ceq = (C% + N%) − {0.19 + 0.017 (W% + 2Mo%) + 0.22V%}

(2) The steel powder for nitrided high-speed tool steel having the chemical composition and Ceq value described in (1 ) above is solidified with HIP in a temperature range of 1200 to 1300 ° C., and then hot plastic After processing, quenching and tempering, the carbide in the metal structure has an average particle size of 4 to 20 μm, the average particle size of carbonitride is 2 μm or less, and the average interparticle distance of the precipitate is 10 μm. A method for producing a nitrided powder high-speed tool steel excellent in wear resistance, characterized by:

(3) After solidifying and forming steel powder for nitride powder high-speed tool steel having the chemical composition and Ceq value described in (1) above in a temperature range of 1100 to 1200 ° C., 1200 to 1300 After high-temperature holding heat treatment for 2 to 6 hours in the temperature range of ° C., plastic processing is performed hot, and then quenching and tempering, the carbide in the metal structure has an average particle size of 4 to 20 μm, and carbonitriding The average particle size of the product is in the range of 2 μm or less, and the average interparticle distance of the precipitate is 10 μm or less.

  As described above, according to the present invention, a nitrided powder high-speed steel that exhibits wear resistance and seizure resistance at the time of high-speed cutting applications such as hobbing and broaching, and has toughness that does not cause chipping, and such high-speed tool steel. The manufacturing method can be provided.

Hereinafter, the present invention will be described in detail.
In order to improve the wear resistance, it is effective to keep high temperature by heat treatment and coarsen hard precipitates (carbide and carbonitride precipitate in nitride powder high-speed tool steel). When the precipitates are enlarged, the precipitates aggregate and grow, so that the wear resistance is improved. However, the number of precipitates decreases, and the distance between the precipitates, that is, the distance between the particles increases. When the distance between the precipitate particles becomes long, the use of the high-speed cutting tool base material as a base material increases the chance of contact between the base phase and the counterpart material, and the base material falls off, that is, chipping occurs. Tool life is shortened. In addition, when fine precipitates disappear during the coarsening process of precipitates, fine precipitates of 2 μm or less have the effect of pinning and suppressing the coarsening of crystal grains during quenching and tempering. Was thought to be coarse and easy to decrease toughness. In the present invention, an attempt was made to obtain steel in which the diameter of the hard precipitate and the distance between the precipitate particles were controlled.

  Nitride powder high-speed tool steel has two types of precipitates, carbide and carbonitride, and the average particle size of carbide and carbonitride is usually about 2 μm or less. In the present invention, the size of each precipitate is controlled, and the carbide is coarsened to 4 to 20 μm, while the carbonitride is kept fine at 2 μm or less, and the coarse carbide and the fine carbonitride are mixed. The coarse carbide contributes to the improvement of wear resistance, and the fine carbonitride improves the toughness by the grain pinning effect and shortens the distance between the precipitate particles, and the effect of suppressing contact with the parent phase when using the tool. It was found that toughness (chipping resistance) was maintained, and as a result, a steel excellent in wear resistance and toughness (chipping resistance) was obtained.

  As a method for controlling the carbide and carbonitride sizes within the above ranges, the HIP molding temperature is 1200 ° C. to 1300 ° C., preferably 1220 ° C. to 1260 ° C. (the HIP molding temperature of normal powder high speed is 1100 to 1150 ° C. ). Alternatively, high-temperature holding heat treatment (soaking) is performed on the HIP solidified molded body at 1200 to 1300 ° C., preferably 1220 to 1260 ° C. for about 2 to 6 hours. The reason why carbides and carbonitrides can be controlled by the above treatment is that there is a difference in coarsening start temperature between carbides and carbonitrides (carbonitrides are more stable than carbides and have high coarsening start temperatures) from 1200 ° C. to 1300 When kept in the temperature range of ° C., the carbide is preferentially coarsened (grown), and the carbonitride is hardly coarsened (grown) and kept fine. In the present invention, this phenomenon is used to control hard precipitates.

Hereinafter, the reason for limitation according to the present invention will be described.
C: 0.8 to 2.5%
C is an element necessary for obtaining hardness and hardenability, and is essential for precipitation of carbides. However, if it is less than 0.8%, the effect is not sufficient. On the other hand, if it exceeds 2.5%, excessively coarse carbides are formed and the toughness is deteriorated, so the range is made 0.8 to 2.5%.

Si: 0.1 to 1.0%
Si is a deoxidizer and is an element necessary for obtaining the hardness of the matrix. However, if it is less than 0.1%, the effect is not sufficiently obtained, and if it exceeds 1.0%, toughness and workability deteriorate, so the range was made 0.1 to 1.0%.

Mn: 0.1 to 1.0%
Mn is a deoxidizer and is an element necessary for obtaining hardenability. However, if the content is less than 0.1%, the effect cannot be obtained sufficiently. If the content exceeds 1.0%, the matrix becomes brittle and the toughness and hot workability deteriorate. 0.0%.

Cr: 3.0-5.0%
Cr is an element necessary for obtaining seizure resistance and hardenability. However, if it is less than 3.0%, the effect is not sufficient. Moreover, since toughness and hot workability will deteriorate when it exceeds 5.0%, the range was made 3.0 to 5.0%.

Mo: 2.0-8.0%
Mo is an element necessary for forming carbide, giving hardenability, hardness and wear resistance, and obtaining temper softening resistance. However, if it is less than 2.0%, the effect is not sufficient. Moreover, since toughness and hot workability will deteriorate when it exceeds 8.0%, the range was made 2.0 to 8.0%.

W: 3.0 to 14.0%
W, like Mo, is an element necessary for forming carbide, imparting hardenability, hardness and wear resistance, and obtaining temper softening resistance. However, if it is less than 3.0%, the effect is not sufficient. Further, if it exceeds 14.0%, the toughness and hot workability deteriorate, so the range was made 3.0 to 14.0%.

V: 2.0 to 10.0%
V is an element necessary for obtaining hardness, seizure resistance and toughness, and becomes VN or VCN, and precipitates carbonitride to improve wear resistance and seizure resistance. However, if it is less than 2.0%, the effect is not sufficient. Moreover, since toughness and a machinability will deteriorate when it exceeds 10.0%, the range was made into 2.0 to 10.0%.

Co: 0 to 10.0%
Co is an element necessary for obtaining heat resistance, wear resistance, and tempering softening resistance. The effect of the present invention can be obtained even if this element is not included, but in tool steel for high-speed cutting applications, heat resistance and resistance to tempering softening are particularly important due to temperature rise during use, so it is preferable to contain it. . However, addition exceeding 10.0% promotes segregation and decarburization of carbides, so the range was made 0 to 10.0%.

N: 0.3 to 1.5%
N is an essential element for precipitating carbonitride. N combines with V to form a vanadium nitride, and improves hardness and seizure resistance. However, if it is less than 0.3%, the effect is not sufficient. Moreover, since toughness will fall when it exceeds 1.5%, the range was made into 0.3 to 1.5%. Preferably it is 0.4 to 1.0%.

Ceq value of 0.1 to 0.8
However, Ceq = (C% + N%) − {0.19 + 0.017 (W% + 2Mo%) + 0.22V%}
The Ceq value is a value indicating the balance between the amount of carbon and nitrogen and the amount of alloy element added, and needs to be controlled in order to precipitate carbide and carbonitride and ensure hardness, hardenability and seizure resistance. However, if it is less than 0.1, the effect is not sufficient, and if it exceeds 0.8, the toughness decreases, so the range was made 0.1 to 0.8. Preferably it is set to 0.2-0.6.

Average particle size of carbide: 4 to 20 μm
The average particle size of the carbide is a necessary condition for obtaining wear resistance. However, if it is less than 4 μm, the effect is not sufficient, and if it exceeds 20 μm, the toughness decreases and chipping occurs, so the range is made 4 to 20 μm. Preferably it is 5-15 micrometers.

Average particle size of carbonitride: 2 μm or less The average particle size of carbonitride is a necessary condition for keeping crystal grains fine and ensuring toughness. However, if it exceeds 2 μm, the crystal grains become coarse during quenching and tempering, and the toughness decreases. Accordingly, the thickness is set to 2 μm or less. Preferably, it is 1.5 μm or less.

Distance between particles of precipitates: 10 μm or less When the distance between particles of precipitates exceeds 10 μm, the distance between the precipitates becomes longer, so that there is a greater chance of direct contact with the parent phase when using the tool. Since the chipping easily occurs, the upper limit is set to 10 μm. Preferably, it is 5 μm.

Hereinafter, the present invention will be specifically described with reference to examples.
A metal powder having a component composition other than nitrogen shown in Table 1 is prepared by a gas atomization method, classified by a sieve having a size of 500 μm or less, and heated and held in a nitrogen atmosphere to contain nitrogen. This alloy powder was sintered under HIP conditions, and thereafter subjected to holding heat treatment in an atmospheric furnace, and a solidified molded body as it was in HIP molding was produced. It was heated to about 1075 ° C. and forged to a diameter of 30 mm, quenched at 1190 ° C., and then tempered three times at 560 ° C. The following investigation was performed on the quenched and tempered steel. The evaluation of wear resistance and toughness was performed by processing the heat-treated product into a hob and performing cutting using the hob.

  The wear resistance and toughness were evaluated based on the amount of wear when SCM415 was used as a work material and the cutting speed per minute was 300 m at a cutting speed of 1 meter per minute. A general-purpose nitride powder high-speed tool steel (Table No. 10) was set to 1, and the wear amount was compared to evaluate the wear resistance. Further, the toughness was evaluated by the presence or absence of chipping at that time. The results are shown in Table 1.

Precipitates in the structure are 20 mm in length, 20 mm in width, 10 mm in length, cut out a square bar, wet-polished, and observed by SEM, and the structure is present in a range of 100 μm ² based on a 1000 times composition image photograph. The average particle diameter of each carbide and carbonitride was calculated using image analysis software, and the interparticle distance between the precipitates. The results are shown in Table 1.

表１に示すように、Ｎｏ．１〜９は本発明例であり、Ｎｏ．１０〜１５は比較例である。

As shown in Table 1, no. 1 to 9 are examples of the present invention. 10-15 are comparative examples.

  As shown in Table 1, Comparative Example No. No. 10 is a general-purpose nitrided powder high-speed steel having a component composition that is inferior in wear resistance due to the small average particle size of carbides. Comparative Example No. No. 11 has a high C, Cr, and V content in the component composition, resulting in low toughness, a large average particle size of carbides, and a large average particle size of carbonitrides, and a long interparticle distance between precipitates. Chipping occurs. Comparative Example No. No. 12 has a high Si content, a low W and V content, a large Ceq value, and a small average particle size of carbides, resulting in poor wear resistance.

  Comparative Example No. No. 13 has a low C and Ceq value in the component composition, a high Mn, and a small average particle size of the carbide, so that the wear resistance is inferior. Comparative Example No. No. 14 has a high C, Mo, W, Co, and N content in the component composition, a large Ceq value, and a large average particle size of carbide of 20 μm or more, resulting in poor toughness, and an average particle size of carbonitride Chipping occurred due to the large diameter and the long interparticle distance of the precipitate. Comparative Example No. No. 15 has a low Cr, Mo, N content, a small Ceq value, and a small average particle size of carbides, and therefore has poor wear resistance.

  On the other hand, No. which is this invention. 1 to 9 all satisfy the component composition, the average particle size of the carbide, the average particle size of the carbonitride, and the interparticle distance of the precipitate, 4 μm or more of the carbide contributes to wear resistance, Carbon nitride of 2 μm or less suppresses grain coarsening during quenching and tempering (improvement of toughness), and the distance between grains of precipitates is 10 μm or less to prevent contact with the parent phase when using a tool and suppress chipping. I understand.

As described above, a nitrided powder high-speed tool steel having both chipping property and wear resistance is provided by appropriately controlling the composition of the powder high-speed steel for high-speed cutting applications according to the present invention and the carbide in the structure. It has an extremely excellent effect that can be achieved.


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (3)

% By mass
C: 0.8 to 2.5%
Si: 0.1 to 1.0%,
Mn: 0.1 to 1.0%,
Cr: 3.0-5.0%,
Mo: 2.0 to 8.0%,
W: 3.0-14.0%,
V: 2.0-10.0%,
Co: 0 to 10%,
N: 0.3 to 1.5%
And a Ceq value of 0.1 to 0.8, a nitrided powder high-speed tool steel in a quenched and tempered state composed of the balance Fe and inevitable impurities, and the carbide in the metal structure has an average particle size 4-20 μm, the average particle size of the carbonitride is in the range of 2 μm or less, and the average interparticle distance of the precipitate is 10 μm or less. Speed tool steel.
However, Ceq = (C% + N%) − {0.19 + 0.017 (W% + 2Mo%) + 0.22V%} The steel powder for nitride powder high-speed tool steel having the chemical composition and Ceq value according to claim 1 is solidified by HIP in a temperature range of 1200 to 1300 ° C, and then plastically processed hot, After that, quenching and tempering, the carbide in the metal structure should have an average particle size of 4 to 20 μm, the average particle size of carbonitride should be 2 μm or less, and the average interparticle distance of precipitates should be 10 μm or less. A method for producing a nitrided powder high-speed tool steel excellent in wear resistance. The steel powder for nitride powder high-speed tool steel having the chemical composition and Ceq value according to claim 1 is solidified by HIP in a temperature range of less than 1100 to 1200 ° C, and then a temperature range of 1200 to 1300 ° C. After 2 to 6 hours of high-temperature holding heat treatment, plastic working is performed hot, and then quenching and tempering are performed, and the carbide in the metal structure is 4 to 20 μm in average particle diameter. A method for producing a nitrided powder high-speed tool steel excellent in wear resistance, characterized in that the diameter is in a range of 2 µm or less and the average interparticle distance of precipitates is 10 µm or less.