Nitrided powder high-speed steel

Abstract

To provide a nitride powder high-speed steel that is excellent in high hardness, toughness, corrosion resistance and wear resistance.SOLUTION: A nitride powder high-speed steel comprises C: 0.60 mass% or more and 1.20 mass% or less, Si: 0.10 mass% or more and 1.00 mass% or less, Mn: 0.10 mass% or more and 1.00 mass% or less, Cr: 6.00 mass% or more and 9.00 mass% or less, Mo: 2.00 mass% or more and 6.00 mass% or less, V: 1.00 mass% or more and 4.00 mass% or less, Co: 2.00 mass% or more and 10.00 mass% or less, N: 0.30 mass% or more and 0.80 mass% or less, Ni: 0.00 mass% or more and 2.00 mass% or less, and Cu: 0.00 mass% or more and 2.00 mass% or less, with the balance being Fe and inevitable impurities. The total content of C and N is 1.10 mass% or more and 1.70 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] This specification relates to powder high-speed steel containing nitrides.

Background Art

[0002] High-speed steel is used for cutting tools, dies, etc. High-speed steel is also referred to as "high-speed tool steel". High-speed steel obtained by powder metallurgy is called "powder high-speed steel". Powder high-speed steel is also referred to as "powder high speed" and "sintered high-speed steel". Powder high-speed steel has high hardness and excellent toughness.

[0003] Japanese Patent Application Laid-Open No. 2013-060617 discloses powder high-speed steel that has been nitrided. This powder high-speed steel is called nitrided powder high-speed steel. Nitrided powder high-speed steel is excellent in corrosion resistance and wear resistance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] There is room for improvement in the performance of nitrided powder high-speed steel. The intention of the applicant is to provide nitrided powder high-speed steel excellent in high hardness, toughness, corrosion resistance and wear resistance.

Means for Solving the Problems

[0007] A preferred nitrided powder high-speed steel is C: 0.60 mass% or more and 1.20 mass% or less, Si: 0.10 mass% or more and 1.00 mass% or less, Mn: 0.10 mass% or more and 1.00 mass% or less, Cr: 6.00 mass% or more and 9.00 mass% or less, Mo: 2.00 mass% or more and 6.00 mass% or less, V: 1.00 mass% or more and 4.00 mass% or less, Co: 2.00 mass% or more and 10.00 mass% or less, N: 0.30 mass% or more and 0.80 mass% or less, Ni: 0.00 mass% or more and 2.00 mass% or less and Cu: 0.00 mass% or more and 2.00 mass% or less and contains the balance being Fe and unavoidable impurities. The total content of C and N is 1.10 mass% or more and 1.70 mass% or less.

Advantages of the Invention

[0008] This nitrided powder high-speed steel is excellent in high hardness, toughness, corrosion resistance, and wear resistance.

Modes for Carrying Out the Invention

[0009] The high-speed steel according to this embodiment can be obtained by sintering nitrided powder. In other words, this alloy is a sintered body. The powder is typically obtained by atomization. This high-speed steel is obtained through heat treatment. Typical heat treatments are annealing, quenching, and tempering.

[0010] [Metallographic Structure] The metallographic structure of the nitrided powder high-speed steel includes a matrix and a large number of metal compounds dispersed in this matrix. The base of the matrix is Fe. In the matrix, other elements are dissolved in Fe. The metal compounds include carbides and nitrides. The nitrides include carbonitrides.

[0011] [Composition] This nitrided powder high-speed steel contains C: 0.60 mass% or more and 1.20 mass% or less, Si: 0.10 mass% or more and 1.00 mass% or less, Mn: 0.10 mass% or more and 1.00 mass% or less, Cr: 6.00 mass% or more and 9.00 mass% or less, Mo: 2.00 mass% or more and 6.00 mass% or less, V: 1.00 mass% or more and 4.00 mass% or less, Co: 2.00 mass% or more and 10.00 mass% or less, N: 0.30 mass% or more and 0.80 mass% or less, Ni: 0.00 mass% or more and 2.00 mass% or less and Cu: 0.00 mass% or more and 2.00 mass% or less. The balance is Fe and inevitable impurities. Hereinafter, the roles of the respective elements in this nitrided powder high-speed steel will be described in detail.

[0012] [Carbon (C)] C combines with other elements to form carbides. These carbides can contribute to the wear resistance of the high-speed steel. From this perspective, the C content is preferably 0.60 mass% or more, more preferably 0.65 mass% or more, and particularly preferably 0.70 mass% or more. Excessive C causes precipitation of excessive carbides. Excessive carbides inhibit the toughness of the high-speed steel. From the perspective of toughness, the C content is preferably 1.20 mass% or less, more preferably 1.15 mass% or less, and particularly preferably 1.10 mass% or less.

[0013] [Silicon (Si)] Si contributes to deoxidation in the steelmaking process. Si also contributes to hardenability. From these perspectives, the Si content is preferably 0.10 mass% or more, more preferably 0.20 mass% or more, and particularly preferably 0.30 mass% or more. Excessive Si inhibits the workability of the high-speed steel. From the perspective of workability, the Si content is preferably 1.00 mass% or less, more preferably 0.90 mass% or less, and particularly preferably 0.80 mass% or less.

[0014] [Manganese (Mn)] Mn contributes to hardenability. From this perspective, the content of Mn is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and particularly preferably 0.30% by mass or more. Excessive Mn inhibits the workability of high-speed steel. From this perspective, the content of Mn is preferably 1.00% by mass or less, more preferably 0.90% by mass or less, and particularly preferably 0.80% by mass or less.

[0015] [Chromium (Cr)] Cr forms carbides. These carbides contribute to the wear resistance of high-speed steel. Furthermore, Cr dissolves in the matrix of the structure of high-speed steel and contributes to corrosion resistance. From these perspectives, the content of Cr is preferably 6.00% by mass or more, more preferably 6.50% by mass or more, and particularly preferably 7.00% by mass or more. Excessive Cr causes excessive precipitation of carbides and inhibits the toughness of high-speed steel. Furthermore, excessive carbides cause crevice corrosion. From the perspectives of toughness and corrosion resistance, the content of Cr is preferably 9.00% by mass or less, more preferably 8.50% by mass or less, and particularly preferably 8.00% by mass or less.

[0016] [Molybdenum (Mo)] Mo forms fine carbides in high-speed steel. These carbides contribute to the hardness and wear resistance of high-speed steel. Furthermore, Mo dissolves in the matrix of the structure of high-speed steel and contributes to corrosion resistance. From these perspectives, the content of Mo is preferably 2.00% by mass or more, more preferably 2.50% by mass or more, and particularly preferably 3.00% by mass or more. Excessive Mo causes excessive precipitation of carbides and inhibits the toughness of high-speed steel. From the perspective of toughness, the content of Mo is preferably 6.00% by mass or less, more preferably 5.50% by mass or less, and particularly preferably 5.00% by mass or less.

[0017] [Vanadium (V)] V forms fine and hard carbides in high-speed steel. V further forms nitrides, which include carbonitrides (such as VCN). The carbides and nitrides contribute to the hardness and wear resistance of high-speed steel. From these viewpoints, the content of V is preferably 1.00 mass% or more, more preferably 1.50 mass% or more, and particularly preferably 2.00 mass% or more. Excessive V inhibits the workability of high-speed steel. From the viewpoint of workability, the content of V is preferably 4.00 mass% or less, more preferably 3.50 mass% or less, and particularly preferably 3.00 mass% or less.

[0018] [Cobalt (Co)] Co is an extremely important element in the alloy according to this embodiment. According to the aforementioned book "Materials, 46(1997)10 (written by Akihiko Hirano, Hideaki Nakayama, Jun Funakoshi, Hiroaki Okano, Akira Kosaka)", the addition of a predetermined amount of Co is considered to inhibit the toughness of high-speed steel. As a result of the study by the present inventor, in the high-speed steel according to this embodiment, Co unexpectedly improves the toughness. Co further contributes to the corrosion resistance of high-speed steel. From the viewpoints of toughness and corrosion resistance, the content of Co is preferably 2.00 mass% or more, more preferably 3.00 mass% or more, and particularly preferably 4.00 mass% or more. From the viewpoint of low cost, the content of Co is preferably 10.00 mass% or less, more preferably 9.00 mass% or less, and particularly preferably 8.00 mass% or less.

[0019] [Nitrogen (N)] N combines with V to form vanadium-based nitrides (including vanadium-based carbonitrides). This nitride contributes to the wear resistance of high-speed steel. From this viewpoint, the content of N is preferably 0.30 mass% or more, more preferably 0.35 mass% or more, and particularly preferably 0.40 mass% or more. Excessive N causes excessive precipitation of nitrides and inhibits the toughness of high-speed steel. From the viewpoint of toughness, the content of N is preferably 0.80 mass% or less, more preferably 0.75 mass% or less, and particularly preferably 0.70 mass% or less.

[0020] [Nickel (Ni)] Ni contributes to the corrosion resistance and toughness of high-speed steel. From this perspective, the Ni content is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and particularly preferably 0.20% by mass or more. Excessive Ni inhibits the hardness of high-speed steel. From the perspective of hardness, the Ni content is preferably 2.0% by mass or less, more preferably 1.80% by mass or less, and particularly preferably 1.60% by mass or less. In this embodiment, Ni is not an essential element. The Ni content may be zero.

[0021] [Copper (Cu)] Cu contributes to the corrosion resistance and toughness of high-speed steel. From this perspective, the Cu content is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and particularly preferably 0.20% by mass or more. Excessive Cu inhibits the hardness of high-speed steel. From the perspective of hardness, the Cu content is preferably 2.0% by mass or less, more preferably 1.80% by mass or less, and particularly preferably 1.60% by mass or less. In this embodiment, Cu is not an essential element. The Cu content may be zero.

[0022] [Fe] The nitrided powder high-speed steel is an Fe-based alloy. This high-speed steel has excellent toughness. From the perspective of toughness, the Fe content is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 75% by mass or more.

[0023] [Impurities] The powder high-speed steel contains inevitable impurities. Typical impurities include O. O causes the formation of inclusions (oxides). Inclusions can be the starting points of fracture. From the perspective of suppressing fracture, the O content (mass basis) is preferably 300 ppm or less, and particularly preferably 200 ppm or less.

[0024] As yet another impurity, tungsten (W) is mentioned. W can contribute to corrosion resistance, but its effect is lower compared to that of Mo. On the other hand, W causes coarsening of primary carbides. Coarse primary carbides inhibit the toughness of high-speed steel. From the perspective of toughness, W is not added to the high-speed steel of the present embodiment. Note that the presence of W as an inevitable impurity is allowed.

[0025] [C%+N%] In the high-speed steel of the present embodiment, the total (C%+N%) of the mass content rate of C (C%) and the mass content rate of N (N%) is an index correlated with the hardness, wear resistance, and toughness of the high-speed steel. From the perspectives of hardness and wear resistance, the total (C%+N%) is preferably 1.10 mass% or more, more preferably 1.15 mass% or more, and particularly preferably 1.20 mass% or more. From the perspective of toughness, the total (C%+N%) is preferably 1.70 mass% or less, more preferably 1.65 mass% or less, and particularly preferably 1.60 mass% or less.

[0026] [Vanadium-based nitride] As described above, this high-speed steel contains vanadium-based nitride. As the vanadium-based nitride, (1) Compounds containing V and N (such as VN, etc.) and (2) Compounds containing V, N, and C (such as VNC, etc.) are mentioned. The area ratio of the vanadium-based nitride in the metal structure of the high-speed steel is an index correlated with wear resistance, corrosion resistance, and toughness. From the perspectives of wear resistance and corrosion resistance, this area ratio is preferably 3.0% or more, more preferably 3.5% or more, and particularly preferably 4.0% or more. From the perspective of toughness, this area ratio is preferably 7.0% or less, more preferably 6.5% or less, and particularly preferably 6.0% or less.

[0027] In the measurement of the area ratio, a backscattered electron image of the polished surface of the high-speed steel is taken with a scanning electron microscope. This backscattered electron image is subjected to binarization processing by image analysis software. On a screen with a magnification of 4000 times, the total area of the vanadium-based nitride is measured, and the area ratio is calculated.

[0028] [Manufacturing Method] In the manufacturing of high-speed steel according to this embodiment, first, powder is produced. The powder can be obtained by gas atomization method, water atomization method, disk atomization method, pulverization method, etc. Preferably, the powder is obtained by gas atomization method. This powder is held in a high-temperature nitrogen-rich atmosphere. By this holding, nitrogen atoms penetrate into and diffuse in the particles. Nitrogen forms nitrides within the particles. This powder is pressurized and solidified in a high-temperature atmosphere to obtain a compact. As a preferable pressurization method, hot isostatic pressing method can be mentioned. In the hot isostatic pressing method, the powder is pressurized at an isotropic pressure under high temperature. Preferably, an inert gas such as argon gas or helium gas is used as the pressurization medium. This compact is forged to obtain a forged product. This forged product is subjected to annealing. Further, quenching and tempering are performed on this forged product to obtain a metal product (intermediate product) made of nitrided powder high-speed steel. In this metal product, nitrides are uniformly dispersed.

Examples

[0029] Hereinafter, the effects of the nitrided powder high-speed steel according to the examples will be clarified, but the scope disclosed in this specification based on the description of these examples should not be construed restrictively.

[0030] [Example 1] The molten metal was subjected to gas atomization to obtain powder. This powder was held in a nitrogen-rich atmosphere at a temperature of 850 °C to obtain a nitrided powder. This powder was filled into a cylindrical steel can. The steel can was subjected to vacuum degassing and then sealed. Hot isostatic pressing was performed in an argon gas atmosphere under the conditions of a pressure of 200 MPa and a temperature of 1170 °C to obtain a compact. This compact was forged at a temperature of 1100 °C to obtain a forged product. This forged product was subjected to annealing at a temperature of 870 °C. From this forged product, test pieces for hardness measurement, impact test, corrosion test, and wear test were cut out. These test pieces were subjected to quenching at a temperature ranging from 1025 °C to 1125 °C and further subjected to tempering at a temperature ranging from 500 °C to 560 °C to obtain test pieces made of the nitrided powder high-speed steel according to Example 1. The composition of this nitrided powder high-speed steel is shown in Tables 1 and 2 below. This nitrided powder high-speed steel contains inevitable impurities in addition to the elements shown in Tables 1 and 2.

[0031] [Examples 2 to 18 and Comparative Examples 1 to 19] Nitrided powder high-speed steels of Examples 2 to 18 and Comparative Examples 1 to 19 were obtained in the same manner as in Example 1, except that the composition was as shown in Tables 1 and 2 below.

[0032]

Table 1

[0033]

Table 2

[0034] In Tables 1 and 2, "-" means that the content is less than the analysis limit value.

[0035] [Hardness] The hardness (HRC) of the test pieces was measured using a Rockwell hardness tester. The results are shown in Tables 3 and 4 below. A nitrided powder high-speed steel with a hardness of 65 HRC or higher is preferred.

[0036] [Impact value] A test piece with a length of 10 mm, a width of 10 mm, and a length of 55 mm was prepared. This test piece has a notch. The size of the test piece is "10R, 2mmC". A Charpy impact test was performed on this test piece in accordance with the provisions of "JIS Z 2242:2005", and the impact value was measured. The results are shown in Tables 3 and 4 below. The nitrided powder high-speed steel with an impact value of 33 J / cm 2 or more is preferable.

[0037] [Corrosion resistance] A cylindrical test piece with a diameter of 13 mm and a length of 22 mm was prepared. This test piece was subjected to a corrosion resistance test. The conditions of this test are as follows. Solution: 1N hydrochloric acid aqueous solution Temperature: 40 °C Time: 6 hours The value obtained by subtracting the mass of the test piece after the test from the mass of the test piece before the test was divided by the test time and the surface area of the test piece before the test to calculate the corrosion rate. The results are shown in Tables 3 and 4 below. The nitrided powder high-speed steel with a corrosion rate of 5.5 mg / cm 2 ·h or less is preferable.

[0038] [Specific wear rate] A test piece with a length of 19 mm, a width of 41 mm, and a height of 6 mm was set on a Ogoshi-type wear test machine, and the specific wear rate was measured under the following conditions. Ring: SCM420 (hardness: 88 HRB) Speed: 0.25 m / S Distance: 200 m Final load: 61.7 N Style: Dry The results are shown in Tables 3 and 4 below. The nitrided powder high-speed steel with a specific wear rate of 3.0×10 -8 mm 2 / kg or less is preferable.

[0039]

Table 3

[0040]

Table 4

[0041] In the high-speed steel according to Comparative Example 1, C is too little, and the area ratio of vanadium-based nitride is small. The hardness of this high-speed steel is insufficient. In the high-speed steel according to Comparative Example 2, C is excessive, and the area ratio of vanadium-based nitride is large. This high-speed steel is inferior in toughness.

[0042] The high-speed steel according to Comparative Example 3 does not contain Si. The hardness of this high-speed steel is insufficient. In the high-speed steel according to Comparative Example 4, Si is excessive. This high-speed steel is inferior in toughness.

[0043] The high-speed steel according to Comparative Example 5 does not contain Mn. The hardness of this high-speed steel is insufficient. In the high-speed steel according to Comparative Example 6, Mn is excessive. This high-speed steel is inferior in toughness.

[0044] In the high-speed steel according to Comparative Example 7, Cr is too little. This high-speed steel is inferior in wear resistance and corrosion resistance. In the high-speed steel according to Comparative Example 8, Cr is excessive. This high-speed steel is inferior in toughness.

[0045] In the high-speed steel according to Comparative Example 9, Mo is too little. This high-speed steel is inferior in wear resistance and corrosion resistance. In the high-speed steel according to Comparative Example 10, Mo is excessive. This high-speed steel is inferior in toughness.

[0046] In the high-speed steel according to Comparative Example 11, V is too little. This high-speed steel is inferior in wear resistance. In the high-speed steel according to Comparative Example 12, V is excessive. This high-speed steel is inferior in toughness.

[0047] In the high-speed steel according to Comparative Example 13, Co is too little. This high-speed steel is inferior in hardness and corrosion resistance.

[0048] In the high-speed steel according to Comparative Example 14, the amount of N is too small, and the area ratio of vanadium-based nitrides is small. This high-speed steel is inferior in wear resistance. In the high-speed steel according to Comparative Example 15, the amount of N is excessive, and the area ratio of vanadium-based nitrides is large. This high-speed steel is inferior in toughness.

[0049] In the high-speed steel according to Comparative Example 16, the amount of Ni is excessive. This high-speed steel is inferior in hardness. In the high-speed steel according to Comparative Example 17, the amount of Cu is excessive. This high-speed steel is inferior in hardness.

[0050] In the high-speed steel according to Comparative Example 18, the total (C% + N%) is too small, and the area ratio of vanadium-based nitrides is small. This high-speed steel is inferior in hardness. In the high-speed steel according to Comparative Example 19, the total (C% + N%) is excessive, and the area ratio of vanadium-based nitrides is large. This high-speed steel is inferior in toughness.

[0051] On the other hand, the powder high-speed steels of each example are excellent in all evaluation items. From these evaluation results, the superiority of this powder high-speed steel is clear.

[0052] [Disclosed Items] Each of the following items is a disclosure of a preferred embodiment.

[0053] [Item 1] C: 0.60 mass% or more and 1.20 mass% or less, Si: 0.10 mass% or more and 1.00 mass% or less, Mn: 0.10 mass% or more and 1.00 mass% or less, Cr: 6.00 mass% or more and 9.00 mass% or less, Mo: 2.00 mass% or more and 6.00 mass% or less, V: 1.00 mass% or more and 4.00 mass% or less, Co: 2.00 mass% or more and 10.00 mass% or less, N: 0.30 mass% or more and 0.80 mass% or less, Ni: 0.00 mass% or more and 2.00 mass% or less and Cu: 0.00 mass% or more and 2.00 mass% or less which contains, the balance being Fe and inevitable impurities, a nitrided powder high-speed steel in which the total content of C and N is 1.10% by mass or more and 1.70% by mass or less.

[0054] [Item 2] The nitrided powder high-speed steel according to Item 1, wherein the content of Ni is 0.10% by mass or more and 2.00% by mass or less.

[0055] [Item 3] The nitrided powder high-speed steel according to Item 1 or 2, wherein the content of Cu is 0.10% by mass or more and 2.00% by mass or less.

[0056] [Item 4] the metal structure contains vanadium-based nitrides, The nitrided powder high-speed steel according to any one of Items 1 to 3, wherein the area ratio of the vanadium-based nitrides in the metal structure is 3.0% or more.

Industrial Applicability

[0057] The above-described nitrided powder high-speed steel can be used for various applications such as cutting tools, dies, injection molding machines, tool holders, punches, hand tools, machine tools, and blades.

Claims

1. C: 0.60% by mass or more and 1.20% by mass or less, Si: 0.10% by mass or more and 1.00% by mass or less, Mn: 0.10% by mass or more and 1.00% by mass or less, Cr: 6.00% by mass or more and 9.00% by mass or less, Mo: 2.00% by mass or more and 6.00% by mass or less, V: 1.00% by mass or more and 4.00% by mass or less, Co: 2.00% by mass or more and 10.00% by mass or less, N: 0.30% by mass or more and 0.80% by mass or less, Ni: 0.00% by mass or more and 2.00% by mass or less and Cu: 0.00% by mass or more and 2.00% by mass or less and the balance is Fe and inevitable impurities, and the total content ratio of C and N is 1.10% by mass or more and 1.70% by mass or less, a nitrided powder high-speed steel.

2. The nitrided powder high-speed steel according to Claim 1, wherein the content ratio of Ni is 0.10% by mass or more and 2.00% by mass or less.

3. The nitrided powder high-speed steel according to Claim 1 or 2, wherein the content ratio of Cu is 0.10% by mass or more and 2.00% by mass or less.

4. The metal structure contains vanadium-based nitride, The nitrided powder high-speed steel according to any one of Claims 1 to 3, wherein the area ratio of the vanadium-based nitride in the metal structure is 3.0% or more. ​

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