Powder high-speed steel

Abstract

To provide a powder high-speed steel having improved wear resistance without significantly impairing its toughness.SOLUTION: A powder high-speed steel is composed of an Fe-based alloy containing C: 1.2 mass% or more and 2.4 mass% or less, Si: 0.1 mass% or more and 1.0 mass% or less, Mn: 0.1 mass% or more and 1.0 mass% or less, Cr: 0.7 mass% or more and 3.0 mass% or less, Mo: 1.5 mass% or more and 8.0 mass% or less, V: 2.5 mass% or more and 7.0 mass% or less, W: 5.0 mass% or more and 16.0 mass% or less, Co: 4.0 mass% or more and 11.0 mass% or less, and inevitable impurities.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a powder high speed steel suitable for cutting tools and the like. [Background technology]

[0002] High speed steel is known as a material for tools used in high speed cutting. High speed steel is also called "high speed tool steel". High speed steel contains C, Cr, W, Mo, V, etc. High speed steel obtained through melting and heat treatment contains primary metal carbides and secondary metal carbides. The size of the primary carbides is about several μm to a dozen μm. The size of the secondary carbides is on the so-called nanometer order. Because it has a structure containing these carbides, high speed steel has excellent heat resistance and wear resistance.

[0003] Powder metallurgy is known as a method for manufacturing high-speed steel. High-speed steel obtained by powder metallurgy is called "powdered high-speed steel". Powdered high-speed steel is also called "powdered high-speed steel" and "sintered high-speed steel". Since it is obtained through sintering, powdered high-speed steel has little segregation of carbides of elements such as W, Mo, and V. Therefore, powdered high-speed steel has excellent toughness. An example of powdered high-speed steel is disclosed in JP 2015-160957 A. Another example of powdered high-speed steel is disclosed in JP 2019-116688 A. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP2015-160957A [Patent Document 2] JP2019-116688A Summary of the Invention [Problem to be solved by the invention]

[0005] The wear resistance of powdered high-speed steel is still insufficient. Therefore, in applications where high wear resistance is required, high-speed steel obtained by melting is mainly used. The wear resistance of powdered high-speed steel can be improved by increasing the size of carbides. However, the coarse carbides may impair the toughness of powdered high-speed steel.

[0006] It is an object of the present invention to provide a powdered high speed steel having increased wear resistance without significantly compromising toughness. [Means for solving the problem]

[0007] The powder high speed steel according to the present invention has the following properties: C: 1.2% by mass or more and 2.4% by mass or less Si: 0.1 mass% or more and 1.0 mass% or less Mn: 0.1 mass% or more and 1.0 mass% or less Cr: 0.7% by mass or more and 3.0% by mass or less Mo: 1.5% by mass or more and 8.0% by mass or less V: 2.5% by mass or more and 7.0% by mass or less W: 5.0 mass% or more and 16.0 mass% or less Co: 4.0 mass% or more and 11.0 mass% or less and Inevitable impurities It is an Fe-based alloy containing

[0008] Preferably, the powder high speed steel has a metal structure including a matrix and primary metal carbides and secondary metal carbides dispersed in the matrix. The number density Nd of the primary metal carbides is 1000 pieces / 10000 μm 2 The maximum major axis length Ma of these primary metal carbides is 5 μm or more. The area ratio Ap of these primary metal carbides is 14.0% or more.

[0009] Preferably, the powder high speed steel has a Rockwell hardness H1 of 67 or greater.

[0010] Preferably, the powder high speed steel has a softening resistance factor Sr of 0.10 or more, calculated by the following formula: Sr = 1 / (H1 - H2) In this formula, H1 represents the Rockwell hardness of powdered high speed steel, and H2 represents the Rockwell hardness of powdered high speed steel when it is held at a temperature of 600°C for 100 hours and then air-cooled. Effect of the Invention

[0011] In the powdered high-speed steel according to the present invention, the secondary metal carbides precipitated by heat treatment (quenching and tempering) are prevented from becoming coarse due to heat. Therefore, the powdered high-speed steel has a high softening resistance. The powdered high-speed steel has excellent wear resistance. The powdered high-speed steel also has excellent toughness. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a graph showing the relationship between the softening resistance factor Sr and the specific wear rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The powdered high speed steel according to the present invention is obtained by sintering the powder. In other words, the powdered high speed steel is a sintered body. The powdered high speed steel can be subjected to a heat treatment. Typical heat treatments are quenching and tempering. The powder is typically obtained by atomization.

[0014] The metal structure of powdered high speed steel after quenching and tempering includes a matrix (martensite phase), many primary metal carbides, and many secondary metal carbides. These primary metal carbides are dispersed in the matrix. These secondary metal carbides are also dispersed in the matrix. Each of the primary metal carbides is precipitated during atomization or sintering. Each of the secondary metal carbides is precipitated by tempering. The primary metal carbides are generally large, and the secondary metal carbides are generally fine.

[0015] [composition] The powder high speed steel according to the present invention is made of an Fe-based alloy. C: 1.2% by mass or more and 2.4% by mass or less Si: 0.1 mass% or more and 1.0 mass% or less Mn: 0.1 mass% or more and 1.0 mass% or less Cr: 0.7% by mass or more and 3.0% by mass or less Mo: 1.5% by mass or more and 8.0% by mass or less V: 2.5% by mass or more and 7.0% by mass or less W: 5.0 mass% or more and 16.0 mass% or less Co: 4.0 mass% or more and 11.0 mass% or less and Inevitable impurities Preferably, the balance of this Fe-based alloy, excluding C, Si, Mn, Cr, Mo, V, W, and Co, is Fe and unavoidable impurities. The role of each element in this powder high speed steel will be described in detail below.

[0016] [Carbon (C)] C forms primary metal carbides. C dissolves in the matrix during quenching and strengthens the structure. Furthermore, C precipitates secondary metal carbides during tempering. Therefore, C can contribute to the wear resistance and strength of high-speed steel. From these viewpoints, the C content is preferably 1.2 mass% or more, more preferably 1.3 mass% or more, and particularly preferably 1.6 mass% or more. Excessive C leads to excessive carbide precipitation and inhibits toughness. Tools containing excess C are prone to chipping. From the viewpoint of toughness, the C content is preferably 2.4 mass% or less, more preferably 2.2 mass% or less, and particularly preferably 1.8 mass% or less.

[0017] [Silicon (Si)] Si contributes to deoxidation in the steelmaking process. Si contributes to hardenability. Si dissolves in the matrix during hardening and contributes to solution strengthening. The dissolved Si promotes the precipitation of secondary metal carbides during tempering. From these viewpoints, the Si content is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and particularly preferably 0.3 mass% or more. Excessive Si inhibits the toughness of high-speed steel. Tools containing excess Si are prone to chipping. From the viewpoint of toughness, the Si content is preferably 1.0 mass% or less, more preferably 0.6 mass% or less, and particularly preferably 0.4 mass% or less.

[0018] [Manganese (Mn)] Mn contributes to deoxidation in the steelmaking process. Mn contributes to hardenability. Mn dissolves in the matrix during hardening and contributes to solution strengthening. The dissolved Mn promotes the precipitation of secondary metal carbides during tempering. A part of Mn dissolves in primary metal carbides. From these viewpoints, the Mn content is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and particularly preferably 0.3 mass% or more. Excess Mn inhibits the toughness of high-speed steel. Tools containing excess Mn are prone to chipping. From the viewpoint of toughness, the Mn content is preferably 1.0 mass% or less, more preferably 0.6 mass% or less, and particularly preferably 0.4 mass% or less.

[0019] Chromium The inclusion of an appropriate amount of Cr is extremely important in the powdered high-speed steel according to the present invention. Cr contributes to hardenability. Cr is an essential element for forming primary metal carbides. Cr is an essential element for the precipitation of secondary metal carbides during tempering. Cr contributes to the hardness of tools. From these viewpoints, the Cr content is preferably 0.7 mass% or more. Cr can dissolve in secondary metal carbides (MC and M2C). Therefore, at a temperature at which metal elements can diffuse (500°C or higher), Cr is supplied from the matrix to the secondary metal carbides, and the secondary metal carbides become coarse. Furthermore, some Cr precipitates as new secondary metal carbides. Compared with W and Mo, Cr has a high diffusion rate in the matrix and a large solid solubility limit in the matrix. Therefore, Cr has a large driving force for coarsening the carbides. Therefore, excessive Cr coarsens the secondary metal carbides when subjected to the influence of heat, and deteriorates the softening resistance of the powdered high-speed steel. In light of softening resistance, the Cr content is preferably equal to or less than 3.0 mass %, more preferably equal to or less than 2.7 mass %, and particularly preferably equal to or less than 2.0 mass %.

[0020] [Molybdenum (Mo)] Mo contributes to hardenability. Mo forms primary metal carbides (MC and M6C). Furthermore, Mo forms secondary metal carbides (MC and M2C) during tempering. Therefore, Mn can contribute to the hardness, wear resistance, and strength of high-speed steel. From these viewpoints, the Mo content is preferably 1.5 mass% or more. Excess Mo inhibits the toughness of high-speed steel. Tools containing excess Mo are prone to chipping. From the viewpoint of toughness, the Mo content is preferably 8.0 mass% or less, more preferably 5.0 mass% or less, and particularly preferably 3.0 mass% or less.

[0021] [Vanadium (V)] V contributes to hardenability. V forms primary metal carbides (MC and M6C). Furthermore, V forms secondary metal carbides (MC and M2C) during tempering. Therefore, V can contribute to the hardness and wear resistance of high-speed steel. From these viewpoints, the V content is preferably 2.5 mass% or more, more preferably 3.0 mass% or more, and particularly preferably 4.0 mass% or more. Excess V inhibits the toughness of high-speed steel. Tools containing excess V are prone to chipping. From the viewpoint of toughness, the V content is preferably 7.0 mass% or less, more preferably 6.5 mass% or less, and particularly preferably 6.0 mass% or less.

[0022] [Tungsten (W)] W contributes to hardenability. W forms primary metal carbides (MC and M6C). Furthermore, W forms secondary metal carbides (MC and M2C) during tempering. Therefore, W can contribute to the hardness and wear resistance of high-speed steel. From these viewpoints, the W content is preferably 5.0 mass% or more, more preferably 9.0 mass% or more, and particularly preferably 13.0 mass% or more. Excess W inhibits the toughness of high-speed steel. Tools containing excess W are prone to chipping. From the viewpoint of toughness, the W content is preferably 16.0 mass% or less, more preferably 15.5 mass% or less, and particularly preferably 15.0 mass% or less.

[0023] [Cobalt (Co)] The inclusion of an appropriate amount of Co is extremely important in the powdered high-speed steel according to the present invention. Co dissolves in the matrix during quenching. The dissolved Co promotes the precipitation of secondary metal carbides (MC and M2C) during tempering, and contributes to the refinement of the secondary metal carbides. Co increases the softening resistance of the powdered high-speed steel. Therefore, Co contributes to the hardness and wear resistance of the powdered high-speed steel. As described above, in the powdered high-speed steel according to the present invention, the Cr content is 3.0 mass% or less. When the powdered high-speed steel having a Cr content within this range further contains a predetermined amount of Co, the diffusion of Cr in the matrix is ​​significantly suppressed and high softening resistance due to Co is achieved. In this powdered high-speed steel, both wear resistance and toughness can be achieved. From these viewpoints, the Co content is preferably 4.0 mass% or more, more preferably 5.0 mass% or more, and particularly preferably 6.0 mass% or more. In the powdered high-speed steel containing an excess amount of Co, a part of Co forms an ordered phase with Fe. This ordered phase impairs the toughness of powdered high speed steel. Tools containing excessive Co are prone to chipping. From the viewpoint of toughness, the Co content is preferably 11.0 mass% or less, more preferably 9.5 mass% or less, and particularly preferably 8.0 mass% or less.

[0024] [Iron (Fe)] As described above, the powdered high-speed steel is made of an Fe-based alloy. This powdered high-speed steel has excellent toughness. From the viewpoint of toughness, the Fe content is preferably 50 mass% or more, more preferably 55 mass% or more, and particularly preferably 60 mass% or more.

[0025] [impurities] Powdered high-speed steel contains unavoidable impurities. A typical impurity is N. N causes the carbides to become coarse. The coarse carbides impair the toughness of the powdered high-speed steel. From the viewpoint of toughness, the N content (by mass) is preferably 300 ppm or less, and particularly preferably 200 ppm or less.

[0026] Another representative impurity is O. O causes the formation of inclusions (oxides). The inclusions can become the starting point of fracture. From the viewpoint of suppressing fracture, the O content (by mass) is preferably 300 ppm or less, and particularly preferably 200 ppm or less.

[0027] The Fe-based alloy may contain metallic impurities.

[0028] [Metal structure] As described above, the metal structure of powdered high speed steel after quenching and tempering includes a matrix and a large number of primary metal carbides and secondary metal carbides dispersed in the matrix. The base of the matrix is ​​Fe. In this matrix, other elements are dissolved in Fe. The primary metal carbides are compounds of C and other elements. The secondary metal carbides are compounds of C and other elements. The quenching temperature and tempering temperature suitable for the composition of the alloy can be selected.

[0029] [Density Nd] In the metal structure after quenching and tempering, the density of the number of primary metal carbides Nd is 1000 pieces / 10000 μm 2 or more is preferable. Primary metal carbides have superior adhesive wear resistance compared to the matrix. Powdered high-speed steel in which the density Nd of primary metal carbides is large has superior wear resistance. The powdered high-speed steel according to the present invention has a large density Nd and suppresses the precipitation of coarse secondary metal carbides, and therefore has superior wear resistance and toughness. From this viewpoint, the density Nd is 1050 particles / 10000 μm 2 More preferably, 1100 pieces / 10000μm 2 More preferably, the density Nd is 2000 pieces / 10000 μm 2 The following is preferred:

[0030] In the measurement of density Nd, a backscattered electron image of the ground surface of powdered high speed steel is taken with a scanning electron microscope (SEM). The primary metal carbides (MC and M6C) in this backscattered electron image are binarized using the image analysis software "Image-J". The number of primary metal carbides is counted on a screen with a magnification of 2000 times. No watershed transformation is used in this measurement. When multiple primary metal carbides are in contact, they are considered as one primary metal carbide.

[0031] [Maximum major axis length Ma] In the metal structure after quenching and tempering, the maximum major axis length Ma of the primary metal carbides is preferably 5 μm or more. As described above, the primary metal carbides have better adhesive wear resistance than the matrix. Powdered high-speed steel having a large maximum major axis length Ma of the primary metal carbides has excellent wear resistance. The powdered high-speed steel according to the present invention has a large maximum major axis length Ma and suppresses the precipitation of coarse secondary metal carbides, so that it is excellent in both wear resistance and toughness. From this viewpoint, the maximum major axis length Ma is more preferably 5.2 μm or more, and particularly preferably 5.5 μm or more. The maximum major axis length Ma is preferably 20 μm or less.

[0032] In measuring the maximum major axis length Ma, a backscattered electron image of the polished surface of powdered high-speed steel is taken with a scanning electron microscope (SEM). The primary metal carbides (MC and M6C) in this backscattered electron image are binarized using the image analysis software "Image-J". On a screen with a magnification of 2000 times, the smallest ellipse that contains each primary metal carbide is assumed. A number of ellipses corresponding to the number of primary metal carbides are assumed. The major axis length of the ellipse with the longest major axis among these ellipses is the maximum major axis length Ma. No watershed transformation is used in this measurement.

[0033] [Area ratio Ap] In the metal structure after quenching and tempering, the area ratio Ap of the primary metal carbides is preferably 14.0% or more. As described above, the primary metal carbides have better adhesive wear resistance than the matrix. Powdered high-speed steel having a large area ratio Ap of the primary metal carbides has excellent wear resistance. The powdered high-speed steel according to the present invention has a large area ratio Ap and suppresses the precipitation of coarse secondary metal carbides, and therefore has excellent wear resistance and toughness. From this viewpoint, the area ratio Ap is more preferably 14.2% or more, and particularly preferably 14.5% or more. The area ratio Ap is preferably 25% or less.

[0034] In measuring the area ratio Ap, a backscattered electron image of the polished surface of powdered high-speed steel is taken with a scanning electron microscope (SEM). The primary metal carbides (MC and M6C) in this backscattered electron image are binarized using the image analysis software "Image-J". The total area of ​​the primary metal carbides is measured on a screen with a magnification of 2000 times, and the area ratio Ap is calculated. No watershed transformation is used in this measurement.

[0035] [Softening resistance factor Sr] FIG. 1 is a graph showing the relationship between the softening resistance factor Sr and the specific wear rate. As shown in this graph, in powdered high-speed steel after quenching and tempering, the specific wear rate correlates with the softening resistance factor Sr. The softening resistance factor Sr is preferably 0.10 or more. A tool made of powdered high-speed steel having a softening resistance factor Sr of 0.10 or more is less likely to wear even with long-term use. From this viewpoint, the softening resistance factor Sr is more preferably 0.11 or more, and particularly preferably 0.12 or more. The softening resistance factor Sr is preferably 0.20 or less.

[0036] The softening resistance factor Sr is calculated by the following formula. Sr = 1 / (H1 - H2) In this formula, H1 represents the Rockwell hardness of powdered high speed steel, and H2 represents the Rockwell hardness of powdered high speed steel when it is held at a temperature of 600°C for 100 hours and then air-cooled.

[0037] The powdered high speed steel after quenching and tempering under predetermined conditions preferably has a Rockwell hardness H1 of 67 or more, particularly preferably 68 or more. The hardness H1 is preferably 75 or less.

[0038] [Powder metallurgy method] The high speed steel according to the present invention can be obtained by powder metallurgy. In the powder metallurgy, metal powder is first produced by gas atomization, water atomization, disk atomization, pulverization, or the like. This powder is made up of a large number of particles. The material of the particles is as follows: C: 1.2% by mass or more and 2.4% by mass or less Si: 0.1 mass% or more and 1.0 mass% or less Mn: 0.1 mass% or more and 1.0 mass% or less Cr: 0.7% by mass or more and 3.0% by mass or less Mo: 1.5% by mass or more and 8.0% by mass or less V: 2.5% by mass or more and 7.0% by mass or less W: 5.0 mass% or more and 16.0 mass% or less Co: 4.0 mass% or more and 11.0 mass% or less and Inevitable impurities Preferably, the balance in this Fe-based alloy, excluding C, Si, Mn, Cr, Mo, V, W and Co, is Fe and unavoidable impurities.

[0039] The metal powder is pressed in a high-temperature atmosphere to solidify, and a compact is obtained. A preferred pressing method is hot isostatic pressing. In hot isostatic pressing, the powder is pressed at a high temperature of several hundred degrees Celsius to 2000 degrees Celsius with an isotropic pressure of several tens to several hundred MPa. Preferably, an inert gas such as argon gas or helium gas is used as the pressurizing medium. The use of an inert gas suppresses oxidation of the metal powder.

[0040] This formed body is subjected to hot working. This formed body is subjected to heat treatment (annealing). Furthermore, this formed body is subjected to quenching and tempering under predetermined conditions. A preferable metal structure is formed by quenching and tempering. In other words, this formed body has a metal structure obtained by quenching and tempering.

[0041] [Application] The present invention is also directed to a tool. The material of the tool according to the present invention is a powder high-speed steel. The powder high-speed steel is C: 1.2% by mass or more and 2.4% by mass or less Si: 0.1 mass% or more and 1.0 mass% or less Mn: 0.1 mass% or more and 1.0 mass% or less Cr: 0.7% by mass or more and 3.0% by mass or less Mo: 1.5% by mass or more and 8.0% by mass or less V: 2.5% by mass or more and 7.0% by mass or less W: 5.0 mass% or more and 16.0 mass% or less Co: 4.0 mass% or more and 11.0 mass% or less and Inevitable impurities The Fe-based alloy preferably contains C, Si, Mn, Cr, Mo, V, W, and Co, and the remainder of the Fe-based alloy is Fe and unavoidable impurities. The powder high speed steel has a metal structure obtained by quenching and tempering. The metal structure includes a matrix and primary metal carbides dispersed in the matrix. The number density Nd of the primary metal carbides is 1000 pieces / 10000 μm 2 The maximum major axis length Ma of the primary metal carbide is 5 μm or more. The area ratio Ap of the primary metal carbide is 14.0% or more. EXAMPLES

[0042] The effects of the present invention will be clarified by the following examples, but the present invention should not be construed as being limited based on the description of these examples.

[0043] [Example 1] The molten metal was gas atomized to obtain a powder. The powder was classified using a sieve with a mesh size of 500 μm to remove coarse particles. The powder was filled into a cylindrical steel can with a diameter of 235 mm and a length of 100 mm. The steel can was vacuum degassed and then sealed. In an argon gas atmosphere, hot isostatic pressing was performed under conditions of a pressure of 147 MPa and a temperature of 1220°C to obtain a compact. The compact was forged at a temperature of 1100°C. The forging ratio was 4. The compact was annealed at a temperature of 870°C for 3 hours. The composition of the compact is shown in Table 1 below. In addition to the elements shown in Table 1, the compact contains unavoidable impurities.

[0044] [Examples 2-15 and Comparative Examples 16-31] Powdered high speed steels of Examples 2-15 and Comparative Examples 16-31 were obtained in the same manner as in Example 1, except that the compositions were as shown in Tables 1 and 2 below.

[0045] [Observation of metal structure] The compact was quenched at 1240° C. and then tempered at 560° C. The area ratio Ap, maximum major axis length Ma, and density Nd of the primary metal carbides were measured using the compact by the above-mentioned method. The results are shown in Tables 1 and 2 below.

[0046] [Softening resistance factor Sr] A block-shaped test piece measuring 15 mm x 15 mm x 15 mm was obtained from the compact. This test piece was quenched at a temperature of 1240°C and then tempered at a temperature of 560°C. The softening resistance factor Sr of this test piece was measured by the above-mentioned method. The average values ​​of five measurements are shown in Tables 1 and 2 below.

[0047] [Specific wear rate] A plate-shaped test piece measuring 7 mm x 25 mm x 50 mm was obtained from the compact. This test piece was quenched at 1240°C and then tempered at 560°C. This test piece was set in an Ohkoshi abrasion tester to measure the specific wear rate. The measurement conditions were as follows: Mating material: SCM420 Wear speed: 3.62m / sec Wear distance: 200m Final load: 6.3kg Lubrication: None Temperature: room temperature The wear scar width obtained in the test was measured, and the wear volume was calculated. The specific wear amount was calculated by dividing this wear volume by the product of the wear distance and the final load. The average values ​​of the results of three measurements are shown in Tables 1 and 2 below.

[0048] [Hardness H1] The compact was quenched at 1240° C. and then tempered at 560° C. The Rockwell hardness H1 of the compact was measured. The average values ​​of five measurements are shown in Tables 1 and 2 below.

[0049] [Transverse bending strength] A bar-shaped test piece measuring 4 mm x 8 mm x 40 mm was obtained from the compact. This test piece was quenched at a temperature of 1240° C., and further tempered at a temperature of 560° C. This test piece was subjected to a flexural test under the following conditions. Crosshead speed: 2mm / min Span: 20mm Temperature: room temperature The average of two measurements was calculated. Powdered high speed steels with an average value of 2000 MPa or greater were rated "G". Powdered high speed steels with an average value of less than 2000 MPa were rated "N". The results are shown in Tables 1 and 2 below.

[0050] [Table 1]

[0051] [Table 2]

[0052] As shown in Tables 1 and 2, the powdered high speed steels of the examples were excellent in all evaluation items. From the above evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0053] The powdered high speed steel according to the present invention can be used in a variety of applications, such as machine tools, hand tools, dies, injection molding machines, die heads, punches, and blades.

Claims

1. The material is C: 1.2% by mass or more and 2.4% by mass or less Si: 0.1% by mass or more and 1.0% by mass or less Mn: 0.1% by mass or more and 1.0% by mass or less Cr: 0.7% by mass or more and 3.0% by mass or less Mo: 1.5% by mass or more and 8.0% by mass or less V: 2.5% by mass or more and 7.0% by mass or less W: 5.0% by mass or more and 16.0% by mass or less and Co: 4.0% by mass or more and 11.0% by mass or less and the balance being Fe and unavoidable impurities, The alloy has a metal structure including a matrix and primary and secondary metal carbides dispersed in the matrix, A backscattered electron image of the polished surface of the metal structure is taken with a scanning electron microscope, and the primary metal carbides in the backscattered electron image are binarized with image analysis software to obtain a screen with a magnification of 2000 times. When the number density Nd, maximum major axis length Ma and area ratio Ap of the primary metal carbides are measured, The density Nd is 1000 pieces / 10000 μm ２ That's all. The maximum major axis length Ma is 5 μm or more, The powder high speed steel has an area ratio Ap of 14.0% or more.

2. 2. The powdered high speed steel according to claim 1, having a Rockwell hardness H1 of 67 or more.

3. 3. The powdered high speed steel according to claim 1, wherein a softening resistance factor Sr calculated by the following formula is 0.10 or more. Sr = 1 / (H1 - H2) (In this formula, H1 represents the Rockwell hardness of the powdered high speed steel, and H2 represents the Rockwell hardness of the powdered high speed steel when it is held at a temperature of 600° C. for 100 hours and then air-cooled.)

4. a step of sintering the powder obtained by atomization to obtain a sintered body in which primary metal carbides are precipitated; quenching the sintered body; and A process of subjecting the sintered body to tempering to precipitate secondary metal carbides. A method for producing powder high speed steel, comprising: The material of the powder high speed steel is C: 1.2% by mass or more and 2.4% by mass or less Si: 0.1% by mass or more and 1.0% by mass or less Mn: 0.1% by mass or more and 1.0% by mass or less Cr: 0.7% by mass or more and 3.0% by mass or less Mo: 1.5% by mass or more and 8.0% by mass or less V: 2.5% by mass or more and 7.0% by mass or less W: 5.0% by mass or more and 16.0% by mass or less and Co: 4.0% by mass or more and 11.0% by mass or less and the balance being Fe and unavoidable impurities, The Fe-based alloy has a metal structure including a matrix and primary metal carbides and secondary metal carbides dispersed in the matrix, A backscattered electron image of the polished surface of the metal structure is taken with a scanning electron microscope, and the primary metal carbides in the backscattered electron image are binarized with image analysis software to obtain a screen with a magnification of 2000 times. When the number density Nd, maximum major axis length Ma and area ratio Ap of the primary metal carbides are measured, The density Nd is 1000 pieces / 10000 μm ２ That's all. The maximum major axis length Ma is 5 μm or more, The method for producing powdered high speed steel, wherein the area ratio Ap is 14.0% or more.

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