Powder metallurgy high-speed steel and preparation method thereof

Abstract

The invention discloses a powder metallurgy high-speed steel and a preparation method thereof, comprising the following steps: adding a whisker dispersion to high-speed steel powder; weighing 1.6-5 parts by weight of rare earth naphthenate, mixing it with a forming matrix and dissolving it in a solvent to prepare a forming agent; mixing the powder obtained after drying and sieving with the forming agent, grinding it, sieving it, and making a pressed blank; and performing die pressing, sintering, heat treatment, and finishing to make powder metallurgy high-speed steel. The present invention utilizes the influence of whisker materials on the performance of high-speed steel in terms of dispersion strengthening, whisker extraction, crack deflection, and crack bridging, and the strengthening and toughening effect of rare earth elements on powder metallurgy high-speed steel in terms of grain refinement, increased density, interface purification, and improved bonding phase, thereby achieving a simultaneous improvement in the wear resistance and toughness of high-speed steel.

Description

Technical Field

[0001] The present invention relates to the field of high-speed steel, in particular to powder metallurgy high-speed steel and a preparation method thereof. Background Art

[0002] High-speed steel (HSS) is a key tool material for high-volume machining and has been widely used in the manufacture of cutting tools with various complex shapes. Compared to traditional cast and forged HSS, powder metallurgy methods for producing HSS overcome issues such as reduced mechanical properties and heat treatment deformation caused by coarse carbides and segregation during the melt production process, resulting in higher mechanical properties. Vacuum sintering is a conventional method for producing powder HSS, often employing supersolidus liquid phase sintering. The sintering liquid phase accelerates material flow, effectively filling pores and promoting densification of the green body.

[0003] To date, methods for improving the strength and toughness of powder metallurgy high-speed steel (HSS) primarily include introducing appropriate hard phase additives, grain refinement, modifying the HSS alloying element composition, optimizing sintering methods, and altering quenching and tempering processes. However, foreign hard phase particles tend to aggregate and form poor interfacial bonds with the iron matrix, often leading to interfacial stress concentration and crack initiation, which in turn reduces the material's toughness. Changing the alloy composition of traditional HSS makes it difficult to improve toughness without sacrificing wear resistance, while grain refinement and optimizing sintering and heat treatment processes also have limited effectiveness.

[0004] Whiskers are high-strength, one-dimensional single crystals with diameters ranging from approximately 1 μm to 10 μm. Their length-to-diameter ratio ranges from 5 to 1000, and their crystal structure is similar to that of diamond. Because whiskers are high-purity materials, they contain only a small amount of chemical impurities and have few or no internal structural defects. They possess advantages such as a high melting point, low density, high tensile strength, high elastic modulus, low thermal expansion, and good compatibility with metal and ceramic matrices. In recent years, the toughening effect of whiskers has been demonstrated in fields such as cemented carbide and ceramic materials. As an ideal material strengthening and toughening additive, whiskers are suitable not only for room temperature but also for high-temperature conditions, enabling materials to possess higher wear resistance, corrosion resistance, fracture toughness, and high-temperature mechanical properties.

[0005] Due to their high cost, whisker additions are currently limited to experimental studies of brittle materials such as cemented carbide and ceramics. However, there are few reports on their use in toughening high-hardness, high-brittle high-speed steel. Furthermore, whiskers are prone to severe agglomeration and entanglement, significantly impacting their reinforcement and toughening effects. Some dispersants can also adversely affect the material after mixing with the matrix.

[0006] Extensive research has examined the effects of rare earth addition on metallic materials, demonstrating that the addition of rare earths or rare earth compounds can hinder grain growth, purify the microstructure, and improve mechanical properties such as strength and toughness. Currently, rare earth addition methods for metallic materials primarily involve pure rare earths, rare earth oxides, and pre-alloyed rare earth powders. However, due to the high chemical activity of most rare earths and their tendency to oxidize, the poor wettability of rare earth oxides, which can negatively impact the matrix, and the high cost and potential introduction of unwanted alloying elements, these methods are difficult to implement in practical production. While single rare earth additions often improve toughness, they can negatively impact strength, hardness, and wear resistance. Pure rare earths and even some rare earth compounds are highly chemically active even at room temperature and easily oxidize, making them unsuitable for large-scale industrial production and difficult to implement in practical applications. Furthermore, rare earth oxides can negatively impact the matrix. Therefore, finding the right rare earth addition method and ensuring that the rare earth addition does not compromise material strength are key to fully realizing the benefits of rare earths.

[0007] Chinese patent publication number CN113512687A discloses a composite rare earth-reinforced powder metallurgy high-speed steel and its preparation method. The addition of rare earth elements effectively purifies and refines the grains of high-speed steel. The enrichment of rare earth elements at grain boundaries and in austenite effectively improves grain boundaries, reduces carbide segregation, and lowers its thermal stability, making it easier to dissolve upon heating. This results in a strong solid solution strengthening effect, significantly increasing the strength of the high-speed steel. This patent achieves composite rare earth-reinforced powder metallurgy high-speed steel by adding composite rare earth elements. However, this patent only improves the hardness and wear resistance of the high-speed steel by adding composite rare earth elements, but does not effectively improve the toughness of the powder metallurgy high-speed steel.

[0008] In summary, current methods for improving the toughness of powder metallurgy high-speed steel (PMHSS) primarily rely on adding hard phases, modifying alloying elements, and altering sintering and heat treatment processes. However, these methods struggle to achieve a balanced balance between wear resistance and toughness. While the addition of rare earth elements to high-speed steel has been widely reported, the methods for adding pure elemental rare earths and rare earth oxides, as well as their trade-offs in material properties, have made large-scale industrial production difficult. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a powder metallurgy high-speed steel and a preparation method thereof that has both high wear resistance and high toughness in view of the shortcomings of the existing technology.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing powder metallurgy high-speed steel, comprising the following steps:

[0011] S1. Take a high-speed steel powder comprising the following components in parts by weight: 1.08-3.4 parts of C, 3.75-4.2 parts of Cr, 2.5-5.25 parts of Mo, 3.1-6.5 parts of V, 9-14.5 parts of W, and 8-11.5 parts of Co;

[0012] S2, adding a whisker dispersion to the high-speed steel powder of S1, wherein the whisker dispersion comprises 0.1 to 2 parts by weight of whiskers, ball milling, taking out the slurry, vacuum drying it, and sieving it;

[0013] S3, weighing 1.6-5 parts by weight of rare earth naphthenate, wherein the mass fraction of rare earth Ce in the rare earth naphthenate is 8% to 12%, mixing with a molding matrix and dissolving in a solvent to prepare a molding agent;

[0014] S4. The powder obtained after drying and sieving in S2 is mixed with the molding agent prepared in S3, ground and sieved to obtain a pressed blank, which is then molded, sintered, heat treated, and finely processed to obtain powder metallurgy high-speed steel.

[0015] The present invention prepares high-speed steel by powder metallurgy. Based on the high-speed steel formula, a uniformly dispersed whisker dispersion is added in the later stage of powder ball milling, and the rare earth element Ce is introduced by mixing rare earth naphthenate with a forming matrix. The inhibitory effect of the whiskers on crack propagation and the adsorption of harmful elements in the material structure by the rare earth element are utilized to improve the strength and toughness of the powder metallurgy high-speed steel, and ensure that the rare earth element is not easily oxidized when added.

[0016] Further preferably, the components of the powder metallurgy high-speed steel are as follows by weight: 2 to 2.45 parts of C, 3.8 to 4 parts of Cr, 3.6 to 5 parts of Mo, 5.1 to 6.3 parts of V, 11 to 14.3 parts of W, 8.5 to 11 parts of Co, 0.2 to 0.8 parts of whiskers, and 0.2 to 0.6 parts of Ce.

[0017] In a preferred embodiment of the present invention, the whisker dispersion in S2 is prepared by uniformly dispersing 0.1 to 2 parts by weight of whiskers in an ethanol-ethylene glycol mixed solution by ultrasonication at a mass ratio of 1:8-12.

[0018] The whiskers need to be made into a uniform whisker dispersion. If the mixed solution is too little, the dispersion effect will be poor, and if it is too much, it will affect the concentration of the ball milling medium. The prepared dispersion needs to be ultrasonically dispersed. If it is not ultrasonically treated, the whiskers will be entangled together, resulting in uneven material properties; and if the ultrasonic dispersion time is too long, the whiskers will be broken and the strengthening and toughening effect of the whiskers will not be able to be exerted.

[0019] The dispersed whisker dispersion liquid needs to be added to the high-speed steel powder after ball milling in time, and then the whiskers can be evenly dispersed in the high-speed steel powder through subsequent ball milling for a certain period of time to ensure the dispersion effect of the whiskers in the system.

[0020] In a preferred embodiment of the present invention, the whiskers in S2 are SiC whiskers or TiC whiskers.

[0021] In a preferred embodiment of the present invention, the high speed steel powder in S1 is prepared by the following method:

[0022] High-speed steel powder is prepared using WC, Mo2C, Cr3C2, VC, graphite powder, Co and Fe powder as raw materials according to the weight parts described in S1;

[0023] In S1, the ball milling medium is anhydrous ethanol, the ball milling ratio is 3-10:1, the rotation speed is 200-300 r / min, and the ball milling time is 24-72 h. More preferably, the ball milling ratio is 4-8:1, and the rotation speed is 250-300 r / min.

[0024] If the ball-to-material ratio is too small or the ball milling time is too short, the powder will be unevenly dispersed, and the high-speed steel produced will have uneven structure and performance, and defects. If the ball-to-material ratio is too large or the ball milling time is too long, the energy consumption will be high, the powder will be too fine, there will be a risk of spontaneous combustion, and it will be difficult to control in production.

[0025] High-speed steel powder can be purchased directly or prepared using the above method.

[0026] In a preferred embodiment of the present invention, the ball milling time in S2 is 1-6 hours. The grinding time after adding the whisker dispersion is 1-6 hours, so that the whiskers are evenly dispersed in the powder. If the grinding time is too long, the ball milling will destroy the structure of the whiskers, causing the whiskers to be broken, thereby having no toughening effect, and the ball milling will increase the whisker surface activation energy, causing the whiskers to agglomerate. If the grinding time is too short, the dispersion effect is poor, and the whiskers themselves are entangled.

[0027] The temperature of vacuum drying in S2 is 75°C to 85°C.

[0028] In a preferred embodiment of the present invention, the molding matrix in S3 is one or more of rubber, paraffin, and polyethylene glycol.

[0029] In a preferred embodiment of the present invention, the ultrasonic dispersion time in S2 is 0.5 h to 2 h. By using ultrasonic dispersion + short-time ball milling, whisker agglomeration is reduced without destroying the whisker structure.

[0030] In a preferred embodiment of the present invention, the solvent in S3 is an organic solvent, which is one or more of gasoline, white spirit, and acetone.

[0031] In a preferred embodiment of the present invention, the mesh size of the sieving in S2 is 80-200 meshes.

[0032] In a preferred embodiment of the present invention, the molding pressure of the blank in S4 is 200 MPa to 400 MPa.

[0033] In a preferred embodiment of the present invention, the sintering in S4 is performed by vacuum sintering or microwave sintering, the sintering temperature is 1150° C. to 1300° C., and the holding time is 0.5-2 h.

[0034] In a preferred embodiment of the present invention, the quenching temperature in S4 is 1150° C. to 1220° C., and the holding time is 2-5 minutes.

[0035] In a preferred embodiment of the present invention, the heat treatment process in S4 is three temperings, the tempering and holding temperature is 500-600° C., and each tempering and holding time is 0.5-1 hour.

[0036] The weight proportion of the forming matrix in S3 is 3-10 parts, and the mass ratio of the solvent to the forming matrix is 1: 1. More preferably, the weight proportion of the forming matrix in S3 is 2.5-4 parts.

[0037] The invention also discloses the powder metallurgy high-speed steel prepared by the preparation method of the powder metallurgy high-speed steel.

[0038] Traditional powder metallurgy high-speed steels have difficulty achieving both high wear resistance and high toughness, especially for high-carbon and high-alloy high-speed steels. Although they can achieve high wear resistance, their toughness is low and the material is extremely prone to brittle fracture. This problem cannot be solved simply by refining the grains, changing the alloy element composition of the high-speed steel, optimizing the sintering and heat treatment processes, etc.

[0039] Whiskers consume more fracture energy by expanding or extending the crack fracture path, thereby achieving the purpose of material strengthening and toughening. Its main mechanisms are crack deflection, fiber pullout, bridging, dispersion and nano-reinforcement. However, whiskers are very easy to agglomerate, and agglomerated whiskers form more defects in the material. Some dispersion methods and dispersants may also have adverse effects on the whisker structure and matrix material.

[0040] The invention relates to a formula and preparation method of powder metallurgy high-speed steel. Nano whiskers and rare earth elements are compositely added during the preparation of the powder metallurgy high-speed steel. The whiskers are subjected to ultrasonic pre-treatment and added in the later stage of ball milling of high-speed steel powder, and the rare earth elements are added simultaneously with a powder forming agent via rare earth naphthenate. This avoids the problems of whisker agglomeration and easy oxidation of rare earth elements, realizes industrialized production of the material, and enables the powder metallurgy high-speed steel to effectively utilize the beneficial effects of whiskers on the performance of the high-speed steel in terms of dispersion strengthening, whisker extraction, crack deflection, crack bridging, etc., and the strengthening and toughening effects of rare earth elements on the high-speed steel in terms of grain refinement, density improvement, interface purification, and bonding phase improvement, thereby improving the toughness of the high-speed steel without sacrificing wear resistance.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention adds whiskers to powder metallurgy high-speed steel to enhance the toughness and improve the dispersion effect of the whiskers.

[0043] 2. Rare earth cyclopentane acid is rich in rare earth element Ce and can be stored at room temperature for a long time. The present invention uses rare earth cyclopentane acid as a powder forming agent and introduces rare earth element Ce without changing the original process to solve the problem of easy oxidation of rare earth.

[0044] 3. The present invention proposes a material toughening method and process for composite addition of whiskers and rare earths during the preparation process of powder metallurgy high-speed steel. The method utilizes the influence of whisker materials on the performance of high-speed steel in terms of dispersion strengthening, whisker pullout, crack deflection, crack bridging, etc., and the strengthening and toughening effect of rare earth elements on powder metallurgy high-speed steel in terms of grain refinement, density improvement, interface purification, and bonding phase improvement, thereby achieving a simultaneous improvement in the wear resistance and toughness of high-speed steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is an electron microscope photograph of the impact fracture of the high-speed steel prepared in Comparative Example 1 of the present invention.

[0046] Figure 2 This is an electron microscope photograph of the impact fracture of the high-speed steel prepared in Example 1 of the present invention.

[0047] Figure 3 This is an electron microscope photograph of the impact fracture of the high-speed steel prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0048] The patent of this invention has been proven feasible through trial production, and the cost increase is controlled within 10%.

[0049] Example 1

[0050] 1. High-speed steel powder with alloying element contents of 2.45% C, 4% Cr, 5% Mo, 6.3% V, 11% W, 11% Co and the balance of Fe powder was placed in a ball mill for ball milling. The ball milling medium was anhydrous ethanol, the ball-to-material ratio was 8:1, the rotation speed was 250 r / min, and the ball milling time was 24 h.

[0051] 2. Weigh 0.4% SiC whiskers of high-speed steel components and ultrasonically disperse them in an ethanol-ethylene glycol mixed solution at a mass ratio of 1:10 for 1 h to obtain a SiC whisker dispersion.

[0052] 3. Add the SiC whisker dispersion into the ball mill and continue wet grinding with high-speed steel powder for 2 hours. The ball-milled powder is vacuum-dried at 80°C and then passed through a 200-mesh sieve.

[0053] 4. Select rare earth cyclopentaneate containing 12% rare earth Ce by mass, weigh rare earth cyclopentaneate containing 0.2% Ce of high-speed steel component and rubber according to proportion, mix and dissolve in gasoline to prepare a molding agent, the mass ratio of gasoline to rubber is 1:1, and the mass of rubber is 5%.

[0054] 5. The sieved dry powder was mixed with 5% forming agent, ground, sieved, and a pressed blank was prepared. The pressed blank was molded at 350 MPa to obtain a powder compact. After vacuum sintering at 1185°C for 1.5 hours, a high-speed steel sintered sample was obtained.

[0055] 6. The high-speed steel sintered sample was quenched at 1180°C and tempered three times at 560°C, with each heat preservation for one hour to obtain powder metallurgy high-speed steel.

[0056] Example 2

[0057] 1. High-speed steel powder with alloying element contents of 2.25% C, 3.8% Cr, 3.6% Mo, 5.1% V, 14.3% W, 10% Co and the balance Fe powder was placed in a ball mill for ball milling. The ball milling medium was anhydrous ethanol, the ball-to-material ratio was 5.5:1, the rotation speed was 280 r / min, and the ball milling time was 36 h.

[0058] 2. Weigh 0.6% TiC whiskers of high-speed steel components and ultrasonically disperse them in an ethanol solution at a mass ratio of 1:10 for 0.5 h to obtain a TiC whisker dispersion.

[0059] 3. Add the TiC whisker dispersion into the ball mill and continue wet grinding with high-speed steel powder for 4 hours. The ball-milled powder is vacuum-dried at 85°C and then passed through a 120-mesh sieve.

[0060] 4. Select rare earth cyclopentaneate containing 8% rare earth Ce by mass, weigh the rare earth cyclopentaneate containing 0.4% Ce of high-speed steel component and rubber according to proportion, mix them and dissolve them in gasoline to prepare a molding agent, the mass ratio of gasoline to rubber is 1:1, and the mass of rubber is 8%.

[0061] 5. The sieved dry powder was mixed with 8% forming agent, ground, sieved, and a pressed blank was prepared. The pressed blank was molded at 300 MPa to obtain a powder compact. After vacuum sintering at 1200°C for 1 hour, a high-speed steel sintered sample was obtained.

[0062] 6. The high-speed steel sintered sample was quenched at 1190°C, kept at 550°C for 1 hour and tempered three times to obtain powder metallurgy high-speed steel.

[0063] Comparative Example 1

[0064] The difference between Comparative Example 1 and Example 1 is that rare earth Ce and whiskers are not added, and steps 2-4 are omitted.

[0065] The specific properties of the prepared powder metallurgy high-speed steel are shown in the following table:

[0066]

[0067]

[0068] As can be seen from the table, the addition of rare earth Ce and whiskers can effectively reduce the grain size of the material structure. Compared with Example 1, the material hardness of Example 1 is increased by 1.5%, and the impact toughness is increased by 22.5%.

[0069] Depend on Figure 1-Figure 3 It can be seen that in Comparative Example 1, no rare earth Ce and whiskers were added, and defects such as holes were obvious. Examples 1-2 of the present application can effectively reduce defects such as holes.

[0070] From the above results, it can be seen that the present invention can significantly improve the hardness and toughness of powder high-speed steel. When the rare earth addition amount is appropriate, the material has good wear resistance, the structure is significantly refined, the carbide is evenly distributed, and defects such as holes can be effectively reduced.

Claims

1. A method for preparing powder metallurgy high-speed steel, characterized in that The following steps are involved: S1. Take high-speed steel powder containing the following components in parts by weight: 1.08-3.4 parts of C, 3.75-4.2 parts of Cr, 2.5-5.25 parts of Mo, 3.1-6.5 parts of V, 9-14.5 parts of W, and 8-11.5 parts of Co, and ball mill for 24-72 hours; S2, adding a whisker dispersion to the high-speed steel powder of S1, wherein the whisker dispersion comprises 0.1 to 2 parts by weight of whiskers, ball milling, taking out the slurry, vacuum drying it, and sieving it; S3, weighing 1.6-5 parts by weight of rare earth naphthenate, wherein the mass fraction of rare earth Ce in the rare earth naphthenate is 8% to 12%, mixing with a molding matrix and dissolving in a solvent to prepare a molding agent; S4. The powder obtained after drying and sieving in S2 is mixed with the molding agent prepared in S3, ground and sieved to obtain a pressed blank, which is then molded, sintered, heat treated, and finely processed to obtain powder metallurgy high-speed steel.

2. The method for preparing powder metallurgy high-speed steel according to claim 1, characterized in that: The whisker dispersion in S2 is prepared by taking 0.1 to 2 parts by weight of whiskers and uniformly dispersing them in an ethanol-ethylene glycol mixed solution at a mass ratio of 1:8-12 by ultrasonication.

3. The method for preparing powder metallurgy high-speed steel according to claim 1, characterized in that: The whiskers in S2 are SiC whiskers or TiC whiskers.

4. The method for preparing powder metallurgy high-speed steel according to claim 1, characterized in that: The high speed steel powder described in S1 is prepared by the following method: High-speed steel powder is prepared using WC, Mo2C, Cr3C2, VC, graphite powder, Co and Fe powder as raw materials according to the weight parts described in S1; The ball milling medium in S1 is anhydrous ethanol, the ball-to-material ratio is 3-10:1, and the rotation speed is 200-300 r / min.

5. The method for preparing powder metallurgy high-speed steel according to claim 1, characterized in that: The ball milling time in S2 is 1-6h.

6. The method for preparing powder metallurgy high-speed steel according to any one of claims 1 to 5, characterized in that: The molding matrix in S3 is one or more of rubber, paraffin, and polyethylene glycol.

7. The method for preparing powder metallurgy high-speed steel according to claim 2, characterized in that: The ultrasonic dispersion time in S2 is 0.5h-2h.

8. The method for preparing powder metallurgy high-speed steel according to any one of claims 1 to 5, characterized in that: The solvent in S3 is an organic solvent.

9. The method for preparing powder metallurgy high-speed steel according to any one of claims 1 to 5, characterized in that: The mesh size of the sieve in S2 is 80-200 mesh.

10. Powder metallurgy high-speed steel produced by the method for producing powder metallurgy high-speed steel according to any one of claims 1 to 9.

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