High-hardness high-wear-resistance powder high-speed steel and preparation method thereof

Abstract

This invention relates to a high-hardness, high-wear-resistant powdered high-speed steel and its preparation method, comprising high-speed steel powder, a hard phase, and a forming agent. The high-speed steel powder, by mass percentage, comprises: 2-3.5% C, 3.78-4.2% Cr, 2.5-5.0% Mo, 5.1-9.5% V, 10-14.5% W, 9-16% Co, with the balance being Fe. The hard phase comprises 0.5-8% of the mass of the high-speed steel powder, and the forming agent comprises 0-5.5% of the mass of the high-speed steel powder. The raw materials for the high-speed steel are WC, Mo2C, Cr3C2, VC, graphite powder, Co, and Fe powder. The hard phase is one or more of B4C, NbC, TaC, TiC, and TiCN, and the particle size of the hard phase is 500 nm to 2 μm. The ultrahard micro powder selected in this invention is prepared by powder metallurgy, resulting in fewer material defects and overcoming problems such as poor bonding force between hard particles and the matrix and poor wettability. The resulting powdered high-speed steel has improved wear resistance, as well as material toughness and stability.

Description

Technical Field

[0001] This invention relates to a high-hardness, high-wear-resistant powder high-speed steel and its preparation method, belonging to the field of high-speed steel. Background Technology

[0002] Currently, the materials widely used in tool manufacturing are high-speed steel and cemented carbide. Although cemented carbide has better wear resistance than high-speed steel, it is expensive and has poor toughness, making it prone to chipping. High-speed steel remains an important tool material for machining with large cutting volumes. With the expanding applications of high-speed steel, the performance requirements are constantly increasing, creating an urgent need for a high-speed steel with higher hardness and wear resistance than traditional high-speed steel and better toughness than cemented carbide. Current efforts to improve high-speed steel performance mainly focus on formula improvements, adjusting the proportion of alloying elements to enhance wear resistance. However, increasing the number of alloying elements raises the melting temperature of high-speed steel, which is limited by process and equipment constraints. Furthermore, improved wear resistance inevitably leads to a decrease in toughness.

[0003] Powder metallurgy can solve the problems of reduced and inconsistent mechanical properties caused by compositional segregation and coarse carbide structure in the traditional casting and forging process of high-speed steel. Powder high-speed steel is generally prepared by processes such as melting, atomization powdering, vacuum deoxidation, billet forming, and sintering. Atomization powdering involves passing molten high-speed steel through an intermediate ladle and a special nozzle, where high-pressure, high-purity inert gas (Ar or N2) is used to spray the molten steel stream, atomizing it into fine droplets that solidify into powder. After cooling, the powder is collected, deoxidized, and billeted before being sintered at high temperature into materials or tools. Under high-speed cooling, primary eutectic carbides do not have time to grow, avoiding the occurrence of coarse carbides and compositional segregation. The performance can be improved by subsequent hot working.

[0004] Traditional powder high-speed steel (SHS) billet preparation and firing generally employ the hot isostatic pressing (HIP) method. The process involves loading SHS powder into a sleeve, vacuum-sealing it after deoxidation, and then placing it into a HIP press. Under high temperature and pressure, the powder is "thermally solidified" into a completely dense compacted entity, i.e., powder metallurgy SHS. Because no liquid phase is generated during the thermal solidification process, PISS retains the characteristic of no macroscopic carbide segregation in the powder particles. However, the traditional PISS preparation method is complex. The smelting, atomization, and HIPS processes are energy-intensive and costly, requiring sophisticated equipment. Since the final shape and size of the HIPS billet vary considerably, traditional PISS often requires multiple hot deformation processes, further increasing energy consumption and cost. Furthermore, atomization uses finished SHS powder as raw material, making it difficult to change the composition during production, and the product is largely imported, resulting in high prices.

[0005] Chinese invention patent application CN103814145A discloses a method for manufacturing high-speed steel. The high-speed steel's chemical composition comprises: 1-3 wt% carbon (C), 3-6 wt% chromium (Cr), 0-7 wt% molybdenum (Mo), 0-15 wt% tungsten (W), 3-14 wt% vanadium (V), 0-10 wt% cobalt (Co), 0-3 wt% niobium (Nb), 0-0.5 wt% nitrogen (N), and 0.2-1 wt% yttrium (Y), with the balance being iron (Fe) and unavoidable impurities, wherein Mo + 0.5 W = 2-10 wt%. However, uneven mixing of multiple raw materials can lead to unstable material properties, coarse microstructure, and large carbides. Furthermore, improving the performance of high-speed steel by changing the proportions of alloying elements presents a problem where wear resistance and toughness cannot be simultaneously achieved.

[0006] Chinese invention patent application CN114686782A discloses a high-strength, high-elasticity high-speed steel and its preparation method. The high-speed steel consists of a steel matrix and intermetallic compounds and a hard second phase dispersed within the steel matrix. The intermetallic compounds include Fe7W6, Fe7Mo6, Co7W6, Co7Mo6, FeCrMo, NbFe2, and TiFe2. The hard second phase is selected from at least one of TiC, TiN, Ti(C,N), TiB2, WC, NbC, and Cr3C2. The preparation method involves weighing raw material powder and mechanically ball-milling it. The ball-milled powder mixture is then pressed into a shape and vacuum sintered. The sintered billet is then hot-forged, and finally, the forged billet undergoes solution treatment and aging. The high-speed steel prepared by this invention exhibits high hot hardness, good microstructure uniformity, and improved strength and elastic modulus to a certain extent. However, the wear resistance of the high-speed steel prepared by this method needs further improvement.

[0007] Adding hard particles to the matrix material, ensuring their fine, dispersed distribution throughout the matrix structure to achieve a strengthening effect, is a common method for strengthening composite materials. In steel, the carbides and oxides are hard and brittle, which can hinder dislocation movement and refine grains, thus playing a strengthening role. Therefore, in high-speed steel, in addition to the carbides formed by the alloying elements themselves, the addition of carbide and oxide particles can overcome the limitations of alloying element strengthening, achieving a simultaneous improvement in wear resistance and toughness. However, this also presents challenges such as poor bonding and wettability between the added hard particles and the iron matrix, as well as the tendency for particles to aggregate, leading to stress concentration at the material interface, crack initiation, and defects. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a powder high-speed steel and its preparation method that can improve the hardness and toughness of powder high-speed steel, in view of the shortcomings of the prior art.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0010] A high-hardness, high-wear-resistant powder high-speed steel comprises high-speed steel powder, a hard phase, and a forming agent. The high-speed steel powder, by mass percentage, comprises: 2-3.5% C, 3.78-4.2% Cr, 2.5-5.0% Mo, 5.1-9.5% V, 10-14.5% W, 9-16% Co, and the balance being Fe. The hard phase comprises 0.5-8% of the mass of the high-speed steel powder, and the forming agent comprises 0-5.5% of the mass of the high-speed steel powder.

[0011] This invention adds a hard phase to powdered high-speed steel raw materials, so that the hard particles are evenly distributed in the matrix structure as fine and dispersed particles. This can prevent the movement of dislocations and refine the grains, thereby playing a strengthening role. It can break through the limitations of alloy element strengthening. While improving wear resistance, the material's toughness and stability are also better than traditional high-speed steel. The addition of a forming agent is beneficial to powder forming.

[0012] Furthermore, the high-hardness, high-wear-resistant powder high-speed steel has a hardness of 72 HRC or higher; the higher the hardness, the better its wear resistance. However, as the hardness increases, the toughness of the powder high-speed steel decreases. This invention improves the hardness and wear resistance of the powder high-speed steel while also maintaining its toughness.

[0013] Furthermore, the molding agent is at least one of paraffin wax and polyethylene wax.

[0014] Furthermore, the raw materials for the high-speed steel powder are WC, Mo2C, Cr3C2, VC, graphite powder, Co, and Fe powder. Thus, using WC, Mo2C, Cr3C2, VC, graphite powder, Co, and Fe powder as raw materials to prepare high-speed steel solves the problems of complex production processes, high energy consumption and costs, high equipment requirements, and difficulty in changing the composition and formulation of high-speed steel compared to traditional powder metallurgy high-speed steel, which involves processes such as smelting, atomization powder preparation, vacuum deoxidation of powder, billet preparation, and firing.

[0015] This application uses carbides as raw materials to prepare high-speed steel. Under certain alloying element ratios, carbon in the matrix can form carbides and intermetallic compounds, maximizing its effect and resulting in high-speed steel with good wear resistance. The carbon added during the high-speed steel preparation process is to compensate for carbon loss due to oxidation or volatilization during preparation; large amounts of carbon addition are not required.

[0016] Furthermore, the hard phase is one or more of B4C, NbC, TaC, TiC, and TiCN. The hard phase exhibits good wettability. All hard phases have high melting points and good stability. The boron (B) element in B4C can activate the sintering of high-speed steel and increase its density; the Nb element not only improves the strength and hardness of the steel but also enhances its corrosion resistance; the Ti element can improve the wear resistance and hardness of high-speed steel, but it reduces sintering activity and interfacial strength.

[0017] Furthermore, the particle size of the hard phase is 500 nm to 2 μm. Thus, by using ultrafine powder as the hard phase, the hard particles are uniformly distributed in the matrix as fine and dispersed particles, resulting in fewer defects and finer grains. This improves both wear resistance and the material's toughness and stability.

[0018] In a preferred embodiment of the present invention, the powder high-speed steel comprises the following elements by weight: 2-2.5% C, 3.8-4% Cr, 4.1-5% Mo, 5.1-6.3% V, 11-14.3% W, 11-16% Co, with the balance being Fe, and also includes 0.5-8% hard phase and 0-5.5% forming agent.

[0019] Based on the same inventive concept, the present invention also provides a method for preparing high-hardness, high-wear-resistant powder high-speed steel, comprising the following steps:

[0020] S1. High-speed steel powder, hard phase powder and forming agent are prepared according to the mass percentage and then ball-milled.

[0021] S2. The powder obtained after ball milling is dried and sieved to obtain a pressed blank.

[0022] S3. The pressed material is pressed into a compact by molding, and the compact is sintered to obtain a sintered sample;

[0023] S4. The sintered sample is heat-treated to obtain powdered high-speed steel.

[0024] Further, in step S1, the ball milling is either dry or wet ball milling. The dry ball milling medium is nitrogen, while the wet ball milling medium is one of anhydrous ethanol, acetone, or n-hexane. The ball-to-material ratio is 3–10:1, the ball milling speed is 200–300 r / min, and the ball milling time is 12–60 h. Ball milling breaks down the raw material into finer particles, which helps to resolve the wettability issue between the ultrahard powder and the matrix.

[0025] Furthermore, in step S3, the sintering process is vacuum sintering or microwave sintering, the sintering temperature is 1120℃~1220℃, and the holding time is 0.5~2h.

[0026] Further, in step S4, the sintered sample is quenched at 1080℃~1200℃ for 2~10 minutes, and then tempered n times, where n is an integer between 2 and 6, the tempering temperature is 500~600℃, and each tempering is held for 0.5~2 hours.

[0027] Furthermore, the powder after ball milling in step S2 is vacuum dried at 75℃~100℃ for 4~20h and then passed through an 80~150 mesh sieve.

[0028] Furthermore, in step S3, the molding pressure is 150MPa to 500MPa.

[0029] In some embodiments of the present invention, no forming agent is added in step S1, and the sintering temperature is 900℃~1000℃; in step S3, the sintering process is spark plasma sintering, the pressure is 30~50MPa, and the holding time is 5~10min.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention uses WC, Mo2C, Cr3C2, VC, graphite powder, Co and Fe powder as raw materials to prepare high-speed steel. Compared with the traditional powder metallurgy high-speed steel, which is prepared by smelting, atomization powder preparation, powder vacuum deoxidation, billet preparation and firing, this invention solves the problems of complex production process, high energy consumption and high cost, high equipment requirements and difficulty in changing the composition formula of high-speed steel.

[0032] (2) By controlling the processes of powder ball milling, pressing sintering and heat treatment of high-speed steel, the problems of inaccurate carbon content, coarse carbides and uneven microstructure distribution in the preparation of powder high-speed steel have been solved.

[0033] (3) By adding superhard micro powders such as B4C, NbC, TaC, TiC, and TiCN as hard phases to high-speed steel, the hard particles are evenly distributed in the matrix structure as fine and dispersed particles, which can prevent the movement of dislocations and refine the grains, thereby playing a strengthening role. It can break through the limitations of alloy element strengthening. While improving wear resistance, the toughness and stability of the material are also better than those of traditional high-speed steel.

[0034] (4) The ultrahard micro powder selected in this invention is prepared by powder metallurgy, which has fewer material defects and overcomes problems such as poor bonding force between hard particles and matrix and poor wettability. Attached Figure Description

[0035] Figure 1 The image shows the metallographic structure of high-speed steel obtained in Comparative Example 1 of this invention (magnification: 2080X).

[0036] Figure 2The image shows the metallographic structure of high-speed steel obtained in Example 1 of this invention (magnification: 2080X).

[0037] Figure 3 This is an electron microscope image of the impact fracture surface of high-speed steel obtained in Comparative Example 1 of this invention.

[0038] Figure 4 This is an electron microscope image of the impact fracture surface of high-speed steel obtained in Example 1 of the present invention. Detailed Implementation

[0039] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0040] Example 1

[0041] A method for preparing high-hardness, high-wear-resistant powder high-speed steel includes the following steps:

[0042] (1) High-speed steel powder: The mass percentages of each element are 11% W, 5% Mo, 4% Cr, 6.3% V, 16% Co, appropriate amount of graphite powder, and balance Fe powder. Take WC, Mo2C, Cr3C2, VC, Co, graphite powder, and Fe powder; Hard phase: Take 4% NbC by mass of high-speed steel powder; Forming agent: Take 2% paraffin by mass of high-speed steel powder; Place the above raw materials in the ball mill jar for ball milling. The ball milling medium is acetone, the ball-to-material ratio is 6:1, the rotation speed is 280 r / min, and the ball milling time is 24 h.

[0043] (2) The ball-milled powder slurry was vacuum dried at 85°C for 6 hours and then passed through an 80-mesh sieve.

[0044] (3) The blank is obtained by molding the blank with a molding pressure of 250MPa.

[0045] (4) The compact is vacuum sintered at 1185℃ for 1 hour.

[0046] (5) The sintered sample was quenched at 1180℃ for 5 minutes, and then tempered three times at 560℃ for 1 hour each time to obtain powder high-speed steel.

[0047] Example 2

[0048] A method for preparing high-hardness, high-wear-resistant powder high-speed steel includes the following steps:

[0049] (1) High-speed steel powder: Take WC, Mo2C, Cr3C2, VC, Co, graphite powder and Fe powder according to the mass percentage of each element as 10% W, 5% Mo, 4% Cr, 9.5% V, 9% Co, appropriate amount of graphite powder and balance Fe powder; Hard phase: Take 2% TiC and 2% TaC of high-speed steel powder by mass of high-speed steel powder; Place the above raw materials in the ball mill jar for ball milling, the ball milling medium is anhydrous ethanol, the ball-to-material ratio is 8:1, the rotation speed is 250 r / min and the ball milling time is 20 h.

[0050] (2) The ball-milled powder slurry was vacuum dried at 90°C for 10 hours and then passed through a 100-mesh sieve.

[0051] (3) The blank is obtained by molding the blank with a molding pressure of 350MPa.

[0052] (4) The compact is vacuum sintered at 1180℃ for 1.5h.

[0053] (5) The sintered sample was quenched at 1175℃ for 6 minutes, and then tempered 4 times at 550℃ for 40 minutes each time to obtain powder high-speed steel.

[0054] Comparative Example 1

[0055] The difference between Comparative Example 1 and Example 1 is that the hard phase NbC was not added in step (1). The specific properties of the powder metallurgy high-speed steels prepared in the above examples and comparative examples are shown in Table 1.

[0056] Table 1. Specific performance parameters of powder metallurgy high-speed steels prepared in Examples 1-2 and Comparative Example 1.

[0057] sample Grain size tissue homogeneity hardness Impact toughness abrasion resistance Comparative Example 1 10μm generally 70.1 HRC <![CDATA[7.8J / cm 2 ]]> good Example 1 5μm uniform 72.9 HRC <![CDATA[13.4J / cm 2 ]]> excellent Example 2 4μm uniform 73.7 HRC <![CDATA[9.7J / cm 2 ]]> excellent

[0058] As shown in Table 1, adding a hard phase can effectively reduce the grain size of the material. Compared with Comparative Example 1, the material hardness of Example 1 increased by 3.99% and the impact toughness increased by 71.79%.

[0059] Depend on Figure 1 , Figure 2 It can be seen that the high-speed steel prepared in Example 1 has a smaller amount of carbides (white in the figure), indicating that the carbides are well dispersed and the structure is uniform.

[0060] Depend on Figure 3 , Figure 4 It can be seen that in Comparative Example 1, the grains are coarse and the bonding between the carbide and the matrix is ​​poor, while in Example 1, the grains are refined, the structure is uniform, and the bonding between the matrix and the carbide is good.

[0061] The above results show that the present invention can significantly improve the hardness and toughness of powder high-speed steel. When the appropriate type and amount of hard phase are selected, the microstructure is significantly refined and the interface bonding is good.

[0062] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A high-hardness, high-wear-resistant powder high-speed steel, characterized in that, The powder comprises high-speed steel powder, a hard phase, and a forming agent. The high-speed steel powder, by mass percentage, consists of: 2-3.5% C, 3.78-4.2% Cr, 2.5-5.0% Mo, 5.1-9.5% V, 10-14.5% W, 9-16% Co, with the balance being Fe. The hard phase comprises 0.5-8% of the mass of the high-speed steel powder, and the forming agent comprises 0-5.5% of the mass of the high-speed steel powder. The hard phase is NbC. The high-hardness, high-wear-resistant powder high-speed steel has a hardness of 72 HRC or higher.

2. The powder high-speed steel according to claim 1, characterized in that, The molding agent is at least one of paraffin wax and polyethylene wax.

3. The powder high-speed steel according to claim 1, characterized in that, The high-speed steel powder includes WC, Mo2C, Cr3C2, VC, graphite powder, Co, and Fe powder.

4. The powder high-speed steel according to claim 1, characterized in that, The particle size of the hard phase is 500 nm to 2 μm.

5. A method for preparing powdered high-speed steel as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. High-speed steel powder, hard phase powder and forming agent are prepared according to the mass percentage and then ball-milled. S2. The powder obtained after ball milling is dried and sieved to obtain a pressed blank. S3. The pressed material is pressed into a compact by molding, and the compact is sintered to obtain a sintered sample; S4. The sintered sample is heat-treated to obtain powdered high-speed steel.

6. The preparation method according to claim 5, characterized in that, In step S1, the ball milling is either dry ball milling or wet ball milling. The dry ball milling medium is nitrogen, and the wet ball milling medium is one of anhydrous ethanol, acetone, or n-hexane. The ball-to-material ratio is 3 to 10:1, the ball milling speed is 200 to 300 r / min, and the ball milling time is 12 to 60 h.

7. The preparation method according to claim 5, characterized in that, In step S3, the sintering process is vacuum sintering or microwave sintering, the sintering temperature is 1120℃~1220℃, and the holding time is 0.5~2h.

8. The preparation method according to claim 5, characterized in that, In step S4, the sintered sample is quenched at 1080℃~1200℃ for 2~10 minutes, followed by n tempering cycles, where n is an integer between 2 and 6, with a tempering temperature of 500~600℃ and each tempering cycle lasting 0.5~2 hours.

9. The preparation method according to claim 5, characterized in that, In step S3, the sintering process is spark plasma sintering. No forming agent is added in step S1. The sintering temperature is 900℃~1000℃, the pressure is 30~50MPa, and the holding time is 5~10min.

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