Method of metal powder injection molding of a wear-resistant steel

Abstract

The application discloses a kind of wear-resistant steel's metal powder injection molding method, it includes the following steps: S1: wear-resistant steel alloy powder injection molding obtains green body, and the green body is catalyzed to be debound, to obtain to be sintered product;S2: the sintered product is placed in sintering furnace sequentially negative pressure debinding, vacuum inner burning and sintering treatment, to obtain sintered part;Wherein, the sintering treatment is: with 0.1~1 ℃ / min heating rate, furnace temperature is increased to 1220~1240 ℃, and keeps warm 60~360min;S3: the sintered part is carried out hot isostatic pressing treatment, to obtain wear-resistant steel.The wear-resistant steel's metal powder injection molding method of the application can prepare wear-resistant steel with density and uniformity of organization, and improve the comprehensive mechanical properties of the wear-resistant steel, it has good popularization prospect and application value.

Description

Technical Field

[0001] This invention relates to the field of metal powder forming, and more particularly to a method for forming metal powder of wear-resistant steel. Background Technology

[0002] As is well known, components in smart wearable devices, such as watchband hinges, hinge structures in foldable phones, and micro-precision transmission gears, often require tiny but high-frequency, high-precision parts. This places extremely high demands on the wear resistance, toughness, and long-term service stability of the steel used in these components. Therefore, there is an urgent need for a high-performance wear-resistant steel to meet the wear resistance requirements under complex stress conditions.

[0003] Metal Injection Molding (MIM) is an advanced near-net-shape manufacturing process that combines modern plastic injection molding with powder metallurgy. This technology involves mixing metal powder with a binder to prepare a feedstock, which is then injected into a mold cavity via an injection molding machine to form a green body. The green body is then debound and sintered at high temperature to obtain a high-density final product. MIM technology overcomes the limitations of traditional powder metallurgy in terms of shape freedom, enabling the mass production of parts with complex three-dimensional geometry, precise micro-dimensions, and high surface quality. It has been widely applied in the fabrication of key components in high-end manufacturing, becoming an important technological approach to solving the molding challenges of complex and precision parts in high-end equipment.

[0004] Although metal powder injection molding (MPIM) has significant advantages in molding complex parts, its application in the preparation of wear-resistant steel still faces many technical challenges. This is because: Wear-resistant steel has a high carbon content, which easily leads to decarburization and uneven carbon distribution during sintering. This results in uneven microstructure, localized brittleness, and premature failure of the manufactured parts. Therefore, to avoid the formation of network carbides and ensure a normal metallographic structure, the sintering temperature of the wear-resistant steel material must be strictly controlled. However, excessively strict temperature control makes it difficult to achieve material density, and the mechanical properties of wear-resistant steel are highly dependent on the material's density. Consequently, current metal powder injection molding processes for manufacturing wear-resistant steel often fail to produce products with adequate density and a normal microstructure. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: the present invention discloses a metal powder injection molding method for wear-resistant steel, so as to solve the problem that the wear-resistant steel prepared by the existing metal powder injection molding process cannot simultaneously achieve both density and microstructure uniformity.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for metal powder injection molding of wear-resistant steel, comprising the following steps: S1: Wear-resistant steel alloy powder is injection molded to obtain a green body, and the green body is catalytically degreased to obtain a product to be sintered; S2: The product to be sintered is placed in a sintering furnace and subjected to negative pressure degreasing, vacuum firing and sintering in sequence to obtain a sintered part; wherein, the sintering process is: the furnace temperature is raised to 1220~1240℃ at a heating rate of 0.1~1℃ / min and held for 60~360min. S3: The sintered part is subjected to hot isostatic pressing to obtain wear-resistant steel.

[0007] Furthermore, in the metal powder injection molding method of the present invention, in step S2, the negative pressure degreasing is as follows: the furnace temperature is raised from room temperature to 250-350°C at a heating rate of 0.1-10°C / min and held for 0-180 min; the temperature is further raised to 400-500°C at a heating rate of 0.1-10°C / min and held for 0-180 min; the temperature is further raised to 550-800°C at a heating rate of 0.1-10°C / min and held for 0-180 min.

[0008] Furthermore, in the metal powder injection molding method of the present invention, in step S2, the vacuum firing is: raising the furnace temperature to 1000~1180℃ at a heating rate of 0.1~10℃ / min, maintaining the furnace pressure <10Pa, and holding the temperature for 30~240min.

[0009] Furthermore, in the metal powder injection molding method of the present invention, in step S3, the sintered part is subjected to hot isostatic pressing treatment, specifically as follows: The sintered part is heated to 1050~1200℃, the pressure inside the furnace is maintained at >100MPa, and the temperature is held for 60~360min. Then it is cooled to room temperature with the furnace to obtain wear-resistant steel.

[0010] Furthermore, in the metal powder injection molding method of the present invention, in step S1, the green blank is obtained by injection molding based on wear-resistant steel alloy powder, specifically: kneading wear-resistant steel alloy powder with a binder to prepare a feedstock; crushing and granulating the feedstock; and injection molding the crushed and granulated feedstock to obtain a green blank.

[0011] Furthermore, in the metal powder injection molding method of the present invention, the binder comprises: polyoxymethylene, polyethylene, paraffin wax, ethylene-vinyl acetate copolymer and stearic acid.

[0012] Furthermore, in the metal powder injection molding method of the present invention, the particle size of the wear-resistant steel alloy powder is ≤50μm.

[0013] Furthermore, in the metal powder injection molding method of the present invention, in step S1, the relative degreasing rate of the green body after catalytic degreasing is >96%.

[0014] Furthermore, the metal powder injection molding method of the present invention also includes step S4: heat treatment of the obtained wear-resistant steel.

[0015] Furthermore, in the metal powder injection molding method of the present invention, the heat treatment includes quenching and tempering, wherein the tempering specifically comprises: The quenched wear-resistant steel is heated to the first tempering temperature under vacuum conditions and held at that temperature for a first preset time, and then air-cooled to room temperature to complete one tempering process. The wear-resistant steel after the first tempering is heated to the second tempering temperature under vacuum and held at that temperature for a second preset time, and then air-cooled to room temperature to complete the second tempering.

[0016] The beneficial effects of this invention are as follows: The metal powder injection molding method for wear-resistant steel designed in this invention strictly controls the heating rate during the sintering process, especially by slowing down the heating rate after vacuum sintering. On the one hand, this helps to prolong the formation and growth time of the sintering neck, promotes spheroidization and shrinkage of pores, and contributes to the densification of the steel. On the other hand, by slowing down the heating rate, it can effectively suppress the formation of network carbides caused by local carbon enrichment, and avoid their continuous distribution at grain boundaries, thereby significantly improving the toughness of the material. This solves the problem of early fracture caused by microstructural embrittlement in wear-resistant steel under the rapid heating process of traditional metal powder injection molding methods. At the same time, this metal powder injection molding method also introduces a hot isostatic pressing process after sintering, so as to promote the healing of internal defects (such as residual pores and cracks) in the steel by applying isotropic pressure to the material under high temperature and high pressure, thereby significantly improving the density and microstructure uniformity of the wear-resistant steel product. It has good prospects for promotion and application value. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the steps in one embodiment of the metal powder injection molding method for wear-resistant steel according to the present invention. Figure 2 The image shows the metallographic structure of the wear-resistant steel in Example 1. Figure 3 The metallographic structure of the wear-resistant steel in Comparative Example 1 is shown. Figure 4 The metallographic structure of the wear-resistant steel in Comparative Example 2 is shown. Figure 5The image shows the metallographic structure of the wear-resistant steel in Comparative Example 3. Detailed Implementation

[0018] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0019] To address the problem that existing metal powder injection molding processes cannot simultaneously achieve both density and microstructure uniformity in wear-resistant steel, this invention discloses a metal powder injection molding method for wear-resistant steel. By optimizing its own process, this method ensures that the wear-resistant steel product has qualified density and excellent microstructure uniformity while being prepared using the metal powder injection molding method, and also achieves excellent comprehensive mechanical properties.

[0020] like Figure 1 As shown, in one embodiment of the present invention, the metal powder injection molding method for the wear-resistant steel includes the following steps S1-S3: S1: A green body is obtained by injection molding of wear-resistant steel alloy powder, and the green body is then subjected to catalytic debinding to obtain the product to be sintered; S2: The above-mentioned products to be sintered are placed in a sintering furnace and subjected to negative pressure degreasing, vacuum firing and sintering treatment in sequence to obtain sintered parts; wherein, the sintering treatment is specifically as follows: the furnace temperature is raised to 1220~1240℃ at a heating rate of 0.1~1℃ / min and held for 60~360min. S3: The above sintered parts are subjected to hot isostatic pressing to obtain wear-resistant steel.

[0021] The metal powder injection molding method for wear-resistant steel designed in this invention strictly controls the heating rate during the sintering process, especially slowing down the heating rate during the sintering process after vacuum firing. This process is crucial for the sintering of wear-resistant steel. On the one hand, it helps to prolong the formation and growth time of the sintering neck, promotes spheroidization and shrinkage of pores, and contributes to the densification of the steel. On the other hand, by slowing down the heating rate, it can effectively suppress the formation of network carbides caused by local carbon enrichment and avoid their continuous distribution at grain boundaries, thereby significantly improving the toughness of the steel. This solves the problem of early fracture caused by microstructural embrittlement in wear-resistant steel under the rapid heating process of traditional metal powder injection molding methods.

[0022] The reason for controlling the sintering process by raising the furnace temperature to 1220-1240℃ at a heating rate of 0.1-1℃ / min and holding it at that temperature for 60-360min is that wear-resistant steel has a relatively high carbon content, resulting in a very low melting point and a narrow sintering temperature window. If carbon accumulates at the grain boundaries, it will cause excessively high carbon content in local areas, leading to melting and the formation of network carbides during sintering, which is a major challenge in sintering wear-resistant steel. This invention, by strictly controlling the heating rate at this stage, allows sufficient time for carbon to diffuse uniformly during sintering, thereby effectively reducing local melting at grain boundaries. Simultaneously, the slower heating rate provides the steel with a smaller temperature gradient and a longer atomic diffusion time, preventing the surface pores from closing too quickly and contributing to an increase in the overall density of the wear-resistant steel.

[0023] Furthermore, in this invention, the metal powder injection molding method incorporates a hot isostatic pressing (HIP) process after sintering to significantly improve the densification of the sample. This aims to resolve the contradiction between achieving high density and a normal metallographic structure in wear-resistant steel during sintering. Obtaining highly densified wear-resistant steel materials through sintering alone is typically very difficult. Increasing the maximum temperature to improve densification can lead to the formation of network carbides, negatively impacting the performance of the wear-resistant steel. Therefore, this invention employs a HIP process to apply isotropic pressure to the material under high temperature and pressure, promoting the healing of internal defects in the steel and thus improving the density and microstructure uniformity of the wear-resistant steel.

[0024] Therefore, this invention can utilize metal powder injection molding to form complex wear-resistant steel parts, thereby meeting the requirements of high-end equipment for forming complex and precision parts with high wear resistance. It has good prospects for promotion and application value.

[0025] It should be noted that in the metal powder injection molding method designed in this invention, in the above step S1, obtaining a green blank based on the injection molding of wear-resistant steel alloy powder can be specifically as follows: kneading wear-resistant steel alloy powder with a binder to prepare a feedstock; crushing and granulating the feedstock, and then injection molding the crushed and granulated feedstock to obtain a green blank.

[0026] In some embodiments, an injection molding machine can be used to injection mold the crushed and granulated feedstock to obtain a green preform. In order to ensure that the green preform is injected evenly and fully without defects, the injection temperature of the injection molding machine can be controlled between 170 and 200°C, the injection pressure can be controlled between 100 and 200 MPa, the holding pressure can be controlled between 80 and 160 MPa, and the mold temperature for injection molding can be controlled between 90 and 120°C.

[0027] Accordingly, in practical applications, in order to facilitate injection molding and ensure the quality and effect of the green body, the particle size of the wear-resistant steel alloy powder can be specifically controlled to be ≤50μm; at the same time, in practical applications, in order to ensure the bonding effect, the components of the binder can specifically include polyoxymethylene, polyethylene, paraffin wax, ethylene-vinyl acetate copolymer and stearic acid.

[0028] Of course, in the metal powder injection molding method for wear-resistant steel designed in this invention, in step S1, the prepared green body also needs to undergo catalytic degreasing treatment. The degreasing must ensure that most of the binder is removed. In practical applications, the relative degreasing rate of the green body under catalytic degreasing can be controlled to be >96% to avoid excessive residual carbon content and unstable performance.

[0029] Accordingly, in order to ensure complete degreasing, after the catalytic degreasing of the green blank and the product to be sintered are completed in step S1, the product to be sintered needs to be degreased a second time in step S2 before vacuum firing in the sintering furnace, namely negative pressure degreasing in step S2.

[0030] It should be noted that, in some embodiments, the above-mentioned negative pressure degreasing can specifically be as follows: the furnace temperature is raised from room temperature to 250-350°C at a heating rate of 0.1-10°C / min, and held for 0-180 min; the temperature is then raised to 400-500°C at a heating rate of 0.1-10°C / min, and held for 0-180 min; the temperature is then raised to 550-800°C at a heating rate of 0.1-10°C / min, and held for 0-180 min.

[0031] In practical applications, the actual process parameters of the above negative pressure degreasing can be adjusted according to the requirements to ensure that all the remaining binder after catalytic degreasing is decomposed by heat and to avoid the binder residue reacting with the steel, thereby affecting the final performance of the material.

[0032] Accordingly, after completing the above-mentioned negative pressure degreasing, the workpiece to be sintered can be further subjected to vacuum firing. Vacuum firing specifically involves raising the furnace temperature to 1000~1180℃ at a heating rate of 0.1~10℃ / min, maintaining the furnace pressure <10Pa, and holding the temperature for 30~240min.

[0033] In practical applications, the reason for controlling the above-mentioned vacuum firing process is to perform deoxidation and decarburization, so as to promote atomic diffusion and help sintering densification.

[0034] It should be noted that, in order to avoid oxidation of the steel in the sintering furnace, in step S2, when the negative pressure degreasing and sintering treatment is carried out in the sintering furnace, the atmosphere inside the sintering furnace can be set to inert. For example, nitrogen is usually blown into the sintering furnace during negative pressure degreasing, and argon is usually used in the sintering furnace during the sintering treatment.

[0035] In this invention, in practical application, after completing the negative pressure degreasing, vacuum firing, and sintering treatment of the product to be sintered as shown in step S2, when performing the hot isostatic pressing treatment as shown in step S3 on the obtained sintered part, the hot isostatic pressing treatment can specifically adopt the following process: The sintered part is heated to 1050~1200℃, the pressure inside the furnace is maintained at >100MPa, and the temperature is held for 60~360min. Then it is cooled to room temperature with the furnace to obtain wear-resistant steel.

[0036] Therefore, based on the process parameters of the hot isostatic pressing treatment mentioned above, isotropic pressure can be applied to the material under high temperature and high pressure, which promotes the healing of internal defects in the steel, thereby improving the density and microstructure uniformity of wear-resistant steel.

[0037] In addition, see further Figure 1 As shown, in order to further improve the mechanical properties of wear-resistant steel, in one embodiment, the metal powder injection molding method designed by the present invention further includes step S4, that is, heat treatment of the obtained wear-resistant steel. The purpose of heat treatment is to make the material have high toughness to meet the application requirements, which generally includes, but is not limited to, quenching treatment and tempering treatment.

[0038] In practical applications, the above tempering process can be specifically described as follows: the quenched wear-resistant steel is heated to the first tempering temperature under vacuum conditions and held at that temperature for a first preset time, and then air-cooled to room temperature to complete the first tempering; the wear-resistant steel after the first tempering is heated to the second tempering temperature under vacuum conditions and held at that temperature for a second preset time, and then air-cooled to room temperature to complete the second tempering.

[0039] To demonstrate that the metal powder injection molding method designed in this invention can produce wear-resistant steel with high density, uniform microstructure, and good mechanical properties, this invention also conducted specific experimental verification, and the following Example 1 and comparative documents 1-3 are provided for verification and illustration: Example 1: The wear-resistant steel alloy powder selected in this embodiment 1 has the following composition: C: 1.5 wt.%, Cr: 12 wt.%, Mo: 0.9 wt.%, V: 0.3 wt.%, Ni: 0.1 wt.%, and the balance Fe; wherein the particle size of the wear-resistant steel alloy powder is <20 μm.

[0040] In this Example 1, wear-resistant steel alloy powder and binder are added to a mixer at a mass ratio of 10:1 and kneaded evenly to obtain feed and then granulated; then the crushed and granulated feed is injection molded to obtain green body; wherein, the binder is composed of 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer and the balance stearic acid.

[0041] In this embodiment 1, the granulated feedstock is specifically injection molded in an injection molding machine and a mold to obtain a green preform; wherein, the injection temperature of the injection molding machine is 195°C, the injection pressure is 200MPa, the holding pressure is 120MPa, and the mold temperature is 100°C.

[0042] Accordingly, the injection-molded green body is catalytically degreased with nitric acid at a flow rate of 4 g / min, a degreasing temperature of 100°C, and a degreasing time of 8.5 h to obtain the product to be sintered.

[0043] Then, the product to be sintered after catalytic degreasing is placed in a sintering furnace for negative pressure degreasing. Nitrogen gas is purged into the sintering furnace at a flow rate of 50 L / min. Simultaneously, during the negative pressure degreasing process, the furnace temperature is increased to 300℃ at a rate of 2.5℃ / min and held for 60 min; then increased to 450℃ at a rate of 2℃ / min and held for 150 min; then increased to 550℃ at a rate of 2℃ / min and held for 120 min; finally, increased to 600℃ at a rate of 2.5℃ / min and held for 30 min, thus completing the negative pressure degreasing process.

[0044] After the negative pressure degreasing is completed, the product to be sintered is further subjected to vacuum firing, that is, the temperature is raised to 1050℃ at a heating rate of 2℃ / min, and the gas pressure inside the furnace is kept <10Pa for 120min to complete the vacuum firing process.

[0045] The material is then sintered in a sintering furnace, where it is heated to 1230°C at a rate of 0.5°C / min and held at that temperature for 120 minutes. During the sintering process, the furnace atmosphere is argon. After sintering, the material is cooled in the furnace until it reaches the desired temperature, thus obtaining the sintered part.

[0046] Accordingly, in this Example 1, after obtaining the above-mentioned sintered part, the sintered part is heated to 1150°C, the pressure inside the furnace is maintained at >120MPa, and the temperature is held for 180 minutes. Then, it is cooled with the furnace to obtain wear-resistant steel after hot isostatic pressing treatment.

[0047] Finally, the obtained wear-resistant steel was subjected to heat treatment: the wear-resistant steel was held at 1040℃ for 60 minutes under vacuum, and then rapidly cooled to room temperature using nitrogen gas at 800 kPa as the cooling medium to complete the quenching treatment; then the quenched sample was held at 580℃ for 240 minutes under vacuum, and then air-cooled to room temperature to complete the first tempering. This process was then repeated once more, holding at 580℃ for 240 minutes under vacuum and then air-cooling to room temperature for the second tempering, to obtain the wear-resistant steel of Example 1.

[0048] Comparative Example 1: The wear-resistant steel alloy powder selected in Comparative Example 1 has the following material composition: C: 1.5 wt.%, Cr: 12 wt.%, Mo: 0.9 wt.%, V: 0.3 wt.%, Ni: 0.1 wt.%, and the balance Fe; wherein the particle size of the wear-resistant steel alloy powder is <20 μm.

[0049] In Comparative Example 1, wear-resistant steel alloy powder and binder were added to a mixer at a mass ratio of 10:1 and kneaded evenly to obtain feed and granulation; then the crushed and granulated feed was injection molded to obtain green body; wherein, the binder was composed of 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer and the balance stearic acid.

[0050] Accordingly, the granulated feedstock is injection molded in an injection molding machine and a mold to obtain a green preform; wherein, the injection temperature of the injection molding machine is 195℃, the injection pressure is 200MPa, the holding pressure is 120MPa, and the mold temperature is 100℃.

[0051] Meanwhile, the injection-molded green body is degreased using nitric acid to obtain the product to be sintered. The acid flow rate is 4 g / min, the degreasing temperature is 100℃, and the degreasing time is 8.5 h.

[0052] Based on this, the product to be sintered after catalytic degreasing is placed in a sintering furnace and subjected to negative pressure degreasing, vacuum firing and sintering in sequence.

[0053] During the negative pressure degreasing process, nitrogen gas is introduced into the sintering furnace at a flow rate of 50 L / min. Simultaneously, the furnace temperature is raised to 300℃ at a heating rate of 2.5℃ / min and held for 60 min. Then, the furnace temperature is raised to 450℃ at a heating rate of 2℃ / min and held for 150 min. Next, the furnace temperature is raised to 550℃ at a heating rate of 2℃ / min and held for 120 min. Finally, the furnace temperature is raised to 600℃ at a heating rate of 2.5℃ / min and held for 30 min to complete the negative pressure degreasing process.

[0054] Meanwhile, after completing the negative pressure degreasing, the temperature of the product to be sintered is raised to 1050℃ at a heating rate of 2℃ / min, and the gas pressure inside the furnace is kept <10Pa for 120min to complete the vacuum firing process.

[0055] The temperature was then increased to 1230℃ at a rate of 0.5℃ / min and held for 120 minutes to complete the sintering process. The furnace atmosphere was argon. After sintering, the furnace was cooled to the required temperature to obtain the sintered part.

[0056] Accordingly, in Comparative Example 1, after obtaining the sintered part, hot isostatic pressing was not performed. Instead, the sintered part was directly used as the finished wear-resistant steel product and subjected to subsequent heat treatment. Specifically, the sintered part was held at 1040°C for 60 minutes under vacuum conditions, and then rapidly cooled to room temperature using nitrogen gas at 800 kPa as the cooling medium to complete the quenching treatment. Then, the quenched wear-resistant steel was held at 580°C for 240 minutes under vacuum conditions, and then air-cooled to room temperature to complete the first tempering. Subsequently, it was held at 580°C for 240 minutes under vacuum conditions, and then air-cooled to room temperature to complete the second tempering, thereby obtaining the wear-resistant steel of Comparative Example 1.

[0057] Comparative Example 2: The material composition of the wear-resistant steel alloy powder selected in Comparative Example 2 is C: 1.5wt.%, Cr: 12wt.%, Mo: 0.9wt.%, V: 0.3wt.%, Ni: 0.1wt.%, and the balance Fe; wherein, the particle size of the wear-resistant steel alloy powder is <20μm.

[0058] In Comparative Example 2, wear-resistant steel alloy powder and binder were added to a mixer at a mass ratio of 10:1 and kneaded evenly to obtain feed and granulation; then the crushed and granulated feed was injection molded to obtain green body; wherein, the binder was composed of 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer and the balance stearic acid.

[0059] Accordingly, the granulated feedstock is injection molded in an injection molding machine and a mold to obtain a green preform; wherein, the injection temperature of the injection molding machine is 195℃, the injection pressure is 200MPa, the holding pressure is 120MPa, and the mold temperature is 100℃.

[0060] Meanwhile, the injection-molded green body is degreased using nitric acid to obtain the product to be sintered. The acid flow rate is 4 g / min, the degreasing temperature is 100℃, and the degreasing time is 8.5 h.

[0061] Based on this, the product to be sintered after catalytic degreasing is placed in a sintering furnace and subjected to negative pressure degreasing, vacuum firing and sintering in sequence.

[0062] During the negative pressure degreasing process, nitrogen gas is introduced into the sintering furnace at a flow rate of 50 L / min. Simultaneously, the furnace temperature is raised to 300℃ at a heating rate of 2.5℃ / min and held for 60 min. Then, the furnace temperature is raised to 450℃ at a heating rate of 2℃ / min and held for 150 min. Next, the furnace temperature is raised to 550℃ at a heating rate of 2℃ / min and held for 120 min. Finally, the furnace temperature is raised to 600℃ at a heating rate of 2.5℃ / min and held for 30 min, thus completing the negative pressure degreasing process.

[0063] During the vacuum firing process, the temperature is raised to 1050℃ at a heating rate of 2℃ / min, and the gas pressure inside the furnace is kept <10Pa for 120min to complete the vacuum firing process.

[0064] The temperature was then increased to 1230℃ at a rate of 2℃ / min, and held for 120 minutes to complete the sintering process. In Comparative Example 2, the sintering process used a conventional heating rate, rather than a slower one.

[0065] Furthermore, in Comparative Example 2, the furnace atmosphere in the sintering section was argon, and the sintered part was obtained by cooling with the furnace after sintering. Then, the sintered part was subjected to hot isostatic pressing treatment, that is, the sintered part was heated to 1150°C, the furnace pressure was maintained at >120MPa, and the temperature was held for 180min, and then cooled with the furnace to obtain wear-resistant steel.

[0066] Accordingly, the obtained wear-resistant steel was also subjected to heat treatment, namely, the wear-resistant steel was held at 1040℃ for 60 min under vacuum conditions, and then rapidly cooled to room temperature with nitrogen gas at 800 kPa as the cooling medium to complete the quenching treatment; then the quenched wear-resistant steel was held at 580℃ for 240 min under vacuum conditions, and then air-cooled to room temperature to complete the first tempering; then it was held at 580℃ for 240 min under vacuum conditions again, and then air-cooled to room temperature to complete the second tempering, so as to obtain the wear-resistant steel of Comparative Example 2.

[0067] Comparative Example 3: The wear-resistant steel alloy powder selected in Comparative Example 3 has the following material composition: C: 1.5 wt.%, Cr: 12 wt.%, Mo: 0.9 wt.%, V: 0.3 wt.%, Ni: 0.1 wt.%, and the balance Fe; wherein, the particle size of the wear-resistant steel alloy powder is <20 μm.

[0068] In Comparative Example 3, wear-resistant steel alloy powder and binder were added to a mixer at a mass ratio of 10:1 and kneaded evenly to obtain feed and granulation; then the crushed and granulated feed was injection molded to obtain green body; wherein, the binder was composed of 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer and the balance stearic acid.

[0069] Accordingly, the granulated feedstock is injection molded in an injection molding machine and a mold to obtain a green preform; wherein, the injection temperature of the injection molding machine is 195℃, the injection pressure is 200MPa, the holding pressure is 120MPa, and the mold temperature is 100℃.

[0070] In Comparative Example 3, the injection-molded green body was degreased using nitric acid to obtain the product to be sintered; the acid flow rate was 4 g / min, the degreasing temperature was 100℃, and the degreasing time was 8.5 h.

[0071] Accordingly, the product to be sintered is placed in a sintering furnace and subjected to negative pressure degreasing, vacuum firing and sintering in sequence.

[0072] During the negative pressure degreasing process, nitrogen gas is introduced into the sintering furnace at a flow rate of 50 L / min. Simultaneously, the furnace temperature is raised to 300℃ at a heating rate of 2.5℃ / min and held for 60 min. Then, the furnace temperature is raised to 450℃ at a heating rate of 2℃ / min and held for 150 min. Next, the furnace temperature is raised to 550℃ at a heating rate of 2℃ / min and held for 120 min. Finally, the furnace temperature is raised to 600℃ at a heating rate of 2.5℃ / min and held for 30 min, thus completing the negative pressure degreasing process.

[0073] During the vacuum firing process, the temperature is raised to 1050℃ at a heating rate of 2℃ / min, and the gas pressure inside the furnace is kept <10Pa for 120min to complete the vacuum firing process.

[0074] Simultaneously, the temperature is increased to 1230℃ at a heating rate of 2℃ / min, and held for 120 minutes to complete the sintering process. During the sintering section, the furnace is filled with an argon atmosphere, and the sintered parts are obtained by cooling the furnace after sintering.

[0075] It should be noted that in Comparative Example 3, neither hot isostatic pressing nor temperature rise rate was controlled; the vacuum firing and sintering processes both used conventional temperature rise rates.

[0076] In Comparative Example 3, the sintered part was held at 1040℃ for 60 min under vacuum conditions, and then rapidly cooled to room temperature using nitrogen gas at 800 kPa as the cooling medium to complete the quenching treatment. The quenched wear-resistant steel was then held at 580℃ for 240 min under vacuum conditions, and then air-cooled to room temperature to complete the first tempering. Subsequently, it was held at 580℃ for 240 min under vacuum conditions, and then air-cooled to room temperature to complete the second tempering, thereby obtaining the wear-resistant steel of Comparative Example 3.

[0077] Therefore, it is evident that by comparing the metal powder forming methods of the wear-resistant steel in Comparative Examples 1-3 with the metal powder forming direction of the wear-resistant steel in Example 1 of the present invention, it is not difficult to see that: compared with Example 1, Comparative Example 1 did not use the hot isostatic pressing process; Comparative Example 2 used a conventional heating rate and did not use a lower heating rate; Comparative Example 3 neither performed hot isostatic pressing nor controlled the heating rate.

[0078] Samples of the wear-resistant steel of Example 1 and the wear-resistant steel of Comparative Examples 1-3 obtained through the above process steps were taken, and the wear-resistant steel of Example 1 and the wear-resistant steel of Comparative Examples 1-3 were cut, ground, polished and etched. Metallographic observation and photography were performed using a metallographic microscope to analyze the metallographic structure. Meanwhile, the wear-resistant steel of Example 1 and the wear-resistant steel of Comparative Examples 1-3 were subjected to mechanical property testing, namely, tensile testing, to test their mechanical properties. The specific method of tensile testing was carried out in accordance with the national standard GB / T228.1-2021 to obtain the yield strength and elongation of the wear-resistant steel of Example 1 and the wear-resistant steel of Comparative Examples 1-3.

[0079] The results of the mechanical property tests and the metallographic structures obtained from the analysis are listed in Table 1: Table 1.

[0080] As can be seen from Table 1 above, the wear-resistant steel of Example 1 prepared by the metal powder injection molding method of the wear-resistant steel designed in this invention has excellent yield strength and elongation. Specifically, its yield strength is 1330 MPa and its elongation is 4.5%. The yield strength of the wear-resistant steel of Example 1 is higher than that of the wear-resistant steel of Comparative Examples 1-3, and the elongation of the wear-resistant steel of Example 1 is significantly greater than that of the wear-resistant steel of Comparative Examples 1-3, indicating that it has good mechanical properties.

[0081] Accordingly, see Table 1, and in conjunction with Figures 2-5Analysis of the metallographic structures of the wear-resistant steels in Example 1 and Comparative Examples 1-3 clearly shows that the wear-resistant steel of Example 1 prepared by the present invention has excellent density, a uniform metallographic structure, and virtually no coarse carbides forming at grain boundaries. While the metallographic structure of the wear-resistant steel in Comparative Example 1 is uniform, it has many internal pores and a low degree of densification. The metallographic structure of the wear-resistant steel in Comparative Example 2 has fewer internal pores, but significant coarse carbides at its grain boundaries. The metallographic structure of the wear-resistant steel in Comparative Example 3 has more pores, and coarse carbides are present at grain boundaries. Therefore, the wear-resistant steel prepared by the metal powder injection molding method of the present invention has a uniform metallographic structure and satisfactory density.

[0082] In summary, the metal powder injection molding method for wear-resistant steel designed in this invention can effectively prepare wear-resistant steel that balances density and microstructure uniformity, resulting in excellent mechanical properties. Furthermore, the use of metal powder injection molding to prepare wear-resistant steel materials overcomes the geometric limitations of traditional processing methods, enabling near-net-shape forming of wear-resistant steel parts with complex three-dimensional shapes, minute dimensions, and high precision in a single step. This process fully combines the technical advantages of powder metallurgy and injection molding, providing a feasible technical path for the mass production and low-cost manufacturing of precision wear-resistant components in high-end equipment.

[0083] Furthermore, this invention strictly controls the heating rate during the vacuum sintering process, especially slowing down the heating rate of the closed pores in the material after vacuum sintering. This process control is beneficial in two ways: firstly, it extends the formation and growth time of the sintering neck, promotes spheroidization and shrinkage of pores, and contributes to the densification of the material; secondly, by slowing down the heating rate, it can effectively suppress the formation of network carbides caused by local carbon enrichment, preventing their continuous distribution at grain boundaries, thereby significantly improving the toughness of the material and solving the problem of early fracture caused by microstructural embrittlement in wear-resistant steel under traditional rapid heating processes.

[0084] Furthermore, the metal powder injection molding method for wear-resistant steel designed in this invention incorporates a hot isostatic pressing (HIP) process after sintering. By applying isotropic pressure to the material under high temperature and high pressure, internal defects are healed, significantly improving the density and microstructure uniformity of the product. This process effectively compensates for the shortcomings of conventional metal powder injection molding methods, which struggle to completely eliminate microscopic defects during sintering. It allows the wear-resistant steel material to achieve high density while maintaining normal grain structure and carbide distribution, avoiding the technical contradiction of coarsening of the microstructure or deterioration of performance due to excessive pursuit of densification.

[0085] Therefore, this invention successfully solves the common industry problem of difficulty in achieving both density and microstructure uniformity when preparing wear-resistant steel using existing metal powder injection molding methods. It significantly improves the comprehensive mechanical properties and service reliability of wear-resistant steel, and has good prospects for promotion and application value.

[0086] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for injection molding wear-resistant steel using metal powder, characterized in that, Including the following steps: S1: Wear-resistant steel alloy powder is injection molded to obtain a green body, and the green body is catalytically degreased to obtain a product to be sintered; S2: The product to be sintered is placed in a sintering furnace and subjected to negative pressure degreasing, vacuum firing and sintering in sequence to obtain a sintered part; wherein, the sintering process is: the furnace temperature is raised to 1220~1240℃ at a heating rate of 0.1~1℃ / min and held for 60~360min. S3: The sintered part is subjected to hot isostatic pressing to obtain wear-resistant steel.

2. The metal powder injection molding method according to claim 1, characterized in that, In step S2, the negative pressure degreasing is performed as follows: the furnace temperature is raised from room temperature to 250-350°C at a heating rate of 0.1-10°C / min and held for 0-180 min; the temperature is then raised to 400-500°C at a heating rate of 0.1-10°C / min and held for 0-180 min; the temperature is then raised to 550-800°C at a heating rate of 0.1-10°C / min and held for 0-180 min.

3. The metal powder injection molding method according to claim 1, characterized in that, In step S2, the vacuum firing process involves raising the furnace temperature to 1000-1180°C at a heating rate of 0.1-10°C / min, maintaining the furnace pressure at <10Pa, and holding the temperature for 30-240 minutes.

4. The metal powder injection molding method according to claim 1, characterized in that, In step S3, the sintered part is subjected to hot isostatic pressing treatment, specifically as follows: The sintered part is heated to 1050~1200℃, the pressure inside the furnace is maintained at >100MPa, and the temperature is held for 60~360min. Then it is cooled to room temperature with the furnace to obtain wear-resistant steel.

5. The metal powder injection molding method according to claim 1, characterized in that, In step S1, green blanks are obtained by injection molding based on wear-resistant steel alloy powder, specifically: the wear-resistant steel alloy powder is kneaded with a binder to prepare a feedstock; the feedstock is crushed and granulated; and the crushed and granulated feedstock is injection molded to obtain green blanks.

6. The metal powder injection molding method according to claim 5, characterized in that, The adhesive comprises: polyoxymethylene, polyethylene, paraffin wax, ethylene-vinyl acetate copolymer, and stearic acid.

7. The metal powder injection molding method according to claim 1, characterized in that, The particle size of the wear-resistant steel alloy powder is ≤50μm.

8. The metal powder injection molding method according to claim 1, characterized in that, In step S1, the relative degreasing rate of the green body undergoing catalytic degreasing is >96%.

9. The metal powder injection molding method according to claim 1, characterized in that, It also includes step S4: heat treating the obtained wear-resistant steel.

10. The metal powder injection molding method according to claim 9, characterized in that, The heat treatment includes quenching and tempering, wherein the tempering process specifically involves: The quenched wear-resistant steel is heated to the first tempering temperature under vacuum conditions and held at that temperature for a first preset time, and then air-cooled to room temperature to complete one tempering process. The wear-resistant steel after the first tempering is heated to the second tempering temperature under vacuum and held at that temperature for a second preset time, and then air-cooled to room temperature to complete the second tempering.

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