Cold pressing forming method for spherical high-speed steel powder

Abstract

The invention belongs to the technical field of powder metallurgy, and particularly relates to a spherical high-speed steel powder cold press forming method which comprises the following steps: step 1, material preparation: selecting spherical high-speed steel powder and a binder in a set proportion as raw materials; 2, material mixing is conducted, specifically, the binder in the step 1 is heated, then the spherical high-speed steel powder is added for mixing and stirring, a mixture is obtained, then the mixture is heated and stirred at least once, and a uniformly-mixed to-be-pressed mixture is obtained; and (3) cold pressing forming is conducted, specifically, the to-be-pressed mixture obtained in the step (2) is put into pressure equipment to be subjected to pressure forming, then cooling is conducted, material returning is conducted, and a high-speed steel powder cold blank is obtained. The prepared high-speed steel cold blank is good in forming and firm in combination, the preparation process is simple and convenient, demolding is easy, and the cold pressing forming problem which cannot be solved by cold isostatic pressing and other processes is effectively solved. The prepared high-speed steel cold blank can be used for sintering and preparing high-speed steel parts.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a method for cold pressing spherical high-speed steel powder. Background Art

[0002] Since high-speed steel powder contains a large amount of carbide phase, it is difficult for the surface of spherical particles to undergo plastic deformation under pressure, and it is difficult for the particles to fit together and bite each other, which makes it difficult to press and form at room temperature or lower temperatures. Therefore, the cold pressing of spherical high-speed steel powder becomes a difficult problem. In addition, if a suitable process is adopted to form it by molding, whether the cold billet can maintain its shape well during demolding becomes another difficult problem. Powder cold pressing and cold isostatic pressing commonly used in research and production require corresponding professional molds, and are often used for low-temperature pressing of metal powders with good plasticity of irregular particle shapes. It can be seen that these two methods are not suitable for spherical powders. Therefore, another way to form spherical powders is needed, such as using reagent-assisted forming.

[0003] Selecting a suitable binder is crucial for metal powder forming. Generally, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), anhydrous ethanol, aviation kerosene, paraffin, carnauba wax, high-density polyethylene resin, polyethylene, polypropylene and stearic acid are often used as related binders and auxiliary agents for metal powder pressing, such as document 1, PowderTechnol. 2009; 193: 162-169, document 2, Mater. Lett. 2023; 342: 134341, document 3, PowderTechnol. 2024; 433: 119214, document 4, Ceram. Int. 2023; 49: 23140-23152.

[0004] By combining one or more of the above reagents, metal powder can be well formed at a lower temperature under a suitable process, and a good cold billet can be pressed out by using a suitable release agent. However, the process of the existing public technology is relatively complicated, which seriously affects the research and development and production efficiency, such as the process described in document 5, J. Mater. Res. Technol. 2024;29: 4433-4444 and the Chinese patent application number CN202110907515.X, entitled A method for preparing complex-shaped powder high-speed steel micro parts.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and to propose a method for cold pressing spherical high-speed steel powder. The method uses spherical high-speed steel powder and a binder in a set proportion as raw materials, and through a simple process, the spherical high-speed steel powder is cold pressed and demolded into a high-speed steel powder cold billet, thereby solving the problems of difficulty, low efficiency and complex process in cold pressing spherical high-speed steel powder.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: In one aspect, the present invention provides a method for cold pressing spherical high-speed steel powder, comprising the following steps: Step 1, material preparation: select spherical high-speed steel powder and binder in a set ratio as raw materials; Step 2, mixing: heating the binder in step 1, then adding the spherical high-speed steel powder to mix and stir to obtain a mixture, and then heating and stirring the mixture at least once to obtain a uniformly mixed mixture to be pressed; Step 3, cold pressing: placing the mixed material to be pressed obtained in step 2 into a pressure device for pressure forming, followed by cooling and withdrawing the material to obtain a high-speed steel powder cold billet.

[0008] Specifically, the spherical high-speed steel powder is tungsten-based high-speed steel powder with a spherical structure and an average particle size of less than 150 μm.

[0009] Furthermore, in step 1, the mass ratio of the spherical high-speed steel powder to the binder is (55-70): (30-45).

[0010] Furthermore, in step 1, the binder includes the following components in percentage by mass: 45% to 59% paraffin, 1% to 5% stearic acid and 40% to 50% high-density polyethylene resin.

[0011] Furthermore, in step 1, the binder comprises the following components in percentage by mass: 45% to 59% carnauba wax, 1% to 5% stearic acid and 40% to 50% polyvinyl alcohol.

[0012] It should be noted that the composition ratio of the binder in the present invention is set to maintain the fluidity and adhesion of the binder solution at the corresponding temperature and facilitate lubrication and demolding; the ratio of spherical high-speed steel powder and binder is set to consider the uniformity of powder distribution and the density of the back-end parts during sintering. Specifically, if the binder content is less than the above range, the spherical high-speed steel powder particles are easy to agglomerate and difficult to disperse; if the binder content is more than the above range, the gaps between the spherical high-speed steel powder particles are too large, which is not conducive to the removal of the binder during the later sintering, and the high-speed steel is not easy to form. On the other hand, it is difficult for the powder particles to sinter together during sintering, and the high-speed steel pores are mostly not dense, resulting in difficulty in forming.

[0013] Furthermore, in step 2, the process of heating the binder is specifically as follows: firstly heating to 140°C~200°C at a rate of 5°C / min~30°C / min, and then keeping the temperature for 5min~15min.

[0014] It should be noted that the binder is heated to be in a solution state, and then the spherical high-speed steel powder is added to the binder as a solvent, so that the binder and the spherical high-speed steel powder can be mixed evenly.

[0015] Furthermore, in step 2, the process of heating the mixture each time is as follows: keeping the mixture at 140° C. to 200° C. for 5 min to 15 min.

[0016] It should be noted that multiple heating is performed to make the mixture better and more evenly mixed.

[0017] Furthermore, in step 2, during the stirring process, the stirring speed is set to 60 r / min~300 r / min, and the stirring time is set to 5 min~15 min.

[0018] Furthermore, in step 3, during the pressurizing process, the pressurizing time is set to 5 min to 25 min, the pressure is set to 5 MPa to 30 MPa, the temperature is set to 50°C to 110°C, and the heat preservation and pressure holding time is set to 5 min to 15 min.

[0019] It should be noted that, during the pressurizing process, the pressurizing time range of the present invention is conducive to the uniform forming of high-speed steel powder. If it is too fast, cracks are likely to occur, and if it is too slow, the time cost is high; the pressure range of the present invention is sufficient to form the current high-speed steel powder. Too much pressure will directly lead to stress cracking, and too little pressure will not allow forming or the density will be low; the temperature range of the present invention puts the binder in a softened state, which is conducive to the pressing and forming of high-speed steel. If the temperature is lower than the set range, the binder has solidified and cannot be pressurized. If the temperature is higher than the set range, the binder is still in a low-fluidity melting state; the heat preservation and pressure holding time range of the present invention can better densify the high-speed steel powder.

[0020] Furthermore, in step 3, the cooling is natural cooling, and the cooling time is 5 min to 15 min.

[0021] Furthermore, in step 3, the pressure equipment is a press.

[0022] On the other hand, the present invention provides a method for cold pressing spherical high-speed steel powder as described above, and the obtained high-speed steel powder cold billet is used for sintering to prepare high-speed steel parts.

[0023] Specifically, the high-speed steel parts include micro-cutting tools, gears and other wear-resistant parts, wherein the HRC value of the high-speed steel parts is 55-68.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention provides a method for cold pressing spherical high-speed steel powder. Aiming at the characteristics that spherical high-speed steel powder contains a large amount of multi-type carbides and is difficult to undergo plastic deformation to embed into each other for forming, the present invention achieves efficient low-temperature forming of spherical high-speed steel powder by setting a proportion of binder and combining a specific process. The high-speed steel cold billet finally prepared has good forming and firm bonding, and the preparation process is simple, which effectively solves the problem of cold pressing of spherical high-speed steel powder that cannot be solved by processes such as cold isostatic pressing.

[0025] 2) Spherical high-speed steel powder has low plasticity, is difficult to form well at low temperature, and has low pressing strength, which makes it difficult to demold. The present invention provides a method for cold pressing of spherical high-speed steel powder. Through press forming and cooling, the pressed blank will shrink. This is because after using the raw materials with a set ratio in the present invention, the binder changes from a melting state at a higher temperature to a solidified state at a low temperature, and its volume will shrink. Therefore, the high-speed steel cold blank is easy to demold, and can be directly demolded without additional demolding agents and demolding molds. After demolding, the cold blank has high bonding strength and is not easy to scatter.

[0026] 3) The present invention provides a method for cold pressing spherical high-speed steel powder. The high-speed steel cold billet prepared by the method has high forming efficiency, and high-speed steel cold billets of different shapes can be prepared according to the press cavity or mold; and the high-speed steel cold billet can be prepared on an assembly line, which is easy to realize industrial production and can be used for sintering to prepare high-speed steel parts such as micro tools. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the present invention.

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0029] Figure 1 This is a flow chart of the method for cold pressing spherical high-speed steel powder of the present invention; Figure 2 This is a macroscopic optical picture of the high-speed steel powder cold billet in Example 1 of the present invention; Figure 3This is a microscopic optical picture of the high-speed steel powder cold billet in Example 1 of the present invention; Figure 4 This is a microscopic optical picture of the high-speed steel powder cold billet in Example 2 of the present invention; Figure 5 This is a microscopic optical picture of the high-speed steel powder cold billet in Example 3 of the present invention; Figure 6 This is a microscopic optical picture of the high-speed steel powder cold billet in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] Here, exemplary embodiments will be described in detail, and the embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are only examples consistent with some aspects of the present invention described in detail in the appended claims. Example 1

[0031] On the one hand, see Figure 1 This embodiment provides a method for cold pressing spherical high-speed steel powder, comprising the following steps: Step 1, selecting spherical high-speed steel powder and binder with a mass ratio of 55:45 as raw materials; The binder comprises the following components in percentage by mass: 45% paraffin wax, 5% stearic acid and 50% high-density polyethylene resin; Step 2, heating the binder in step 1 to 140°C at a rate of 5°C / min, keeping the temperature for 5 minutes, then adding the spherical high-speed steel powder in step 1 to the heated binder from top to bottom, stirring with a stirrer at a speed of 60r / min for 5 minutes to obtain a mixture; Step 3, keeping the mixture obtained in step 2 at 140° C. for 5 minutes, and then stirring with a stirrer at a stirring speed of 60 r / min for 5 minutes to obtain a uniformly mixed mixture to be pressed; Step 4, putting the mixture to be pressed obtained in step 3 into a press for press forming, then naturally cooling for 5 minutes, and then slowly withdrawing the material from the press to obtain a high-speed steel powder cold billet with a diameter of 30 mm, a height of 20 mm, a dense microstructure, and uniformly dispersed powder particles without agglomeration; During the press forming process, the press time was set to 5 min, the pressure was 5 MPa, the temperature was 50°C, and the heat preservation and pressure holding time was 5 min.

[0032] The high speed steel powder cold blank obtained by cold pressing in this embodiment is as follows Figure 2 and Figure 3 As shown by Figure 2It can be seen that the high-speed steel powder cold billet prepared in this embodiment is well formed and firmly bonded; Figure 3 It can be seen that the particles in the high-speed steel powder cold billet prepared in this embodiment are evenly distributed, without agglomeration, and no defects such as holes are found.

[0033] On the other hand, this embodiment provides a method for cold pressing spherical high-speed steel powder as described above. The obtained high-speed steel powder cold billet is used for sintering to prepare high-speed steel parts, such as micro-tools, gears and other wear-resistant parts. Example 2

[0034] This embodiment provides a method for cold pressing spherical high-speed steel powder, comprising the following steps: Step 1, selecting spherical high-speed steel powder and binder with a mass ratio of 70:30 as raw materials; The binder comprises the following components in percentage by mass: 59% paraffin wax, 1% stearic acid and 40% high-density polyethylene resin; Step 2, heating the binder in step 1 to 200° C. at a rate of 30° C. / min, and keeping the temperature for 15 minutes, then adding the spherical high-speed steel powder in step 1 into the heated binder while stirring, and stirring with a stirrer at a speed of 300 r / min for 15 minutes to obtain a mixture; Step 3, the mixture obtained in step 2 is kept at 200° C. for 15 minutes, and then kept at 160° C. for 8 minutes, and stirred with a stirrer during the insulation process, the stirring speed is 300 r / min, and the stirring time is 15 minutes to obtain a uniformly mixed mixture to be pressed; Step 4, placing the mixture to be pressed obtained in step 3 into a press for press forming, then naturally cooling for 15 minutes, and then slowly withdrawing the material from the press to obtain a high-speed steel powder cold billet with a diameter of 20 mm and a height of 25 mm; During the press forming process, the press time was set to 25 minutes, the pressure was 30 MPa, the temperature was 110°C, and the heat preservation and pressure holding time was 15 minutes.

[0035] like Figure 4 This is an optical photograph of the microstructure of the high-speed steel powder cold billet prepared in this embodiment after polishing. It can be seen from the figure that the high-speed steel powder cold billet has a dense structure without cracks or holes, and the high-speed steel powder particles are evenly dispersed without agglomeration. Example 3

[0036] This embodiment provides a method for cold pressing spherical high-speed steel powder, comprising the following steps: Step 1, selecting spherical high-speed steel powder and binder with a mass ratio of 62.5:37.5 as raw materials; The binder comprises the following components in percentage by mass: 52% paraffin wax, 3% stearic acid and 45% high-density polyethylene resin; Step 2, heating the binder in step 1 to 170°C at a rate of 17.5°C / min, keeping the temperature for 10 minutes, then adding the spherical high-speed steel powder in step 1 into the heated binder, stirring with a stirrer at a speed of 180r / min for 10 minutes to obtain a mixture; Step 3: The mixture obtained in step 2 is kept at 190° C. for 12 minutes, and then stirred with a stirrer at a stirring speed of 180 r / min for 10 minutes to obtain a uniformly mixed mixture to be pressed. Step 4, putting the mixture to be pressed obtained in step 3 into a press for press forming, then naturally cooling for 10 minutes, and then slowly withdrawing the material from the press to obtain a high-speed steel powder cold billet with a diameter of 10 mm, a height of 50 mm, a dense microstructure, and uniformly dispersed powder particles without agglomeration; During the press forming process, the press time was set to 15 minutes, the pressure was 17.5 MPa, the temperature was 80°C, and the heat preservation and pressure holding time was 10 minutes.

[0037] like Figure 5 This is an optical photograph of the microstructure of the high-speed steel powder cold billet prepared in this embodiment after polishing. It can be seen from the figure that the high-speed steel powder cold billet has a dense structure without cracks or holes, and the high-speed steel powder particles are tightly embedded in the binder. Example 4

[0038] This embodiment provides a method for cold pressing spherical high-speed steel powder, comprising the following steps: Step 1, selecting spherical high-speed steel powder and binder with a mass ratio of 60:40 as raw materials; The binder comprises the following components in percentage by mass: 50% paraffin, 2% stearic acid and 48% high-density polyethylene resin; Step 2, heating the binder in step 1 to 160° C. at a rate of 20° C. / min, keeping the temperature for 8 min, then adding the spherical high-speed steel powder in step 1 to the heated binder from top to bottom, stirring with a stirrer at a speed of 200 r / min for 8 min to obtain a mixture; Step 3, keeping the mixture obtained in step 2 at 160° C. for 8 min, and then stirring with a stirrer at a stirring speed of 200 r / min for 8 min to obtain a uniformly mixed mixture to be pressed; Step 4, putting the mixture to be pressed obtained in step 3 into a press for press forming, then naturally cooling for 8 minutes, and then slowly withdrawing the material from the press to obtain a high-speed steel powder cold billet with a diameter of 50 mm, a height of 10 mm, a dense microstructure, and uniformly dispersed powder particles without agglomeration; During the press forming process, the press time was set to 10 min, the pressure was 10 MPa, the temperature was 100°C, and the heat preservation and pressure holding time was 8 min.

[0039] like Figure 6 This is an optical photograph of the microstructure of the high-speed steel powder cold billet prepared in this embodiment. It can be seen from the figure that the high-speed steel powder cold billet has a dense structure without cracks or holes, and the high-speed steel powder particles are evenly dispersed without agglomeration.

[0040] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0041] It should be understood that the present invention is not limited to what has been described above and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for cold pressing spherical high-speed steel powder, characterized in that: The following steps are involved: Step 1, material preparation: select spherical high-speed steel powder and binder in a set ratio as raw materials; Step 2, mixing: heating the binder in step 1, then adding the spherical high-speed steel powder to mix and stir to obtain a mixture, and then heating and stirring the mixture at least once to obtain a uniformly mixed mixture to be pressed; Step 3, cold pressing: placing the mixed material to be pressed obtained in step 2 into a pressure device for pressure forming, followed by cooling and withdrawing the material to obtain a high-speed steel powder cold billet.

2. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 1, the mass ratio of the spherical high-speed steel powder to the binder is (55-70): (30-45).

3. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 1, the binder includes the following components in percentage by mass: 45% to 59% paraffin, 1% to 5% stearic acid and 40% to 50% high-density polyethylene resin.

4. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 1, the binder includes the following components in percentage by mass: 45% to 59% carnauba wax, 1% to 5% stearic acid and 40% to 50% polyvinyl alcohol.

5. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 2, the process of heating the binder is specifically as follows: firstly heating the temperature to 140°C~200°C at a rate of 5°C / min~30°C / min, and then keeping the temperature for 5min~15min.

6. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 2, the process of heating the mixed material each time is as follows: keeping the mixed material at 140° C. to 200° C. for 5 min to 15 min.

7. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 2, during the stirring process, set the stirring speed to 60 r / min~300 r / min and the stirring time to 5 min~15 min.

8. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 3, during the press forming process, the press time is set to 5 min to 25 min, the pressure is set to 5 MPa to 30 MPa, the temperature is set to 50°C to 110°C, and the heat preservation and pressure holding time is set to 5 min to 15 min.

9. The method for cold pressing spherical high-speed steel powder according to claim 1, characterized in that: In step 3, the cooling is natural cooling, and the cooling time is 5 min to 15 min.

10. A high-speed steel powder cold billet obtained by the method for cold pressing spherical high-speed steel powder as claimed in any one of claims 1 to 9 is used for sintering to prepare high-speed steel parts.

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