Method for improving wear resistance of existing grade powder metallurgy high-speed steel

Abstract

The invention discloses a method for improving wear resistance of existing-mark powder metallurgy high-speed steel. High-speed steel powder which contains a large-size vanadium carbide phase and has the same content of alloying elements such as Cr, Mo and W as those of a to-be-improved grade is added on the basis of powder metallurgy high-speed steel of an existing grade, sintering densification is carried out through a hot isostatic pressing process step, thermal deformation operation such as forging or hot rolling is carried out, and then quenching and tempering treatment are carried out to obtain a finished product. The typical carbide microstructure of the finished product is composed of carbide smaller than 4 microns and vanadium carbide of 5-10 microns. The prepared powder high-speed steel is larger in contact area with a friction pair in the friction process, in addition, vanadium carbide and a base body keep good interface bonding, the powder high-speed steel is not prone to falling off in the dual friction process, the powder high-speed steel plays a role of a supporting point on a contact surface, the pressure and abrasion of the friction pair to the contact surface can be effectively relieved, and therefore the abrasion resistance is improved. The hardness and toughness of the powder high-speed steel are equivalent to those of conventional grade powder high-speed steel, but the wear resistance is improved by 20-25%, and the bending strength is improved by 10-15%.

Description

Technical Field

[0001] The invention belongs to the field of metal materials and relates to a preparation method for improving the wear resistance of powder metallurgy high-speed steel. Background Art

[0002] High-speed steel (HSS) is a high-alloy tool steel primarily alloyed with tungsten, molybdenum, chromium, vanadium, and cobalt. It features high hardness (HRC63-70), excellent wear and heat resistance, and a well-balanced balance of strength and toughness. It is widely used in the manufacture of impact-resistant metal cutting tools, high-temperature bearings, extrusion and stamping dies, rollers, and speed skate blades. Powdered HSS is produced by atomizing molten HSS with high-pressure argon or nitrogen to produce a fine HSS powder. This powder is then pressed at high temperatures into a dense billet, which is then forged into a product or tool shape. Compared to traditional casting and forging processes, powder metallurgy can increase the alloy content to 40% while keeping carbides smaller. The resulting material exhibits higher strength, wear resistance, and impact toughness, meeting the demands of high-impact, high-removal machining.

[0003] The performance of powder high-speed steel (PHS) is closely related to alloy composition, carbide size, and heat treatment regime. Currently, there are over a dozen grades of PHS, varying in composition and performance, allowing users to select based on specific operating conditions. For high wear resistance, select grades with high carbon and vanadium content, such as K390 and CPM10V. For high toughness and moderate wear resistance, select low-carbon grades such as S590 and M390. Among currently established domestic and international grades, representative PHS grades with the best wear resistance include K390, CPM10V, and ASP2053. These grades typically have carbon contents of 2.4-2.5wt%, vanadium contents of 8-10wt%, and alloying elements such as Mo, W, and Cr, each containing 3-4wt%. Further improving wear resistance requires additional alloying elements, which increases material cost and results in poor processability, making them difficult to process through hot deformation processes such as forging and hot rolling. Therefore, it is imperative to further improve the wear resistance of the alloy on the basis of the existing alloy composition and ensuring deformable processing to meet the high wear resistance requirements of some cutting tools. Summary of the Invention

[0004] The purpose of the present invention is to further improve the wear resistance of existing powder metallurgy high-speed steel without affecting its toughness and hot working performance, to prepare powder metallurgy high-speed steel materials that take into account machinability, wear resistance and toughness, and to solve the problem that it is difficult to further improve the wear resistance of existing materials. The main solution is to embed a large-particle vanadium carbide hard phase on the basis of the microstructure of the existing powder metallurgy high-speed steel through an innovative method. The contact area with the friction pair during the friction process is larger. In addition, the vanadium carbide maintains a good interface bond with the matrix and is not easy to fall off during the friction with the pair. It acts as a support point on the contact surface, reducing the pressure and wear of the friction pair on the contact surface, which is conducive to improving wear resistance.

[0005] A method for improving the wear resistance of an existing grade of powder metallurgy high-speed steel is characterized by adding a high-speed steel powder containing a large-sized vanadium carbide phase and having the same content of alloying elements as the grade to be improved, such as Cr, Mo, and W, to the existing grade of powder metallurgy high-speed steel; then sintering and densifying the steel through a hot isostatic pressing process; and then subjecting the steel to forging or hot rolling thermal deformation operations, quenching, and tempering to obtain a finished product; the finished product typically has a carbide microstructure consisting of carbides less than 4 microns and vanadium carbides of 5-10 microns; the prepared powder high-speed steel has a larger contact area with a friction pair during friction; in addition, the vanadium carbide maintains a good interface bond with the matrix and is not easily detached during friction with the pair, acting as a support point on the contact surface, effectively reducing the pressure and wear of the friction pair on the contact surface, thereby improving wear resistance.

[0006] The method for improving the wear resistance of existing powder metallurgy high-speed steel is characterized by the following specific steps: 1) Use vacuum gas atomization powder making technology to prepare spherical metal powders of conventional grades, such as K390 and CPM10V. The C content is usually 2.3-2.7%; the Cr, W, and Mo contents are 3.5-4.0%; the V content is 8.5-10.0%, and the balance is Fe. The powder particle size is less than 120 microns, the oxygen content is less than 80ppm, and the nitrogen content is less than 600ppm. 2) Use vacuum melting process to melt high alloy master alloy rods, usually with a C content of 3.0-3.2%, a V content of 14-16%, an oxygen content of less than 20ppm, and the contents of Cr, W, Mo and other components are the same as those of the conventional alloy to be improved. Cast into cast rods with a diameter of 30-35mm; 3) Processing the high-alloyed rods from step 2) into electrode rods, and using a plasma rotating electrode atomization powder making process to prepare high-alloyed spherical powders, wherein the prepared powders have a particle size of 40-60 μm; 4) adding the spherical powder prepared in step 3) to the conventional grade powder prepared by the vacuum gas atomization process in step 1), and sintering the resulting mixed powder to densify it according to conventional hot isostatic pressing process steps at a sintering temperature of 1150-1180° C., a pressure of 110-120 MPa, and a holding time of 60-90 minutes to obtain a dense sintered ingot; 5) The sintered densified block is subjected to thermal deformation operations such as forging or hot rolling as needed, with the thermal deformation temperature being 1100°C-1160°C; after thermal deformation, the block is furnace annealed at 820-880°C, with a holding time of 90-120 minutes, and then cooled in the furnace; 6) The hot-deformed and annealed block is quenched and tempered using a vacuum gas quenching process at a quenching holding temperature of 1180-1185°C. The holding time depends on the size of the block, usually 1 min / mm. After the holding is completed, gas quenching is performed at a gas quenching pressure of 8-10 bar. The quenched block material is tempered at 550-560°C for 60-90 minutes. The tempering is repeated three to four times to obtain the finished product.

[0007] Furthermore, in step 3), the rotation speed of the highly alloyed spherical powder is controlled at 8000-9000 rpm, the plasma arc current is controlled at 7000-8000 amperes, and the particle size of the prepared powder is 40-60 microns.

[0008] Furthermore, in the mixed powder of step 4), the mass ratio of the powder of step 1) to the powder of step 3) is (80-85%): (15-20%).

[0009] Furthermore, the typical carbide microstructure of the finished product in step 6) is composed of carbides smaller than 4 microns and vanadium carbides of 5-10 microns; the carbides include vanadium carbide, chromium carbide, tungsten carbide, and molybdenum carbide.

[0010] The powder high-speed steel prepared using the above process has hardness and toughness comparable to conventional powder high-speed steel, but with wear resistance increased by 20-25% and bending strength increased by 10-15%. This method retains the material's machinability and toughness while achieving higher hardness and wear resistance.

[0011] Principle of the present invention: The main mechanism of improving wear resistance by using the above-mentioned process method is to embed a certain content of highly wear-resistant vanadium carbide particles of appropriate size into the matrix of conventional powder steel, which can significantly improve wear resistance without affecting the toughness and processing performance of conventional powder steel.

[0012] The size of conventional powder high-speed steel carbides (mainly vanadium carbide) is usually less than 4 microns, and the structure is uniform, such as Figure 1As shown in the figure, the carbides are evenly distributed in the matrix. This uniform structure can easily fall off along with the matrix alloy during the friction with the friction pair. If a proper amount of large-particle vanadium carbide phase is embedded on the basis of the conventional powder high-speed steel structure, it will be embedded in the matrix and the contact area with the friction pair will be larger, as shown in the figure. Figure 2 As shown, it is not easy to fall off during the friction with the pair, and at the same time acts as a support point on the contact surface, reducing the pressure and wear of the friction pair on the contact surface, which is beneficial to improving wear resistance.

[0013] The key to this invention is how to embed large-sized vanadium carbide phases into conventional powder steel. Conventional powder metallurgy methods, i.e., directly adding vanadium carbide, have the problem of poor interface bonding with the matrix and difficulty in sintering to a dense consistency. Based on the composition of conventional grades, this invention increases the C and V contents and uses vacuum induction melting to prepare alloy rods as electrodes. The vanadium carbide obtained by vacuum melting is coarse, with a maximum size of 20 microns, such as Figure 3 As shown, the rotary atomization powder making technology is then used. This technology uses plasma to arc and melt the end of the high-speed rotating electrode rod under the protection of a high-purity inert atmosphere. The centrifugal force generated by the high-speed rotation of the electrode rod is used to throw the molten metal into atomized small droplets. The atomized metal droplets are condensed into spherical powder under an inert atmosphere. While the alloy rod is melting, it is centrifugally atomized into powder. Since the time from melting to centrifugal throwing is short, large-particle vanadium carbide does not have time to completely melt and becomes small-particle vanadium carbide. By controlling the current and rotation speed, the viscosity and superheat of the molten alloy can be adjusted to achieve control of the size of the small-particle vanadium carbide. The experimental results show that the ideal particle size of vanadium carbide in the powder is 5-10 microns. Figure 4 The cross section of the powder shows that the vanadium carbide size is determined by Figure 3 The 20 microns are changed to 5-10 microns and distributed in the matrix; at the same time, in order to ensure that the basic structure of the added alloy powder is the same as that of the conventional brand powder, Cr, Mo, and W are used in the same content as the conventional brand powder to be improved in wear resistance. In this way, the powder containing large-particle vanadium carbide obtained by rotary atomization is added to the powder of conventional alloy components at an appropriate content. When the hot isostatic pressing sintering process is used, the following can be obtained: Figure 2The structure shown is a combination of large-sized and conventional-sized carbides. Conventional-sized carbides ensure that the material has the required strength and toughness, while large-sized carbides improve wear resistance on this basis. Although embedding large particles can help further improve wear resistance, the proportion needs to be strictly controlled. Adding too much will affect the overall toughness and wear resistance of the material. Therefore, it is necessary to control the proportion of large particles within a reasonable range by controlling the proportion of high-alloyed powder added to conventional powder. Experimental results show that the reasonable mass content of high-alloyed spherical powder added to conventional powder is 15-20%. Using the above scheme, through heat treatment, under the same friction and wear test conditions, the wear amount is reduced by 20-25% after adding high-alloyed powder, which means that the wear resistance is improved by 20-25%. At the same time, the bending strength is increased by 10-15%, the impact toughness of the material is only reduced by 2-3%, and the hot workability remains unchanged, indicating that this method can significantly improve wear resistance without affecting processability and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Typical structure of conventional grade powder high speed steel, Figure 2 Typical organization of the material of the present invention, (a) is the typical organization, (b) is the magnified organization of the white frame in (a), Figure 3 Vacuum melting structure of high alloy alloy, Figure 4 Cross-sectional structure of highly alloyed powder prepared by plasma rotary atomization. The black blocks in the figure are vanadium carbide. DETAILED DESCRIPTION

[0015] Example 1 Improving the wear resistance of K390 powder high-speed steel

[0016] In the first step, K390 spherical metal powder was prepared using vacuum gas atomization technology. The composition of the powder was C: 2.47%, Cr: 4.20%, Mo: 3.8%, V: 9.0%, W: 1.0%, Co: 2.0%, Si: 0.55%, Mn: 0.40%, and the balance was Fe. The powder had a particle size of less than 120 microns, an oxygen content of less than 80 ppm, and a nitrogen content of less than 600 ppm. In the second step, a high-alloyed master alloy rod is melted by vacuum melting process. The composition is C content 3.1%, V content 15%, oxygen content less than 20ppm, and other elements are the same as K390, namely Cr: 4.20%, Mo: 3.8%, W: 1.0%, Co 2.0%, Si 0.55%, Mn 0.40%, and the balance is Fe. The rod is cast into a diameter of 35mm. In the third step, the high-alloyed rods prepared in step 2) are processed into electrode rods, and a plasma rotating electrode atomization pulverization process is used to produce high-alloyed spherical powders. The rotation speed is controlled at 8000 rpm and the plasma arc current is controlled at 7000 amperes. The prepared powder particle size is 40-60 microns. In the fourth step, 18% by weight of the spherical powder prepared by the process of step 3) was added to the conventional grade powder prepared by the vacuum gas atomization process in step 1). The resulting mixed powder was sintered and densified according to conventional hot isostatic pressing process steps. The sintering temperature was 1180°C, the pressure was 120 MPa, and the holding time was 90 minutes. The final mass ratio of the powder of step 1) to the powder of step 2) was 82:18. After sintering, a dense sintered ingot was obtained. The fifth step is to forge the densified block after sintering into a 20 mm bar. The temperature of forging hot deformation is 1150 ° C. After hot deformation, the block is furnace annealed at 880 ° C. The annealing temperature is 120 minutes and the block is cooled in the furnace. In the sixth step, the heat-deformed and annealed block is quenched and tempered using a vacuum gas quenching process with a quenching holding temperature of 1180°C and a holding time of 20 minutes. After the holding is completed, gas quenching is performed with a gas quenching pressure of 10 bar. The quenched block material is tempered with a tempering process of 550°C for 60 minutes. The tempering is repeated three times to obtain the finished product.

[0017] Under the same friction conditions, the wear of the powder high-speed steel prepared by the above process is 22% lower than that of K390, that is, the wear resistance is improved by 22%; at the same time, its hardness and toughness are comparable to those of K390.

[0018] Example 2 Improving the wear resistance of CPM10V powder high-speed steel

[0019] In the first step, vacuum gas atomization technology was used to prepare CPM10V spherical metal powder, whose composition was C: 2.45%, Cr: 5.25%, Mo: 1.35%, V: 9.75%, and the balance was Fe. The powder had a particle size of less than 120 microns, an oxygen content of less than 80ppm, and a nitrogen content of less than 600ppm. In the second step, a high-alloyed master alloy rod is melted using a vacuum melting process. The composition is 3.1% C, 15% V, and less than 20 ppm oxygen. The other elements are the same as CPM10V, namely 5.25% Cr, 1.35% Mo, and the balance is Fe. The rod is cast into a diameter of 32 mm. In the third step, the high-alloyed rods from step 2) are processed into electrode rods, and a plasma rotating electrode atomization process is used to produce high-alloyed spherical powders. The rotation speed is controlled at 9000 rpm and the plasma arc current is controlled at 8000 amperes. The prepared powder particle size is 40-60 microns. In the fourth step, 20% by weight of the spherical powder prepared by the process of step 3) was added to the conventional grade powder prepared by the vacuum gas atomization process in step 1). The resulting mixed powder was sintered and densified according to conventional hot isostatic pressing process steps. The sintering temperature was 1170°C, the pressure was 120 MPa, and the holding time was 90 minutes. The final mass ratio of the powder of step 1) to the powder of step 2) was 80:20. After sintering, a dense sintered ingot was obtained. The fifth step is to forge the densified block after sintering into a 20 mm bar. The temperature of forging hot deformation is 1130 ° C. After hot deformation, the block is furnace annealed at 850 ° C for 90 minutes and then cooled in the furnace. In the sixth step, the heat-deformed and annealed block is quenched and tempered using a vacuum gas quenching process with a quenching holding temperature of 1180°C and a holding time of 20 minutes. After the holding is completed, gas quenching is performed with a gas quenching pressure of 9 bar. The quenched block material is tempered with a tempering process of 560°C for 90 minutes. The tempering is repeated three times to obtain the finished product.

[0020] Under the same friction conditions, the wear of the powder high-speed steel prepared by the above process is 25% lower than that of K390, that is, the wear resistance is improved by 25%; at the same time, its hardness and toughness are equivalent to those of K390.

Claims

1. A method for improving the wear resistance of existing grades of powder metallurgy high-speed steel, characterized in that: On the basis of existing grades of powder metallurgy high-speed steel, high-speed steel powder containing large-sized vanadium carbide phase and with the same Cr, Mo, and W alloying element content as the grade to be improved is added, and then sintered and densified by hot isostatic pressing process steps, and then subjected to forging or hot rolling hot deformation operation, and then quenching and tempering treatment to obtain the finished product; The typical carbide microstructure of the finished product is composed of carbides less than 4 microns and vanadium carbides of 5-10 microns. The prepared powder high-speed steel has a larger contact area with the friction pair during the friction process. In addition, the vanadium carbide maintains a good interface bonding with the matrix and is not easy to fall off during the friction with the pair. It acts as a support point on the contact surface, which can effectively reduce the pressure and wear of the friction pair on the contact surface, thereby improving wear resistance.

2. The method for improving the wear resistance of existing grade powder metallurgy high-speed steel according to claim 1, characterized in that: The specific steps are as follows: 1) Use vacuum gas atomization technology to prepare spherical metal powders of conventional grades, typically K390, CPM10V, with a C content of 2.3-2.7%; Cr, W, and Mo contents of 3.5-4.0%; V content of 8.5-10.0%, with the balance being Fe. The powder particle size is less than 120 microns, the oxygen content is less than 80 ppm, and the nitrogen content is less than 600 ppm. 2) Using vacuum melting process to melt high alloy master alloy rods, the composition is C content of 3.0-3.2%, V content of 14-16%, oxygen content of less than 20ppm, Cr, W, Mo and other components are the same as the conventional alloy composition to be improved, and cast into cast rods with a diameter of 30-35mm; 3) Processing the high-alloyed rods from step 2) into electrode rods, and using a plasma rotating electrode atomization powder making process to prepare high-alloyed spherical powders, wherein the prepared powders have a particle size of 40-60 μm; 4) adding the spherical powder prepared in step 3) to the conventional grade powder prepared by the vacuum gas atomization process in step 1), and sintering the resulting mixed powder to densify it according to conventional hot isostatic pressing process steps at a sintering temperature of 1150-1180° C., a pressure of 110-120 MPa, and a holding time of 60-90 minutes to obtain a dense sintered ingot; 5) The sintered densified block is subjected to forging or hot rolling thermal deformation operation as required, with the thermal deformation temperature being 1100°C-1160°C; after thermal deformation, the block is furnace annealed at 820-880°C, with a holding time of 90-120 minutes, and then cooled in the furnace; 6) The heat-deformed and annealed block is quenched and tempered using a vacuum gas quenching process with a quenching and holding temperature of 1180-1185°C. The holding time is 1 min / mm depending on the size of the block. After the holding is completed, gas quenching is performed with a gas quenching pressure of 8-10 bar. The quenched block material is tempered at 550-560°C for 60-90 minutes. The tempering is repeated three to four times to obtain the finished product.

3. The method for improving the wear resistance of existing grade powder metallurgy high-speed steel according to claim 2, characterized in that: Step 3) The high alloy spherical powder is prepared at a rotation speed of 8000-9000 rpm and a plasma arc current of 7000-8000 amperes, and the particle size of the prepared powder is 40-60 microns.

4. The method for improving the wear resistance of existing grade powder metallurgy high-speed steel according to claim 2, characterized in that: In the mixed powder of step 4), the mass ratio of the powder of step 1) to the powder of step 3) is (80-85%): (15-20%).

5. The method for improving the wear resistance of existing grade powder metallurgy high-speed steel according to claim 2, characterized in that: The typical carbide microstructure of the finished product in step 6) is composed of carbides smaller than 4 microns and vanadium carbides of 5-10 microns; the carbides include vanadium carbide, chromium carbide, tungsten carbide, and molybdenum carbide.

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