Extruded rod with dense inner surface for powder metallurgy parts and method for manufacturing parts

Abstract

The present invention relates to an extruded rod for making the inner surface of a powder metallurgy part dense and a method for manufacturing the part, wherein the extruded rod for making the inner surface of a powder metallurgy part dense comprises a core rod, whose longitudinal section is basically T-shaped, comprising a vertically arranged rod body and a connector arranged at the top of the rod body; an extruded piece is annular and is sleeved on the periphery of the rod body and is located below the connector; it is characterized in that: there are at least two extruded pieces, and they are arranged at intervals along the length direction of the rod body, and a support ring in annular shape and sleeved on the periphery of the rod body is arranged between two adjacent extruded pieces, and the size of the outer contour of each extruded piece gradually increases from bottom to top. The extruded rod can intermittently slide and extrude the inner surface of the central hole of the subsequent part to be extruded, thereby improving the inner surface density of the part to be extruded, reducing surface pores, and improving the inner surface density of the central hole of the part to be extruded.

Description

Technical Field

[0001] The invention belongs to the field of powder metallurgy, and in particular relates to an extruded rod for making the inner surface of a powder metallurgy part dense, and a method for manufacturing the powder metallurgy part by using the extruded rod. Background Art

[0002] Powder metallurgy is a technical discipline that manufactures metal powders and uses metal powders (including non-metallic powders mixed in) as raw materials to manufacture materials or products by the basic methods of forming and sintering. In a broad sense, it also includes the technology of using oxides, nitrides, carbides and other non-metallic compound powders as raw materials to manufacture materials or products by forming-sintering methods. The powder metallurgy process is a technical process in which the raw material powder is added to a certain mold cavity and then pressurized and formed, and then sintered under certain conditions, or sintered in a specific mold to obtain a product. With the development of industry, powder metallurgy is a technology that can manufacture parts with complex shapes, save raw materials, energy, and labor, and is suitable for mass production.

[0003] Powder metallurgy is an effective process for producing high-strength and complex-shaped parts. Currently, by using high-performance powders, molding, sintering and special post-processing, powder metallurgy can produce parts with a density of more than 7.4g / cm 3 Iron-based parts. The double pressing and double firing technology can greatly increase the density of the product. Using ordinary atomized iron powder through forming and sintering, the density of iron-based powder metallurgy parts can only reach 7.1g / cm 3 About. If the density of powder metallurgy parts is to be further improved, a forming-pre-sintering-re-pressing-secondary sintering re-pressing and re-firing process can be adopted. Pre-sintering has two functions: first, annealing the powder that has been hardened during forming to reduce the yield strength of the iron powder particles, which is conducive to increasing the density during secondary pressing; second, removing the organic lubricant in the product. Due to its low density, organic lubricants occupy a large space in the product. These lubricants are difficult to compress during forming, and the increase in density is limited. More than 95% of the lubricant can be removed during pre-firing, and the position occupied by the lubricant can be compressed during re-pressing, which is conducive to increasing the density. For parts with complex shapes, forming requires expensive CNC presses, but re-pressing is more difficult, and it is difficult to make each step dense or difficult to select dense parts.

[0004] For powder metallurgy parts of other materials, most of them are produced by powder making, mixing, encapsulation, extrusion (forging), machining and other methods. The performance of the parts is good, even better than that of directly forged parts, but the process of parts is long and the manufacturing cost is high. The manufacturing of parts is not a near-net forming process, and the advantages of powder metallurgy technology cannot be fully utilized.

[0005] As electromechanical application parts, the traditional method is to form them through mechanical processing. The main processing methods for machined parts are currently forming steel directly through mechanical processing and forming through cold extrusion. Among them, the mechanical processing method has a long process, a low raw material utilization rate of about 40-60%, a high product cost, poor consistency, and low production efficiency, which is difficult to meet the requirements of large-scale consistency.

[0006] The cold extrusion method generally requires warm forging and then cold extrusion. The forging has high dimensional accuracy, good dimensional consistency, smooth surface, high tooth shape accuracy of the internal gear, clear gear contour, and less machining allowance on the outer surface; the material utilization rate reaches about 90%; due to the large deformation, the life of the warm forging die (die) is 5000 to 6000 pieces, while the life of the cold extrusion die (punch) is 8000 to 10000 pieces; the appearance of the cold extrusion is smooth, the machining allowance is small, which significantly reduces the subsequent machining workload, the production cycle is short, and the production efficiency is high. However, the cold extrusion method has a large die loss, and the cost is difficult to meet the requirements of the automobile, motorcycle and other industries.

[0007] Therefore, new manufacturing methods need to be developed to solve problems such as precision, density and strength of powder metallurgy products. Summary of the invention

[0008] The first technical problem to be solved by the present invention is to provide an extrusion rod for making the inner surface of a powder metallurgy part dense, which can uniformly extrude subsequent parts to be extruded, in view of the current status of the above-mentioned prior art.

[0009] The second technical problem to be solved by the present invention is to provide a method for manufacturing high-density and high-strength powder metallurgy parts in view of the current status of the above-mentioned prior art.

[0010] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: an extruded rod for making the inner surface of a powder metallurgy part dense, comprising

[0011] The mandrel has a substantially T-shaped longitudinal section, and comprises a vertically arranged rod body and a connector arranged on the top of the rod body;

[0012] An extrusion piece is annular and is sleeved on the periphery of the rod body and located below the connector;

[0013] The feature is that there are at least two extrusion pieces, which are spaced apart along the length direction of the rod body, and a ring-shaped support ring is arranged between two adjacent extrusion pieces and sleeved on the outer periphery of the rod body, and the outer contour size of each extrusion piece gradually increases from bottom to top.

[0014] In order to achieve the gradual expansion of the subsequent parts to be extruded, preferably, the gradient difference △L between the outer contour dimensions of two adjacent extrusions is 0.01%~8.0%, wherein △L=(L1-L2) / L1, L1 is the outer contour dimension of the extrusion located above, and L2 is the outer contour dimension of the extrusion located below. In this way, extrusions with different outer contour dimensions are sequentially slid and extruded intermittently on the inner surface of the central hole of the part to be extruded, thereby improving the surface density of the part to be extruded, reducing surface pores, and improving the inner surface density of the central hole of the part to be extruded.

[0015] In order to prevent the support ring from interfering with the part to be extruded, the projection of the support ring along the vertical direction falls within each of the extruded parts.

[0016] In order to improve the extrusion capacity, the number of the extrusion pieces is 2 to 30.

[0017] The support ring and the extrusion member are limited on the rod body, and can be fixed by welding, bonding, or locking with nuts. However, from the perspective of convenient disassembly and replacement of the extrusion member, preferably, a guide member is provided under the lowest extrusion member, and the guide member is annular and located outside the rod body. A nut for locking the guide member, the support ring and the extrusion member to the rod body is provided under the guide member, and the nut is located on the periphery of the rod body.

[0018] The technical solution adopted by the present invention to solve the above second technical problem is: a method for manufacturing powder metallurgy parts using the above extruded rod, characterized in that it at least includes the following steps:

[0019] 1) Material composition design: carbon, iron, chromium, molybdenum, copper and nickel are mixed into a mixed powder according to the following mass percentages, and the composition is according to the following mass percentages: carbon: 0-1.5%, copper: 0-4%, nickel: 0-5%, molybdenum: 0-2%, chromium: 0-6%, unavoidable impurities not exceeding 2%, lubricant 0.1-1%, iron: balance; among them, chromium, molybdenum, copper and nickel are added in the form of iron alloy or master alloy, carbon is added in the form of graphite, and then a lubricant with a mass percentage content of 0.1-1% is added;

[0020] 2) Pressing: Press the mixed powder in step 1) on a press to a density of 6.4-7.4 g / cm 3 The pressing pressure of the green parts is greater than 400MPa;

[0021] 3) Sintering: The green body of the part in step 2) is sintered at a temperature of 1000°C to 1350°C for 5 to 180 minutes;

[0022] 4) Extrusion: The part to be extruded with a central hole is placed in the central opening of the female die for extrusion. The outer contour of each extruded part is larger than the inner contour of the central hole of the part to be extruded. During extrusion, each of the extruded parts can pass through the central hole of the part to be extruded from top to bottom.

[0023] 5) Heat treatment: Heat treatment of the extruded parts.

[0024] In order to prevent excessive elastic deformation of the part to be extruded during extrusion, the horizontal distance of the cross section of the inner contour of the opening of the female mold is D1, and the horizontal distance of the cross section of the outer contour of the part to be extruded is D2, where D1=(1.001~1.200)D2.

[0025] Preferably, parts with a carbon content higher than 0.2%, or a total molybdenum, chromium, and nickel alloy content higher than 2%, can be annealed between step 3) and step 4), with an annealing temperature of 750 to 1080°C, an annealing holding time of 5 to 200 minutes, and a cooling rate from the annealing temperature to 300°C of less than 1.5°C / s after annealing. This annealing process can reduce hardness, make the structure uniform, eliminate or reduce internal stress, obtain better material toughness, and make the material easier to extrude.

[0026] Preferably, in step 4), the total extrusion deformation design amount Δd = (d max -d 0 ) / d 0 , the total extrusion deformation design amount △d should be controlled within 10%. Too large total extrusion deformation will cause the mold to be subjected to excessive compressive stress and easily damaged or significantly reduce the life of the mold.

[0027] Preferably, in step 5), the quenching temperature is 750-1250°C, the quenching holding time is 30-45 minutes, the tempering temperature is 150-600°C, and the tempering holding time is 5-200 minutes. Quenching can improve the structure, strength, hardness and wear resistance; tempering can eliminate or reduce quenching stress, improve brittleness after quenching, and make the size and performance of parts more stable.

[0028] Compared with the prior art, the advantages of the present invention are: the extrusion rod of the present invention can intermittently slide and extrude the inner surface of the central hole of the subsequent part to be extruded, thereby improving the inner surface density of the part to be extruded, reducing the surface pores, and improving the inner surface density of the central hole of the part to be extruded; its preparation method combines the advantages of powder metallurgy process and metal extrusion forming, can produce parts with complex shapes, and at the same time, the precision of the parts is high. During the extrusion process, the movement of the extrusion rod causes the material to flow, thereby improving the density of some areas of the powder metallurgy parts; in addition, due to the use of powder metallurgy process, the shape of the part to be extruded is closer to the shape of the final product, so the extrusion margin is small and the mold life is long. At the same time, due to the increase in density, the performance of the parts is greatly improved compared with ordinary powder metallurgy parts, expanding the application field of powder metallurgy. Using this method, the required surface shape is processed after sintering by extrusion, which improves the application range of the powder metallurgy process, and has high precision and good surface finish. Compared with the traditional powder metallurgy process, the product has a higher density, and the overall density of thin-walled parts can exceed 7.60g / cm 3 , close to the level of powder forging, and the surface relative density can reach more than 99%, basically achieving surface densification. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic structural diagram of the part to be extruded in this embodiment;

[0030] Figure 2 It is the main view of the part to be extruded;

[0031] Figure 3 is a cross-sectional view of an extruder;

[0032] Figure 4 for Figure 3 Schematic diagram of the structure of the extruded part;

[0033] Figure 5 A cross-sectional view of the part to be extruded placed in the female die;

[0034] Figure 6 A cross-sectional view of a part to be extruded placed in a female die;

[0035] Figure 7 Schematic diagram of the structure of the female mold in this embodiment;

[0036] Figure 8 A schematic diagram of the contours of the part to be extruded and the extruded part after uniform extrusion;

[0037] Fig. 9 It is a schematic diagram of the contours of the part to be extruded and the extruded part after only partial extrusion by non-uniform extrusion;

[0038] Fig.10This is the morphology of the central hole of the part to be extruded before extrusion;

[0039] Fig.11 This is the morphology of the central hole of the part to be extruded after extrusion;

[0040] Fig.12 for Fig.11 Scan of the inner surface of the central hole of the extruded part after heat treatment. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below with reference to the accompanying drawings. Example 1

[0042] like Figures 1 to 12 Shown is a first preferred embodiment of the present invention.

[0043] like Figure 3 As shown, the extrusion system of this embodiment includes a female die 2 and an extrusion rod 1 for densifying the inner surface of a powder metallurgy part. The female die 2 is provided with an opening 21 in the center thereof for placing a part 3 to be extruded having a central hole 31 therein. A step 211 is formed in the opening 21 for placing the part 3 to be extruded. Figure 7 As shown, the longitudinal section of the opening 21 of the female mold 2 is T-shaped. Figure 1 As shown, the part 3 to be extruded has a central hole 31 in the center.

[0044] like Figure 3As shown, the extruded rod 1 of this embodiment includes a core rod 11, an extrusion piece 12, a support ring 13, a guide piece 14 and a nut 15. The core rod 11 is arranged vertically, and the longitudinal section of the core rod 11 is basically T-shaped. The core rod 1 includes a vertically arranged rod body 111 and a connector 112 arranged at the top of the rod body 111. The extrusion piece 12 is annular and is sleeved on the periphery of the rod body 111 and is located below the connector 112. The central opening 121 of the extrusion piece 12 is a non-circular hole, so that the extrusion piece 12 only moves up and down relative to the core rod 11. In this embodiment, there are 3 or 4 extrusion pieces 12, and they are arranged at intervals along the length direction of the rod body 111. A support ring 13 in annular shape and sleeved on the periphery of the rod body 111 is arranged between two adjacent extrusion pieces 12, and the projection of the support ring 13 along the vertical direction falls within each extrusion piece 12. The size of the outer contour of each extrusion piece 12 increases gradually from bottom to top, and the size of the outer contour of each extrusion piece 12 is larger than the size of the inner contour of the central hole 31 of the part 3 to be extruded. Specifically, the gradient difference △L between the outer contour sizes of two adjacent extrusion pieces 12 is 0.01%~8.0%, wherein △L=(L1-L2) / L1, L1 is the size of the outer contour of the extrusion piece 12 located above, and L2 is the size of the outer contour of the extrusion piece 12 located below. In addition, the guide piece 14 is located below the lowest extrusion piece 12, and is annular and sleeved on the periphery of the rod body 111. The nut 15 is located below the guide piece 14, and the nut 15 is connected to the periphery of the rod body 111 and locks the guide piece 14, the support ring 13 and the extrusion piece 12 on the rod body 111.

[0045] like Figure 3 As shown, the part 3 to be extruded is placed on the step 211 and is located in the opening 21, and the nut 15 is located in the central hole 31 of the part 3 to be extruded. When the part 3 to be extruded is extruded, the guide 14 and each extrusion piece 12 gradually pass through the central hole 31 of the part 3 to be extruded from top to bottom, and the extrusion pieces 12 with different outer contour sizes slide and extrude intermittently on the inner surface of the central hole 31 of the part to be extruded in turn. After uniform extrusion, see Figure 8 As shown, the inner surface density of the part to be extruded is improved, the surface pores are reduced, and the inner surface density of the central hole 31 of the part to be extruded is improved. The outer contour size in the above embodiment, that is, when the outer contour of the extruded part is circular, the outer contour size is the outer diameter.

[0046] The present embodiment uses the above-mentioned extruded rod to prepare the method for manufacturing powder metallurgy parts, which comprises the following steps in sequence:

[0047] 1) Material composition design: sintered steel, such as a mixture of iron-chromium-molybdenum pre-alloyed powder and carbon-copper powder, is used, and its composition by mass percentage is: atomized iron powder is 96.8%; carbon is 0.70%, copper powder is 2%, and then a lubricant with a content of 0.5% is added;

[0048] 2) Pressing: Press the mixed powder in step 1) on a press with a pressing pressure of 600 MPa to a density of 7.1 g / cm 3 Green parts;

[0049] 3) Sintering: The green body of the part in step 2) is sintered at a temperature of 1200°C for 20 minutes;

[0050] 4) Annealing: The annealing temperature is 850°C, the atmosphere is nitrogen, the annealing holding time is 60 minutes, and the cooling rate from the annealing temperature to 300°C after annealing is 0.1°C / s.

[0051] 5) Extrusion: Place the annealed part 3 to be extruded with the central hole 31 in the central opening 21 of the female die 2 for extrusion; there are three extrusion pieces 12 in the extruder, therefore, three-gear extrusion pieces are used for extrusion, the total extrusion deformation design amount △d = (dmax-d0) / d0, the total extrusion deformation design amount △d is 5%, the first gear extrusion amount is 1%, the second gear extrusion amount is 1.5%, and the third gear extrusion amount is 2.5%, wherein the first gear extrusion is the extrusion amount after the extrusion piece 12 at the bottom is extruded, the second gear extrusion is the extrusion amount after the extrusion piece 12 at the middle is extruded, and the third gear extrusion is the extrusion amount after the extrusion piece 12 at the top is extruded; for details, see Figure 8 As shown, the extrusion amount is relatively uniform, that is, the distance between the outer contour of the extrusion piece and the central hole of the part to be extruded 3 is equal everywhere in the circumferential direction. Fig. 9 Compared with the uneven extrusion, the density is higher. Fig.11 shown.

[0052] 6) Heat treatment: The extruded parts are heat treated, where the quenching temperature is 850°C, the quenching holding time is 30 minutes, the carbon potential is 0.7%, the tempering temperature is 200°C, and the tempering holding time is 120 minutes. The morphology of the inner surface of the central hole of the part is shown in Fig.12 As shown, we can see that after heat treatment, the metallographic structure of the dense layer on the surface of the inner hole has been changed from the original pearlite to martensite, and its surface hardness, strength and wear resistance have been improved. Example 2

[0053] The difference between this embodiment and the above-mentioned embodiment 1 is that the extrusion amount of each gear in step 5) is different. Specifically, the total extrusion deformation design amount △d is 5%, the first gear extrusion amount is 2.5%, the second gear extrusion amount is 1.5%, and the third gear extrusion amount is 1%, wherein the first gear extrusion is the extrusion amount after the extrusion part 12 located at the bottom is extruded, the second gear extrusion is the extrusion amount after the extrusion part 12 located in the middle is extruded, and the third gear extrusion is the extrusion amount after the extrusion part 12 located at the top is extruded. Example 3

[0054] The difference between this embodiment and the above-mentioned embodiment 1 is that the component design and parameter selection in the preparation method are different, as follows:

[0055] The present embodiment uses the above-mentioned extruder to prepare the method for manufacturing powder metallurgy parts, which comprises the following steps in sequence:

[0056] 1) Material composition design: sintered steel, such as a mixture of iron-chromium-molybdenum pre-alloyed powder and carbon-copper powder, is used, and its composition by mass percentage is: atomized iron powder is 95.6%; carbon is 0.80%, copper powder is 3%, and then a lubricant with a content of 0.6% is added;

[0057] 2) Pressing: Press the mixed powder in step 1) on a press with a pressing pressure of 550 MPa to a density of 7.0 g / cm 3 Green parts;

[0058] 3) Sintering: The green body of the part in step 2) is sintered at a temperature of 1300°C for 30 minutes;

[0059] 4) Extrusion: The sintered part 3 to be extruded is placed in an extruder for extrusion; there are four extrusion pieces 12 in the extruder, so a four-gear extrusion piece is used for extrusion, and the total extrusion deformation design amount △d = (dmax-d0) / d0, the total extrusion deformation design amount △d is 7%, the first gear extrusion amount is 2.5%, the second gear extrusion amount is 2.0%, the third gear extrusion amount is 1.5%, and the fourth gear extrusion amount is 1.0%. The first gear extrusion amount, the second gear extrusion amount, the third gear extrusion amount, and the fourth gear extrusion amount are the corresponding extrusion amounts after the extrusion piece is extruded from bottom to top;

[0060] 5) Heat treatment: The extruded parts are heat treated, where the quenching temperature is 850°C, the quenching holding time is 30 minutes, the carbon potential is 0.7%, the tempering temperature is 200°C, and the tempering holding time is 120 minutes. Example 4

[0061] The difference between this embodiment and the above-mentioned embodiment 1 is that: there are differences in the sintering parameters in step 3), specifically: the green body of the part is sintered at a temperature of 1280°C, and the sintering time is 50min; the extrusion amounts of each gear in step 4) are different, specifically: the total extrusion deformation design amount △d = (dmax-d0) / d0, the total extrusion deformation design amount △d is 7%, the first gear extrusion amount is 2.5%, the second gear extrusion amount is 2.0%, the third gear extrusion amount is 2.0%, and the fourth gear extrusion amount is 1.5%. The first gear extrusion amount, the second gear extrusion amount, the third gear extrusion amount, and the fourth gear extrusion amount are respectively the corresponding extrusion amounts after the extruded part is extruded from bottom to top; the horizontal distance of the cross section of the inner contour of the opening 21 of the female mold 2 is D1, and the horizontal distance of the cross section of the outer contour of the part 3 to be extruded is D2, wherein D1=1.01D2, see specifically Figure 7 shown. Example 5

[0062] 1) Material composition design: sintered steel is used, and its composition by mass percentage is: atomized iron powder is 83.9%; copper powder is 4%, nickel powder is 5%, molybdenum powder is 1%, chromium powder is 6%, and then a lubricant with a content of 0.1% is added;

[0063] 2) Pressing: Press the mixed powder in step 1) on a press with a pressing pressure of 600 MPa to a density of 6.4 g / cm 3 Green parts;

[0064] 3) Sintering: The green body of the part in step 2) is sintered at a temperature of 1000°C for 5 minutes;

[0065] 4) Annealing: The annealing temperature is 1080°C, the atmosphere is nitrogen, the annealing holding time is 5 minutes, and the cooling rate from the annealing temperature to 300°C after annealing is 0.1°C / s.

[0066] 5) Extrusion: The annealed part 3 to be extruded is placed in the extruder for extrusion; there are three extrusion pieces 12 in the extruder, therefore, three-gear extrusion pieces are used for extrusion, the total extrusion deformation design amount △d = (dmax-d0) / d0, the total extrusion deformation design amount △d is 5%, the first gear extrusion amount is 1%, the second gear extrusion amount is 1.5%, and the third gear extrusion amount is 2.5%, wherein the first gear extrusion is the extrusion amount after the extrusion piece 12 at the bottom is extruded, the second gear extrusion is the extrusion amount after the extrusion piece 12 at the middle is extruded, and the third gear extrusion is the extrusion amount after the extrusion piece 12 at the top is extruded; for details, see Figure 5 As shown, the extrusion amount is relatively uniform, that is, the distance between the outer contour of the extrusion piece and the central hole of the part 3 to be extruded is equal everywhere in the circumferential direction. Figure 7 Compared with uneven extrusion, its density is higher.

[0067] 6) Heat treatment: The extruded parts are heat treated, wherein the quenching temperature is 1250°C, the quenching holding time is 40 minutes, the carbon potential is 0.7%, the tempering temperature is 150°C, and the tempering holding time is 5 minutes. The horizontal distance of the cross section of the inner contour of the opening 21 of the female die 2 is D1, and the horizontal distance of the cross section of the central hole 31 of the part to be extruded 3 is D2, wherein D1=1.001D2. Example 6

[0068] 1) Material composition design: sintered steel is used, and its composition by mass percentage is: atomized iron powder is 92.5%; carbon powder is 1.5%, nickel powder is 2%, molybdenum powder is 2%, chromium powder is 1%, and then a lubricant with a content of 1% is added;

[0069] 2) Pressing: Press the mixed powder in step 1) on a press with a pressing pressure of 600 MPa to a density of 7.4 g / cm 3 Green parts;

[0070] 3) Sintering: The green body of the part in step 2) is sintered at a temperature of 1350°C for 180 minutes;

[0071] 4) Annealing: The annealing temperature is 750°C, the atmosphere is nitrogen, the annealing holding time is 200 minutes, and the cooling rate from the annealing temperature to 300°C after annealing is 0.1°C / s.

[0072] 5) Extrusion: The annealed part 3 to be extruded is placed in the extruder for extrusion; there are three extrusion pieces 12 in the extruder, therefore, three-gear extrusion pieces are used for extrusion, the total extrusion deformation design amount △d = (dmax-d0) / d0, the total extrusion deformation design amount △d is 5%, the first gear extrusion amount is 1%, the second gear extrusion amount is 1.5%, and the third gear extrusion amount is 2.5%, wherein the first gear extrusion is the extrusion amount after the extrusion piece 12 at the bottom is extruded, the second gear extrusion is the extrusion amount after the extrusion piece 12 at the middle is extruded, and the third gear extrusion is the extrusion amount after the extrusion piece 12 at the top is extruded; for details, see Figure 5 As shown, the extrusion amount is relatively uniform, that is, the distance between the outer contour of the extrusion piece and the central hole of the part 3 to be extruded is equal everywhere in the circumferential direction. Figure 7 Compared with uneven extrusion, its density is higher.

[0073] 6) Heat treatment: The extruded parts are heat treated, wherein the quenching temperature is 750°C, the quenching holding time is 45 minutes, the carbon potential is 0.7%, the tempering temperature is 600°C, and the tempering holding time is 200 minutes. The horizontal distance of the cross section of the inner contour of the opening 21 of the female die 2 is D1, and the horizontal distance of the cross section of the central hole 31 of the part to be extruded 3 is D2, wherein D1=1.200D2.

Claims

1. An extruded rod for dense inner surface of powder metallurgy parts, Features: Included The core rod (11) has a substantially T-shaped longitudinal section and comprises a vertically arranged rod body (111) and a connecting head (112) arranged on the top of the rod body (111); An extrusion piece (12) is annular and is sleeved on the periphery of the rod body (111) and is located below the connecting head (112); The extrusion pieces (12) are arranged at intervals along the length direction of the rod body (111); a support ring (13) in an annular shape and sleeved on the outer periphery of the rod body (111) is arranged between two adjacent extrusion pieces (12); the outer contour size of each extrusion piece (12) gradually increases from bottom to top; the gradient difference △L of the outer contour size of two adjacent extrusion pieces (12) is 0.01%~8.0%, wherein △L=(L1-L2) / L1, L1 is the outer contour size of the extrusion piece (12) located at the top, and L2 is the outer contour size of the extrusion piece (12) located at the bottom. ); the projection of the support ring (13) along the vertical direction falls within each of the extrusion pieces (12); there are 2 to 30 extrusion pieces (12); a guide piece (14) is arranged below the lowest extrusion piece (12); the guide piece (14) is annular and is located outside the rod body (111); a nut for locking the guide piece (14), the support ring (13) and the extrusion piece (12) on the rod body (111) is arranged below the guide piece (14); the nut (15) is located on the periphery of the rod body (111).

2. A method for manufacturing a powder metallurgy part using the extruded rod according to claim 1, It is characterized in that At least the following steps are included: 1) Material composition design: carbon, iron, chromium, molybdenum, copper and nickel are mixed into a mixed powder according to the following mass percentages, and the composition is according to the following mass percentages: carbon: 0-1.5%, copper: 0-4%, nickel: 0-5%, molybdenum: 0-2%, chromium: 0-6%, unavoidable impurities not exceeding 2%, lubricant 0.1-1%, iron: balance; among them, chromium, molybdenum, copper and nickel are added in the form of iron alloy or master alloy, carbon is added in the form of graphite, and then a lubricant with a mass percentage content of 0.1-1% is added; 2) Pressing: Press the mixed powder in step 1) on a press to a density of 6.4-7.4 g / cm 3 The pressing pressure of the green parts is greater than 400MPa; 3) Sintering: The green body of the part in step 2) is sintered at a temperature of 1000°C to 1350°C for 5 to 180 minutes; 4) Extrusion: placing the part (3) to be extruded having a central hole (31) in the central opening (21) of the female die (2) for extrusion, wherein the outer contour of each extrusion piece (12) is larger than the inner contour of the central hole (31) of the part (3) to be extruded, and during extrusion, each extrusion piece (12) can pass through the central hole (31) of the part (3) to be extruded from top to bottom; 5) Heat treatment: Heat treatment of the extruded parts.

3. The manufacturing method according to claim 2, Features: The horizontal distance of the cross section of the inner contour of the opening (21) of the female mold (2) is D1, and the horizontal distance of the cross section of the outer contour of the part to be extruded (3) is D2, wherein D1=(1.001~1.200)D2.

4. The manufacturing method according to claim 2, Features: For parts with a carbon content higher than 0.2%, or a molybdenum, chromium, and nickel alloy content higher than 2%, an annealing treatment may be performed between step 3) and step 4), with an annealing temperature of 750 to 1080°C, an annealing holding time of 5 to 200 minutes, and a cooling rate from the annealing temperature to 300°C after annealing of less than 1.5°C / s.

5. The manufacturing method according to claim 2, Features: In step 5), the quenching temperature is 750~1250℃, the quenching holding time is 30~45min, the tempering temperature is 150~600℃, and the tempering holding time is 5~200min.

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