JP3871825B2 - Recompression molded body of metallic powder molding material, sintered body obtained from the recompression molded body, and production method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present inventionBakedSuitable for obtaining various structural machine parts made of sintered metal, obtained from recompression molded body of metallic powder molding material and recompression molded bodyBakedThe present invention relates to ligations and methods for producing them.
[0002]
[Prior art]
  BakedThe basics of the process to obtain the sintered metal are mixing of raw material powder-compacting-BakedThis is post-treatment (heat treatment, etc.). Although a product may be obtained only by the said process, in many cases, additional processing and various processes are performed according to the objective between or after each process.
[0003]
  For example, JP-A-1-123005 disclosesBakedIn order to obtain a machine part having high mechanical strength due to the sintered metal, the mixed powder is compacted to form a preform, and the preform is temporarily formed.BakedAfter forming the molding material, re-compression molding (cold forging) of this molding material,BakedYui (BookBakedA manufacturing method is disclosed.
[0004]
  Specifically, the recompression molding (cold forging) process of the molding material is composed of a temporary compression molding process and a main compression molding process, and a liquid lubricant is applied to the surface of the molding material to perform temporary compression molding. Thereafter, a negative pressure is applied to the molding material to suck and remove the lubricant, and then the molding material is subjected to main compression molding.
[0005]
  This prevents the lubricant remaining inside the preform from becoming porous by preventing the collapse of the minute voids inside the preform, thereby reducing the density of the product from 7.4 to 7.5 g. / Cm ^Three In other words, a product having higher mechanical strength than the conventional one can be obtained.
[0006]
[Problems to be solved by the invention]
  By the way, in the conventional example, focusing on the recompression molding process of the molding material, by increasing the density in the recompression molding, a product having a relatively high mechanical strength is obtained. There is a limit to the mechanical strength of the product obtained by this.
[0007]
  Therefore, in order to further increase the mechanical strength of the product, it is considered effective to increase the amount of carbon in the product, that is, the amount of graphite added to the metal powder, but generally the amount of graphite is increased. If so, the elongation of the molding material is reduced and the hardness is increased, so that the deformability when the molding material is recompressed is lowered, and there arises a problem that the recompression molding becomes difficult.
[0008]
  For example, according to the description on page 90 of the 2nd powder metallurgy development case presentation text (November 15, 1985, published by the Japan Powder Metallurgy Association), a carbon amount of 0.05 to 0.5% is formed. In the material, the elongation is 10% at the maximum, and it is shown that the hardness in this case is HRB83. However, experience shows that if the elongation of the molding material is 10% or less and the hardness exceeds HRB60, it is difficult to re-compress molding of the molding material. It has been desired to obtain a molding material having low properties and excellent deformability.
[0009]
  The inventorsBakedResearch has been conducted to obtain various mechanical structural parts with high mechanical strength using sintered metal.BakedTo form a molding material, which is then recompressed andBakedIn the case of obtaining a mechanical part by linking, the molding material plays an important factor in determining the ease of recompression molding and the mechanical properties of the resulting mechanical part. Recognizing that it is necessary to obtain a molding material having a high elongation, low hardness and excellent deformability, the research was advanced.
[0010]
  As a result of research, the properties of the molding material containing the predetermined amount of graphite, particularly the elongation and hardness, which are important properties for the ease of re-compression molding of the molding material, are preliminarily measured before the molding material is formed. The density of the compact and the preliminaryBakedIt has been found that it is determined by the structure of the molding material obtained by the process, especially the form of carbon contained in the molding material.
[0011]
  The present invention has been devised in view of the above-mentioned conventional situation,BakedSuitable for obtaining mechanical parts with high mechanical strength due to sintered metal, obtained from a recompression molded body of a metal powder molding material having excellent deformability and the recompression molded bodyBakedAn object is to provide a ligation and a method for producing them.
[0012]
[Means for Solving the Problems]
    Therefore, the invention according to claim 1 has a density of 7.3 g obtained by compacting a metallic powder obtained by mixing 0.3% by weight or more of graphite with a metallic powder containing iron as a main component. / Cm ^Three The above preforms800-1000 ° CTemporary at temperatureBakedAs a result, graphite remains at the grain boundaries of the metal powder.Perlite precipitated in the vicinity of the ferrite structure or graphite.Forming a metal powder molding material having a structure, and recompressing the metal powder molding material;The whole has a ferrite structure or a structure in which pearlite is deposited in the vicinity of graphite.The
[0013]
  According to the second aspect of the present invention, a metal powder obtained by mixing 0.3% by weight or more of graphite with a metal powder containing iron as a main component is compacted to a density of 7.3 g / cm. ^Three A preforming step for obtaining the above preform and a preform obtained in this preforming step800-1000 ° CTemporary at temperatureBakedAs a result, graphite remains at the grain boundaries of the metal powder.Perlite precipitated in the vicinity of the ferrite structure or graphite.Temporarily obtaining a metal powder molding material having a textureBakedThe tie process and this provisionalBakedA recompression molded body is obtained from a recompression process of recompressing the metallic powder molding material obtained in the binding process.
[0014]
  According to a third aspect of the present invention, in the configuration of the second aspect of the present invention, the pre-forming step is formed by pressing the metallic powder filled in the forming space of the forming die with the upper punch and the lower punch. The molding die has a large-diameter portion into which the upper punch is inserted, a small-diameter portion into which the lower punch is inserted, and a tapered portion that connects the large-diameter portion and the small-diameter portion. One or both of the punch and the lower punch are configured to have a notch for increasing the volume of the molding space at the outer peripheral end of the end surface facing the molding space of the molding die.
[0015]
  The invention according to claim 4 has a density of 7.3 g obtained by compacting a metallic powder obtained by mixing 0.3% by weight or more of graphite with a metallic powder containing iron as a main component. / Cm^ThreeThe above-mentioned preform is pre-sintered at a temperature of 800 to 1000 ° C., graphite remains at the grain boundary of the metal powder, and the whole is a ferrite structure or a metal powder having a structure in which pearlite is precipitated in the vicinity of the graphite A molding material is formed, the metal powder molding material is recompressed to form a recompression molded body having a ferrite structure or a structure in which pearlite is precipitated in the vicinity of graphite on the ferrite base, and The compression molded body is re-sintered at a temperature of 700 to 1300 ° C., and the graphite diffused in the ferrite or pearlite structure of the metal powder and the structure in which the graphite existing in the grain boundary of the metal powder diffused into the ferrite base. It is a sintered body having a remaining structure.
[0016]
  Further, the invention according to claim 5 is a method of compacting a metallic powder obtained by mixing 0.3% by weight or more of graphite with a metallic powder containing iron as a main component, and having a density of 7.3 g / cm.^ThreeThe preforming step for obtaining the above preformed body, and the preformed body obtained in this preforming step are pre-sintered at a temperature of 800 to 1000 ° C., and the graphite remains at the grain boundary of the metal powder. Temporary sintering process to obtain a metal powder molding material having a ferrite structure or a structure in which pearlite is precipitated in the vicinity of graphite, and recompression by recompressing the metal powder molding material obtained in this temporary sintering process The sintered compact is obtained from a recompression process for obtaining a compact and a re-sintering process for re-sintering the recompression compact obtained in the recompression process.
[0017]
  According to a sixth aspect of the present invention, in the configuration of the fifth aspect of the present invention, the preforming step is formed by pressing the metallic powder filled in the molding space of the molding die with the upper punch and the lower punch. The molding die has a large-diameter portion into which the upper punch is inserted, a small-diameter portion into which the lower punch is inserted, and a tapered portion that connects the large-diameter portion and the small-diameter portion. One or both of the punch and the lower punch are configured to have a notch for increasing the volume of the molding space at the outer peripheral end of the end surface facing the molding space of the molding die.
[0018]
  The invention according to claim 7 is the structure according to claim 5 or 6, wherein the re-sintering temperature in the re-sintering step is 700 to 1300 ° C.
[0019]
  The invention according to claim 8 is a powder obtained by compacting a metal powder obtained by mixing 0.3% by weight or more of graphite with a metal powder containing iron as a main component, and has a density of 7.3 g. / Cm^ThreeThe above-mentioned preform is pre-sintered at a temperature of 800 to 1000 ° C., graphite remains at the grain boundary of the metal powder, and the whole is a ferrite structure or a metal powder having a structure in which pearlite is precipitated in the vicinity of the graphite A molding material is formed, and the metal powder molding material is recompressed to form a recompression molded body having a ferrite structure or a structure in which pearlite is precipitated in the vicinity of graphite on the ferrite base, and The sintered compact is re-sintered at a temperature of 700 to 1300 ° C., and graphite diffuses and remains in the structure in which the graphite existing at the grain boundaries of the metal powder diffuses into the ferrite ground and in the ferrite or pearlite structure of the metal powder. A sintered body having a texture in a state of being formed is formed, and the sintered body is subjected to a heat treatment.
[0020]
  According to the ninth aspect of the present invention, a metal powder obtained by mixing 0.3% by weight or more of graphite with a metal powder containing iron as a main component is compacted to a density of 7.3 g / cm.^ThreeThe preforming step for obtaining the above preformed body, and the preformed body obtained in this preforming step are pre-sintered at a temperature of 800 to 1000 ° C., and the graphite remains at the grain boundary of the metal powder. Temporary sintering process to obtain a metal powder molding material having a ferrite structure or a structure in which pearlite is precipitated in the vicinity of graphite, and recompression by recompressing the metal powder molding material obtained in this temporary sintering process Re-compression process to obtain a molded body, re-sintering process to obtain a sintered body by re-sintering the re-compression molded body obtained in this re-compression process, and sintering obtained in this re-sintering process A sintered body is obtained from a heat treatment step of heat-treating the body.
[0021]
  According to a tenth aspect of the present invention, in the configuration of the ninth aspect of the invention, the pre-forming step is formed by pressing the metallic powder filled in the forming space of the forming die with the upper punch and the lower punch. The molding die has a large-diameter portion into which the upper punch is inserted, a small-diameter portion into which the lower punch is inserted, and a tapered portion that connects the large-diameter portion and the small-diameter portion. One or both of the punch and the lower punch are configured to have a notch for increasing the volume of the molding space at the outer peripheral end of the end surface facing the molding space of the molding die.
[0022]
  The invention described in claim 11 is the structure of the invention described in claim 9 or 10, wherein the re-sintering temperature in the re-sintering step is 700-1300 ° C.
[0023]
  In the invention according to claim 1, the recompression molded body of the present invention is obtained by recompression molding of a metal powder molding material (hereinafter simply referred to as a molding material). It is obtained by pre-sintering a preform obtained by molding at a temperature of 800 to 1000 ° C.
[0024]
  The metallic powder is formed by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component. By making the amount of graphite added to the metal powder 0.3% by weight or more, the mechanical strength of the sintered body obtained by recompression molding and re-sintering of the molding material is approximately the same as that of the cast forging material. It can be increased.
[0025]
  The density of the preform is 7.3 g / cm.^ThreeIt is said above. The density of the preform is 7.3 g / cm^ThreeBy setting it as the above, the elongation of the shaping | molding raw material obtained by pre-sintering this preforming body can be enlarged, and hardness can be made low.
[0026]
  The density is 7.3 g / cm^ThreeThe structure of the molding material obtained by presintering the above preform is a structure in which graphite remains in the grain boundary of the metal powder. This indicates that almost no carbon is diffused inside the crystal of the metal powder, and at least graphite is diffused into the crystal grains so as to be solid-solved or not in a state of forming carbides. Specifically, the structure of the metal powder is entirely a ferrite structure or a structure in which pearlite is deposited in the vicinity of graphite. For this reason, the said molding material has the property that elongation is large and hardness is low, and it has the outstanding deformability.
[0027]
  In addition, the density is 7.3 g / cm^ThreeIn the above preform, the voids between the metal powder particles are not continuous and are in an isolated state, whereby a molding material having a large elongation after pre-sintering is obtained. That is, when the gaps between the particles of the metal powder are continuous, in addition to the atmospheric gas in the furnace entering the interior of the preform during preliminary sintering, the gas generated from the graphite inside Although carburization will be promoted by diffusing to the surroundings, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the molding material has a density of 7.3 g / cm.^ThreeBy doing so, carbon diffusion hardly occurs when pre-sintering the preform, indicating that it is hardly affected by the amount of graphite, and almost no carbon diffusion occurs. This indicates that the hardness of the molding material obtained by preliminary sintering can be kept low.
[0028]
  Further, by the preliminary sintering, sintering by surface diffusion or melting at the contact surface between the metal powder particles occurs over a wide range, so that a large elongation can be obtained.
[0029]
  The recompression molding of the molding material obtained by presintering the preform is preferably performed at room temperature. In this case, since the molding material has excellent deformability, it is easily recompressed.
[0030]
  For this reason, a recompression molded body having a small molding load in the recompression molding and high dimensional accuracy is obtained. The recompression molded body has a structure in which the metal particles of the molding material are greatly deformed and flattened by recompression molding, and the molding material has a structure in which graphite remains in the grain boundary of the metal powder. In this state, it is excellent in machinability and lubricity.
[0031]
  Therefore, according to the first aspect of the present invention, a recompression molded body of a metal powder molding material having excellent deformability, which is suitable for obtaining a mechanical part having high mechanical strength due to sintered metal, can be obtained.
[0032]
  3. The invention according to claim 2, wherein the preform is obtained by a preforming step, the molding material is obtained by pre-sintering the preform in the provisional sintering step, and the recompression molding is obtained by recompressing the molding material. Obtained by recompression molding in the process.
[0033]
  The metallic powder to be compacted in the preforming step is formed by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component. By making the amount of graphite added to the metal powder 0.3% by weight or more, the mechanical strength of the sintered body obtained by recompression molding and re-sintering of the molding material is approximately the same as that of the cast forging material. Can be increased.
[0034]
  The density of the preform formed in the preforming step is 7.3 g / cm.^ThreeIt is said above. The density of the preform is 7.3 g / cm^ThreeBy setting it as the above, the elongation of the shaping | molding raw material obtained by pre-sintering this preforming body by a pre-sintering process can be enlarged, and hardness can be made low.
[0035]
  The density is 7.3 g / cm^ThreeThe structure of the molding material obtained by pre-sintering the above preform in the pre-sintering step is a structure in which graphite remains in the grain boundary of the metal powder. This indicates that almost no carbon is diffused inside the crystal of the metal powder, and at least graphite is diffused into the crystal grains so as to be solid-solved or not in a state of forming carbides. Specifically, the structure of the metal powder is entirely a ferrite structure or a structure in which pearlite is deposited in the vicinity of graphite. For this reason, the said molding material has the property that elongation is large and hardness is low, and it has the outstanding deformability.
[0036]
  In addition, the density is 7.3 g / cm^ThreeIn the above preform, the voids between the metal powder particles are not continuous and are in an isolated state, whereby a molding material having a large elongation after pre-sintering in the pre-sintering step is obtained. That is, when the gaps between the particles of the metal powder are continuous, in addition to the atmospheric gas in the furnace entering the interior of the preform during preliminary sintering, the gas generated from the graphite inside Although carburization will be promoted by diffusing to the surroundings, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the molding material has a density of 7.3 g / cm.^ThreeBy doing so, carbon diffusion hardly occurs when pre-sintering the preform, indicating that it is hardly affected by the amount of graphite, and almost no carbon diffusion occurs. This indicates that the hardness of the molding material obtained by preliminary sintering can be kept low.
[0037]
  Further, by the preliminary sintering in the preliminary sintering process, surface diffusion or melting at the contact surface between the metal powder particles occurs over a wide range, so that a large elongation can be obtained.
[0038]
  In the invention according to claim 3, the preforming step of the preform is performed by pressurizing the metallic powder filled in the molding space of the molding die with the upper punch and the lower punch. In this case, the preform as a whole is 7.3 g / cm.^ThreeAlthough the above-mentioned high density is obtained and the friction between the preform and the molding die is increased, the density of the preform is locally low at the notch provided in one or both of the upper punch and the lower punch. This will reduce the friction. For this reason, the preform is easily released from the molding die in combination with the action of the tapered portion formed in the molding space of the molding die, and the density is 7.3 g / cm.^ThreeThe above preform is obtained.
[0039]
  800-1000 degreeC is selected as the temporary sintering temperature of the said temporary sintering process. As a result, a molding material having an excellent deformability having a structure in which graphite remains in the grain boundary of the metal powder, having an elongation of 10% or more and a hardness of HRB 60 or less is obtained.
[0040]
  The recompression process is preferably performed at room temperature. In this case, since the molding material has excellent deformability, it is easily recompressed.
[0041]
  For this reason, a recompression molded body having a small molding load in the recompression molding and high dimensional accuracy is obtained. The recompression molded body has a structure in which the metal particles of the molding material are greatly deformed and flattened by recompression molding, and the molding material has a structure in which graphite remains in the grain boundary of the metal powder. In this state, it is excellent in machinability and lubricity.
[0042]
  Therefore, according to the second aspect of the present invention, there is provided a method for producing a recompression molded body of a metal powder molding material having excellent deformability, which is suitable for obtaining a mechanical part having high mechanical strength due to sintered metal. can get.
[0043]
  According to the invention of claim 3, the density is 7.3 g / cm.^ThreeThe above preform can be easily obtained.
[0044]
  In the invention according to claim 4, the sintered body of the present invention is obtained by re-sintering the recompression molded body at a temperature of 700 to 1300 ° C. The recompression molded body is obtained by recompression molding a metal powder molding material, and the metal powder molding material is a preform formed by compacting metal powder at a temperature of 800 to 1000 ° C. Obtained by presintering.
[0045]
  The metallic powder is formed by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component. By making the amount of graphite added to the metal powder 0.3% by weight or more, the mechanical strength of the sintered body obtained by recompression molding and re-sintering of the molding material is approximately the same as that of the cast forging material. It can be increased.
[0046]
  The density of the preform is 7.3 g / cm.^ThreeIt is said above. The density of the preform is 7.3 g / cm^ThreeBy setting it as the above, the elongation of the shaping | molding raw material obtained by pre-sintering this preforming body can be enlarged, and hardness can be made low.
[0047]
  The density is 7.3 g / cm^ThreeThe structure of the molding material obtained by presintering the above preform is a structure in which graphite remains in the grain boundary of the metal powder. This indicates that almost no carbon is diffused inside the crystal of the metal powder, and at least graphite is diffused into the crystal grains so as to be solid-solved or not in a state of forming carbides. Specifically, the structure of the metal powder is a ferrite structure as a whole or a structure in which pearlite is deposited in the vicinity of graphite. For this reason, the said molding material has the property that elongation is large and hardness is low, and it has the outstanding deformability.
[0048]
  In addition, the density is 7.3 g / cm^ThreeIn the above preform, the voids between the metal powder particles are not continuous and are in an isolated state, whereby a molding material having a large elongation after pre-sintering is obtained. That is, when the gaps between the particles of the metal powder are continuous, in addition to the atmospheric gas in the furnace entering the interior of the preform during preliminary sintering, the gas generated from the graphite inside Although carburization will be promoted by diffusing to the surroundings, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the molding material has a density of 7.3 g / cm.^ThreeBy doing so, carbon diffusion hardly occurs when pre-sintering the preform, indicating that it is hardly affected by the amount of graphite, and almost no carbon diffusion occurs. This indicates that the hardness of the molding material obtained by preliminary sintering can be kept low.
[0049]
  Further, by the preliminary sintering, sintering by surface diffusion or melting at the contact surface between the metal powder particles occurs over a wide range, so that a large elongation can be obtained.
[0050]
  The recompression molding of the molding material obtained by presintering the preform is preferably performed at room temperature. In this case, since the molding material has excellent deformability, it is easily recompressed, and a recompression molded body with a small molding load of recompression molding and high dimensional accuracy is obtained.
[0051]
  The sintered body is obtained by re-sintering the re-compressed molded body, and this sintered body is in a state where graphite existing at the grain boundary of the metal powder diffuses into the ferrite ground (solid solution or forms a carbide). The structure is a structure in which graphite is diffused and remains at a predetermined ratio in the structure and the ferrite or pearlite structure of the metal powder. In this case, the predetermined ratio includes a case where the residual amount of graphite is zero.
[0052]
  The residual ratio of graphite varies depending on the re-sintering temperature, and the higher the re-sintering temperature, the lower the residual ratio of graphite. Accordingly, mechanical properties such as a predetermined strength can be selected for the sintered body.
[0053]
  Therefore, according to the invention described in claim 4, the recompression molded body of the metal powder molding material having excellent deformability, which is suitable for obtaining a mechanical part having high mechanical strength by the sintered metal, is re-sintered. Thus obtained sintered body is obtained.
[0054]
  6. The invention according to claim 5, wherein the preform is obtained by a preforming step, the molding material is obtained by pre-sintering the preform in a pre-sintering step, and the recompression molding is obtained by recompressing the molding material. It is obtained by recompression molding in the process, and the sintered body is obtained by re-sintering the recompression molded body.
[0055]
  The metallic powder to be compacted in the preforming step is formed by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component. By making the amount of graphite added to the metal powder 0.3% by weight or more, the mechanical strength of the sintered body obtained by recompression molding and re-sintering of the molding material is approximately the same as that of the cast forging material. Can be increased.
[0056]
  The density of the preform formed in the preforming step is 7.3 g / cm.^ThreeIt is said above. The density of the preform is 7.3 g / cm^ThreeBy setting it as the above, the elongation of the shaping | molding raw material obtained by pre-sintering this preforming body by a pre-sintering process can be enlarged, and hardness can be made low.
[0057]
  The density is 7.3 g / cm^ThreeThe structure of the molding material obtained by presintering the above preform in the presintering step is a structure in which graphite remains at the grain boundaries of the metal powder. This indicates that almost no carbon is diffused inside the crystal of the metal powder, and at least graphite is diffused into the crystal grains so as to be solid-solved or not in a state of forming carbides. Specifically, the structure of the metal powder is entirely a ferrite structure or a structure in which pearlite is deposited in the vicinity of graphite. For this reason, the said molding material has the property that elongation is large and hardness is low, and it has the outstanding deformability.
[0058]
  In addition, the density is 7.3 g / cm^ThreeIn the above preform, the voids between the metal powder particles are not continuous and are in an isolated state, whereby a molding material having a large elongation after pre-sintering in the pre-sintering step is obtained. That is, when the gaps between the particles of the metal powder are continuous, in addition to the atmospheric gas in the furnace entering the interior of the preform during preliminary sintering, the gas generated from the graphite inside Although carburization will be promoted by diffusing to the surroundings, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the molding material has a density of 7.3 g / cm.^ThreeBy doing so, carbon diffusion hardly occurs when pre-sintering the preform, indicating that it is hardly affected by the amount of graphite, and almost no carbon diffusion occurs. This indicates that the hardness of the molding material obtained by preliminary sintering can be kept low.
[0059]
  Further, by the preliminary sintering in the preliminary sintering process, surface diffusion or melting at the contact surface between the metal powder particles occurs over a wide range, so that a large elongation can be obtained.
[0060]
  In the invention according to claim 6, the preforming step of the preform is performed by pressing the metal powder filled in the molding space of the molding die with the upper punch and the lower punch. In this case, the preform as a whole is 7.3 g / cm.^ThreeAlthough the above-mentioned high density is obtained and the friction between the preform and the molding die is increased, the density of the preform is locally low at the notch provided in one or both of the upper punch and the lower punch. This will reduce the friction. For this reason, the preform is easily released from the molding die in combination with the action of the tapered portion formed in the molding space of the molding die, and the density is 7.3 g / cm.^ThreeThe above preform is obtained.
[0061]
  The sintered body is obtained by re-sintering the re-compressed molded body in the re-sintering step, and the sintered body diffuses graphite (existing solid solution or carbide) in the ferrite ground at the grain boundary of the metal powder. A structure in which the graphite is diffused and remains at a predetermined ratio in the ferrite or pearlite structure of the metal powder. In this case, the predetermined ratio includes a case where the residual amount of graphite is zero.
[0062]
  The residual ratio of graphite in the sintered body varies depending on the re-sintering temperature, and the higher the re-sintering temperature, the lower the residual ratio of graphite. Accordingly, mechanical properties such as a predetermined strength can be selected for the sintered body.
[0063]
  According to the invention of claim 7, 700 to 1300 ° C. is selected as the re-sintering temperature in the re-sintering step. As a result, a sintered body having a low graphite diffusion rate and a high residual rate of graphite is obtained in the low temperature range of the re-sintering temperature, and a large amount of graphite is diffused and the residual rate is high in the high temperature range of the re-sintering temperature. There can be obtained a sintered body with a small amount of crystal regrowth and the highest strength.
[0064]
  Therefore, according to the seventh aspect of the present invention, a recompression molded body of a metal powder molding material having excellent deformability, which is suitable for obtaining a machine part having high mechanical strength by sintered metal, is re-sintered. Thus, a method for producing a sintered body is obtained.
[0065]
  According to the invention of claim 8, the density is 7.3 g / cm.^ThreeThe above preform can be easily obtained.
[0066]
  According to the invention of claim 8, the sintered body in a state where the diffusion of graphite is small and the residual ratio of graphite is high, and the residual ratio is low due to a large amount of graphite diffusing depending on the re-sintering temperature. In addition, a sintered body having a maximum strength and a small crystal regrowth is obtained.
[0067]
  In the invention according to claim 8, the sintered body of the present invention is obtained by subjecting a sintered body obtained by re-sintering the recompression molded body at a temperature of 700 to 1300 ° C. The recompression molded body is obtained by recompression molding a metal powder molding material, and the metal powder molding material is a preform formed by compacting metal powder at a temperature of 800 to 1000 ° C. Obtained by presintering.
[0068]
  The metallic powder is formed by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component. By making the amount of graphite added to the metal powder 0.3% by weight or more, the mechanical strength of the sintered body obtained by recompression molding and re-sintering of the molding material is approximately the same as that of the cast forging material. It can be increased.
[0069]
  The density of the preform is 7.3 g / cm.^ThreeIt is said above. The density of the preform is 7.3 g / cm^ThreeBy setting it as the above, the elongation of the shaping | molding raw material obtained by pre-sintering this preforming body can be enlarged, and hardness can be made low.
[0070]
  The density is 7.3 g / cm^ThreeThe structure of the molding material obtained by presintering the above preform is a structure in which graphite remains in the grain boundary of the metal powder. This indicates that almost no carbon is diffused inside the crystal of the metal powder, and at least graphite is diffused into the crystal grains so as to be solid-solved or not in a state of forming carbides. Specifically, the structure of the metal powder is a ferrite structure as a whole or a structure in which pearlite is deposited in the vicinity of graphite. For this reason, the said molding material has the property that elongation is large and hardness is low, and it has the outstanding deformability.
[0071]
  In addition, the density is 7.3 g / cm^ThreeIn the above preform, the voids between the metal powder particles are not continuous and are in an isolated state, whereby a molding material having a large elongation after pre-sintering is obtained. That is, when the gaps between the particles of the metal powder are continuous, in addition to the atmospheric gas in the furnace entering the interior of the preform during preliminary sintering, the gas generated from the graphite inside Although carburization will be promoted by diffusing to the surroundings, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the molding material has a density of 7.3 g / cm.^ThreeBy doing so, carbon diffusion hardly occurs when pre-sintering the preform, indicating that it is hardly affected by the amount of graphite, and almost no carbon diffusion occurs. This indicates that the hardness of the molding material obtained by preliminary sintering can be kept low.
[0072]
  Further, by the preliminary sintering, sintering by surface diffusion or melting at the contact surface between the metal powder particles occurs over a wide range, so that a large elongation can be obtained.
[0073]
  The recompression molding of the molding material obtained by presintering the preform is preferably performed at room temperature. In this case, since the molding material has excellent deformability, it is easily recompressed.
[0074]
  The sintered body is obtained by re-sintering the re-compressed molded body, and this sintered body is in a state where graphite existing at the grain boundary of the metal powder diffuses into the ferrite ground (solid solution or forms a carbide). The structure and the metal powder have a structure in which graphite is diffused and remains at a predetermined ratio in the ferrite or pearlite structure. In this case, the predetermined ratio includes a case where the residual amount of graphite is zero.
[0075]
  The residual ratio of graphite in the sintered body varies depending on the re-sintering temperature, and the higher the re-sintering temperature, the lower the residual ratio of graphite. Accordingly, mechanical properties such as a predetermined strength can be selected for the sintered body.
[0076]
  A heat treatment is applied to a sintered body obtained by re-sintering the recompressed molded body at a temperature of 700 to 1300 ° C. The heat treatment is performed by various treatments such as induction hardening, carburizing and quenching, nitriding, and combinations thereof. The sintered body formed by re-sintering the re-compressed body at a temperature of 700 to 1300 ° C. has a high density without voids by re-compression molding, so that the diffusion of carbon by heat treatment goes from the surface to the inside. It becomes less according to. For this reason, the sintered body subjected to the heat treatment has increased hardness in the vicinity of the surface, and the inside has toughness, and has excellent mechanical properties as a whole.
[0077]
  Therefore, according to the eighth aspect of the present invention, a recompressed molded body of a metal powder molding material having excellent deformability, which is suitable for obtaining a machine part having high mechanical strength due to sintered metal, is re-sintered. A sintered body obtained by subjecting the sintered body to heat treatment is obtained.
[0078]
  10. The invention according to claim 9, wherein the preform is obtained by a preforming step, the molding material is obtained by pre-sintering the preform in the provisional sintering step, and the recompression molding is obtained by recompressing the molding material. It is obtained by re-compression molding in the process, and the sintered body is obtained by re-sintering the re-compression molded body, and this sintered body is subjected to heat treatment.
[0079]
  The metallic powder to be compacted in the preforming step is formed by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component. By making the amount of graphite added to the metal powder 0.3% by weight or more, the mechanical strength of the sintered body obtained by recompression molding and re-sintering of the molding material is approximately the same as that of the cast forging material. Can be increased.
[0080]
  The density of the preform formed in the molding process is 7.3 g / cm.^ThreeIt is said above. The density of the preform is 7.3 g / cm^ThreeBy setting it as the above, the elongation of the shaping | molding raw material obtained by pre-sintering this preforming body by a pre-sintering process can be enlarged, and hardness can be made low.
[0081]
  The density is 7.3 g / cm^ThreeThe structure of the molding material obtained by presintering the above preform in the presintering step is a structure in which graphite remains at the grain boundaries of the metal powder. This indicates that almost no carbon is diffused inside the crystal of the metal powder, and at least graphite is diffused into the crystal grains so as to be solid-solved or not in a state of forming carbides. Specifically, the structure of the metal powder is a ferrite structure as a whole or a structure in which pearlite is deposited in the vicinity of graphite. For this reason, the said molding material has the property that elongation is large and hardness is low, and it has the outstanding deformability.
[0082]
  In addition, the density is 7.3 g / cm^ThreeIn the above preform, the voids between the metal powder particles are not continuous and are in an isolated state, whereby a molding material having a large elongation after pre-sintering in the pre-sintering step is obtained. That is, when the gaps between the particles of the metal powder are continuous, in addition to the atmospheric gas in the furnace entering the interior of the preform during preliminary sintering, the gas generated from the graphite inside Although carburization will be promoted by diffusing to the surroundings, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the molding material has a density of 7.3 g / cm.^ThreeBy doing so, carbon diffusion hardly occurs when pre-sintering the preform, indicating that it is hardly affected by the amount of graphite, and almost no carbon diffusion occurs. This indicates that the hardness of the molding material obtained by preliminary sintering can be kept low.
[0083]
  Further, by the preliminary sintering in the preliminary sintering process, surface diffusion or melting at the contact surface between the metal powder particles occurs over a wide range, so that a large elongation can be obtained.
[0084]
  In the invention according to claim 9, the preforming step of the preform is performed by pressing the metal powder filled in the molding space of the molding die with the upper punch and the lower punch. In this case, the preform as a whole is 7.3 g / cm.^ThreeAlthough the above-mentioned high density is obtained and the friction between the preform and the molding die is increased, the density of the preform is locally low at the notch provided in one or both of the upper punch and the lower punch. This will reduce the friction. For this reason, the preform is easily released from the molding die in combination with the action of the tapered portion formed in the molding space of the molding die, and the density is 7.3 g / cm.^ThreeThe above preform is obtained.
[0085]
  In the invention according to claim 9, 800 to 1000 ° C. is selected as the preliminary sintering temperature in the preliminary sintering step. As a result, a molding material having an excellent deformability having a structure in which graphite remains in the grain boundary of the metal powder, having an elongation of 10% or more and a hardness of HRB 60 or less is obtained.
[0086]
  The recompression process is preferably performed at room temperature. In this case, since the molding material has excellent deformability, it is easily recompressed.
[0087]
  For this reason, a recompression molded body having a small molding load in the recompression molding and high dimensional accuracy is obtained.
[0088]
  The sintered body is obtained by re-sintering the re-compressed molded body in the re-sintering step, and the sintered body diffuses graphite (existing solid solution or carbide) in the ferrite ground at the grain boundary of the metal powder. The metal powder has a structure in which graphite is diffused and remains at a predetermined ratio in the ferrite or pearlite structure. In this case, the predetermined ratio includes a case where the residual amount of graphite is zero.
[0089]
  The residual ratio of graphite in the sintered body varies depending on the re-sintering temperature, and the higher the re-sintering temperature, the lower the residual ratio of graphite. Accordingly, mechanical properties such as a predetermined strength can be selected for the sintered body.
[0090]
  According to the invention of claim 11, 700 to 1300 ° C. is selected as the re-sintering temperature in the re-sintering step. As a result, a sintered body having a low graphite diffusion rate and a high residual rate of graphite is obtained in the low temperature range of the re-sintering temperature, and a large amount of graphite is diffused and the residual rate is high in the high temperature range of the re-sintering temperature. There can be obtained a sintered body with a small amount of crystal regrowth and the highest strength.
[0091]
  A heat treatment is applied to a sintered body obtained by re-sintering the recompressed molded body at a temperature of 700 to 1300 ° C. The heat treatment is performed by various treatments such as induction hardening, carburizing and quenching, nitriding, and combinations thereof. The sintered body formed by re-sintering the re-compressed body at a temperature of 700 to 1300 ° C. has a high-density structure without voids by re-compression molding. Less as you go. For this reason, the sintered body subjected to the heat treatment has increased hardness in the vicinity of the surface, and the inside has toughness, and has excellent mechanical properties as a whole.
[0092]
  Therefore, according to the eleventh aspect of the present invention, the recompression molded body of the metal powder molding material having excellent deformability, which is suitable for obtaining a mechanical part having high mechanical strength by the sintered metal, is re-sintered. Thus, a method for producing a sintered body obtained by heat-treating the sintered body is obtained.
[0093]
  According to the invention of claim 11, the density is 7.3 g / cm.^ThreeThe above preform can be easily obtained.
[0094]
  According to the invention described in claim 11, according to the re-sintering temperature, the sintered body in a state where the diffusion of graphite is small and the residual ratio of graphite is large, and the residual ratio is low due to the diffusion of many graphites. In addition, a sintered body having a maximum strength and a small crystal regrowth can be obtained.
[0095]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0096]
  FIG. 1 is an explanatory diagram of a manufacturing process of a recompression molded body of a metal powder molding material and a sintered body obtained from the recompressed molded body, and FIG. 2 shows a manufacturing process of a preformed body, showing an embodiment of the present invention. A state in which the metal powder is filled in the molding space of the molding die (a), a state in which the metal powder is pressurized with the upper punch and the lower punch (b), and molding for taking out the preform after completion of the pressurization. FIG. 3 is an explanatory view showing a state in which the die starts to be lowered (c) and a state in which the preform is taken out (d). FIG. 3 shows a preform formed from a metallic powder mixed with 0.5% by weight of graphite at 800 ° C. FIG. 4 is a drawing showing the relationship between the density and elongation of a molding material obtained by pre-sintering as data (a) and graph (b), FIG. 4 is a drawing showing the structure of the molding material, and FIG. .3g / cm^ThreeFIG. 6 is a drawing showing the change in elongation when the amount of graphite and the pre-sintering temperature are changed in data (a) and graph (b), and FIG. 6 shows a density of 7.5 g / cm.^ThreeFIG. 7 is a drawing showing the change in elongation when the amount of graphite and the pre-sintering temperature are changed in data (a) and graph (b), and FIG. 7 shows a density of 7.3 g / cm.^ThreeFIG. 8 is a drawing showing the change in hardness when the amount of graphite and the pre-sintering temperature are changed in data (a) and graph (b), and FIG. 8 shows a density of 7.5 g / cm.^ThreeFIG. 9 is a graph showing data (a) and graph (b) showing changes in hardness when the amount of graphite and the pre-sintering temperature are changed, and FIG. . Density of 7.3 g / cm formed from metallic powder mixed with 5 wt%^ThreeAnd 7.5 g / cm^ThreeFIG. 10 shows the relationship between the pre-sintering temperature and the yield stress for the molding material of FIG. 10 as data (a) and graph (b). FIG. 10 shows a metallic material in which 0.5% by weight of graphite having a particle size of 5 μm is mixed. The density formed from the powder is 7.3 g / cm^ThreeAnd 7.5 g / cm^ThreeFIG. 11 shows the relationship between the pre-sintering temperature and the yield stress in the data (a) and the graph (b), FIG. 11 shows the structure of the recompression molded product, and the recompression molding is mild ( a) Further, in the case of recompression molding, the drawing shown in (b), FIG. 12 is a drawing showing the structure of the sintered body, FIG. 13 is a graph showing changes in the graphite residual ratio when the re-sintering temperature is changed, FIG. 14 is a drawing showing a) and graph (b), FIG. 14 is a drawing showing changes in tensile strength when the re-sintering temperature is changed, FIG. 15 is a drawing showing data (a) and graph (b), and FIG. FIG. 16 shows the change in hardness when the sintering temperature is changed, as shown in data (a) and graph (b). FIG. 16 shows the heat treatment of the sintered body obtained by changing the re-sintering temperature under predetermined conditions. FIG. 17 shows the relationship between the re-sintering temperature and the tensile strength with the data (a) and the graph (b). The relationship between the distance and the hardness of the surface of the heat-treated material was subjected to heat treatment in the conditions is a drawing showing the data (a), and a graph (b).
[0097]
  In the figure, 1 is a preforming step, 2 is a preliminary sintering step, 3 is a recompression step, 4 is a re-sintering step, and 5 is a heat treatment step.
[0098]
  In the preforming step 1, the metal powder 7 is compacted to obtain a preform 8, and in the preliminary sintering step 2, the preform 8 is temporarily sintered to obtain a metal powder molding material 9, In the recompression step 3, the metal powder molding material 9 is recompressed and a recompression molded body 10 is obtained. In the re-sintering step 4, the re-compression molded body 10 is re-sintered to obtain a sintered body 11, and in the heat treatment step 5, the sintered body 11 is subjected to heat treatment.
[0099]
  First, the preforming step 1 is a step of compacting the metallic powder 7 to obtain a preformed body 8, and in this embodiment, as shown in FIGS. The powder 7 is filled in the molding space 15 of the molding die 14 and is pressed by the upper punch 16 and the lower punch 17, whereby the preform 8 is obtained. In this case, the metallic powder 7 and the forming die 14 are in a normal temperature state.
[0100]
  Specifically, the metallic powder 7 is formed by mixing 0.3% by weight or more of graphite 7b with metal powder 7a containing iron as a main component. By setting the amount of graphite 7b added to the metallic powder 7 to 0.3% by weight or more, a recompression molded body 10 obtained by recompressing the metallic powder molding material 9 or this recompressed molded body The mechanical strength of the sintered body 11 obtained by re-sintering 10 can be increased to the same extent as that of the cast forged material.
  The forming space 15 of the forming die 14 filled with the metallic powder 7 includes a large diameter portion 19 into which the upper punch 16 is inserted, a small diameter portion 20 into which the lower punch 17 is inserted, and the large diameter portion 19 and the small diameter. The taper part 21 which connects the part 20 is provided.
[0101]
  One or both of the upper punch 16 and the lower punch 17 inserted into the molding space 15 of the molding die 14, in this embodiment, the upper punch 16 has an outer periphery of the end surface 22 facing the molding space 15 of the molding die 14. A notch 23 for increasing the volume of the molding space 15 is formed at the end. In this embodiment, the notch 23 has a bowl-shaped cross section and is formed in an annular shape.
[0102]
  Reference numeral 24 denotes a core inserted into the molding space 15 of the molding die 14, and the preform 24 formed in the molding space 15 is formed in a substantially cylindrical shape by the core 24.
[0103]
  In the preforming step 1, first, a metal powder 7 formed by mixing 0.3 wt% or more of graphite 7 b into a metal powder 7 a containing iron as a main component in a molding space 15 of a molding die 14 ( (See FIG. 2 (a)).
[0104]
  Next, the upper punch 16 and the lower punch 17 are inserted into the molding space 15 of the molding die 14 to press the metallic powder 7. Specifically, the upper punch 16 is inserted into the large diameter portion 19 of the molding space 15, and the lower punch 17 is inserted into the small diameter portion 20 of the molding space 15 and pressurized. At this time, the upper punch 16 in which the notch 23 is formed stops in the large diameter portion 19 (see FIG. 2B).
[0105]
  After the metallic powder 7 is pressed and compacted, the upper punch 16 is retracted (raised) and the molding die 14 is lowered (see FIG. 2 (c)), and the compacted preform is molded. The body 8 is taken out from the molding space 15 (see FIG. 2D).
[0106]
  By the way, in general, when metal powder is compacted, the friction between the compacted product and the mold increases as the density of the compacted product increases. Due to the spring back of the product, it becomes difficult to take out the compacted product from the mold. For this reason, although it is said that it is difficult to obtain a high-density compacting product, in the said pre-molding process 1, this is solved advantageously.
[0107]
  That is, since the forming space 15 of the forming die 14 includes the tapered portion 21, the tapered portion 21 has a so-called draft angle, and the compacted preform 8 can be easily taken out. Further, the upper punch 16 is formed with a notch 23 for enlarging the volume of the molding space 15 at the outer peripheral end of the end surface 22 desired in the molding space 15 of the molding die 14. Thus, the density of the preformed body 8 is locally reduced, the friction between the preformed body 8 and the molding die 14, the spring back of the preformed body 8, etc. are kept low, and the preformed body 8 can be easily taken out. become.
[0108]
  Thereby, the density is 7.3 g / cm.^ThreeThe above preform 8 can be easily obtained.
[0109]
  The density of the preform 8 is 7.3 g / cm.^ThreeBy setting it as the above, the elongation of the metallic-powder shaping | molding raw material 9 (it is explained in full detail later) obtained by pre-sintering this preforming body 8 by the pre-sintering process 2 can be enlarged. That is, as shown in FIG. 3, the density of the preform 8 is 7.3 g / cm.^ThreeBy setting it as the above, the elongation of the metal-powder shaping | molding raw material 9 can be 10% or more.
[0110]
  Next, the preformed body 8 obtained in the preforming step 1 is temporarily sintered in the provisional sintering step 2. As a result, as shown in FIG. 4, a metallic powder molding material 9 having a structure in which graphite 7b remains at the grain boundaries of the metallic powder 7a is obtained. When the entire graphite 7b remains at the grain boundary of the metal powder 7a, the entire structure of the metal powder 7a is a ferrite (F) structure, and when a part of the graphite 7b remains. The structure of the metal powder 7a exhibits a structure in which pearlite (P) is precipitated in the vicinity of the graphite 7b on the ferrite ground. At least, the graphite 7b does not have a structure in which all of the graphite 7b is diffused and dissolved in crystal grains or a carbide is formed. For this reason, the said metal powder molding raw material 9 has the property that elongation is large and hardness is low, and has the outstanding deformability.
[0111]
  In addition, the density is 7.3 g / cm^ThreeIn the preformed body 8 described above, the gaps between the particles of the metal powder 7a are not continuous and are in an isolated state, whereby a metal powder molding material 9 having a large elongation after pre-sintering is obtained. That is, when the gaps between the particles of the metal powder 7a are continuous, the atmosphere gas in the furnace penetrates deeply into the preformed body 8 through the gaps during temporary sintering, Although the gas generated from the graphite diffuses around and promotes carburization, since the voids are isolated, this is advantageously prevented, resulting in a large elongation. This means that the elongation of the metal powder molding material 9 has a density of 7.3 g / cm.^ThreeBy the above, it has shown that it is hardly influenced by the quantity of graphite 7b. This is because almost no carbon diffusion occurs when the preform 8 is temporarily sintered. Further, since the carbon is hardly diffused when the preformed body 8 is pre-sintered, the hardness of the metal powder molding material 9 obtained by pre-sintering can be kept low.
[0112]
  In addition, by the preliminary sintering step 2, sintering by surface diffusion or melting at a contact surface between the particles of the metal powder 7a occurs over a wide range, thereby obtaining a large elongation, preferably an elongation of 10% or more. It becomes.
[0113]
  As the preliminary sintering temperature in the preliminary sintering step 2, a temperature of 800 to 1000 ° C. is preferably selected. By setting the pre-sintering temperature in the pre-sintering step 2 to 800 to 1000 ° C., the metal powder molding material 9 obtained through the pre-sintering step 2 is re-compressed to obtain a re-compression molded body 10. In this case, an excellent deformability is imparted to the metal powder molding material 9 in order to reduce the deformation resistance in the recompression molding and facilitate the molding process.
[0114]
  That is, as shown in FIGS. 5 and 6, by pre-sintering the preform 8 at a temperature of 800 to 1000 ° C., a metallic powder molding material 9 having an elongation of 10% or more is obtained. Moreover, as shown in FIG.7 and FIG.8, the metal powder molding raw material 9 whose hardness is HRB60 or less is obtained by pre-sintering at 800-1000 degreeC. The hardness of HRB 60 or less of the metallic powder molding material 9 is softer than the hardness obtained by annealing a low carbon steel having a carbon content of about 0.2%.
[0115]
  Further, as shown in FIGS. 9 and 10, the yield stress of the metal powder molding material 9 is 202 to 272 MPa when the pre-sintering temperature is in the range of 800 to 1000 ° C., and this value has a carbon content of 0.1. It becomes a value smaller than the yield stress of low carbon steel of about 2%.
[0116]
  Next, the metal powder molding material 9 obtained in the preliminary sintering step 2 is recompressed in the recompression step 3 to obtain a recompression molded body 10. The recompression molding of the metallic powder molding material 9 is preferably performed at room temperature. In this case, the metallic powder molding material 9 has an excellent deformability, so that it is easily recompressed and no scale is generated.
[0117]
  As a result, a recompression molded body 10 having a small molding load for recompression molding and high dimensional accuracy is obtained.
[0118]
  The recompression molded body 10 has a structure in which graphite 7b remains at the grain boundaries of the metal powder 7a. As shown in FIG. 11, the particles of the metal powder 7a are flattened according to the degree of recompression molding. It has become a shape. That is, in the light recompression molding, the particles of the metal powder 7a are slightly flattened so that many of the voids between the particles are eliminated (see FIG. 11 (a)). The particles of the metal powder 7a are greatly flattened to form a structure in which voids between the particles are substantially eliminated (see FIG. 11B).
[0119]
  The recompression molded body 10 has a structure in which the particles of the metal powder 7a of the metal powder molding material 9 are greatly deformed and flattened, and the structure of the metal powder molding material 9 is the metal powder 7a. Since the graphite 7b remains in the grain boundary, the machinability and lubricity are excellent.
[0120]
  Therefore, the recompression molded body 10 of the metallic powder molding material 9 having an excellent deformability and a method for producing the same, which are suitable for obtaining a machine part having high mechanical strength due to the sintered metal, can be obtained.
[0121]
  Further, the taper portion 21 is formed on the forming die 14 of the preforming step 1 and the notch 23 is formed on the upper punch 16, so that the density is 7.3 g / cm.^ThreeThe above preform 8 can be easily obtained.
[0122]
  In addition, by setting the preliminary sintering temperature in the preliminary sintering step 2 to 800 to 1000 ° C., it has a structure in which the graphite 7b remains at the grain boundaries of the metal powder 7a, and the elongation is 10% or more. The hardness becomes HRB 60 or less, and the metallic powder molding material 9 having more excellent deformability is obtained.
[0123]
  Next, the recompression molded body 10 obtained in the recompression process 3 is re-sintered in the re-sintering process 4 to obtain a sintered body 11. As shown in FIG. 12, the sintered body 11 is composed of graphite 7b existing at the grain boundary of the metal powder 7a diffusing into the ferrite ground (forming a solid solution or carbide), and other structure, and ferrite of the metal powder 7a. Or it is set as the structure of the state which the graphite 7b has diffused and remain | survived by the predetermined ratio in the pearlite structure | tissue. In this case, the residual amount of the graphite 7b may be zero.
[0124]
  The residual rate of graphite 7b in the sintered body 11 varies depending on the re-sintering temperature. The higher the re-sintering temperature, the lower the residual rate of graphite 7b (see FIG. 13). Accordingly, the sintered body 11 can be selected from mechanical properties such as a predetermined strength.
[0125]
  The re-sintering temperature in the re-sintering step 4 is preferably 700 to 1300 ° C. As a result, the sintered body 11 is obtained in which the graphite 7b is less diffused in the low temperature region of the re-sintering temperature and the residual ratio of the graphite 7b is high, and much of the graphite 7b is diffused in the high temperature region of the re-sintering temperature. As a result, the sintered body 11 is obtained in which the remaining rate is small, the crystal regrowth is small, and the strength is the highest.
[0126]
  Specifically, as shown in FIGS. 14 and 15, when the re-sintering temperature is a relatively low temperature of 700 to 1000 ° C., the work hardening generated in the recompression process 3 is recovered, but the graphite 7b As diffusion begins to progress, a fine structure of crystal grains is obtained by mild re-sintering, so that strength is increased and hardness is increased. Depending on the shape of the recompression molding in the recompression step 3, the degree of recovery of work hardening is large, and after softening gradually, it may be cured again at about 1000 ° C.
[0127]
  Further, when the re-sintering temperature is a relatively high temperature of 1000 to 1300 ° C., the residual ratio of the graphite 7b decreases, and the graphite 7b diffuses (forms a solid solution or carbide) in the ferrite ground. Strength increases and hardness increases. However, when the re-sintering temperature exceeds 1100 ° C., a decrease in the total carbon amount accompanying an increase in the amount of decarburization and a tendency for strength and hardness to decrease due to regrowth of crystal grains begin to appear and exceed 1300 ° C. Then, since a coarse structure is generated due to excessive growth of crystal grains, both strength and hardness are greatly reduced. Therefore, the re-sintering temperature is desirably in the range of 700 to 1300 ° C., and most preferably in the range of 900 to 1200 ° C. in order to obtain a stable structure.
[0128]
  Accordingly, a sintered body 11 obtained by re-sintering a recompression molded body 10 of a metallic powder molding material 9 having excellent deformability, which is suitable for obtaining a mechanical part having high mechanical strength by a sintered metal, and The manufacturing method is obtained.
[0129]
  In addition, since the re-sintering temperature in the re-sintering process is set to 700 to 1300 ° C., by selecting the re-sintering temperature, sintering in a state where the diffusion of the graphite 7b is small and the residual ratio of the graphite 7b is large. The sintered body 11 in which the body 11 and a large amount of graphite 7b are diffused and the residual ratio is small, the crystal regrowth is small, and the strength is maximum is obtained.
[0130]
  Next, heat treatment is performed on the sintered body 11 in the heat treatment step 5. The heat treatment in the heat treatment step 5 is performed by various treatments such as induction hardening, carburizing and quenching, nitriding, and combinations thereof. As a result, the heat-treated sintered body 11 has supersaturated graphite 7b as a solid solution, or fine carbides or nitrides are precipitated to form a hardened layer, and excellent mechanical properties are imparted.
[0131]
  Specifically, as shown in FIG. 16, the heat-treated sintered body 11 can obtain a higher tensile strength than the sintered body 11 in a re-sintered state by forming a hardened layer. Further, since the sintered body 11 formed by re-sintering the re-compression molded body 10 at a predetermined temperature has a high-density structure without voids by the re-compression molding in the re-compression step 3, the diffusion of carbon is It decreases as it goes from the surface to the inside. For this reason, as shown in FIG. 17, the sintered body 11 subjected to the heat treatment has increased hardness near the surface and has toughness inside, and has excellent mechanical properties as a whole. .
[0132]
  Therefore, heat treatment is performed on a sintered body obtained by re-sintering a recompressed molded body of a metal powder molding material having excellent deformability, which is suitable for obtaining a machine part having high mechanical strength by sintered metal. A sintered body formed and a method for producing the same are obtained.
[0133]
  Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to this embodiment and can be changed without departing from the gist of the invention. For example, the preform 8 may be formed by so-called warm forming in which the metallic powder 7 and the mold are heated to a predetermined temperature and the yield point of the metallic powder 7 is lowered. Good.
[0134]
  Moreover, although the embodiment in which the notch 23 for expanding the volume of the molding space 15 is formed in the upper punch 16 in the preforming step 1 has been described, the notch 23 may be provided in the lower punch 17. Further, both the upper punch 16 and the lower punch 17 may be provided.
[0135]
【The invention's effect】
  As described above in detail, according to the present invention, a recompression molded body of a metal powder molding material having excellent deformability, which is suitable for obtaining a mechanical part having high mechanical strength by sintered metal, and A sintered body obtained from the recompression molded body and a method for producing them are obtained.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram of a manufacturing process of a recompression molded body of a metal powder molding material and a sintered body obtained from the recompression molded body, showing an embodiment of the present invention.
FIG. 2 shows a manufacturing process of a preform, in a state where metal powder is filled in a forming space of a forming die (a), a state where metal powder is pressed with an upper punch and a lower punch (b), pressurization It is explanatory drawing shown in the state (c) which started lowering | hanging the shaping | molding die for taking out a preforming body after completion, and the state (d) which takes out a preforming body.
FIG. 3 shows the relationship between the density and elongation of a molding material obtained by pre-sintering a preform formed from a metallic powder mixed with 0.5% by weight of graphite at 800 ° C., data (a), And a graph (b).
FIG. 4 is a drawing showing a structure of a molding material.
FIG. 5 shows a density of 7.3 g / cm.^ThreeIt is drawing which shows the change of the elongation at the time of changing the amount of graphite and pre-sintering temperature with data (a) and a graph (b) about the shaping | molding raw material of this.
Fig. 6 Density is 7.5g / cm^ThreeIt is drawing which shows the change of the elongation at the time of changing the amount of graphite and pre-sintering temperature with data (a) and a graph (b) about the shaping | molding raw material of this.
FIG. 7 shows a density of 7.3 g / cm.^ThreeIt is drawing which shows the change of the hardness at the time of changing the amount of graphite and temporary-sintering temperature with data (a) and a graph (b) about the forming raw material of this.
[Fig. 8] Density is 7.5 g / cm^ThreeIt is drawing which shows the change of the hardness at the time of changing the amount of graphite and temporary-sintering temperature with data (a) and a graph (b) about the forming raw material of this.
FIG. 9 shows a density of 7.3 g / cm formed from a metallic powder in which 0.5% by weight of graphite having a particle size of 20 μm is mixed.^ThreeAnd 7.5 g / cm^ThreeIt is drawing which shows the relationship between temporary sintering temperature and a yield stress by data (a) and a graph (b) about the forming raw material of this.
FIG. 10 shows a density of 7.3 g / cm formed from a metallic powder in which 0.5% by weight of graphite having a particle size of 5 μm is mixed.^ThreeAnd 7.5 g / cm^ThreeIt is drawing which shows the relationship between temporary sintering temperature and a yield stress by data (a) and a graph (b) about the forming raw material of this.
FIG. 11 is a drawing showing the structure of a recompression molded body when the recompression molding is mild (a) and when the recompression molding is further performed (b).
FIG. 12 is a drawing showing the structure of a sintered body.
FIG. 13 is a drawing showing data (a) and graph (b) showing changes in the residual ratio of graphite when the re-sintering temperature is changed.
FIG. 14 is a drawing showing data (a) and graph (b) showing changes in tensile strength when the re-sintering temperature is changed.
FIG. 15 is a drawing showing data (a) and graph (b) showing changes in hardness when the re-sintering temperature is changed.
FIG. 16 shows data (a) and graph (b) showing the relationship between the re-sintering temperature and the tensile strength when the sintered body obtained by changing the re-sintering temperature is heat-treated under a predetermined condition. It is a drawing.
FIG. 17 is a drawing showing the relationship between the distance from the surface of a heat-treated body heat-treated under a predetermined condition and the hardness in data (a) and graph (b).
[Explanation of symbols]
    1 Pre-forming process
    2 Pre-sintering process
    3 Recompression process
    4 Re-sintering process
    5 Heat treatment process
    7 Metallic powder
    8 Pre-formed body
    9 Metallic powder molding material
    10 Recompression molding
    11 Sintered body

Claims (11)

A preform having a density of 7.3 g / cm ³ or more obtained by compacting a metal powder obtained by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component is 800 and preliminary sintering at a temperature of to 1000 ° C., the graphite remains in the grain boundary of the metal powder to form a metallic powder-molded material having a whole perlite is precipitated in the vicinity of the ferrite structure or graphite structure, wherein re compression molding metallic powders molding material, characterized by comprising possess the whole perlite is precipitated in the vicinity of the ferrite structure or graphite structure, recompression molded body. A preforming step of compacting metal powder obtained by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component to obtain a preform with a density of 7.3 g / cm ³ or more. And the preformed body obtained in this preforming step is pre- sintered at a temperature of 800 to 1000 ° C., and graphite remains at the grain boundaries of the metal powder, and the whole is a ferrite structure or pearlite is in the vicinity of the graphite. a provisional sintering step of obtaining a metallic powder-molded material having a deposited structure, characterized by comprising a recompression step of recompressing shaping the resulting metallic powder-molded material in the temporary sintering process, re A method for producing a compression molded body.   The preforming step is formed by pressing the metal powder filled in the molding space of the molding die with an upper punch and a lower punch, and the molding space of the molding die has a large diameter portion into which the upper punch is inserted. And a small-diameter portion into which the lower punch is inserted, and a tapered portion that connects the large-diameter portion and the small-diameter portion, and one or both of the upper punch and the lower punch has an outer periphery of an end face that faces the molding space of the molding die. The method for producing a recompression molded body according to claim 2, wherein the end portion is provided with a notch for increasing the volume of the molding space. A preform having a density of 7.3 g / cm ³ or more obtained by compacting metal powder obtained by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component is 800 Preliminarily sintered at a temperature of ˜1000 ° C. to form a metallic powder molding material having graphite remaining in the grain boundary of the metal powder, and the entire ferrite structure or pearlite deposited in the vicinity of the graphite, The metal powder molding material is recompressed to form a recompression molded body having a ferrite structure or a structure in which pearlite is deposited in the vicinity of graphite on the ferrite base, and the recompressed molded body is further formed in a range of 700 to 1300. Re-sintered at a temperature of ℃, the structure in which the graphite present at the grain boundaries of the metal powder diffuses into the ferrite ground, and the structure in which the graphite diffuses and remains in the ferrite or pearlite structure of the metal powder It is characterized by having , The sintered body. A preforming step of compacting metal powder obtained by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component to obtain a preform with a density of 7.3 g / cm ³ or more. And the preformed body obtained in this preforming step is pre- sintered at a temperature of 800 to 1000 ° C., and graphite remains at the grain boundaries of the metal powder, and the whole is a ferrite structure or pearlite is in the vicinity of the graphite. A pre-sintering step of obtaining a metal powder molding material having a deposited structure, a re-compression step of re-compressing the metal powder molding material obtained in the pre-sintering step to obtain a re-compression molded body, and and re-sintering step of re-sintering the re-compacted body obtained in recompression step, characterized Tona Rukoto method of sintered body. The preforming step is formed by pressing the metal powder filled in the molding space of the molding die with an upper punch and a lower punch, and the molding space of the molding die has a large diameter portion into which the upper punch is inserted. And a small-diameter portion into which the lower punch is inserted, and a tapered portion that connects the large-diameter portion and the small-diameter portion, and one or both of the upper punch and the lower punch has an outer periphery of an end face facing the molding space of the molding die the end, characterized that you have provided a cutout to increase the volume of the molding space, the production method of the sintered body according to claim 5, wherein. The re-sintering temperature of the re-sintering process is characterized 700-1300 ° C. der Rukoto method according to claim 5 or 6 sintered body according. A preform having a density of 7.3 g / cm ³ or more obtained by compacting metal powder obtained by mixing 0.3% by weight or more of graphite with metal powder containing iron as a main component is 800 Preliminarily sintered at a temperature of 100 to 100 ° C. to form a metal powder molding material having graphite remaining in the grain boundary of the metal powder and having a ferrite structure or a structure in which pearlite is precipitated in the vicinity of the graphite, The metal powder molding material is recompressed to form a recompression molded body having a ferrite structure or a structure in which pearlite is deposited in the vicinity of graphite on the ferrite base, and the recompressed molded body is 700- Re-sintered at a temperature of 1300 ° C., and the structure in which the graphite existing at the grain boundary of the metal powder diffuses into the ferrite ground, and the structure in which the graphite diffuses and remains in the ferrite or pearlite structure of the metal powder Forming a sintered body having The sintered body to heat treatment, characterized in Rukoto such is decorated, the sintered body. A preforming step of compacting a metal powder obtained by mixing 0.3% by weight or more of graphite with a metal powder containing iron as a main component to obtain a preform having a density of 7.3 g / cm ³ or more. And the preformed body obtained in this preforming step is pre-sintered at a temperature of 800 to 1000 ° C., and graphite remains at the grain boundaries of the metal powder, and the whole is a ferrite structure or pearlite is in the vicinity of the graphite. A pre-sintering step of obtaining a metal powder molding material having a deposited structure, a re-compression step of re-compressing the metal powder molding material obtained in the pre-sintering step to obtain a re-compression molded body, and A re-sintering step of re-sintering the re-compression molded body obtained in the re-compression step to obtain a sintered body, and a heat treatment step for heat-treating the sintered body obtained in the re-sintering step. characterized Rukoto method of the sintered body. The preforming step is formed by pressing the metal powder filled in the molding space of the molding die with an upper punch and a lower punch, and the molding space of the molding die has a large diameter portion into which the upper punch is inserted. And a small-diameter portion into which the lower punch is inserted, and a tapered portion that connects the large-diameter portion and the small-diameter portion, and one or both of the upper punch and the lower punch has an outer periphery of an end face facing the molding space of the molding die the end, characterized that you have provided a cutout to increase the volume of the molding space, the production method of the sintered body according to claim 9, wherein. The re-sintering temperature of the re-sintering process is characterized 700-1300 ° C. der Rukoto method according to claim 9 or 10 sintered body according.

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