JP4807519B2 - Method for producing sintered forged member - Google Patents

Description

  The present invention relates to a method for producing a sintered forged member, and more particularly to a method for producing a sintered forged member in which shot blasting (sealing treatment) using a steel shot material having low hardness is performed after preliminary sintering.

  As a technology for manufacturing forged parts such as connecting rods of engines, a compacted body is produced by compacting iron-based metal powder with a lubricant added, and the compacted body is pre-sintered to produce a lubricant. , Followed by a main sintering treatment, followed by hot forging, and then a shot peening treatment is applied to the surface of the molded product (this is referred to as a “normal production method”).

  In the sintered forged member manufactured by this normal manufacturing method, the main sintered process and hot forging are performed while leaving a large number of micropores on the surface of the temporary sintered body. There is a problem that a decarburization phenomenon in which the carbon component is removed from the metal structure of the surface layer portion, and a soft and low-strength ferrite structure is likely to be generated, and oxygen enters the interior during the main sintering process and hot forging. Oxide is generated and the strength of the forged product is reduced. FIG. 14 is a micrograph of the metal structure of the surface layer portion of the sintered forged member (finished product) manufactured by the above-described normal manufacturing method, and the decarburized ferrite structure in which the surface layer portion of about 190 μm from the surface is whitened by decarburization. It has become.

Manufacturing techniques for solving the problems of decarburization and oxide formation have also been proposed.
For example, in Patent Document 1, after a green compact is pre-sintered at a temperature of about 650 to 980 ° C., a shot material having a hardness of HRC 47 to 51 (HV 471 to 528) is less than 100 m / s. Is subjected to a shot peening process for projecting at a projection speed of 60 ° C., followed by a main sintering process for 60 minutes or less at a temperature of less than about 1340 ° C., and then a hot forging process, followed by a shot peening process on the surface of the molded product. A method is disclosed.

In the method for producing a sintered forged member described in Patent Document 1, strength sufficient to cope with handling and the like is obtained because sintering is performed to a pre-sintered body, and carbon and copper components are diffused with respect to iron powder. Since it is not advanced, ductility is ensured and the surface portion of the pre-sintered body can be well sealed (caulked).
US Application Publication No. 2004/0005237

  However, although the pre-sintered body has a hardness of less than HV100 and is not so hard, a shot material having a hardness of HRC 47 to 51 (HV471 to 528) is projected onto the presintered body at a high speed of 100 m / sg. A shot peening process is performed. Therefore, the corners and ridges of the pre-sintered body are damaged and become in a thin state, the shape damage becomes significant, the forged product has a weight shortage and a lack of thickness, the yield is remarkably lowered, and as a result The manufacturing cost of a forging member becomes high.

  FIG. 16 is a view showing an external appearance of a pre-sintered body 100 of an engine connecting rod manufactured by the manufacturing method of Patent Document 1 and subjected to shot peening treatment on the pre-sintered body 100. As shown in FIGS. 16A and 16B, it can be seen that the missing wall defects 101 to 103 are generated in the corners and ridges of the pre-sintered body 100. Moreover, when the pre-sintered body 100 is subjected to the shot peening treatment, a number of sharp shot ball fragments generated by cracking of the hard and brittle shot material are pierced on the surface of the pre-sintered body 100 to reduce the caulking action or forging. Later, it remains as inclusions and tends to be the starting point of fatigue failure.

FIG. 17 is a photomicrograph of a pre-sintered body of a connecting rod of an engine manufactured by the manufacturing method of Patent Document 1 and subjected to shot peening treatment on the pre-sintered body but not etched at the corners. (Magnification: 100 times) The lower black island-shaped portion is a visible hole having a width of 1.5 mm, and a thin-wall defect is also generated in the upper right corner.
An object of the present invention is to provide a method for producing a sintered forged member that enables simple and excellent sealing treatment (caulking) and can significantly improve the quality of the sintered forged member.

  The method for producing a sintered forged member according to claim 1 is a method for producing a sintered forged member, the first step of pre-sintering a compacted body obtained by compacting iron-based metal powder containing carbon. Next, the pre-sintered body is shot blasted with a steel shot material having a hardness of HV 100 to 350, and the surface portion of the pre-sintered body is sealed, and then the pre-sintered body is sintered. It is characterized in that it comprises a third step of performing a sintering process and a fourth step of hot forging the sintered body that has been subjected to the main sintering process.

  The method for producing a sintered forged member according to claim 2 is the invention according to claim 1, wherein the shot blasting treatment in the second step uses a steel shot material having a particle size of 0.3 to 0.7 mm, and 30 to 80 m / It is characterized by performing at a projection speed of s.

  The method for producing a sintered forged member of claim 3 is characterized in that, in the invention of claim 1 or 2, the preliminary sintering treatment in the first step is performed at a temperature of 800 to 1000 ° C. in a non-oxidizing atmosphere. .

  According to a fourth aspect of the present invention, there is provided a method for producing a sintered forged member according to any one of the first to third aspects, wherein the sintered forged member is a connecting rod of an engine.

  According to the invention of claim 1, in the second step, in order to perform a sealing process to close the micropores in the surface portion of the pre-sintered body by shot blasting with a steel shot material having a low hardness of HV100 to 350, Since the surface can be stably sealed without damaging the surface of the pre-sintered body, it is possible to reliably prevent decarburization during the main sintering process and hot forging, and to keep the metal inside. Oxide is hardly generated, and a sintered forged member having excellent fatigue strength and quality can be manufactured.

  According to invention of Claim 2, the shot blast process of a 2nd process is performed at the projection speed of 30-80 m / s using the steel shot material with a particle size of 0.3-0.7 mm. Thus, by making the shot blast treatment conditions appropriate so as to achieve a mild shot blast treatment, the sealing treatment can be reliably and efficiently performed without damaging the surface of the pre-sintered body.

According to the invention of claim 3, since the pre-sintering process in the first step is performed at a temperature of 800 to 1000 ° C. in a non-oxidizing atmosphere, the strength of the pre-sintered body is increased without causing a decarburization phenomenon. It can be ensured and the sealing process can be performed stably.
According to the invention of claim 4, a high quality engine connecting rod made of the sintered forged member can be manufactured.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment when a manufacturing method for manufacturing a sintered forged member according to the present invention is applied to manufacture of a connecting rod of an engine will be described based on the drawings.

  The present embodiment is an example when the method for manufacturing a sintered forged member of the present invention is applied to a manufacturing method for manufacturing a connecting rod of an engine. FIG. 1 is a flowchart showing a plurality of steps of the method for producing a sintered forged member, and reference symbol Pi (i = 1, 2,...) Denotes each step.

  As shown in FIG. 1, first, in the compacting process of P1, the sintered powder is based on iron and contains 1.5 to 4.0 wt% Cu (copper) and 0.35 to 0.80 wt% C ( The compacted body of the connecting rod is molded by compacting the sintered powder containing carbon) as a raw material using a compacting machine and a predetermined mold. In addition, zinc stearate is added to the above sintered powder as a compacting lubricant, and manganese sulfide and calcium oxide may be added to improve machinability.

  Next, in the pre-sintering process of P2, the green compact obtained by compacting as described above is pre-sintered. At this time, a plurality of green compacts are accommodated in a sintering furnace, and the inside is made a nitrogen gas-based hydrogen gas reducing atmosphere that is a non-oxidizing atmosphere, and an atmospheric temperature of 800 to 1000 ° C. for 1 to 1.5 hours. Then, the zinc stearate lubricant is burned off, cooled with nitrogen gas, released to the atmosphere, and gradually cooled. This pre-sintering increases the strength of the green compact.

  Next, in the shot blasting process of P3, the above pre-sintered compacted body is shot blasted and the surface portion is sealed. This shot blasting process uses a steel shot material (for example, steel round cut wire) having a low hardness (for example, HV 100 to 350) and a particle size of 0.3 to 0.7 mm, and a projection speed of 30 to 80 m / s. In addition, the surface portion of the pre-sintered body is sealed by shot blasting at a projection amount of 100 kg / min or less.

  Here, when the hardness of the steel shot material is less than HV100, a sufficient sealing action cannot be obtained, which is not preferable. Further, when the hardness of the steel shot material is higher than HV350, the surface of the pre-sintered body is damaged, which is not preferable. The same applies to the particle diameter of the steel shot material. If the particle diameter is less than 0.3 mm, a sufficient sealing action cannot be obtained, which is not preferable. On the other hand, when the particle size exceeds 0.7 mm, the surface of the pre-sintered body is damaged, which is not preferable. The same applies to the projection speed, and a projection speed of less than 30 m / s is not preferable because a sufficient sealing action cannot be obtained. Further, a projection speed of more than 80 m / s is not preferable because it damages the surface of the pre-sintered body. In addition, even when the projection amount exceeds 100 kg / min, the surface of the pre-sintered body is damaged, which is not preferable.

  As shown in FIG. 2, a plurality of pre-sintered green compacts W are rolled while being conveyed by a rubber belt conveyor 10 extending into the shot blast processing apparatus SA, and installed above. Alternatively, the steel shot material 12 is projected from two sets of impellers 11 installed on the upper side and the lower side, so that the entire surface portion of the green compact W is shot blasted and sealed.

  In addition to the belt conveyor 10, a chain conveyor may be adopted, and a rotating drum may be adopted instead of the belt conveyor. Instead of the inline shot blast processing apparatus SA shown in FIG. 2, a batch shot blast processing apparatus SB shown in FIG. 3 may be adopted. Further, instead of projecting the steel shot material by the impeller 11, the steel shot material may be projected by air blow.

  Next, in the main sintering process of P4, the main compaction process is performed on the green compact W after the shot blasting process. In this case, the plurality of compacted compacts W are accommodated in a sintering furnace, and are performed in a nitrogen gas-based hydrogen gas reducing atmosphere at an ambient temperature of 1000 to 1300 ° C. for a treatment time of 15 minutes to 2 hours. By this main sintering process, Cu and C are dissolved in iron of the base material.

Next, in the hot forging process of P5, the sintered body subjected to the main sintering process as described above is set in a predetermined die of a hot forging molding apparatus and hot forged to form a connecting rod shape. To do.
Next, in the deburring process of P6, a plurality of sintered forged bodies after hot forging are put into a rotary drum type deburring apparatus to perform deburring processing.

  Next, in the shot peening treatment process of P7, shot peening treatment is performed on the entire surface portion of the sintered forged body after deburring. This shot peening treatment uses a steel shot material (for example, steel round cut wire) having a high hardness (for example, HRC 40 to 50) and a particle size of 0.5 to 0.7 mm, and a projection speed of 50 to 85 m / s. And a projection amount of 90 to 215 kg / min. By this shot peening treatment, since a high residual compressive stress is applied to the entire surface portion of the connecting rod molded body that is a sintered forged member, the fatigue strength characteristics of the connecting rod can be enhanced.

The process P2 corresponds to the first process, the process P3 corresponds to the second process, the process P4 corresponds to the third process, and the process P5 corresponds to the fourth process.
Next, the operation and effect of the method for manufacturing a sintered forged member described above will be described.
In the process of P3, the surface portion of the pre-sintered body is sealed by shot blasting with a low hardness steel shot material of HV100 to 350, so that the surface portion of the pre-sintered body is not damaged. Therefore, it is possible to reliably prevent the decarburization phenomenon from occurring during the main sintering process or hot forging, and it is difficult for metal oxides to be generated inside. Since it is hard to produce | generate, the fatigue strength characteristic and the sintered forging member excellent in quality can be manufactured.

  The shot blast treatment is performed using a steel shot material having a particle size of 0.3 to 0.7 mm and a projection rate of 30 to 80 m / s and a projection amount of 100 kg / min or less. Thus, by making the shot blast treatment conditions appropriate so as to achieve a mild shot blast treatment, the sealing treatment can be reliably and effectively performed without damaging the surface of the pre-sintered body. In addition, since the steel shot material with low hardness is employed, the shot material is not easily broken, and fragments of the shot material do not remain on the surface of the pre-sintered body.

  The pre-sintering process in the process of P2 is performed at a temperature of 800 to 1000 ° C. in a nitrogen-based hydrogen reducing atmosphere that is a non-oxidizing atmosphere, so that the strength of the pre-sintered body is reduced without causing a decarburization phenomenon. The sealing process can be stably performed in the process of P3. Thus, a high quality engine connecting rod made of sintered forged members can be manufactured.

Next, a pre-sintered body in the middle of production by the method for producing a sintered forged member described above, a micrograph of the structure of the sintered forged member (conrod molded body) after completion, and measurement results on quality and performance will be described. .

Table 1 shows the processing conditions and evaluations of five examples performed to obtain appropriate processing conditions for shot blasting employed in the process P3. The evaluation with ○ indicates good. Even when the hardness of the steel shot material was HV350, the surface of the pre-sintered body was hardly damaged. In the condition 2, the projection speed was high and the amount of projection was large, so that the corners of the pre-sintered body were slightly rounded and did not come off, so the evaluation is a triangular mark but can be adopted. .

  FIG. 4 shows the appearance of the pre-sintered body 20 obtained by subjecting the pre-sintered body to shot blasting under the following conditions. The shape of the corners and ridges are not damaged or collapsed, and the surface is damaged. Not done. Shot blasting conditions: Steel shot material (steel round cut wire, particle size 0.6 mm, hardness HV 100 to 150, projection speed 70 m / s, projection amount 50 kg / min (impeller type), projection time 90 seconds / 20 pieces.

  FIG. 5 is a photomicrograph (magnification: 100 times) of a cross-section of a metal structure that has not been subjected to etching treatment of a pre-sintered body manufactured by the normal manufacturing method according to the comparative example. It can be seen that many black voids (micropores) are generated in the surface layer portion of the pre-sintered body. Therefore, decarburization proceeds during the main sintering and hot forging, oxides are easily generated, and residual voids are easily generated inside. FIG. 6 is a photomicrograph (magnification: 100 times) of the metal structure of the pre-sintered body 20 according to the embodiment shown in FIG. It can be seen that the surface of the pre-sintered body 20 is almost completely sealed. Moreover, the residual vacancies remaining in the interior are significantly fewer than those in FIG.

  FIG. 7 is a micrograph (magnification: 100 times) of the metal structure of the prior art pre-sintered body that has not been etched, and FIG. 8 is a pre-sintered body according to the example shown in FIG. It is a microscope picture (magnification: 100 times) of the metal structure which has not performed the etching process of 20 corners. The sealing is the same as in FIG. It can be seen that the shape of the corners of the pre-sintered body 20 is maintained, and no damage has occurred on the surface of the pre-sintered body 20.

  9-15 is a figure regarding the quality etc. of the finished product of the sintered forged member (connecting rod molded object) manufactured by the process of said P1-P7, FIG. 9 is a figure of the sintered forged member 30 (connecting rod molded object). FIG. 10 is a cross-sectional view taken along the line XX of FIG. 9, and is a diagram indicating each part # 1 to # 4. FIG. 11 shows a compressive residual stress of each part shown in FIG. 10 for a connecting rod molded body (normal product) as a comparative example manufactured by the normal manufacturing method and a connecting rod molded body (invented product) manufactured by the method of the example. It is a graph which shows the measurement result.

  As can be seen from FIG. 11, the inventive product is given a compressive residual stress as high as about 110 to 160% compared to the normal product. In the invention product, as a result of good sealing by shot blasting, since decarburization hardly occurred and no oxide was generated, the metal structure of the sintered forged member 30 was hard and excellent in strength. The treatment is effectively performed, high compressive residual stress is imparted, and fatigue strength characteristics are excellent.

  FIG. 12 shows the measurement results of the surface hardness of the normal product, and FIG. 13 shows the measurement results of the surface hardness of the invention product. Regarding the hardness at the shallowest part of the surface, the normal product has a hardness of HV 260 to 300, whereas the invention product has a hardness of HV 310 to 380, indicating that the shot peening treatment has been effectively performed.

  FIG. 14 is a micrograph (comparative example) of 100 times of the metal structure etched in any part of # 1 to # 4 in FIG. 10 in the normal product, and FIG. It is a 100-times microscope picture of the processed metal structure. The range of about 190 μm in the surface layer portion of FIG. 14 is a soft ferrite structure that has been decarburized and whitened, and the deeper part is a hard pearlite structure than the range of about 190 μm. In the product shown in FIG. 15, the whitened decarburized structure does not exist in the surface layer portion, and it is a hard pearlite structure from the surface to the deep part.

An example in which the embodiment is partially changed will be described.
Although the said Example demonstrated the manufacturing method which manufactures the connecting rod of the engine which is a sintered forging member as an example, the manufacturing method of the sintered forging member of this invention is various sintered forging members other than the connecting rod of an engine. This method can also be applied.
In addition, the manufacturing method of the sintered forged member of the above embodiment can be changed to a member weapon without departing from the spirit of the present invention.

It is a flowchart which shows the manufacturing method of the sintered forge member which concerns on the Example of this invention. It is a schematic sectional drawing of a shot blast processing apparatus. It is a schematic sectional drawing of another shot blast processing apparatus. It is a top view of the preliminary sintered compact after a shot blast process. It is a microscope picture of the metal structure of the preliminary sintered compact (normal article) of a comparative example. It is a microscope picture of the metal structure of the pre-sintered body (invention product) of FIG. It is a microscope picture of the metal structure of the preliminary sintered compact (normal article) of a comparative example. It is a microscope picture of the metal structure of the pre-sintered body (invention product) of FIG. It is a top view of a connecting rod molded object. FIG. 10 is a sectional view taken along line XX in FIG. 9. It is a graph of the residual stress measurement result of the surface part in the completed sintered forged member (normal product) which concerns on a comparative example, and the completed sintered forged member (invention product) which concerns on an Example. It is a graph of the measurement result of the surface hardness in the normal product of FIG. It is a graph of the measurement result of the surface hardness in the invention of FIG. It is a microscope picture of the metal structure in the normal goods of FIG. It is a microscope picture of the metal structure in the invention of FIG. It is a schematic plan view of the pre-sintered body after the shot peening process in the manufacturing method of the sintered forge member which concerns on the prior art described in patent document 1. It is an enlarged view of the A section of FIG. It is an enlarged view of the B section of FIG. It is a microscope picture of the metal structure of the pre-sintered body of FIG.

Explanation of symbols

SA, SB shot blast processing equipment 11 impeller 12 steel shot material W pre-sintered body

Claims (4)

In a manufacturing method for manufacturing a sintered forged member,
A first step of pre-sintering a green compact obtained by compacting an iron-based metal powder containing carbon, and then subjecting the pre-sintered body to shot blasting with a steel shot material having a hardness of HV 100 to 350 A second step of sealing the surface portion of the preliminary sintered body;
Next, a third step of subjecting the pre-sintered body to a main sintering process,
Next, a fourth step of hot forging the sintered body subjected to the main sintering treatment,
A method for producing a sintered forged member, comprising:   2. The sintered forging according to claim 1, wherein the shot blasting process in the second step is performed using a steel shot material having a particle diameter of 0.3 to 0.7 mm and a projection speed of 30 to 80 m / s. Manufacturing method of member.   The method for producing a sintered forged member according to claim 1 or 2, wherein the preliminary sintering treatment in the first step is performed at a temperature of 800 to 1000 ° C in a non-oxidizing atmosphere.   The method for producing a sintered forged member according to any one of claims 1 to 3, wherein the sintered forged member is a connecting rod of an engine.