JP2007077468A - Method for manufacturing sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a sintered compact, which makes the sintered compact easily machined and inhibits the increase of the machining cost. <P>SOLUTION: The method for manufacturing the sintered compact comprises: steps (steps S1 and S2) of producing a compact by pressure-molding a metallic powder containing 0.4 to 1.0 mass% C and Fe as a main component; a calcination step (step S3) of calcining the compact to produce a calcined body; a machining step (step S4) of machining the calcined body after the calcination step; and a step (step S5) of fully firing the calcined body at 1,100°C to 1,300°C, which is a temperature higher than that in the calcination step, after the machining step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a sintered body, and more specifically to a method for manufacturing a sintered body having a complicated shape that cannot be formed only by pressure molding using a mold.

  For example, sintered bodies such as gears, joints, and cams with complex shapes, and parts with complex partial shapes such as bent holes and elongated holes, are pressure molded using a mold. It is impossible to obtain a desired shape only with this. For this reason, conventionally, a sintered body having a complicated shape has been manufactured by a combination of pressure molding and machining, for example, by the following method. First, a mixed powder of raw material powder and additive powder is put into a mold and pressure-molded to produce a molded body. Next, this molded body is sintered, and the obtained sintered body is machined to form a desired shape. That is, in the said manufacturing method, it shape | molds in a complicated shape by giving a machining after sintering.

  In particular, a sintered body made of a metal powder containing C and greater than 0.4 mass% and not more than 1.0 mass% and having Fe as a main component is easily quenched by sintering, and the hardness of the resulting sintered body Is expensive. For this reason, in the manufacturing method described above, machining by cutting becomes difficult and grinding is required, which increases the processing cost.

Therefore, a manufacturing method that can solve the above problems to some extent is disclosed in, for example, Japanese Patent Laid-Open No. 55-122804 (Patent Document 1). Patent Document 1 discloses a method for manufacturing the following sintered body part. First, the raw material powder and the additive powder are mixed at a predetermined ratio to obtain a mixed powder. The mixed powder is added with a lubricant for lubrication and filled in a mold and pressed by a press device. A powder compact having a shape is formed. The shape of the powder compact to be molded in this pressure molding process is the basic form of the part shape in consideration of the subsequent machining, and the structure of the mold used for molding becomes complicated and many types It is a shape that can avoid. Next, the powder molded body is machined to form the powder molded body so as to have a final part shape. The machining range in this machining process is a remaining shape part necessary as a part shape based on the shape molded by the mold in the pressure molding process. Next, the powder compact machined into a part shape is placed in a heating furnace and heated to sinter. When the sintering is completed, a sintered body having a predetermined part shape is obtained. That is, in the said manufacturing method, it shape | molds in a complicated shape by machining the molded object before sintering. Since the molded body before sintering has a lower hardness than the sintered body obtained after sintering, machining becomes easy and increase in processing cost can be suppressed.
JP-A-55-122804

  However, even the manufacturing method disclosed in Patent Document 1 cannot sufficiently solve the above problem. The reason for this will be described below.

  In the green body before sintering, the metal powders are not metallurgically bonded, and the mechanical strength is not sufficient. For this reason, in the manufacturing method of patent document 1, when performing a machining process, a molded object tends to chip. Further, the molded body is easily chipped due to the chucking force of the molded body when machining. For this reason, it is necessary to pay attention so that the molded body is not chipped when machining, and the problem that machining is difficult cannot be solved sufficiently.

  In addition, the molded body before sintering contains a lubricant for reducing the friction between the mold and the mixed powder during pressure molding. Since the lubricant has a high viscosity, the lubricant adheres to a tool used for machining when machining, and resistance to machining increases. As a result, the problem that the tool is easily damaged and the processing cost increases cannot be sufficiently solved.

  Accordingly, an object of the present invention is to provide a method for manufacturing a sintered body that is easy to machine and can suppress an increase in processing cost.

  The method for producing a sintered body according to the present invention includes pressure-molding a metal powder containing C (carbon) greater than 0.4 mass% and 1.0 mass% or less and containing Fe (iron) as a main component. The step of producing a molded body by the above, the temporary firing step of pre-baking the molded body to obtain a temporary fired body, the machining step of machining the temporary fired body after the temporary firing step, and the post-machining step, 1100 ° C. And a step of subjecting the temporary sintered body to the main firing at a temperature of 1300 ° C. or lower and higher than the temperature of the preliminary firing step.

  According to the method for producing a sintered body of the present invention, sintering of metal powders proceeds in the pre-baking step, and the machine of the pre-fired body after the pre-baking step compared to the mechanical strength of the molded body before the pre-baking step. Strength increases. Therefore, the temporary fired body is less likely to be chipped when machining, and machining is facilitated. Further, since the lubricant contained in the metal powder is also removed during the preliminary firing, the lubricant does not stick to the tool in the machining process, and the resistance to machining is reduced. As a result, the tool is less likely to be damaged, and an increase in processing cost can be suppressed.

  Moreover, since the temperature of a temporary baking process is lower than the temperature of main baking, the spreading | diffusion of C in a metal powder in a temporary baking process is suppressed compared with main baking. For this reason, martensite structure, bainite structure, and pearlite structure are not easily generated in the pre-baking process, and the hardness of the pre-fired body immediately after the pre-baking process is kept lower than the hardness of the sintered body after the main baking. Can do. Thereby, machining becomes easy and increase in processing cost can be suppressed.

  Further, by performing the main firing at a temperature of 1100 ° C. or higher, C in the metal powder is sufficiently diffused to generate a martensite structure, a bainite structure, or a pearlite structure, and the sintered compact machine obtained Strength can be increased. Further, by performing the main firing at a temperature of 1300 ° C. or lower, it is possible to prevent dimensional accuracy from being lowered due to sintering and melting of the sintered body.

  Furthermore, a sufficient amount of hard martensite structure can be generated in the main firing by using a metal powder containing C in a proportion larger than 0.4% by mass and containing Fe as a main component. Mechanical strength can be improved. Further, by using a metal powder containing C at a ratio of 1.0% by mass or less and containing Fe as a main component, it is possible to suppress the formation of the pro-eutectoid cementite structure and the embrittlement during the main firing. It is possible to suppress a decrease in the mechanical strength of the sintered body.

  In the present specification, “having Fe as a main component” means that Fe is contained in a proportion of 90% by mass or more.

  Preferably in the said manufacturing method, the temperature of a temporary baking process is 800 degreeC or more and 1050 degrees C or less. More preferably, the temperature of the pre-baking step is 820 ° C. or higher and 970 ° C. or lower.

  By setting the temperature of the pre-baking step to 800 ° C. or higher, more preferably 820 ° C. or higher, the sintering of Fe in the metal powder can be further promoted, and the mechanical strength of the molded body before the pre-baking step can be increased. In comparison, the mechanical strength of the pre-baked body after the pre-baking step can be improved. Further, by setting the temperature of the pre-baking step to 1050 ° C. or lower, more preferably 970 ° C. or lower, the diffusion of C into the metal powder can be further suppressed, and the formation of martensite structure can be suppressed. Furthermore, generation of a pearlite structure and a bainite structure can also be suppressed. As a result, mechanical strength does not increase excessively in the pre-baking step, and machining is facilitated.

  Preferably in the said manufacturing method, the metal powder further contains Cu (copper). Cu improves the strength of the temporarily fired body after the temporary firing by bonding Cu atoms together in the temporary firing step. Thereby, the temporarily fired body is less likely to be chipped during machining, and machining is facilitated.

  Preferably in the manufacturing method, the metal powder further contains at least one selected from the group consisting of Cr (chromium), Mo (molybdenum), Ni (nickel), and Mn (manganese).

  Since Cr, Mo, Ni, and Mn are elements that improve the hardenability, a sintered body of metal powder containing these elements has higher hardness than a sintered body containing C alone. . For this reason, the effect of this invention becomes more remarkable.

  In the above manufacturing method, the machining is preferably cutting. More preferably the machining is turning, milling or drilling.

  By performing the machining step by these processing methods, the temporarily fired body after the temporary firing can be formed into a desired shape, and a sintered body having a complicated shape can be produced. Further, machining becomes easy, and an increase in machining cost can be suppressed.

  According to the method for manufacturing a sintered body of the present invention, machining is easy, and an increase in processing cost can be suppressed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a method of manufacturing a sintered body according to an embodiment of the present invention in the order of steps. With reference to FIG. 1, first, the raw material powder and the additive powder are mixed to produce a mixed powder (step S1). As the raw material powder, a metal powder containing Fe that is greater than 0.4 mass% and 1.0 mass% or less and whose main component is Fe is used. The metal powder may further contain Cu, Cr, Mo, Ni, or Mn.

  The average particle size of the metal powder is preferably 100 μm or less, for example. Further, as the metal powder, for example, a powder produced by a water or gas atomization method, a reduction method, a carbonyl method, or a pulverization method is used.

  The additive powder contains, for example, a lubricant and a binder. Examples of the lubricant include higher fatty acid type, metal salt type of higher fatty acid, wax type, higher alcohol type, polytetrafluoroethylene (Teflon (registered trademark)), high molecular weight polyethylene, thermoplastic polyamide, 6-nylon, 6- 6 nylon and 6-12 nylon are used. Examples of the binder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyvinyl chloride, polyvinylidene chloride, and polyamide. Various resins such as polyester, polyether, polyvinyl alcohol, and copolymers thereof, various waxes, paraffin, higher fatty acids (eg, stearic acid), higher alcohols, higher fatty acid esters, higher fatty acid amides, and the like are used. In the present invention, the additive powder is not essential, and only the raw material powder may be used.

  Next, the obtained mixed powder is pressure-molded to form a molded body (step S2). Specifically, the mixed powder is filled in a mold and pressed by a press device to form a molded body having a predetermined shape. The pressure molding is performed at a pressure of 100 MPa to 1500 MPa, for example. The shape of the molded body molded by this pressure molding is preferably a shape that can be easily pressure-molded using a mold and is a shape that is the basis of the shape of the final sintered body. In other words, in the case of pressure molding, it is preferable not to mold a complicatedly shaped part in the final sintered body, but to mold only a part that can be easily pressure-molded using a mold. .

  Subsequently, the obtained mixed powder compact is temporarily fired (step S3). Pre-baking is preferably performed at 800 ° C. or higher, for example, and more preferably at 820 ° C. or higher. When the mixed powder is fired at the above temperature, sintering of Fe proceeds, and the mechanical strength of the temporarily fired body after the temporary firing becomes higher than the mechanical strength of the compact before the temporary firing. Further, the lubricant contained in the mixed powder is removed.

  On the other hand, the temporary baking is performed at a temperature lower than the main baking described later. For example, the pre-baking is preferably performed at 1050 ° C. or less, and more preferably at 970 ° C. or less. When the mixed powder is fired at the above temperature, C in the mixed powder is not sufficiently diffused, so that a martensite structure is hardly generated. In addition, the formation of pearlite structure and bainite structure is also suppressed. As a result, the hardness of the temporarily fired body immediately after the temporary firing becomes lower than the hardness of the final sintered body. That is, the mechanical strength of the pre-fired body becomes higher than the mechanical strength of the molded body before the pre-fired by pre-baking. On the other hand, the hardness of the temporarily fired body is lower than the hardness of the sintered body after the main firing. Moreover, when the metal powder contains Cu, the strength of the temporarily fired body after the temporary firing is increased by bonding of Cu atoms.

  Next, the temporarily fired body is machined (step S4). By this machining, a temporary fired body is formed into a final sintered body shape. In other words, at the time of machining, a portion having a complicated shape that has not been molded at the time of pressure molding is molded based on the shape molded at the time of pressure molding. As machining, for example, cutting is performed.

  Here, examples of the cutting process include turning, milling, or drilling. FIG. 2 is a diagram for explaining the turning process. Referring to FIG. 2, for example, provisionally calcined body 1 a after calcining having a cylindrical shape is placed on a lathe (not shown), and calcined body 1 a is rotated around the axis of the cylinder. In this state, while temporarily pressing the tool 10 against the outer peripheral surface of the cylinder, the tool 10 is moved relatively to the left in the drawing along the axis, and the outer peripheral surface of the temporary fired body 1a is shaved to obtain the temporary fired body 1b.

  FIG. 3 is a diagram for explaining milling. Referring to FIG. 3, a tool (milling) 11 having a blade on the circumference is rotated about a rotating shaft 11a and pressed against the surface of the plate-like temporary fired body 1a. In this state, the temporarily fired body 1a is relatively moved in the right direction in the drawing, and the surface of the temporarily fired body 1a is shaved to obtain the temporarily fired body 1b.

  Further, FIG. 4 is a diagram for explaining drilling. Referring to FIG. 4, a tool (drill) 12 having a spiral groove extending from the lower end is rotated about a rotation axis. In this state, the tool 12 is relatively moved downward in the figure, and the lower end of the tool 12 is pressed against the temporary fired body 1a. Thereby, the temporary calcination body 1b with which the hole 2 was opened is obtained.

  In machining, the calcined body can be formed into a desired shape by appropriately combining the above processing methods. The calcined body can be formed into a desired shape by the above processing method, and a sintered body having a complicated shape can be produced. Further, machining becomes easy, and an increase in machining cost can be suppressed.

  Next, the temporarily fired body is finally fired (step S5) to obtain a sintered body. The main firing is performed at a temperature of 1100 ° C. or higher and 1300 ° C. or lower. By performing the main baking at 1100 ° C. or higher, the diffusion of C proceeds and the martensite structure is easily generated. As a result, the mechanical strength of the sintered body becomes higher than the mechanical strength of the molded body before the main firing. In addition, when the metal powder contains Cu, Cr, Mo, Ni, or Mn, the hardenability is improved, so that quenching can be performed without a special cooling device. Mechanical strength can be improved. On the other hand, by performing the main baking at 1300 ° C. or lower, it is possible to prevent a decrease in dimensional accuracy during sintering and melting of the sintered body.

  Next, the sintered body is heat treated (step S6). This heat treatment is performed at a temperature of 150 ° C. to 500 ° C., for example. Thereby, the distortion which arose in the case of machining etc. is removed, or the toughness of the martensite which arose in the main sintering process is improved. This heat treatment is not an essential step and may be omitted. The sintered body of the present embodiment is completed through the above steps.

  According to the method for manufacturing a sintered body of the present embodiment, the sintering of the metal powder proceeds during the temporary firing (step S3), and compared with the mechanical strength of the molded body before the temporary firing. The mechanical strength of the temporarily fired body is increased. Therefore, when performing the machining (step S4), the temporarily fired body is not easily chipped, and the machining is facilitated. Even if the metal powder contains a lubricant, the lubricant is removed by the heat of pre-baking, so that the lubricant does not stick to the tool during machining and resistance to machining is reduced. As a result, the tool is less likely to be damaged, and an increase in processing cost can be suppressed.

  Moreover, since the temperature of temporary baking is lower than the temperature of main baking (step S5), the spreading | diffusion of C in a metal powder is suppressed in the case of temporary baking. For this reason, it becomes difficult to produce a martensite structure at the time of temporary firing, and the mechanical strength of the temporary fired body can be kept lower than the mechanical strength of the sintered body after the main firing. Thereby, machining becomes easy and increase in processing cost can be suppressed.

  Further, by performing the main firing at a temperature of 1100 ° C. or higher, C in the metal powder can be sufficiently diffused to form a martensite structure, and the mechanical strength of the obtained sintered body can be increased. . Further, by performing the main firing at a temperature of 1300 ° C. or lower, it is possible to prevent dimensional accuracy from being lowered due to sintering and melting of the sintered body.

  Furthermore, a hard martensite structure can be produced in a sufficient amount during the main firing by using a metal powder containing C in a proportion larger than 0.4% by mass and containing Fe as a main component. The mechanical strength of the bonded body can be improved. Further, by using a metal powder containing C at a ratio of 1.0% by mass or less and containing Fe as a main component, it is possible to suppress the formation of a cementite structure and embrittlement during the main firing. The decrease in the mechanical strength of the sintered body can be suppressed.

  In the present Example, the effect of the manufacturing method of the sintered compact of this invention was confirmed. First, powders having the compositions shown in Table 1 (numbers are mass%) were prepared. Subsequently, the powder was pressure-molded to obtain a ring-shaped molded body having an outer diameter of 40 mm, an inner diameter of 10 mm, and a height of 40 mm. Next, for Examples 1 to 17 (examples of the present invention), the compacts were temporarily fired at the temperatures shown in Table 1 to obtain temporary fired bodies. On the other hand, Comparative Examples 9 to 12 were subjected to main firing at a temperature of 1130 ° C. for 10 minutes or at a temperature of 1250 ° C. for 30 minutes to obtain sintered bodies. Comparative Examples 1-7 were not fired at all. Lathe machining was performed on the outer diameter portion of each of the obtained samples of the temporarily fired bodies of Examples 1 to 17, the fired bodies of Comparative Examples 8 to 12, and the molded bodies of Comparative Examples 1 to 7. Then, the number of processing until the tool life was reached and the sample chipping rate were investigated. In addition, about 100 specimens that did not reach the tool life even after 100 pieces were processed, the test was terminated with 100 pieces. Lathe processing was performed under the conditions of a feed rate of 0.1 mm / rev, a cutting depth of 0.2 mm, a rotation speed of 1000 rpm, and a cutting frequency of 50 times per sample. Moreover, a carbide tool was used as the tool, and no cutting fluid was used. Table 1 shows the obtained tool life and chipping rate.

  With reference to Table 1, in Examples 1-17, it turns out that it is excellent in tool life compared with Comparative Examples 1-12, and a chipping rate is small. In particular, in Examples 1 to 13, the tool life number was 97 or more, and the chipping rate was 9% or less. From the above results, it can be seen that the method for manufacturing a sintered body according to the present invention is easy to machine and can suppress an increase in processing cost.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is suitable for a method of manufacturing a sintered body having a complicated shape that cannot be formed only by pressure molding using a mold.

It is a figure which shows the manufacturing method of the sintered compact in one embodiment of this invention in order of a process. It is a figure for demonstrating turning. It is a figure for demonstrating milling. It is a figure for demonstrating a drill process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a Temporary baking body after temporary baking, 1b Temporary baking body after machining, 2 holes, 10-12 tool, 11a Rotating shaft.

Claims (6)

A step of producing a molded body by press-molding a metal powder containing 0.4 mass% and 1.0 mass% or less of C and containing Fe as a main component;
A pre-baking step of pre-baking the molded body to obtain a pre-fired body;
After the temporary firing step, a machining step for machining the temporary fired body,
A method for producing a sintered body, comprising: a step of subjecting the temporarily fired body to a main firing at a temperature of 1100 ° C. to 1300 ° C. and higher than the temperature of the temporary firing step after the machining step.   The method for producing a sintered body according to claim 1, wherein the temperature of the preliminary firing step is 800 ° C. or higher and 1050 ° C. or lower.   The method for producing a sintered body according to claim 2, wherein the temperature of the preliminary firing step is 820 ° C. or higher and 970 ° C. or lower.   The said metal powder is a manufacturing method of the sintered compact in any one of Claims 1-3 which further contains Cu.   The said metal powder is a manufacturing method of the sintered compact in any one of Claims 1-4 which further contains at least 1 sort (s) chosen from the group which consists of Cr, Mo, Ni, and Mn.   The method for manufacturing a sintered body according to claim 1, wherein the machining is a cutting process.

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