JPH0665609A - Production of ferrous sintered and forged parts - Google Patents

Abstract

PURPOSE:To improve the machinability, elongation property, hardness and strength of outer races for automobiles consisting of the ferrous sintered and forged parts. CONSTITUTION:The forged parts 1 are cooled down to <=650 deg.C within 15-200 seconds from the point of the time the withdrawal from dies 30 for forging ends. The temp. of the forged parts 1 at the point of the time the withdrawal ends is about 800 deg.C. The precipitation of bainite and martensite is prevented and machinability and elongation property are improved by cooling the forged parts down to <=650 deg.C by spending >=15 seconds. Surface decarburization and the formation of coarser crystal grains are prevented and the hardness and strength are improved by cooling the forged parts down to <=650 deg.C within <=200 seconds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an iron-based sintered forged body obtained by molding a raw material powder and forging a sintered body.

[0002]

2. Description of the Related Art Conventionally, a raw material powder containing a metal as a main component is molded by a powder molding die, the green compact after the molding is sintered, and the sintered body after the sintering is molded into a forging metal. A sintered forged body formed by forging with a die is known. FIG. 6 shows an example of such a sintered forged body. This sintered forged body is used for outer race 1 which is a transmission part of automobile.
The iron-based material has a density of about 7.8 g / cm ³ and its optimum hardness is Vickers hardness Hv = 240 to 300 in terms of machinability and strength. The outer race 1 has an annular shape, and has a plurality of tooth portions 2 on the outer peripheral surface. The outer diameter of the outer race 1 is about 150 mm.

Here, an example of a conventional method for manufacturing the outer race 1 will be described. First, the raw material powder is molded by a powder-molding die (powder molding step), and the green compact after molding is heated and sintered at 1130 ° C. for 20 minutes in a sintering furnace (sintering step). Next, the sintered body that has been cooled after being temporarily stored and transported is reheated to about 1000 ° C in a heating furnace (reheating process), and then the reheated sintered body is compressed with a forging die. And forge (forging process). Further, after the forged body is allowed to cool in the air, the forged body is secondarily sintered at 1130 ° C. (secondary sintering step). This secondary sintering is carried out for the purpose of recovering the surface decarburization of the forged body after forging, and removing the oxide film. Further, conventionally, a method without a reheating step has also been adopted. In this method, for example, in an RX gas atmosphere, the green compact is heated to 1150 ° C. in 7 minutes, heated at 1150 ° C. for 15 minutes to sinter, and then the heated sintered body is immediately heated. Forge.

[0004]

In any case, in the conventional method, after the forging, the outer race 1 which is an iron-based sintered forged body is naturally left to cool in the air.
Since the temperature decrease of the outer race 1 was gradual, the hardness and strength of the outer race 1 became low due to the decarburization of the surface of the outer race 1 and the coarsening of the crystal grains. There was a problem that could not be obtained.

The present invention is intended to solve such a problem, and does not reduce machinability and extensibility.
The purpose is to improve the hardness and strength of an iron-based sintered forged body.

[0006]

In order to achieve the above-mentioned object, a method for manufacturing an iron-based sintered forged body according to the present invention comprises a powder molding step of molding a raw material powder, and a green compact after the powder molding step. Sintering step to sinter, the forging step of forging the heated sintered body after this sintering step with the forging die, and 15 to 200 seconds from the end of withdrawing the forged body from the forging die At 650
And a temperature control step of cooling to below ℃.

The iron-based sintered forged body of the present invention is a method for producing an iron-based sintered forged body, which is an outer race.

[0008]

In the method for producing an iron-based sintered forged body of the present invention, the raw material powder is molded in the powder molding step, the green compact is then sintered in the sintering step, and then the heated powder is heated in the forging step. The forged body is forged by the forging die, but in the subsequent temperature control process, the forging body is cooled to 650 ° C or less within 15 to 200 seconds after the completion of extraction from the forging die, and machinability and elongation are improved. The hardness and strength of the sintered forged body are improved without lowering the property. That is, if the time for lowering to 650 ° C. is 15 seconds or less, martensite, bainite, etc. are precipitated and machinability and extensibility are deteriorated, which is not preferable. On the other hand, when the time to decrease to 650 ° C is 200 seconds or more, the crystal grains become coarse and decarburization occurs on the surface of the sintered forged body, so that sufficient hardness and strength cannot be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The iron-based sintered forged body manufactured in this example is the outer race 1 as shown in FIG. 6 described above. First, based on FIG. 1, the whole apparatus used for manufacturing the outer race 1 will be described. In the figure, 11 is a mixer, and this mixer 11 mixes plural kinds of raw material powders containing iron as a main component. A molding machine 12 is for compressing and molding the mixed raw material powder. Reference numeral 13 denotes a discharge device. The discharge device 13 is a compact 1 that is molded one by one in the molding machine 12 (hereinafter, the same reference numeral 1 is used for compacts and sintered compacts before becoming a sintered forged body). Are placed side by side on the stainless steel wire net 14. 15 is a cassette, and this cassette 15 is a green compact 1
The metal net 14 on which is mounted is stored in a plurality of layers.
Further, 16 is a sintering furnace, which is for sintering the green compact 1 and has a mesh belt conveyor 17 for carrying and carrying a metal net 14 on which the green compact 1 is placed. is doing. Reference numeral 18 is a charging device, and this charging device 18 feeds the metal nets 14 housed in the cassette 15 on which the powder compacts 1 are placed one by one onto the belt conveyor 17 of the sintering furnace 16. Reference numeral 19 denotes a discharge device. The discharge device 19 is for placing the wire nets 14 on which the sintered body 1 obtained by sintering the green compact 1 is placed on a pallet 20 for transportation in a plurality of stages. . Further, 21 is a forging charge device. The forging charge device 21 unloads the metal net 14 placed on the pallet 20 and unloads the sintered body 1 from the metal net 14 to put the empty metal net 14 on the porter 22. It is a stack. 23 is a weight sorter. This weight sorter 23
Is for weight-selecting the sintered bodies 1 sent one by one from the forging charge device 21. A heating furnace 24 heats the weight-selected sintered body 1, and has a mesh belt conveyor 25 on which the sintered body 1 is placed. Denoted at 26 is a take-out device, which takes out the heated sintered body 1 from the heating furnace 24. 27 is a handling robot, and the handling robot 27 carries the sintered bodies 1 one by one into the forging machine 28 from the take-out device 26. The forging machine 28 has a discharging / lubricating device 29 and a forging die 30. 31 is a forced cooling device, this forced cooling device 31,
The outer race 1 immediately after forging is cooled by an air flow, and has a mesh belt conveyor 32 on which the outer race 1 is mounted. Reference numeral 33 denotes a forging discharge device. The forging discharge device 33 is for arranging the cooled outer race 1 in the iron wire mesh container 35 on the pallet 34 for transporting in a front-back and left-right direction and stacking them vertically. Next, a method for manufacturing the outer race 1 will be described. First, the raw material powders mixed by the mixer 11 are supplied to the molding machine 12 to mold the green compact 1 (powder molding step). After leaving the molding machine 12, the green compacts are placed side by side on a wire net 14 via a discharge device 13, and the metal nets 14 on which the green compact 1 is placed are arranged in a plurality of stages on a cassette 15. They are stacked and stored, and sent to the sintering process. In this sintering step, the wire net 14 on which the green compact 1 is placed is transferred from the cassette 15 to the sintering furnace 16 one by one by the charging device 18.
It is placed on the belt conveyor 17 of. The green compact 1 placed on the belt conveyor 17 is sent into the sintering furnace 16,
Here, it is heated at 1130 ° C. for about 20 minutes and sintered to form a sintered body 1. The wire net 14 on which the sintered body 1 is placed is conveyed by a belt conveyor 17 and exits from the sintering furnace 16, and then is stacked on a pallet 20 by a discharge device 19 in multiple stages.

Next, the pallet 20 on which the metal net 14 on which the sintered body 1 is placed is sent to a forging line. In this forging line, first, the forging charge device 21 unloads the wire nets 14 stacked on the pallet 20 in a plurality of stages, and unloads the sintered body 1 from the wire nets 14 to select a weight sorter.
Sent to 23. In addition, the empty wire net 14 is a porter 22
Then, it is put back into the powder molding process. On the other hand, after the weight of the sintered body 1 is sorted by the weight sorter 23, the sintered body 1 is sorted.
Is placed on the belt conveyor 25 of the heating furnace 24 and carried into the heating furnace 24. Then, the sintered body 1 is reheated to 1150 ° C. in the heating furnace 24 (reheating step). Then, the heated sintered bodies 1 are discharged from the heating furnace 24 and then sent into the forging machine 28 one by one through the take-out device 26 and the handling robot 27. Then, the sintered body 1 is compressed and forged by the forging die 30 of the forging machine 28 (forging step). The temperature of the outer race 1 during this forging is about 900 to 1050 ° C. Then, the outer race 1 exits from the forging machine 28, is placed on the belt conveyor 32 of the forced cooling device 31, and is cooled in this forced cooling device 31 by the air flow from about 800 ° C to 650 ° C or less in about 30 seconds. (Forced cooling process as a temperature control process). Further, the outer race 1 thus cooled is aligned by the forging discharge device 33 in the iron wire mesh container 35 on the pallet 34 in the front-rear direction, left-right direction, and stacked and stored in the upper-lower direction, and sent to the next process such as shot. . At that time, as described above, the outer race 1 that has been forged is quickly cooled in the forced cooling step, so that the forging discharge device 33 can also be boxed promptly after forging,
Increases efficiency. This is not limited to the case where an automatic device such as the forging discharge device 33 is used, and the same applies to the case where the box is manually packed. Next, the forced cooling will be described in more detail with reference to FIG. FIG. 2 shows twelve examples (Nos. 1 to 12) of actually measured temperature change patterns of the outer race 1. The alloy composition of the outer race 1 in these examples is 0.5% carbon, 2% copper and the balance iron. In FIG. 2, the vertical axis represents temperature and the horizontal axis represents time from the time when the temperature of the outer race 1 is 830 ° C. Further, in FIG. 2, a region indicated by F + P is a precipitation region of ferrite and pearlite, a region indicated by B is a precipitation region of bainite, and a region indicated by M is precipitation of martensite. Area. And, the Vickers hardness Hv of the outer race 1 of No. 1 to 12 is 579, 544, 304 and 29, respectively.
9, 288, 280, 265, 269, 249, 244, 223, 206
Became. As can be seen from these data, in the range of Vickers hardness Hv = 240 to 300, No. 4 (Hv = 29
9) ~ No. 10 (Hv = 244) outer race 1 is included. Based on the time it takes for the temperature of the outer race 1 to drop to 650 ° C, if this time is 15 seconds or less,
Like the data of No. 3, martensite, bainite, etc. are precipitated and the machinability and extensibility of the outer race 1 are reduced. On the other hand, when it is 200 seconds or more, the hardness of the outer race 1 becomes excessively low and the strength also decreases. this is,
This is due to coarsening of the crystal grains and decarburization of the surface of the outer race 1. On the other hand, the temperature of the outer race 1 when it is taken out from the forging die 30 is about 800 ° C.
Therefore, the forced cooling is about 15 to 200 seconds after the end of the extraction from the forging die 30, and the outer race 1 is heated to 650 ° C.
It is preferable to cool to the following. Conversely, 15 ~
By cooling to 650 ℃ or less in 200 seconds, precipitation of martensite, bainite, etc. can be prevented, machinability and extensibility of the outer race 1 can be improved, and surface decarburization and coarsening of crystal grains can be prevented. The outer race 1 having desired hardness and strength can be obtained.

FIG. 3 shows the results of a crush test of the outer race 1 manufactured under various conditions. In the crush test, as shown in FIG. 4, the outer race 1 is sandwiched between a pair of upper and lower presses 41 and 42, and the upper press 41 is lowered. The stroke of this press 41 is measured by one dial gauge 43. did. In FIG. 3, the vertical axis represents the load and the horizontal axis represents the stroke. And the condition A is
As described in the "Prior art" section, forged without a reheating step and then allowed to cool in the air (black circles and solid lines). Condition B: What was forged in the air (squares and alternate long and short dash lines), conditions C is forcibly cooled as in this example (triangle and two-dot chain line). The x mark at the right end of each diagram indicates a crush point. As can be seen from FIG. 3, the outer race 1 forged without the reheating step and then left to cool in the air has a large resistance to a load, but lacks in extensibility. Further, the outer race 1 reheated, forged and then left to cool in the air has excellent extensibility, but has low resistance to load. On the other hand, the outer race 1 which was reheated, forged and then forcibly cooled as in this example is excellent in both resistance to load and elongation.

Further, FIG. 5 shows measurement results of tensile strength, yield point, elongation rate and Charpy impact value of the outer race 1 manufactured under various conditions. Condition K
Is forcibly cooled after forging as in the present embodiment, condition J
In the condition W, the same raw material powder as that used in the condition K is forged and then left to cool in the air, and in the condition W, the same raw material powder as that used in the condition K is used and then subjected to secondary sintering. The condition X is that a raw material powder of a complete alloy of iron, nickel and molybdenum is sintered, forged, allowed to cool in the air, and then secondarily sintered. As can be seen from FIG. 5, those that are forcibly cooled after forging as in this example (condition K) are those that are allowed to cool in the air after forging (condition J) and those that undergo secondary sintering (condition W).
Compared to, the strength and elongation are excellent and the toughness is high. Further, comparing the condition K with the condition X, although the condition K is partially inferior in performance, there is an effect that the cost can be made significantly lower than the condition X.

The present invention is not limited to the above embodiment, and various modifications can be made. For example,
Although the iron-based sintered forged body of the above-mentioned embodiment was the outer race which is a transmission part of an automobile, the present invention can of course be applied to a sintered forged body other than the outer race. And the sintered forged body is small, 650 in less than 15 seconds
If the temperature drops below ℃, heat or heat the sintered forged body after forging to 650 in 15 to 200 seconds.
It is advisable to lower the temperature to below ℃. Further, in the above-mentioned embodiment, the sintered body cooled after sintering is reheated and then forged, but the sintered body in the heated state may be immediately forged after sintering. Further, in the above embodiment, the outer race immediately after forging is cooled by the air flow by the forced cooling device, but it may be cooled by nitrogen gas.

[0014]

According to the present invention, in the method for manufacturing an iron-based sintered forged body, the sintered forged body is cooled to 650 ° C or less in 15 to 200 seconds from the end of extraction from the forging die, While providing excellent machinability and extensibility, it is possible to prevent decarburization of the surface of the sintered forged body and improve the hardness and strength of the sintered forged body.

Further, according to the present invention, since the iron-based sintered forged body is the outer race, a predetermined hardness can be obtained,
A good outer race can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an apparatus used for manufacturing an outer race of the present invention.

FIG. 2 is a diagram showing a temperature change of an outer race after forging.

FIG. 3 is a load vs. stroke diagram when the outer race is crushed.

FIG. 4 is a schematic explanatory diagram of an apparatus used for a crush test.

FIG. 5 is a diagram showing characteristics of an outer race.

FIG. 6 is a perspective view of an outer race.

[Explanation of symbols]

 1 Outer lace, green compact, sintered body 30 Forging die

Claims (2)

[Claims] 1. A powder molding step for molding a raw material powder, a sintering step for sintering a green compact after the powder molding step, and a heated die after the sintering step for a die for forging. Of a ferrous sintered forging body characterized by having a forging step of forging by the above method and a temperature control step of cooling the forged body to 650 ° C or less in 15 to 200 seconds from the end of extraction from the forging die. Production method. 2. The method for manufacturing an iron-based sintered forged body according to claim 1, wherein the sintered forged body is an outer race.