JPH1180810A - Production of ferrous sintered parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain parts in a complicated shape excellent in dimensional precision and strength by subjecting a powdery sintered body using powder essentially consisting of iron as the raw material to quenching and thereafter working the sintered body by using a die in a state of being heated in a specified temp. range. SOLUTION: A powdery sintered body using powder essentially consisting of iron as the raw material is quenched to make its strength high, thereafter, this sintered body is worked by using a die in a state of being heated at 100 to 550 deg.C. In this way, the warm deformation resistance of the material can be reduced without deteriorating the characteristics of the material after cooling. When the sintered body is recompressed by a die heated at a room temp. to 550 deg.C while the temp. is as it is, since its deformation, resistance is low, the dimensional modification thereof can easily be executed. Moreover, after it is drawn out from the die, air cooling is executed, by which sintered parts having a structure obtd. by refining the quenched structure and excellent in dimensional precision can be obtd. Furthermore, since induction hardening is not required and only the execution of ordinary quenching is enough, batch treatment is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an iron-based sintered part.

[0002]

2. Description of the Related Art Conventionally, a method for producing an iron-based sintered component is to heat and sinter a green compact obtained by compressing a powder raw material into a desired shape to obtain a sintered component. Thereafter, for those requiring strength, tempering is performed after tempering after a quenching step. In addition, there is a step (sizing) of re-compression in a mold to correct dimensions of parts that require dimensional accuracy.

[0003]

However, after quenching, deformation resistance increases, so that sizing cannot be performed sufficiently. On the other hand, when quenching is performed after sizing is performed before quenching, dimensional distortion due to quenching appears and dimensional accuracy is degraded. Therefore, dimensional accuracy is ensured by machining in the final step, but there is a problem that the cost is high.

To solve this problem, Japanese Patent Laid-Open Publication No. 55-1285
No. 04 discloses a tempering process at 550 to 750 ° C. after a quenching step to obtain a tempered structure suitable for recompression.
It proposes performing recompression. However, in this method, since the tempering temperature is high, there is a problem that the material is softened and the strength is deteriorated.

Japanese Patent Application Laid-Open No. 61-210106 discloses that
It has been proposed to subject the sintered body to quenching only to the surface layer by induction hardening and then to recompress the sintered body. According to this method, the dimension can be corrected by the deformability inside the sintered body, but only the outermost surface can be hardened. In addition, since the high-frequency heat treatment cannot be performed in a batch process, there is a problem in that productivity is lower than that of a normal batch-type quenching, and that it cannot be applied to a complicated shape.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an iron-based sintered part capable of manufacturing a complicated-shaped iron-based sintered part having excellent dimensional accuracy and strength with high productivity.

[0007]

According to a method of manufacturing an iron-based sintered component of the present invention, a sintering process is performed on a powder sintered body made of a powder mainly composed of iron, and then the sintered body is subjected to quenching. It is characterized in that processing is performed using a mold while being heated to 100 ° C. or more and 550 ° C. or less.

After the sintered component has been strengthened by quenching, it is heated to a temperature range of 100 ° C. or more and 550 ° C. or less, so that the deformation resistance of the material can be reduced. When the sintered body is recompressed at the same temperature in a mold at room temperature to 550 ° C., the dimensions can be easily corrected because of low deformation resistance. After being extracted from the mold, by air cooling, a sintered part having a quenched structure having a refined structure and excellent dimensional accuracy can be obtained. In addition, since it is not necessary to perform induction hardening treatment, ordinary quenching treatment is sufficient, batch processing becomes possible, and productivity can be improved, and it can be applied to complicated shapes.

[0009] By setting the temperature of the sintered body at 100 ° C or more and 550 ° C or less when processing the sintered body using the mold, deformation during warming can be performed without deteriorating the material properties after cooling. Resistance can be reduced. This heating temperature is 1
If the temperature is lower than 00 ° C., the deformation resistance of the material cannot be reduced, and if the heating temperature exceeds 550 ° C., the material after cooling is softened, so that the effect of the quenching treatment is reduced.

When a material having good hardenability is used,
If the cooling capacity after heating of the sintering furnace is excellent, the sintered body becomes a quenched structure only in the sintering step, and it is difficult to correct the dimensions. In this case, similarly, after the sintering step, the sintered component is heated to 100 ° C. or more and 550 ° C. or less, and sizing is performed with a mold at room temperature to 500 ° C. to obtain an iron-based sintered component having good dimensional accuracy. be able to.

When the sintered body is processed using a mold at room temperature to 500 ° C. in a state where the sintered body is heated to 100 ° C. or more and 550 ° C. or less, the temperature of the mold is the temperature of the sintered body. It is desirable that:

The present invention is a method for improving the dimensional accuracy after quenching of an iron-based sintered part, and is effective for powder materials of various components which are strengthened by quenching.
Further, the present invention is effective in any shape requiring high dimensional accuracy regardless of the shape of the sintered body.

[0013] Preferably, in the above aspect, the step of processing the sintered body using a mold includes a step of compressing the sintered body in a mold, a step of passing the sintered body through a mold die, or a step of Through an inner diameter mold.

In this way, not only in the step of compressing the sintered body in the mold, but also in the case where dimensional accuracy in the outer shape is particularly required, the dimensions are corrected by penetrating the mold die under the above-mentioned temperature conditions. be able to. Similarly, when the dimensional accuracy on the inner shape is particularly required, the dimensional accuracy can be corrected by piercing the inner diameter die under the above-mentioned temperature conditions. Further, it is also possible to correct the mold only at a portion where dimensional accuracy is required depending on the shape under the above temperature conditions.

In the above aspect, preferably, a material composition comprising an additional element and an unavoidable impurity that satisfies that the main component is iron and that the value of X represented by the following formula is 20 or more is used.

X = 550− (350 × weight% C) − (4
0 x wt% Mn)-(35 x wt% V)-(20 x wt% Cr)-(17 x wt% Ni)-(10 x wt% C)
u)-(10 x wt% Mo)-(5 x wt% W) + (1
5 ×% by weight Co) + (30 ×% by weight Al) As a result, a martensitic structure at the time of quenching appears remarkably, and it is effective to perform dimensional correction at the same time as its tempering effect.

The value of X in the above equation represents the martensitic transformation temperature. If the value of X is lower than 20, no martensite structure is formed even at room temperature, so that there is no quenching effect.

Preferably, in the above aspect, the step of processing the sintered body by using a mold includes the step of:
It is carried out in a state where it is heated to 0 ° C. or less.

When the tempering temperature exceeds 250 ° C. and becomes around 300 ° C., brittleness occurs and the impact value decreases. Also 15
If the temperature is less than 0 ° C., the softening of the sintered body is not sufficient, and the dimensional accuracy is reduced due to a large deformation resistance when the dimensions are corrected by a mold. Heating in this temperature range makes tempering unnecessary, so heating in this temperature range is economically excellent.

In the above aspect, preferably, the temperature of the mold when processing the sintered body using the mold is set to ± 5 ° C. of the target temperature.
And the heating temperature of the sintered body is controlled within a range of ± 20 ° C. of the target temperature.

In the step of continuously compressing the heated sintered body, there is a concern that the mold temperature will increase. When the mold temperature exceeds the desired temperature ± 5 ° C., the dimensions change due to the thermal expansion and contraction of the mold, and the dimensions greatly deviate from the target values. If the temperature of the sintered body exceeds the desired temperature of ± 20 ° C., a difference occurs in the sintered body deformation resistance, and the dimensional accuracy in the compression direction deteriorates due to the difference in the amount of deformation during compression.

The mold temperature is preferably in the range of room temperature to 500 ° C. If the temperature exceeds 500 ° C., the strength of the mold itself is concerned, so an expensive heat-resistant alloy must be used. The mold temperature is particularly preferably in the range of room temperature to 100 ° C. As the mold temperature exceeds 100 ° C. and becomes higher, the rigidity of the mold decreases, and the mold easily deforms, so that the dimensional accuracy of the sintered body deteriorates. The higher the temperature, the lower the workability. In addition, lubrication between the sintered component and the mold becomes difficult, and seizure easily occurs. On the other hand, if the temperature is from room temperature to 100 ° C., workability is good. In addition, since the mold temperature is expensive, it is not necessary to cool the mold below normal temperature.

In the above aspect, preferably, the pressure applied to the sintered body when processing the sintered body using a mold is 0.1 t.
on / cm ² or more and 10 ton / cm ² or less.

When the pressure for re-compression and piercing by the mold exceeds 10 ton / cm ² , the mold is greatly consumed and easily broken. If it is less than 0.1 ton / cm ² , it is difficult to sufficiently plastically deform the sintered body.

In the above aspect, preferably, when the sintered body is compressed in the mold, the sintered body is held in the mold for one second or more, and then is extracted from the mold.

If the holding of the sintered body in the mold is less than 1 second, the surface layer portion in the sintered body is cooled to near the mold temperature.
Cooling is insufficient inside and the temperature distribution is large. Since the sintered body is pulled out of the mold as it is and air-cooled, the temperature difference between the inside and outside of the sintered body causes the amount of heat shrinkage to deteriorate the accuracy.
If the holding time in the mold is 1 second or longer, the temperature difference between the inside and outside will be small, and the influence on the dimensional accuracy will be small. In view of the productivity, it is not preferable to hold for a long time, and therefore it is preferable to be about 1 second to 5 seconds.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a process chart showing a method for manufacturing an iron-based sintered part according to Embodiment 1 of the present invention.

Referring to FIG. 1, nickel (N
i) 4%, copper (Cu) 1.5%, molybdenum (M
o) 0.5% graphite powder and 0.8% lubricant in iron-based pre-alloy powder of 0.5%, manganese (Mn) 0.2%, and the balance being iron (Fe) The powder was blended and mixed with a V-type mixer for 30 minutes to obtain a raw material powder. The value of X (martensite transformation temperature) in this raw material powder is 2
79.

[0030] The above-mentioned powder was used to obtain a powder having a diameter of φ5 shown in FIGS.
Molding density 7.0 g / c in a ring shape of 0 × φ40 × 10
m ³ to obtain a green compact (Step 1:
S1). This green compact is heated at 1150 ° C. in a belt type sintering furnace.
For 1 hour in a nitrogen atmosphere (Step 2: S2), and then heated at 850 ° C. for 1 hour, poured into quenching oil at 80 ° C., and quenched (Step 3: S2).
3). The quenched sample was heated and recompressed under the conditions shown in Table 1 below (step 4: S
4). The dimensions of the mold for recompression were set to the dimensions that were thermally expanded when the sintered body was heated under the respective conditions. The mold temperature was controlled under all conditions, and the mold temperature was set to 20 ± 3 ° C.

For each of the recompressed samples, 50 samples were tested under the conditions shown in Table 1, and 25 samples were sampled to measure dimensional accuracy and hardness.

The dimensional accuracy was evaluated by measuring the outer diameter and inner diameter of each sample in 45 directions at intervals of 45 °, and subtracting the minimum value from the maximum value in 100 data of each of the outer diameter and inner diameter in the data of 25 samples. The difference was defined as the dimensional accuracy of each of the outer diameter and the inner diameter. Table 1 shows the results.

The sintering material shown in Table 1 is a work that has been subjected to the sintering step, and the quenched material is a work that has been subjected to the quenching step.

[0034]

[Table 1]

In this product shape, the dimensional accuracy, which is a standard for omitting machining, is an outer diameter tolerance of ± 25 μm. That is, if the width is within the range of 50 μm, the dimensional accuracy is good.

From the above results, from the viewpoint of dimensional accuracy,
It has been found that the conditions a to s of the examples of the present invention are in a favorable range. That is, the sintered body is kept at 100 ° C. or more and 550 ° C.
It has been found that an iron-based sintered part having excellent dimensional accuracy can be obtained by processing using a mold in a heated state below.

If the sintered body heating temperature is less than 100 ° C.,
Sufficient deformability was not obtained, and the effect of improving dimensional accuracy was small (condition a). In addition, as the heating temperature of the sintered body became higher, the temperature of the work after being extracted from the mold also became higher, and the dimensional accuracy was deteriorated due to the heat shrinkage after the extraction. In addition, the hardness decreases due to the tempering effect due to the high heating temperature, and 550
When the temperature exceeds ℃, the sintering material and hardness did not change much, and the effect of quenching decreased (conditions S and S).

In particular, it has also been found that the best product with high dimensional accuracy and little decrease in hardness can be obtained when the heating temperature is in the range of 150 ° C. to 250 ° C.

Example 2 Using the raw material of Example 1, a work which had been molded, sintered and quenched under the same conditions was heated and recompressed under the conditions shown in Table 2 below. Heating temperature 200 which was good in Example 1
The experiment was performed using the condition of ° C. and changing the conditions of the compression pressure and the pressure holding time.

[0040]

[Table 2]

In Table 2, the press pressure was changed for each of the samples. At a sample cell pressure of 0.08 ton / cm ² , the pressure was insufficient and the work could not be pushed into the mold. Good dimensional accuracy was obtained up to the sample source. If the pressing pressure exceeds 10 ton / cm ² , there is a risk of mold breakage and mold wear, which is not practical.

The compression holding time was changed for the samples 10 to 10. This is a holding time in a state where the upper punch of the press is lowered to the lowest point. All of the samples テ to ヌ have good dimensional accuracy, but the dimensional accuracy of the sample の with a holding time of 0.5 seconds was inferior to that of the samples 〜 to ヌ. This is because the work temperature at the time of extraction is 150 ° C because the holding time in the mold is short.
° C or more, and precision deterioration was caused by heat shrinkage deformation.

Example 3 3 % by weight of copper (Cu) 2%, balance iron (Fe)
0.8% of graphite powder and 0.8% of lubricant powder were blended with the iron-based pre-alloy powder to be used as a raw material powder by mixing with a V-type mixer for 30 minutes. The value of X described above in this raw material powder was 242.

The above-mentioned powder was formed into a green compact in the shape shown in FIGS. 3A and 3B so as to have a molding density of 7.0 g / cm ³ . This green compact is 1150 in a belt type sintering furnace.
After heating and sintering in a nitrogen atmosphere for 1 hour at
The mixture was heated at 50 ° C. for 1 hour, poured into a quenching oil at 60 ° C., and quenched. Thereafter, recompression was performed under the conditions shown in Table 3 below.

Under the conditions shown in Table 3, 50 samples were recompressed, and 25 samples were sampled to measure dimensional accuracy and hardness. The evaluation method of dimensional accuracy is to measure the outer diameter of each sample in four directions at 45 ° intervals, and define the difference between the maximum and minimum values of the outer circumference in the data of 25 samples as the dimensional accuracy of the outer and inner diameters did. Table 3 shows the results.

In the condition (4), the temperature of the mold was controlled by using a water cooling device, and the temperature of the mold could be controlled to 20 ° C. ± 3 ° C., but the condition was not controlled.

[0047]

[Table 3]

From the above results, the best dimensional accuracy was obtained under the conditions.

Under the condition (3), since the temperature of the mold was not controlled, the mold temperature rose from the initial temperature of 20 ° C. to 92 ° C. after recompression of 50 samples. For this reason, the dimensional accuracy was reduced.

Example 4 An experiment was conducted using the following two kinds of powders. The above-mentioned values of X in the above two types of powders were numerical values in parentheses.

(A) Fe-4Ni-1.5Cu-0.5Mo-0.5C (X = 279) (B) Fe-5Ni-16Cr-2Mn-1Si-0.15C (X = 18) Example 2 In the same manner as described above, the raw material powder was formed into a green compact in the shape shown in FIGS. 3A and 3B so as to have a molding density of 7.0 g / cm ³ . This green compact is 1250 ° C. in a batch type sintering furnace.
After heating and sintering in vacuum for 1 hour, the mixture was heated at 900 ° C. for 1 hour and poured into a quenching oil at 60 ° C. to perform a quenching treatment. After that, 7 ton /
A recompression treatment was performed at a pressure of cm ² . The workpiece heating temperature at the time of sizing was kept at room temperature under the conditions (H) and (F), and was set at 200 ° C. under the conditions (H) and (F). The holding time in the mold during compression was 1 second. The method for evaluating the dimensional accuracy is the same as that of the second embodiment.

[0052]

[Table 4]

In the case where the powder of B is used in condition (f), Ms
(Martensite Transformation Point) Since the temperature X was below room temperature, no martensite transformation occurred during quenching and the hardness was low even after quenching. Therefore, there was no significant difference in dimensional accuracy after recompression between the condition using the process of the present invention and the condition where sizing was performed at room temperature as in the past. This allows the process to be described as X =
It has proven to be pointless to apply to less than 20 powders.

On the other hand, in the conditions (c) and (h) in which the raw material A where X = 279 was used, the condition in which the work was recompressed at room temperature showed little improvement in dimensional accuracy. In C, the dimensional accuracy was greatly improved.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. 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.

[0056]

As described above, in the method for manufacturing an iron-based sintered part according to the present invention, after the sintered part is strengthened by quenching, it is heated to a temperature range of 100 ° C. to 550 ° C. . This heating can reduce the deformation resistance of the material, so that the dimension can be easily corrected using a mold. Further, according to this method, since a process such as induction hardening is not required, it is possible to manufacture an iron-based sintered part having a complicated shape with high productivity.

If the heating temperature is lower than 100 ° C., the deformation resistance of the material cannot be reduced, and the heating temperature is 550 ° C.
If the temperature exceeds the limit, the material after cooling is softened, so that the effect of the quenching treatment is reduced.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for manufacturing an iron-based sintered part in Example 1 of the present invention.

FIG. 2 is a view showing a specific shape of an iron-based sintered part.

FIG. 3 is a view showing a specific shape of an iron-based sintered part.

Claims (9)

[Claims] After quenching a powder sintered body made of a powder mainly composed of iron as a raw material, the sintered body is heated to 100 ° C.
A method for producing an iron-based sintered part, characterized in that processing is performed using a mold while being heated to at least 550 ° C. or lower. 2. The manufacturing of an iron-based sintered part according to claim 1, wherein the step of processing the sintered body using the mold includes a step of compressing the sintered body in the mold. Method. 3. The method for manufacturing an iron-based sintered part according to claim 1, wherein the step of processing the sintered body using the mold includes a step of passing the sintered body through a mold die. 4. The method for producing an iron-based sintered part according to claim 1, wherein the step of processing the sintered body using the mold includes a step of passing the sintered body through an inner diameter mold. 5. The method according to claim 1, wherein the main component is iron, and
Characterized by using a material composition consisting of an additive element and an unavoidable impurity that satisfies a value of 20 or more,
A method for producing an iron-based sintered part according to claim 1. X = 550− (350 ×% by weight C) − (40 ×% by weight M)
n)-(35 x wt% V)-(20 x wt% Cr)-
(17 × wt% Ni) − (10 × wt% Cu) − (10
X weight% Mo)-(5 x weight% W) + (15 x weight% C)
o) + (30 x wt% Al) 6. The iron-based sintering according to claim 1, wherein the step of processing the sintered body using the mold is performed while the sintered body is heated to 150 ° C. or more and 250 ° C. or less. The method of manufacturing the part. 7. The temperature of the mold when processing the sintered body using the mold is controlled within a range of ± 5 ° C. of a target temperature, and the heating temperature of the sintered body is set to a target temperature. The method for producing an iron-based sintered part according to claim 1, wherein the control is performed within a range of ± 20 ° C. 8. The iron according to claim 1, wherein a pressure applied to the sintered body when the sintered body is processed using the mold is 0.1 ton / cm ² or more and 10 ton / cm ² or less. Method for manufacturing sintered parts. 9. The iron system according to claim 2, wherein, when compressing the sintered body in the mold, the sintered body is taken out of the mold after holding the sintered body in the mold for at least one second. Manufacturing method of sintered parts.