JPH08144006A - Production of sintered compact of stainless steel powder - Google Patents

Abstract

PURPOSE: To carry out degreasing and sintering without varying the compsn. of powdery starting material. CONSTITUTION: Green parts each consisting of stainless steel powder and an org. binder are degreased in an active atmosphere at about 400 deg.C and residual carbon and residual oxygen in the parts are removed by heating to 1,000 deg.C in an atmosphere under a reduced pressure of 10<-4> Torr. The parts are then sintered by heating to >=1,100 deg.C in an inert atmosphere under a pressure of 1-10Torr. The evaporation of Cr in the powdery starting material can be prevented and the objective sintered compacts are obtd. without varying the compsn. of the starting material.

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 a stainless powder sintered body having excellent corrosion resistance.

[0002]

2. Description of the Related Art As a method for producing a stainless powder sintered body having excellent corrosion resistance, a method described in JP-A-4-147950 has been known. In this method, green parts are heated to 600 ° C in a nitrogen atmosphere at a heating rate of 10 ° C / h to degrease them into brown parts, and then the brown parts are heated at 1150 ° C for 0.1 Torr.
Sintering under reduced pressure of r or less for 1 hour, more specifically 1150
Sintered under reduced pressure of 10 ^-4 Torr for 1 hour, followed by A
Sintering is performed at 1350 ° C. for 2 hours in an r gas atmosphere. This method produces a sintered alloy steel having excellent corrosion resistance by optimizing the amount of carbon and the amount of oxygen in the sintered alloy.

[0003]

However, according to the above-mentioned method, even if the carbon content and the oxygen content in the sintered alloy are optimized, the sintering is performed at 1150 ° C. for 1 hour under a high vacuum of 10 ⁻⁴ Torr. When Cr is performed, Cr is reduced, but scattering (evaporation) of Cr having a low vapor pressure is started. As a result, Cr in the sintered alloy that has been sintered is reduced, so that there is a problem that it does not reach the originally expected corrosion resistance. Further, due to the decrease in Cr, the composition in the alloy may deviate from the JIS standard value. For example, using SUS316L powder, SUS3
Even if you try to obtain a 16L sintered body, the sintered body is SUS316
There are inconveniences such as not becoming L. Furthermore, if degreasing is performed in an inert atmosphere, it cannot follow a rapid temperature rise (large temperature rising gradient), and the binder (binder) cannot be completely removed unless the temperature is raised to a high temperature of 600 ° C. However, there is a problem that it takes a very long time and the manufacturing cost becomes high.

The present invention has been made in consideration of the above circumstances, and does not deviate from the composition range of the raw material powder.
It is an object of the present invention to provide a method capable of producing a stainless sintered body having excellent corrosion resistance in a short time.

[0005]

In order to achieve the above object, the invention according to claim 1 kneads a stainless powder and an organic binder into a compound, and injection-molds this compound into a green part. Process,
The method includes a step of degreasing the green parts into brown parts. After degreasing the green parts under an active atmosphere, the green parts are heated to 1000 ° C. under a reduced pressure atmosphere of at least 10 ⁻⁴ Torr to remove residual carbon and residual oxygen. And then at least 1 in an inert atmosphere of 1-10 Torr
It is characterized by heating to 100 ° C. or higher and sintering.

According to the first aspect of the present invention, by degreasing the green part formed in a desired shape by injection molding in an active atmosphere, decomposition of the binder is promoted rather than degreasing in an inert atmosphere such as nitrogen. Therefore, the degreasing time can be significantly shortened. Further, the brown part obtained by degreasing is further heated under a reduced pressure of at least 10 ^-4 Torr, whereby the carbon remaining in the brown part is bonded to a metal element such as Fe or Cr. Since the oxygen is effectively reduced, it is possible to perform sintering while preventing carbonization of Cr. When the sintering is completed, the sintered alloy can be densified.
By stopping this reduced pressure atmosphere at a temperature of up to 1000 ° C., the correlation with the corrosion resistance becomes very strong. That is, this makes it possible to prevent the evaporation of Cr having a low vapor pressure, and since the temperature rises in an inert atmosphere thereafter, the Cr amount does not significantly change from the composition of the raw material powder. A product of stainless alloy steel having a desired composition can be obtained by heating to a temperature of ℃ or more and sintering. Since the inert atmosphere at this time is for preventing the evaporation of Cr, a large amount of gas is not necessary,
A pressure of about 1 to 10 Torr is sufficient.

According to the second aspect of the present invention, degreasing is performed under atmospheric pressure at 400 ° C. or lower. According to the invention of claim 2, degreasing can be easily performed in an active atmosphere by using the atmosphere for degreasing. Degreasing in this atmosphere is performed at a temperature of up to 400 ° C., but this degreasing has the same effect as degreasing performed by raising the temperature to a higher temperature in an inert atmosphere. Further, since the temperature is up to 400 ° C., it is possible to prevent the powder from being oxidized by degreasing, and there is no fear of nitriding which may occur when degreasing with nitrogen at high temperature.

[0008]

【Example】

(Example 1) SUS316L water atomized powder having a particle size of 15 μm under, and the main components are paraffin wax, polystyrene (PS), acrylic (PMMA), ethylene-
An organic binder made of vinyl acetate copolymer (EVA) or the like was kneaded at a weight ratio of 9: 1 to obtain a molding compound, and this compound was used as a raw material and injection-molded into a desired shape. The obtained green parts are 25 ℃ / h under air
The temperature was raised up to 120 ° C. and held at this temperature for 1 hour, then raised up to 365 ° C. at a temperature raised up to 50 ° C./h and held for 2.5 hours for degreasing. Then, the obtained brown parts were subjected to 30 ^-5 Torr under a reduced pressure atmosphere of 30 ^-5 Torr.
After heating to 1000 ° C. at a rate of 0 ° C./h, after that, the temperature was raised to 1320 ° C. at the same rate (300 ° C./h) in an inert atmosphere of Ar gas at 5 Torr, and after that, the temperature was maintained for 1 hour and allowed to cool, Sintering was completed to obtain a sintered body. After this sintering, barrel polishing was used to carry out burr treatment to obtain a product. Then, this product was subjected to a chemical resistance / resistance test using artificial gastric juice and 50 autoclaves. Moreover, the amount of carbon, the amount of oxygen, and the amount of Cr in the sintered body were analyzed. The results are shown in Table 1.

[0009]

[Table 1]

(Example 2) SU having a particle size of 20 μm under
S630 gas atomized powder, and the main component is paraffin wax, polystyrene (PS), acrylic (PMMA)
An organic binder composed of, for example, was kneaded at a weight ratio of 7: 1 to obtain a molding compound. This compound was used as a raw material and injection-molded into a desired shape. The obtained green part was heated to 120 ° C. at a temperature rising temperature of 25 ° C./h in the air and held for 1 hour, and then heated to 50 ° C./h. 375 at warm temperature
After the temperature was raised to ° C, it was held for 2.5 hours for degreasing.
Then, the obtained frown parts are heated to 1000 ° C. at a rate of 30 ° C./h in a reduced pressure atmosphere of 10 ⁻⁴ Torr,
Thereafter, 1320 in an inert gas atmosphere of Ar gas at 5 Torr
The temperature was raised to the same temperature (300 ° C./h), and the temperature was maintained for 1 hour and allowed to cool, and then the sintering was completed to obtain a sintered body. Then, a solution heat treatment and a precipitation hardening treatment were performed, and thereafter, a burr treatment was performed by barrel polishing to obtain a product. Then, this product was subjected to a chemical resistance / resistance test using artificial gastric juice and 50 autoclaves. Moreover, the amount of carbon, the amount of oxygen, and the amount of Cr in the product were analyzed. Table 1 shows the results.

(Example 3) SU having a particle size of 15 μm under
S316L water atomized powder, main component is paraffin wax, polystyrene (PS), acrylic (PMM
A) and an organic binder such as EVA were kneaded at a weight ratio of 9: 1 to obtain a molding compound. Using this compound as a raw material, injection molding was performed into a desired shape, and the obtained green parts were heated at a temperature of 25 ° C./h for 12 hours.
After the temperature was raised to 0 ° C. and kept for 1 hour, the temperature was raised to 365 ° C. at a temperature raising temperature of 50 ° C./h and kept for 2.5 hours to perform degreasing. And the obtained Fraun parts are 10 ^-5 Tor
In a decompressed atmosphere of r, heated to 900 ° C. at a rate of 300 ° C./h, thereafter heated to 1320 ° C. in an inert atmosphere of Ar gas at 5 Torr at the same rate (300 ° C./h), and then held for 1 hour. After cooling, the sintering was completed to obtain a sintered body. After this sintering, barrel polishing was used to carry out burr treatment to obtain a product. Then, this product was subjected to a chemical resistance / resistance test using artificial gastric juice and 50 autoclaves. Moreover, the amount of carbon, the amount of oxygen, and the amount of Cr in the sintered body were analyzed. Table 1 shows the results.

(Comparative Example 1) Using a compound similar to that of Example 1, one brown part degreased under the same conditions was used.
1 at a rate of 300 ° C / h in a reduced pressure atmosphere of 0 ^-4 Torr
After heating to 150 ° C., in an inert atmosphere of Ar gas at 5 Torr, the temperature is increased to 1320 ° C. at the same rate (300 ° C. /
The temperature was raised in h), the temperature was maintained for 1 hour, the mixture was allowed to cool, and then the sintering was completed to obtain a sintered body. After this sintering, barrel polishing was used to carry out burr treatment to obtain a product. Then, this product was subjected to a chemical resistance / resistance test using artificial gastric juice and 50 autoclaves. Moreover, the amount of carbon, the amount of oxygen, and the amount of Cr in the sintered body were analyzed. The results are shown in Table 1.

(Comparative Example 2) Using a compound similar to that of Example 2, one brown part degreased under the same conditions was used.
1 at a speed of 300 ° C / h under a reduced pressure atmosphere of 0 ^-2 Torr
After heating up to 000 ° C., thereafter in an inert atmosphere of Ar gas at 5 Torr up to 1320 ° C. at the same rate (300 ° C. /
The temperature was raised in h), the temperature was maintained for 1 hour, the mixture was allowed to cool, and then the sintering was completed to obtain a sintered body. After this sintering, barrel polishing was used to carry out burr treatment to obtain a product. Then, this product was subjected to a chemical resistance / resistance test using artificial gastric juice and 50 autoclaves. Moreover, the amount of carbon, the amount of oxygen, and the amount of Cr in the sintered body were analyzed. The results are shown in Table 1.

(Comparative Example 3) Using a compound similar to that of Example 3, 1 part of a brown part degreased under the same conditions was used.
Up to 050 ° C, under reduced pressure of 10 ^-5 Torr, 300 ° C
Heating to 1050 ° C. at a rate of / h, and then 5 times Ar gas
In an inert atmosphere of Torr, the temperature was raised up to 1320 ° C. at the same rate (300 ° C./h), held for 1 hour and allowed to cool, and then sintering was completed to obtain a sintered body. After sintering, it was subjected to burr treatment by barrel polishing to obtain a product. Then, this product was subjected to a chemical resistance / resistance test using artificial gastric juice and 50 autoclaves. In addition, the amount of carbon, the amount of oxygen, and Cr in the sintered body
The amount was analyzed. Table 1 shows the results.

In Examples 1 to 3, the amounts of carbon and oxygen contained in the sintered body were good results as shown in Table 1, and the amount of Cr was almost the same as the amount contained in the raw material powder. There was no change, and there were no components deviating from the values of each contained component defined in JIS standard, and the steel type was the same as the raw material powder. On the other hand, in Comparative Examples 1 and 3, the amounts of carbon and oxygen contained were almost the same as those in the example, but the amount of Cr was small, and the result was out of the JIS standard SUS316L.
Further, in Comparative Example 2, the amount of Cr was within the standard value, but the amount of carbon and oxygen contained was large, and the result was that the carbon was out of the JIS standard. In Comparative Example 1, the amount of Cr is SU
The value outside the standard value of S316L is 10 ^-4 during sintering.
This is because Cr having a low vapor pressure was evaporated by performing the Torr vacuum condition up to 1150 ° C. Comparative Example 3
In the above, the vacuum was applied only by 50 ° C. higher than the standard value, but it is considered that the amount of Cr decreased because the degree of vacuum was high. Further, in the method of Comparative Example 2, it is considered that oxygen was not sufficiently reduced due to the low degree of vacuum, and therefore the amount of carbon and oxygen in the sintered body increased.
In the chemical resistance / resistance test, in the method shown in the comparative example, deterioration was seen as compared with the method of the example due to improper carbon, oxygen, and Cr. The effect of was sufficient.

[0016]

According to the present invention, it is possible to produce a highly corrosion-resistant stainless sintered body by optimizing not only carbon and oxygen in the sintered body but also the amount of Cr. Since the inert gas to be sealed is the minimum amount necessary to prevent Cr from evaporating, it can be realized at a low cost without using a large amount of a relatively expensive inert gas.

Claims (2)

[Claims] 1. A step of kneading a stainless powder and an organic binder into a compound, injection molding the compound into a green part, degreasing the green part into a brown part, and the brown part A manufacturing method comprising a step of sintering to obtain a sintered body, after degreasing the green part under an active atmosphere,
Heating to 00 ° C. under a reduced pressure atmosphere of at least 10 ⁻⁴ Torr to remove residual carbon and residual oxygen, and then 1 to 1
A method for producing a stainless powder sintered body, which comprises heating to at least 1100 ° C. or more and sintering in an inert atmosphere of 0 Torr. 2. The method for producing a stainless powder sintered body according to claim 1, wherein the degreasing is performed in a normal pressure atmosphere of 400 ° C. or less.