JPH05186810A - Method for brazing iron-based sintered parts in sintering - Google Patents

Abstract

PURPOSE:To produce an iron-base sintered parts having intricate shape excellent in bonding strength by using a Cu-Ni-Mn based brazing filler metal incorporating a specified content of Fe. CONSTITUTION:An iron-based green compact is sintered and simultaneously brazed with the brazing filler metal contg. 16-30wt.% Fe. In this case, the green compact is heated in a vacuum atmosphere from room temp. to a specified temp. higher than the m.p. of the brazing filler metal and lower than 1080 deg.C and held at that temp. The atmosphere is changed into a reduction atmosphere, and the green compact is heated from the specified temp. to the sintering temp. of the green compact in the reduction atmosphere and held at this temp.

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 part having a complicated shape by sintering and brazing an iron-based green compact.

[0002]

2. Description of the Related Art Generally, iron-based sintered parts are mainly composed of iron powder, and other metal powders are compounded to have a predetermined component composition, mixed, and then molded into a predetermined shape with a mold to obtain a green compact. And is manufactured by sintering this green compact in a reducing atmosphere.

However, a sintered part having a complicated shape which is difficult to be formed by a die is formed into a plurality of divided parts, and these parts are combined and brazed or simultaneously brazed at the time of sintering. It was made.

The brazing filler metal used for the above brazing is Ni: 30 to 50%, Mn: 15 to 25%, F by weight.
e: 3 to 15%, Si: 1 to 5%, B: 0.5 to 2%, and a Cu alloy powder made of Cu with the rest being a green compact, or Ni: 30 to 50%, Mn: 15-25
%, Si: 1 to 5%, B: 0.5 to 2%, the rest is Cu alloy powder consisting of Cu, Fe powder: 3 to 15%
The mixed powder obtained by mixing is used as a green compact.

When the powder compact brazing filler metal is placed at or near the joints of the respective parts and heated in a reducing gas atmosphere such as hydrogen gas, butane shift gas, or ammonia decomposition gas, the brazing filler metal melts and permeates. The joints of the above parts are brazed (for the brazing method, see Japanese Patent Laid-Open No. 2-1
5875, JP-A-2-247303, etc.).

[0006]

However, the above-mentioned conventional reducing gas generally contains a trace amount of water, and when brazing is performed in a reducing gas atmosphere containing this trace amount of water,
When Mn contained in the brazing material is oxidized and Mn is oxidized, the fluidity of the brazing material is reduced, the wettability to the base material is extremely reduced, and the brazing material may not be melted, resulting in poor brazing. However, there has been a problem that the strength of the brazed portion is reduced due to the poor brazing. In addition, although a brazing material containing a large amount of Fe is commercially available, the brazing material containing a large amount of Fe has a high melting point and at the same time the surface tension of the molten brazing material rises, further reducing the wettability to the base material. As a result, the penetrating force into the iron-based sintered component is reduced, and therefore, the brazing property is also reduced, and the strength of the brazed portion is reduced due to poor brazing, which is a problem.

[0007]

Therefore, the present inventors have
A brazing method for iron-based green compact sintering that further improves the brazing property of a brazing material containing a large amount of Fe (Fe: 16% or more) and does not reduce the strength of the brazing part due to poor brazing. As a result of research for development, (a) When the temperature range from room temperature where brazing proceeds to 1080 ° C. or lower is maintained in a vacuum atmosphere, oxidation of Mn due to the influence of water is prevented as in the conventional reducing atmosphere. Even if the brazing material contains a large amount of Fe, the surface tension of the molten brazing material lowers and penetrates into the interface of the bonding surface and the inside of the iron-based green compact, and the brazing material spreads almost all over the bonding surface. (In this case, since the temperature is low, the sintering of the iron-based green compact is insufficient), (b) Subsequently, in the range of more than 1080 ° C to the sintering temperature, the normal iron-based green compact is sintered. Atmosphere (Dew point: -40 ℃ to -5 ℃ By sintering in a reducing atmosphere containing a small amount of water), Mn of the brazing material is oxidized and the wettability to the iron-based green compact is extremely reduced, and the fluidity of the brazing material is reduced even at high temperature. However, it has been found that the penetration of the brazing material can be prevented and, at the same time, the sintering of the iron-based green compact can sufficiently proceed to obtain a desired strength.

The present invention was made on the basis of such findings, and Fe: 1: 1 was formed at the same time as sintering of an iron-based green compact.
In a method for producing an iron-based sintered component by brazing using a Cu-Ni-Mn-based brazing material containing 6 to 30% by weight, in a vacuum atmosphere, from room temperature to a melting point of the brazing material or more and 1080C or less. After raising the temperature to a predetermined temperature within the temperature range, the temperature is maintained within this temperature range, and then the atmosphere is converted into a reducing atmosphere, and in this reducing atmosphere, the temperature of the melting point of the brazing material or more and 1080 ° C. or less. The method is characterized by a brazing method during sintering of an iron-based sintered component which is heated to a sintering temperature of the iron-based green compact from a predetermined temperature within the range and then maintained at this sintering temperature.

Next, the reason why the atmosphere and temperature of the present invention are limited as described above will be explained.

(A) Vacuum atmosphere and temperature Cu—Ni—M containing Fe: 16 to 30 wt% from room temperature
If a reducing atmosphere is used as in the conventional method up to a predetermined temperature within the temperature range of the melting point of the n-based brazing material to 1080 ° C.
Oxidizes to make the brazing filler metal less likely to melt, and makes it difficult for the brazing filler metal to permeate the joint surface interface of the iron-based green compact and the base metal. Therefore, in this temperature range, a vacuum (preferably 1 × 10 5
^It is necessary to maintain a vacuum of ^-2 Torr or less).
If the temperature is maintained above 080 ° C., the brazing material will penetrate too much into the iron-based green compact and the strength of the joint will decrease. Therefore, the upper limit of the temperature of the vacuum atmosphere is set to 1080 ° C.

Fe: Cu containing 16 to 30% by weight
The melting point of the —Ni—Mn-based brazing material is in the range of 940 to 1050 ° C.

(B) Reducing Atmosphere and Temperature After the brazing, the atmosphere exceeding 1080 ° C. up to the sintering temperature and the atmosphere for maintaining the sintering temperature must have a dew point on the Mn oxidation side, and an inevitable trace amount. It is preferable to use a commercially available reducing gas containing water as the atmosphere. Mn
Is not on the oxidation side, and when a reducing gas with a special amount of water removed is used as the atmosphere gas, the dew point disappears on the Mn oxidation side and M
Since n is not oxidized and is at a high temperature, the fluidity of the brazing material becomes too good, and pores and the like are likely to occur at the interface of the joint surface, which is not preferable.

Therefore, in the reducing gas atmosphere containing no trace amount of water, a trace amount of water is positively added within a range that does not impair the characteristics of the iron-based sintered part so that the dew point is on the Mn oxidation side. There is a need to.

The sintering temperature of the iron-based green compact is generally 11
The reducing atmosphere gas in the range of 00 to 1250 ° C. and on the Mn oxidation side is a gas having a dew point of −40 ° C. or higher.

The method of brazing at the time of sintering of the iron-based sintered component of the present invention will be specifically described with reference to the drawings, but the method of the present invention is not limited to the above drawings. Absent.

FIG. 1 is a schematic diagram of a pattern showing a brazing method during sintering of an iron-based sintered component of the present invention. In FIG. 1, the vertical axis represents temperature, Ts is the sintering temperature,
T ₁ is a brazing material melting temperature suitable for brazing to 1080 ° C.
It is a predetermined temperature within the following range. The horizontal axis shows elapsed time, and the atmosphere holding time is shown.

FIG. 2 is a sectional explanatory view showing a method of installing the green compact and the brazing material in the brazing method during sintering of the iron-based sintered part of the present invention.

FIG. 3 is an explanatory cross-sectional view showing a method for measuring the strength of the brazed portion of an iron-based sintered component that has been brazed and sintered by the method of the present invention.

In order to sinter the ring-shaped green compact 1 and the disc-shaped green compact 2 at the same time as brazing, first, as shown in FIG. 2 is placed on the inner surface of the ring-shaped green compact 1 and the ring-shaped brazing material 3
Is placed in a heating furnace (not shown) while being placed on the disk-shaped green compact 2. In this case, as shown in FIG.
It is preferable that the ring-shaped green compact 1 and the disk-shaped green compact 2 are placed on the jig 4 to fix their positions and then charged into the heating furnace.

The ring-shaped green compact 1, the disk-shaped green compact 2 and the ring-shaped brazing material 3 are charged into the heating furnace together with the jig 4, and then the inside of the heating furnace is vacuumed as shown in FIG. The temperature is maintained in the atmosphere, the temperature is raised to the brazing temperature T _1, and the temperature is maintained at T ₁ . At this T ₁ temperature, the brazing material 3 can be melted and brazed, but the temperature is insufficient for sintering the ring-shaped green compact 1 and the disk-shaped green compact 2.

Next, as shown in FIG. 1, the atmosphere in the heating furnace is replaced with a reducing atmosphere on the Mn oxidation side, the temperature is raised to the sintering temperature Ts of the green compact, and the temperature is maintained at this temperature. After the sintering is completed, the furnace is cooled.

The brazing strength of the iron-based sintered component thus manufactured is smaller than the outer diameter of the ring-shaped sintered body 1 ', as shown in FIG. Placed on a table 7 having a space 6 having an inner diameter larger than the outer diameter of the punch, the punch 8 is pressed against the disc-shaped sintered body 2'with a force F, and the breaking load when the brazing portion 5 breaks is measured. The brazing strength (kgf / mm ² ) = breaking load / brazing area was calculated.

[0023]

[Examples] In% by weight as raw material powder (hereinafter,% is% by weight)
Average particle size of Ni: 41.3%, Mn: 17.0%, and the balance of Cu and unavoidable impurities:
Cu alloy powder of 150 μm (hereinafter referred to as A powder), N
i: 40.1%, Mn: 16.2%, B: 1.47%,
Si: 2.00% contained, the rest consisting of Cu and unavoidable impurities, Cu alloy powder (hereinafter referred to as B powder) having an average particle diameter of 170 μm, Ni: 29.3%, Mn1
2.3%, Fe: 21.5%, B: 1.10%, Si:
Cu alloy powder containing 1.43% and the rest consisting of Cu and unavoidable impurities and having an average particle size of 160 μm (hereinafter, C
Powder), Ni: 32.4%, Mn 12.5%, F
e: 19.4%, B: 1.03%, Si: 1.51%, and the rest Cu alloy powder (hereinafter referred to as D powder) having an average particle diameter of 160 μm and consisting of Cu and unavoidable impurities, and , Average particle size: 100 μm and purity: 9
Atomized pure Fe powder having 9.5% (hereinafter, pure Fe)
Powder) was prepared.

As shown in Table 1, pure Fe powder was blended or not blended with these powders A to D, 1% of paraffin wax was added and wet blended, and pressure: 6 ton / cm ²
Then, a ring-shaped brazing material 3 having a size of an outer diameter of 15 mm was produced.

On the other hand, an Fe powder containing C: 0.7% and Cu: 2% and the balance of Fe and inevitable impurities was prepared, and this powder was press-molded at a pressure of 7 ton / cm ² , Ring-shaped green compact 1 having dimensions of outer diameter: 32 mm, inner diameter: 15.8 mm, thickness: 10 mm and disc-shaped green compact 2 having dimensions of outer diameter: 27 mm, thickness: 7 mm
Was produced.

The ring-shaped green compact 1 and the ring-shaped brazing filler metal 3 are combined as shown in FIG. 2, charged into a heating furnace together with the jig 4, and the inside of the heating furnace is evacuated to a vacuum of 1 × 10 ⁻³ Torr. After that, the temperature in the heating furnace was raised to the temperature T ₁ shown in Table 1 and brazing was performed. Then, the atmosphere in the heating furnace was replaced with the reducing gas atmosphere shown in Table 1, and the temperature was maintained at the sintering temperature Ts. Then, the brazing methods 1 to 7 of the present invention and the comparative brazing methods 1 to 4 were carried out.

For comparison, the conventional brazing method was carried out by simultaneously sintering and brazing under the conditions shown in Table 1 without changing the atmosphere in the heating furnace.

The sintered part thus obtained is placed on a table 7 as shown in FIG. 3, and pressed by a punch 8 until the brazing part 5 is broken, and the unit area of the brazing part is The cross-sectional strength (kgf / mm ² ) per hit, that is, the brazing strength was determined, and the results are shown in Table 1.

[0029]

[Table 1]

[0030]

From the results shown in Table 1, Fe: 16-
The brazing strength of the iron-based sintered parts obtained by the brazing methods 1 to 7 of the present invention in which a Cu-Ni-Mn-based brazing material containing 30% is used and the atmosphere is replaced with a reducing atmosphere is It can be seen that the value is even better than the brazing strength obtained by brazing only in the reducing atmosphere by the brazing method.

Comparative Example 1 which deviates from the conditions of the present invention
It can be seen that the brazing strengths of 4 to 4 (values deviating from the conditions of the present invention are marked with *) are slightly lowered.

As described above, according to the brazing method of the present invention, an iron-based sintered component having a brazing strength superior to the conventional one can be obtained, and it can be used under more severe conditions than the conventional one. It is possible to provide shaped iron-based sintered parts, which can greatly contribute to the development of the industry.

[Brief description of drawings]

FIG. 1 is a schematic view of a pattern showing a brazing method during sintering of an iron-based sintered component of the present invention.

FIG. 2 is a cross-sectional explanatory view showing a method of installing a green compact and a brazing material in a brazing method during sintering of an iron-based sintered component of the present invention.

FIG. 3 is an explanatory sectional view showing a method for measuring the brazing strength of an iron-based sintered component that is brazed and sintered by the method of the present invention.

[Explanation of symbols]

 1 ring-shaped green compact 1'ring-shaped green compact 2 disc-shaped green compact 2'disk-shaped sintered compact 3 ring-shaped brazing material 4 jig 5 brazing part 6 space 7 units 8 punches

Claims (1)

[Claims] 1. An iron-based green compact is sintered at the same time as Fe: 16.
In a method for producing an iron-based sintered component, which is brazed using a Cu-Ni-Mn-based brazing material containing 30 to 30% by weight, the melting point of the brazing material is not less than 1080 from room temperature in a vacuum atmosphere.
After raising the temperature to a predetermined temperature within a temperature range of ℃ or less, maintaining within this temperature range, the atmosphere is then converted into a reducing atmosphere, and in the reducing atmosphere, the melting point of the brazing filler metal is not lower than 1080 ° C. A method of brazing during sintering of iron-based sintered parts, which is characterized in that the temperature is raised from a predetermined temperature within the temperature range to the sintering temperature of the iron-based green compact and maintained.