JPS62202044A - Manufacture of sintered alloy superior in high temperature wear resistance - Google Patents

Abstract

PURPOSE:To obtain the titled alloy superior in high temp. strength at a prescribed porosity value or less, by liquid phase sintering a compact of iron material powder contg. one or two kinds among Co alloy powder, low m.p. such as iron phosphide, triiron monophosphide and Cu. CONSTITUTION:Iron metal powder contg. one or two kinds among Co alloy powder contg. respective prescribed quantities of Mo, Cr, Si, etc., phosphor alloy powder selected from phosphor alloy powder such as copper phosphide, triiron monophosphide and Cu is compacted. Next, the compact is brought into contact with molten infiltrating agent while being heated to a temp. higher than liquid phase forming temp. of iron metal powder by 0-50 deg.C. In this way, the infiltrating agent is infiltrated into pores in compact, and the compact is sintered to obtain the aimed sintered alloy having <=3% porosity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a sintered alloy with excellent high-temperature wear resistance. Typical applications of sintered alloys with excellent high-temperature wear resistance include valve train members used in internal combustion engines, such as valve seats.

A valve seat is a member incorporated into a cylinder head of an internal combustion engine. When the engine valve is seated on the valve seat, the mixed gas and combustion gas are sealed. Since this valve seat operates under severe conditions, high-temperature strength and high-temperature wear resistance are particularly required.

[Prior Art] Valve train members such as the valve seat 1 used in internal combustion engines are
From the process of compression molding alloy steel powder such as tool steel type or high speed ## type to form a compacted compact, and the process of heating the compacted compact to a predetermined temperature and sintering it to form a sintered alloy. Often manufactured. With the recent improvement in the performance of internal combustion engines, there is an increasing need to further improve the high-temperature strength, high-temperature wear resistance, etc. of valve train members.

In consideration of such requirements, for example, the present applicant has published his published patents No. 60-215736 and No. 60-218451.
At @, we sinter a compact of alloy steel powder to minimize residual pores, and infiltrate copper into the residual pores to improve strength, lubricity, and wear resistance at high temperatures. We have developed a method for manufacturing sintered alloys. Furthermore, in Japanese Patent Application No. 59-15346, the present applicant has disclosed a manufacturing method in which copper powder and alloy steel powder are mixed and sintered, thereby achieving reduction in manufacturing steps and costs, and in addition to infiltration. We have developed a new manufacturing method that can obtain properties equivalent to those of sintered alloys manufactured by the method.

[Problems to be Solved by the Invention] The present invention was developed as part of the above-mentioned method for manufacturing a sintered alloy according to the applicant's own invention.
The object of the present invention is to provide a manufacturing method capable of forming a sintered alloy with excellent high-temperature wear resistance properties.

[Structure of the Invention] (Means for Solving the Problems) The method for producing a sintered alloy with excellent high-temperature wear resistance of the present invention includes:
A first step of forming a raw material powder compact consisting of a cobalt-based alloy powder, a low-melting point compound such as iron phosphide and triiron phosphide, and an iron-based metal powder containing one or two of copper; heating the molded body to generate a liquid phase to perform liquid phase sintering;
This method is characterized by comprising a second step of forming a sintered alloy with a porosity of 3% or less.

When copper is added by infiltration, the temperature is above the melting point of copper,
and while heating the compact to a temperature 0 to 50°C higher than the liquid phase formation temperature of the iron-based metal powder, contact with a molten infiltrant to infiltrate the pores of the compact with the infiltrant, and A third step is added in which main sintering is performed to form a sintered alloy with a porosity of 3% or less.

That is, the method of manufacturing a sintered alloy with excellent high-temperature wear resistance according to the present invention involves mixing a cobalt-based alloy powder into the conventionally used composite #L steel powder, and removing the cobalt-based alloy powder during sintering. It dissolves and elutes around the carbide in the porous base material to strengthen the bond between the base material and the carbide.

Especially cobalt alloys! It has excellent strength at 100°C, and has a great effect of retaining and covering carbides on the base material even under sliding friction conditions at 600 to 700°C, and has characteristics that greatly contribute to improving wear resistance due to the so-called cobblestone effect of wear-resistant particles. The present invention has been made with this point in mind.

(Detailed Description of the Structure of the Invention) The present invention is comprised of a first step of forming a molded body and a second step of performing liquid phase sintering. A third step is added to infiltrate the copper.

In the first step, cobalt alloy powder, copper phosphide, -
A molded body is formed from a low melting point compound such as triiron phosphide and iron-based metal powder containing one or two types of copper. The low melting point compound can be selected from phosphorus alloy powders such as copper phosphide and triiron phosphide. The molded body is generally a porous body with many pores.

The composition of the above cobalt-based alloy powder is molybdenum 10-3
0% by weight, chromium 0.5-15% by weight, silicon 0.5
~3.01 ffi%, balance of cobalt, plus 0.5 to 10 ffi% of tungsten, 0.2 to 5 ffi of vanadium
It consists of one or more of 10.05 to 3.0% by weight of the heaviest niobium.

In this composition, chromium and molybdenum form carbides,
Contributes to wear resistance. They also form a slight solid solution in the base material to improve strength, particularly high-temperature strength. Below the lower limit of the limited concavity as described above, there is little effect, and when the upper limit is exceeded, the degree of damage to the mating material increases. Silicon is effective in making carbides spheroidal and lowering the sintering temperature, but if it is used in excess of a limited value, it will cause a decrease in sinterability and strength. Tungsten, vanadium, and niobium form carbides and contribute to improving wear resistance, but if the value is less than the limit value, the effect is small, and if the limit value is exceeded, the carbide becomes harsh and undesirable.

The above-mentioned iron-based metal powder has a variety of compositions selected depending on the type of sintered alloy and its use.1. Generally, tool steel type or high speed steel type can be used. The particle size and shape of the iron-based metal powder may be selected as required, but particles of about -100 mesh can be used. Also, spray powder can be used.

Iron-based metal powder containing low melting point compounds contains chromium 2.5~2
An alloy steel powder having a composition of 5% heavy chain, 0.2 to 3.0% heavy chain carbon, unavoidable impurities, and the balance iron is mixed with a low melting point alloy powder such as steel phosphide or triiron phosphide. It is composed of a mixed powder, and it is preferable that phosphorus in the mixed powder is 0.1 to 0.8% by weight.

When using pure copper, commercially available electrolytic copper powder can be used as the copper. Further, a copper alloy powder containing 60% or more of copper may be used.

In the second step, the molded body is heated to generate a liquid phase to perform liquid phase sintering. By performing this second step, the bonding of the powder particles constituting the compact can be strengthened,
Therefore, compared to the case where normal sintering is performed, the necks of the powder particles can be bonded more strongly.

The temperature at which a low melting point liquid phase occurs varies depending on the components and composition of the low melting point compound, but when a low melting point liquid phase is partially formed in the molded article, the expansion curve of the molded article changes rapidly. Therefore, the liquid phase formation temperature can be determined from the degree of change in this expansion curve.

The third step is performed when copper is added by infiltration, and the molded body is heated to a temperature higher than the melting point of copper to infiltrate the pores of the molded body with the infiltrant, and the main body of the molded body is heated. Sintering is performed to form a sintered alloy with a porosity of 3% or less.

If the third step is performed, the infiltration can be promoted by the low melting point liquid phase generated in the compact, and therefore the sintered alloy can be further densified, and the porosity is 3% or less, for example as described below. As shown in the examples, it can be significantly reduced by 1.5 to 2.8%.

Infiltration agent mainly composed of copper is pure copper or 60% by weight of copper.
The copper alloy containing the above is infiltrated at the same time as sintering, but the proportion of the infiltration opening in the sintered alloy is approximately 5 to 15% in terms of the sintered alloy.
is preferred. The same applies when adding copper to the mixed powder. If it exceeds 15%, the strength of the base material decreases, and furthermore, the high temperature decrease due to embrittlement of grain boundaries becomes significant, which is not preferable.

[Effects of the Invention] According to the Tl4J manufacturing method of the present invention, the porosity is 2.8% or less, the radial crushing strength is 105 kgf/mm2 or more, and the high-temperature wear resistance is improved, as shown by the test values in the examples described later. It is possible to produce a sintered alloy with excellent high-temperature wear resistance and a wear width of 13 μm or less for the sheet material and 2.2 μm or less for the valve material.

[Example] First, Example 1 will be explained.

By weight: chromium 12%, carbon 1.5%, molybdenum: 1%, vanadium niQ 8%, silicon: 0.2%,
Manganese 0.3%, oxygen: 0.04%, balance iron and 1
Spray alloyed steel powder (-100 mesh) consisting of impurities of less than % was used. In addition, in the cobalt-based alloy powder, the entire cobalt-based alloy powder is 1 ('10111%), and the weight ratio is molybdenum = 28%, chromium 8%, silicon = 2%.
, the balance being cobalt, and an atomized alloy powder (-200 mesh) consisting of 1% or less of impurities. Then, so that the whole powder has a heavy chain weight of 100%, cobalt alloy powder = 10% and graphite powder = 1.1% (-
350 mesh) - Saniron phosphide powder: 1.5% (-20
0 mesh), copper powder 28% (-145 mesh) was added, and zinc stearate 0.8% was added as a lubricant outside the composition.
% to form a mixed powder. This mixed powder was compression molded at 7°0 t/cm2 to form φ10R1Il+
A green compact (molded body) having a diameter of 25111° and a length of 20+1111 was obtained.

The green compact was placed in an ammonia decomposition gas atmosphere at 1140°C.
C. for 30 minutes to generate a low melting point liquid phase to perform liquid phase sintering. In this way, a test piece made of sintered alloy was manufactured.

In addition, test pieces of Examples 2 to 5 were manufactured in the same manner under the conditions shown in Tables 1 and 2. In Examples 1.4, copper was added by a mixing method, while in Examples 3 and 5, copper was added by an infiltration method, but the latter method added copper by compression molding pure copper powder (M-copper powder) or copper alloy powder. A green compact with a diameter of 10III 11φ25 m and a length of 3 m was placed over the powder compact made of the iron-based mixed powder, and heated in this state for 30 minutes in an ammonia decomposition gas atmosphere to form a liquid phase. Simultaneous sintering and infiltration were carried out under the same conditions, thereby producing a test piece made of a sintered alloy.

Note that the sample of the comparative example had the same composition as the sample shown in Example 1 except that the cobalt-based metal powder was removed, and a test piece was manufactured in the same manner as in the example.

(Test) Regarding the test pieces of Examples 1 to 5, the porosity and high temperature (500
℃) The radial crushing strength and high temperature wear resistance were investigated.

The results are shown in Table 3. High temperature wear resistance is φ14mm,
A test piece with a diameter of 18 mm and a length of 15 III m was fabricated. The test piece was moved up and down 1200 times per minute with an amplitude of 2 mm, and its end face was pressed against a planar valve-equivalent material with a surface pressure of 45 kOf/mm2. was rotated at 5 rpm and an Ul1 test was conducted. The wear test was carried out by heating the surface of the valve-equivalent material to 500° C. and introducing exhaust gas from a gasoline engine into the contact portion of the test piece. Moreover, the time for one test was 7 hours.

The results of each test are shown in Table 3. The porosity is 1.8 in Example 1.
%, 2.5% in Example 2, 1.5% in Example 3, 2.3% in Example 4, and 2.8% in Example 5. The high temperature radial pressure strength (500°C) was 115 kgf/mm in Example 1.
! , 130kOf/mm2 in Example 2, 110kOf/mmz in Example 3, and 105kgf/mmz in Example 4.
mm2, Actual Table 3 Test Results In Example 5, it was 105 kgf/mm'. The wear width in the high temperature abrasion resistance test was 11 for the sheet material in Example 1.
μm, valve material 1.5 μm, sheet material 4 μm in Example 2
In Example 3, the sheet material was 8 μm; the valve material was 2.0 μm; in Example 4, the sheet material was 10 μm; the valve material was 1.7 μm; in Example 5, the sheet material was 13 μm; the valve material was 1.5 μm.

The test results of the comparative example are that the porosity is 3.4% and the high temperature radial crushing strength is 1.
The wear width in the 20 kQf/mm21 high temperature abrasion resistance test was 18 μm for the seat material and 2.5 μm for the valve material.

Procedural amendment (voluntary) April 3, 1985 Patent Application No. 044617 of 1985 2, Title of invention Method for producing sintered alloy with excellent high-temperature wear resistance 3, Relationship with the person making the amendment Patent Applicant: 1 Toyotacho, Toyota City, Aichi Prefecture (320) Toyota Motor Corporation Representative: Kiyohaka Matsumoto (1 person) 4. Agent: 3-3-4 Meieki, Nakamura-ku, Nagoya City, Aichi Prefecture 450 5. Column 6 of the detailed description of the invention in the counter specification of the amendment, contents of the amendment (1) Line 20 of page 6 of the specification [copper j to line 1 of page 7 (- When "copper" is added by the infiltration method between "copper" and "infiltration is added to..." Insert "simultaneously with sintering".

(2) Insert "strong" between "temperature decrease" and "temperature decrease by 1 degree" on page 10, line 13 of the specification.

Claims (6)

[Claims] (1) A first step for forming a compact from raw material powder consisting of a cobalt alloy powder, a low melting point compound such as iron phosphide or triiron phosphide, and an iron metal powder containing one or two of copper.
A sintered alloy with excellent high-temperature wear resistance consists of a second step of heating the compact to generate a liquid phase and performing liquid phase sintering to form a sintered alloy with a porosity of 3% or less. Manufacturing method of bonded metal. (2) When copper is added by infiltration, the temperature is higher than the melting point of copper and 0 to 50° lower than the liquid phase formation temperature of the iron-based metal powder.
While heating the molded body to a high temperature, contacting the molded body with a molten infiltrant to infiltrate the pores of the molded body with the infiltrant,
The method for producing a sintered alloy with excellent high-temperature wear resistance as set forth in claim 1, which adds a third step of performing main sintering of the compact to form a sintered alloy with a porosity of 3% or less. . (3) The cobalt alloy powder contains 10 to 30% by weight of molybdenum, 0.5 to 15% by weight of chromium, and 0.5 to 3% by weight of silicon.
0% by weight, balance cobalt composition plus tungsten 0
．． It is an alloy containing one or more of 5 to 10% by weight, vanadium 0.2 to 5% by weight, and niobium 0.05 to 3.0% by weight, and the total of tungsten, vanadium, and niobium is 18% by weight or less. A method for producing a sintered alloy having excellent high-temperature wear resistance according to claim 1. (4) The iron-based metal powder consists of an alloy steel powder with a composition of 2.5 to 25% by weight of chromium, 0.2 to 3.0% by weight of carbon, unavoidable impurities, and the balance iron, copper phosphide, and -phosphorus. It is composed of a mixed powder mixed with low melting point compounds such as saniron oxide.
The method for producing a sintered alloy with excellent high-temperature wear resistance according to claim 1, wherein the mixed powder contains 0.1 to 0.8% by weight of phosphorus. (5) The method for producing a sintered alloy with excellent high-temperature wear resistance according to claim 2, wherein the infiltrant powder is pure copper or a copper alloy powder containing 60% by weight or more of copper. (6) Alloy steel powder contains molybdenum 0.3 to 6.5% by weight
, tungsten 0.5-12% by weight, vanadium 0.2
Claim 4 contains one or more of 5 to 5.5% by weight, 0.05 to 3.0% by weight of niobium, and the total amount of molybdenum, tungsten, vanadium, and niobium is 16% by weight or less. A method for producing a sintered alloy with excellent high-temperature wear resistance as described in 2.