JPH0372052A - Manufacture of wear-resistant sintered alloy - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of the Co-base hard grains themselves, to reduce pores in a matrix structure and to improve its hardness by regulating mixed powder having specified compsn. of which ferroalloy powder is added to ferrous and Co-base alloy powder as a raw material and subjecting a sintered body to soln. treatment and precipitation treatment. CONSTITUTION:Mixed powder of ferrous alloy powder constituted of, by weight, 7 to 22% Ni, 16 to 26% Cr, <=3% Mo, <=0.2% C, <=1% Si, <=2% Mn, <=1% inevitable impurities and the balance Fe, ferroalloy powder in which the content of one or more kinds among P, B, Si, Mn and Mo is regulated to 0.5 to 5.0% to the total content and Co-base alloy powder, 5 to 40% to the total content, is used. Material powder of which the above powder is mixed with a suitable amt. of lubricant is subjected to compacting and sintering to obtain a sintered body. The sintered body is successively subjected to soln. treatment and precipitation hardening treatment and is thereafter subjected to Pb impregnation treatment, by which the wear-resistant sintered alloy can be obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a wear-resistant sintered alloy suitable for constructing parts that require wear resistance and corrosion resistance, such as engine valve seats. It is related to.

(Prior art) Hard particle dispersed sintered alloys have come to be used as metal materials for components that require wear resistance and corrosion resistance under high temperatures, such as engine valve seats. . In general, the hard particle dispersed sintered alloy uses Fe-based alloy, high carbon ferromolybdenum, etc. as hard particles, and uses Fe-based C, Co, etc. for iron-based alloy powder.
, Mo.

It has a structure in which Cr, W, V, etc. are added to improve wear resistance, corrosion resistance, and toughness.

A sintered alloy with such a structure is considered to be porous with many pores formed between crystal grains within the film, but it is used as a valve seat in engines that use leaded gasoline. In this case, the valve seats are exposed to higher temperatures than valve seats in other engines, so the purpose of reducing the temperature of the part of the valve seat that contacts the valve face and For the purpose of increasing the temperature, lead (Pb) and copper (Cu) are
A method is used in which the pores are impregnated with the pores.

On the other hand, like LPG fuel engines for forklifts,
In the case of valve seats used in engines whose maximum rotational speed is about half that of a passenger car engine and which are frequently operated intermittently, when the surface temperature at the contact part with the valve is relatively low,
Moisture contained in the air or lubricating oil condenses and adheres to the contact area, and the condensed water reacts with sulfur oxides contained in the combustion products discharged to the exhaust valve side of the engine, producing sulfuric acid. (H, So,) will be generated, and there is a problem that corrosion, wear, etc. will occur at the contact portion of the valve seat with the valve.

In order to deal with the above-mentioned problems, it is required to maintain the conventional strength and significantly improve copper corrosion abrasion resistance.
As disclosed in Publication No. 3-114947, iron-based alloy powder CC: 0.2% by weight or less, Mo: 3.0% by weight or less, Ni: 8 to 22% by weight, Cr: 16 to 26% by weight. %, at least one of Ti, Ta, and Nb = 0.5
~6.0% by weight), a method in which 45 to 40% by weight of Co-based alloy powder is mixed and sintered has already been proposed.

Although the above-mentioned known examples of sintered alloy materials can improve the corrosion resistance of the Co-based hard particles themselves and the matrix structure, they are insufficient in reducing pores and improving the hardness of the matrix structure, and there is still room for improvement. It still exists.

The present invention has been made in view of the above points, and in addition to improving the corrosion resistance of the Co-based hard particles themselves and the corrosion resistance of the matrix structure, the present invention also aims to reduce pores in the matrix structure and improve the corrosion resistance of the matrix structure. The purpose is to improve the hardness of the ground structure.

(Means for solving the problem) In the present invention, as a means for solving the above problem, N
i:'/-22% by weight, Cr: 16-26% by weight, MO
: 3% by weight or less, C: 0.2% by weight or less, Si 1% by weight
Hereinafter, an iron-based alloy powder having a composition of 2% by weight or less of Mn, 1% or less of unavoidable impurities, and the balance of Fe, P, B,
A ferroalloy powder in which at least one of SiSMnSMo is 05 to 5.0% by weight based on the total amount;
A raw material powder for sintering obtained by mixing an appropriate amount of lubricant with a mixed alloy powder consisting of 5 to 40% by weight of Co-based alloy powder based on the total amount is compressed into a predetermined shape, and then sintered. The sintered body obtained by sintering is sequentially subjected to solution treatment and precipitation hardening treatment, and then subjected to Pb impregnation treatment.

The composition of the iron-based alloy powder constituting the sintered body obtained as described above was determined as described above based on the following reasons.

Ni combines with Fe during sintering to turn the matrix structure of the sintered alloy into austenite, thereby improving the toughness of the matrix structure. and N in the parent organization.
As a result of experiments to determine the Ni content, it was found that if the Ni content is less than 7% by weight, the austenite structure that makes up the matrix structure becomes unstable, and if it exceeds 22% by weight, the matrix structure becomes unstable. It was confirmed that the hardness of the tissue decreased. Therefore, the Ni content in the iron-based alloy powder is 7 to 2
It is desirable that the content be within the range of 2% by weight.

Cr contributes to improving the high temperature strength, corrosion resistance, and oxidation resistance of the parent structure. And Cr in iron-based alloy powder
As a result of conducting experiments to determine the content of Cr, it was found that when Ni is included at the same time, when the Cr content is less than 16% by weight, the high-temperature strength, corrosion resistance, and oxidation resistance of the matrix structure are sufficiently improved. It was also confirmed that when the amount exceeds 26% by weight, the hardness of the matrix structure decreases. Therefore, the content of Cr in the iron-based alloy powder is preferably in the range of 16 to 26% by weight.

Mo serves to improve the high temperature strength and toughness of the host structure. As a result of conducting experiments to determine the content of Mo in iron-based alloy powder, it was found that when the content of Mo exceeds 3%, the austenite structure constituting the matrix structure becomes unstable. confirmed. Therefore, it is desirable that the content of Mo in the iron-based alloy powder is 3% by weight or less.

C is inevitably included in the manufacturing process of iron-based alloy powder, and combines with Cr during sintering to produce Cr carbide that causes Cr-deficient areas in the matrix structure.

Therefore, the content of C in the iron-based alloy powder is 0.2
It is desirable that the amount is less than % by weight.

Both Si and Mn contribute to improving the hardness of the base structure, but if they are present too much, they will lead to a decrease in toughness. Therefore,
The contents of Si and Mn in the iron-based alloy powder are desirably 1% by weight or less and 2% by weight or less, respectively.

The particle size of this iron-based alloy powder is preferably 80 mesosites or less in order to maintain good formability and sinterability.

In addition, C, P,
The reason why the ferroalloy powder contains at least one of B, Si, Mn, and Mo in an amount of 0.5 to 5.0% by weight based on the total amount is based on the following reason.

P, B1Si, and Mn%Mo form liquid phase components during sintering, improve the density of the sintered alloy, and serve to reduce the number of pores generated in the matrix structure. As a result of conducting an experiment to define the content of at least one of PSBSSi, Mn, and Mo in the mixed alloy powder,
If the content of at least one of P, BsSi-, Mn, and MO is less than 0.5% by weight, the amount of liquid phase component generated during sintering will be insufficient and the sintered alloy will have a high If densification is not promoted and the proportion of pores generated in the matrix tissue exceeds 10%, and if it exceeds 5.0% by weight, the proportion of pores produced in the matrix tissue is already below 0%, and it has been confirmed that no further effect commensurate with the increased cost can be obtained. Therefore, K'
4 P, B, S i, M in ei gold alloy powder
The content of at least one of n and Mo is 0.5 to
It is desirable to set the range to 50%. The reason why the effective porosity is set to 10% or less is that a sintered body with a porosity of this level exhibits corrosion resistance comparable to that of ingot material. The particle size of this ferroalloy powder is preferably 150 mesh or less, and it is desirable that the particle size of 80 to 200 mesh is suppressed to 30% or less when the iron-based alloy powder and ferroalloy powder are combined. moreover,
Ferroalloy powder usually contains C, but in order to compensate for this C content, graphite powder (0.5 to 2
．． 0% by weight) may be added.

Furthermore, the reason why the proportion of the Co-based alloy powder in the mixed alloy powder is set to 5 to 40% by weight is based on the following reason.

The Co-based alloy powder itself has excellent corrosion resistance, and also produces hard particles that are dispersed and mixed into the matrix structure during sintering, contributing to improving the wear resistance of the matrix structure. As a result of conducting an experiment to define the proportion of Co-based alloy powder in the mixed powder, we found that
If the proportion of O-based alloy powder is less than 5% by weight, the amount of hard particles generated during sintering will be insufficient, and the base structure will not have sufficient wear resistance. It was confirmed that when the amount of hard particles is exceeded, the toughness of the matrix structure decreases as the number of hard particles increases. Therefore, the proportion of the Co-based alloy powder in the mixed alloy powder is preferably in the range of 5 to 40% by weight.

In addition, if the particle size of the Co-based alloy powder exceeds 80 mesh, the strength of the compact when compacted will be low, and the sintered area with the matrix structure will be small, causing hard particles to form due to the load during operation, etc. 80 meters because the hard particles tend to fall off and the area occupied by the hard particles becomes smaller, requiring a large amount of hard particles to be added.

It is desirable that it be less than

(Function) In the present invention, the following effects can be obtained by the above means.

That is, Ni: 7-22 weight% Weight r: 16-26 weight%
, Mo: 3 weight 1% or less, C: 0.2 weight % or less,
sl: 1% by weight or less, Mn: 2% by weight or less, unavoidable impurities: 1% by weight or less, Fe: the balance, and at least one of PSB and SiSMnSMo is 0 relative to the total amount. .5 to 5.0% by weight of ferroalloy powder and 5 to 40% by weight of the total amount.
The mixed alloy powder obtained by mixing an appropriate amount of lubricant with the mixed alloy powder consisting of Co-based alloy powder and The corrosion resistance and wear resistance of the matrix structure of the sintered body are improved, and the sintered body is sequentially subjected to solution treatment and precipitation hardening treatment, and then Pb impregnation treatment. , carbide is uniformly and finely dispersed, and hardness and wear resistance are further improved.

(Effect of the invention) According to the invention, Ni: 7 to 22% by weight, Cr: 16 to 22% by weight
26@% by weight, Mo: 3% by weight or less, C: 0.2% by weight or less, Si: 1% or less, Mn: 2% by weight or less,
Unavoidable impurities = 1% by weight or less, Fe balance iron-based gold powder, and at least one of P, B, Si, Mn, and Mo is 0.5 to 5.0% by weight based on the total amount A mixed alloy powder consisting of a ferroalloy powder having a ferroalloy powder and a Co-based alloy powder having a content of 5 to 40% by weight based on the total amount is mixed with an appropriate amount of a lubricant to form a mixed alloy powder into a predetermined shape. By compression molding and then sintering,
The sintered body, which is supposed to improve the corrosion resistance and wear resistance of the base structure, is subjected to solution treatment and precipitation hardening treatment in sequence, and then Pb impregnation treatment. Not only does corrosion resistance improve, but carbides are uniformly and finely dispersed, resulting in further improvements in hardness and wear resistance, which is an excellent effect.

(Example) Hereinafter, the method for manufacturing a wear-resistant sintered alloy of the present invention will be explained based on a specific example.

First, a raw material powder for sintering having the following composition is prepared.

Stainless steel copper powder (iron alloy powder) as matrinox 70% composition 1
2.8 wt% Ni, 17.2 wt% Cr, 02 wt% M
n, 0.9 wt% S1.001 wt% C12, 5 wt% Mo, 0.5 wt% Nb, residual Fe particle size: 177 μm
Ferroalloy powder, 10% by weight Composition: 4.2% by weight C12, 4% by weight P, 942% by weight
MO14, 3 wt% Cr, residual Fe particle size: 74 μm or less Stellite powder (trade name) as Co-based alloy powder, 20 wt% group 1i: 1.2
1 wt% Cl2L 58 wt% Cr, 2,26 wt% F
e, 2.39% by weight Ni, 1.26% Si, 4.6
4% by weight W1 remainder C.

The chamber diameter is 44 to 177 μm for each of the above groups 55. Raw material powder for sintering is prepared by adding 1% by weight of zinc stearate, which acts as a lubricant, to the mixed alloy powder obtained by mixing stainless steel powder, ferroalloy powder, and Co-based alloy powder. be done. In the case of this example, Nb:0 in the iron-based alloy powder
．． 5% by weight, this Nb acts to preferentially combine with C to form carbides during sintering, thereby suppressing the formation of Cr carbides and forming grain boundaries in the host structure. This suppresses the occurrence of Cr-deficient areas. Moreover, there are Ti and Ta that have the same effect as Nb, and it is permissible to use at least one of these. When at least one of these Nb, Ti, and Ta is added, the content is preferably in the range of 0.5 to 6.0% by weight.

5 tons of the raw material powder for sintering. □! A green compact is formed by molding into a predetermined shape with a compression pressure of , solution treatment, and precipitation hardening treatment.

(1) Sintering/solution treatment The green compact that has been subjected to the Wanox removal treatment as described above is heated to 1100'C at a heating rate of 10°C/min in vacuum (5X 10-'Torr). After heating and holding at 1100°C for 10 minutes, increase the temperature to 1100°C at a heating rate of 5°C/min.
Heat to 20°C and hold at 1120°C for 30 minutes.

Thereafter, it was slowly cooled down to 1100°C at a cooling rate of 5°C/min, held at 1100°C for 20 minutes, and then rapidly cooled in an N2 gas atmosphere.

The sintered body thus obtained has a hardness of approximately HRB: 60, and since the hardness is insufficient, the following precipitation hardening treatment is performed.

(n) Precipitation hardening treatment a) The sintered body after quenching and solid solution treatment is heated in vacuum (5X 10-'To
rr), heated to 750°C at a heating rate of 10°C for 7 minutes, held at 750°C for 10 minutes, then heated to 760°C at a heating rate of 5°C/min, and heated at 760°C for 9 minutes.
The sample was held for 0 minutes, and then rapidly cooled in a N gas atmosphere.

b) Tempering After leaving it for 30 minutes after the above-mentioned quenching treatment, heat it in a vacuum (5X
10-' Torr), heated to 550'C at a heating rate of 1007 minutes, held at 550°C for 10 minutes, then heated to 560°C at a heating rate of 5°C/min, Hold at °C for 90 minutes, then quench in a N, gas atmosphere.

The sintered body obtained as above had a porosity of 9°8%.
, hardness HRB: 70-75.

When the above sintered body was impregnated with Pb using an impregnating device (for example, an autoclave) and sealed, a sintered body with hardness HRB: 85 to 90 and excellent corrosion and wear resistance properties was obtained. Obtained.

The internal metal structure of the sintered body thus obtained is shown in FIG. 1 as a micrograph. According to the photograph in FIG. 1, it can be seen that fine carbides are dispersed and precipitated in the austenite matrix structure (the gray part in the photograph). The white spherical portions in the base tissue are Co-based hard particles. Also,
The black parts dotted in the matrix structure are pores that account for 10% or less of the matrix structure, and contain 1 Pb. That is, by the above solution heat treatment, Cr carbide and σ
The phase is redissolved to prevent intergranular corrosion.

Next, the results of comparison between the sintered body obtained in this example and a comparative example will be described.

Comparative Example 1 has C:0. g ~ 1.2% by weight, Cr: 5.0
~80% by weight, Mo: 0°3~0.8% by weight, C
Cu/
It is impregnated with 13.0 to 21.0% by weight.

Comparative example 2 has C: 0.4 to 0.8% by weight, Cr: 0.5
~2°0 weight%, Mo:3. (1-7.0% by weight, C
o: 10 to 15% by weight, Ni: 0.5 to 2.0% by weight, and Fe: the balance, in which Tribaloy alloy is dispersed and l'b: 13 to 23% by weight. It is impregnated with.

Comparative Example 3 is a sintered body with the same composition as this example, and P
Only ba+ was applied without solution treatment or precipitation hardening treatment.

Then, test pieces were cut out from those of this example and those of Comparative Examples 1 to 3, and 0.1% sulfuric acid (H
, So, ) was immersed in aqueous acid, constantly stirred with a magnetic stirrer, and the corrosion resistance was compared by measuring the loss of corrosion and abrasion after a predetermined period of time.The results shown in the characteristic diagram in Figure 2 were compared. Obtained.

In addition, valve seats were formed from those of this example and those of Comparative Examples 1 to 3, and each valve seat was
We compared the wear resistance by measuring the amount of wear on each valve seat after 100 hours of continuous operation at a rotation speed of 2400 rpm when installed in a gas specification engine.The characteristics shown in Figure 3 were compared. The results shown in the figure were obtained.

The valves made of 5UH-35 were used to come into sliding contact with each valve seat during engine operation.

According to the above measurement results, the sintered body of this example is the same as that of comparative example 1.
．． It is clear that this sintered body exhibits extremely superior properties in terms of corrosion resistance and abrasion resistance compared to the sintered body No. 2. The sintered body of Comparative Example 3 exhibits almost the same corrosion resistance as the sintered body of this example, but is inferior to the sintered body of this example in wear resistance.

[Brief explanation of drawings]

Figure 1 is a micrograph showing the internal metal structure of a sintered body produced by the method for producing a wear-resistant sintered alloy of the present invention, and Figure 2 is a micrograph showing the internal metal structure of a sintered body produced by the method for producing a wear-resistant sintered alloy of the present invention. FIG. 3 is a characteristic diagram for comparing the corrosion resistance of the sintered body (i.e., Example) and Comparative Examples 1 to 3. , Example) and Comparative Examples 1 to 3 in terms of wear resistance. jllE 1 to 2 Figure 3

Claims (1)

[Claims] 1, Ni: 7-22% by weight, Cr: 16-26% by weight,
Mo: 3% by weight or less, C: 0.2% by weight or less, Si: 1
An iron-based alloy powder having a composition of 2% by weight or less, Mn: 2% by weight or less, unavoidable impurities: 1% by weight or less, and Fe: the balance;
A ferroalloy powder in which at least one of P, B, Si, Mn, and Mo accounts for 0.5 to 5.0% by weight based on the total amount, and a Co-based alloy that contains 5 to 40% by weight based on the total amount. For a sintered body obtained by compression-molding a raw material powder for sintering obtained by mixing an appropriate amount of lubricant into a predetermined shape and then sintering a mixed alloy powder consisting of powder, After sequentially performing solution treatment and precipitation hardening treatment, P
b. A method for producing a wear-resistant sintered alloy, which comprises performing an impregnation treatment.