JPH07109025B2 - High temperature wear resistant sintered alloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sintered alloy that is mainly used as a valve seat material of an internal combustion engine and has excellent wear resistance particularly at high temperatures.

<< Prior Art >> Among the sintered alloys suitable for the valve seat, a conventional material that can be compared with the present invention is, for example, the high-temperature wear-resistant sintered alloy disclosed in Japanese Patent Publication No. 59-37342.

This alloy has an overall composition of 0.7 to 10% by weight, Ni0.
5 to 7.5%, Mo 1 to 15%, W 0.1 to 4.8%, Cu 0.5 to 3%, Fe balance, and its structure is 0.2 to 1.5% copper. D phase with rich nature 10 to 50
%, And 2 to 15% of B phase having the following composition, which is rich in wear resistance, are dispersed in the iron-based sintered alloy.

Phase B: 50-70Mo-Fe This sintered alloy is composed of a heat-corrosion-resistant alloy phase with an improved composition of austenitic stainless steel and an intermetallic compound, with a pearlite matrix solid-solution strengthened by copper having a shock absorbing effect. By dispersing the hard phase and the characteristics of each phase, high temperature wear resistance is imparted by the synergistic effect.

<< Problems to be Solved by the Invention >> Recently, operating conditions of automobile engines have become more and more severe due to high power performance, and the valve seat of the valve mechanism can withstand severe operating environments more than ever before. It is inevitable.

Therefore, it is more wear resistant than the above-mentioned sintered alloy,
A valve seat material excellent in material strength at high temperature is desired.

<< Means for Solving the Problems >> The present invention is based on the conventional sintered alloy described above (Japanese Patent Publication No. 59-37342).
), Especially by examining the composition and structure of the material matrix and the dispersion material to improve high temperature strength and wear resistance, and to impart lubricity to prevent adhesive wear. Has an aim.

In order to achieve the above object, in the sintered alloy according to the present invention, the matrix is strengthened by forming a structure in which a sorbite phase or bainite phase is scattered in Fe-C-Ni-Co solid solution phase. . Then, a phase rich in heat and corrosion resistance (A phase) and a hard phase rich in wear resistance against low-speed sliding (B phase or C phase) are dispersed in this base, and lead is introduced into the pores if necessary. The characteristics of each phase can be filled and the required characteristics can be satisfied by a synergistic effect.

More specifically, the sintered alloy according to the present invention is roughly classified into three kinds of modes depending on the combination of hard phases dispersed in a matrix, and the first mode is solvite in a Fe-C-Ni-Co solid solution phase. In the matrix where at least one of the phase and the bainite phase is scattered in the spots, the A phase having the following composition, which is rich in heat and corrosion resistance, is 10 to 20.
%, And a B phase having a high wear resistance in an amount of 5 to 15% dispersed therein, which is a sintered alloy having excellent wear resistance at high temperatures, the overall composition of which is C0.2 to a weight ratio. 0.8%, Ni6
~ 26%, Cr1 ~ 4%, Mo2.7 ~ 13%, W0.2 ~ 2%, Co5 ~ 15%,
It is the balance of Fe.

B phase: 50 to 70 Mo-Fe And the second aspect is a sintered alloy having a structure in which the B phase in the first aspect is replaced by the following C phase, and the entire composition thereof is accompanied by the substitution of the dispersed phase, C0.2 ~ 0.8%, Si0.2 ~ 3.3%, Ni6 ~
26%, Cr1-4%, Mo1.8-8%, Co5-15%, W0.2-2%, Fe
It is the rest.

C phase: 4 to 22Si-33 to 36Mo-Fe Furthermore, in the third aspect, the A phase is kept as it is and the B phase in the first aspect and the C phase in the second aspect are added in a total amount of 5 to 15
%, The total composition is C0.2-0.8%, Si
3.3% or less, Ni6 to 26%, Cr1 to 4%, Mo1.9 to 13%, Co5 to 15
%, W 0.2 to 2%, and the balance of Fe.

The invention in which lead is infiltrated into the pores of the sintered alloy in the first to third aspects is the sintered alloy according to the second invention.

Next, the production method of the sintered alloy according to the present invention will be briefly described. The raw material is iron powder in a weight ratio of 5 to 23% nickel powder,
Improved composition of 15% cobalt powder, austenitic stainless steel Cr10-20%, Ni10-14%, Mo2-10%, W2-10, F
e 10 to 20% of iron alloy powder (Phase A) consisting of the balance and graphite powder
0.2-0.8%, 50-70% Mo-Fe alloy powder (Phase B) and 33
~ 36% Mo-4 to 22% Si-Fe alloy powder (C phase) at least one kind is mixed at 5 to 15%, and a molding lubricant such as zinc stearate is further added.

Then, the molding and sintering are performed by a usual method, and
The sintered alloys of the first to third aspects according to the invention can be obtained. The sintered alloy of the second invention is obtained by immersing this sintered body in a molten lead bath and infiltrating lead into the pores.

Numerical value ranges constituting the sintered alloy according to the present invention thus obtained will be described below.

<< Action >> The base is Fe-C-Co-Ni system.

Co is added in the form of cobalt powder and is a component that mainly improves heat resistance. It has the effect of preventing the strength from decreasing at high temperatures by diffusing into Fe and forming a solid solution with Ni. The effect is recognized when the addition ratio of this cobalt powder is 5% or more,
Even if added over 15%, the effect is small for the cost, so the addition ratio was set to 5-15%.

Ni is added as a powder such as carbonyl nickel powder and after sintering forms a solid solution with Fe and Co to improve the toughness and impact wear resistance of the substrate. Further, the portion where Ni is diffused into the Fe-C system has a bainite or sorbite structure, which contributes to wear resistance. The wear characteristics due to the addition of Ni are Co
There is an interaction with the added amount, and the above Co added amount range 5 to 15
%, Even if the amount of Ni powder added is less than 5%,
On the other hand, if it is more than 23%, the wear resistance will be poor.
The wear resistance is best when the amount of powder added is 15%.

C is added as graphite powder and solid-solved in the matrix to form Fe-C-Ni-Co.
Helps to form a solid solution and bainite or sorbite phase, increasing the hardness of the matrix. The carbon content of the sintered body is preferably in the range of 0.2 to 0.8% in total composition, and if it is less than this, sufficient hardness cannot be obtained, and conversely if it is too much, a cementite structure precipitates and the matrix material is It becomes brittle.

As mentioned above, the calculated composition of the base consisting of Fe, C, Co and Ni is Ni 7-38%,
Co5.8 ~ 22%, C0.3 ~ 1.1%, Fe balance.

Further, the etching structure of the base is in a state in which a white background structure made of a solid solution of Fe-C-Co-Ni is dotted with lumps of bainite or sorbite structure in spots.

A ferrite structure or a pearlite structure may be present in a part of the bainite-like or sorbite-like structure. This is a core of large Fe particles that does not allow the required amount of Ni and the like to diffuse, but there is no effect on strength and wear resistance.

Furthermore, Co, Ni may be added partly in the form of alloy iron powder, but if all of them are added as alloy powder, a mottled structure cannot be obtained,
Since the compressibility of the powder also deteriorates, it is preferable to add each powder individually.

Next, the A phase having high heat resistance and corrosion resistance is dispersed in the base to alleviate the decrease in strength at high temperature. This phase is added in the form of an alloy powder, and is a material in which austenitic stainless steel species is basically selected from the viewpoint of the characteristics that the A phase should have, and necessary improvements are made thereto.

That is, the composition of the phases is Ni10-14%, Cr10-20%, Mo2-10
%, W2-10%, Fe balance, and compared with SUS316L,
W is added to improve the anti-creep property, and Mo is slightly increased to improve the acid corrosion resistance.

In addition, the effect was recognized when the amount of phase A added was 10% or more.
Even if it drops below 20%, it will not be effective for the cost.

Furthermore, when the selected hard phase (B phase or C phase) is dispersed, the wear resistance is significantly improved.

Particularly, in the case of fuel in which a large amount of combustion products adhered to the seat surface of the valve seat are generated, the effect is remarkable, and the wear resistance against low speed sliding is improved. Although this hard phase is added in the form of alloy powder, the necessary requirements are excellent corrosion resistance, it is hard enough to prevent the mating member from wearing, and even if added in a large amount, the formability is good, and the usual method is used. And the like can be mentioned.

This hard phase powder is a commercially available 50-70% Mo-Fe alloy (B
Phase), or 33 to 36% Mo-4 to 22% Si-Fe alloy (C phase)
Corresponds to this.

Further, whether the B phase and the C phase are used alone or in combination, the wear resistance is remarkably improved when the addition amount is 5% or more.
If it exceeds 15%, not only the effect is not accompanied, but also the compressibility of the powder is deteriorated, the material strength tends to be deteriorated, and the mating member tends to be easily worn. Therefore, the maximum should be 15%.

Above, 10-20% of A phase and 5-15% of B on the base of patch tissue
Table I shows the overall composition of the sintered alloy of the first invention (first to third aspects) according to the present invention in which at least one of the phase and the C phase is dispersed.

Next, the alloy obtained by infiltrating lead into the sintered alloy has a good compatibility with the mating material and further has improved wear resistance.

The density of the sintered body is optimally 6.9 to 7.2 g / cm ³ . If the density is too low, it easily wears, and on the contrary, if the density is high, the molding pressure becomes high, which is disadvantageous in terms of workability and die wear.
Further, in the fourth invention, the lead infiltration property deteriorates with the phenomenon of the amount of holes.

<< Explanation of Examples >> Example 1 (Influence of addition of cobalt powder) First, 10% by weight of carbonyl nickel powder was added to iron powder,
The composition is 15% Cr-12% Ni-6% Mo-6% W-Fe alloy iron powder (A phase) 15%, 65% Mo alloy iron powder (B phase) 10%.
%, Graphite powder 0.8%, and zinc stearate powder 0.5% were added to prepare a mixed powder.

Further, in addition to this mixed powder composition, 6 kinds of mixed powders were prepared in which cobalt powder was added at 3%, 5%, 10%, 15%, and 20% by weight ratio.

Next, the sample was prepared by adjusting the compacting density so that the sintering density becomes 7.0 g / cm ³ and compacting it into a predetermined shape, and then sintering at a temperature of 1140 ° C. for 30 minutes in a reducing gas atmosphere. Then, each sintered body was obtained.

Then, each sintered body was immersed in a molten lead bath at a temperature of 550 ° C., and by applying a pressure of 8 atm, lead was infiltrated into the pores to obtain a sample.

The result of measuring the radial crushing strength of each sample at room temperature to 350 ° C. is shown in the graph of FIG. As is clear from this graph, when the temperature exceeds 200 ° C., the radial crushing strength tends to decrease, but when the amount of cobalt powder added is 5% or more, the decrease is small.

However, there is not much difference between 15% and 20%, and it can be seen that the upper limit of 15% is sufficient.

Example 2 (Influence of Addition Amount of Nickel Powder) Iron powder having a composition of 15% Cr-12% Ni-6% Mo-6% W-balance
15% of iron alloy powder consisting of Fe (A phase), 10% of 65% Mo alloy iron powder (B phase), 0.8% of graphite powder, and 0.5% of zinc stearate powder are fixed, and the addition amount of cobalt powder is 5%. %,Ten
%, 15%, and 18 kinds of mixed powders prepared by adding 5%, 10%, 15%, 20%, and 25% of nickel powder to these mixed powder compositions. Molded, sintered and lead infiltrated as in.

Next, the valve seats made of these materials were used as test materials and a simulated engine tester was used to compare the amount of wear for each valve seat.

This abrasion tester is a mechanism that drives the cam shaft with a motor while heating the valve and valve seat to a predetermined temperature with LPG combustion gas. The temperature, rotation speed, valve spring pressure, etc. can be set arbitrarily. Therefore, it is possible to perform a severe test in a short period of time.

The material of the mating valve is 21% Cr-4% Ni heat-resisting steel (21-4N), the rotation speed is 5200 rpm, and the valve seat temperature is 300
℃ was set and the total wear of the valve seat and the mating valve was measured after 30 hours of continuous operation.

The graph of FIG. 2 shows the relationship between the amount of cobalt powder and nickel powder added and the amount of wear, and the amount of wear is indicated by contour lines every 5 μm.

The contour line of the wear amount is an inverse parabola as is clear from the graph, which shows that there is a mutual influence of the cobalt powder addition amount and the nickel powder addition amount. That is, the larger the amount of cobalt powder added, the smaller the amount of wear.When the amount of nickel powder added is 15%, the amount of wear shows a minimum value, and the amount of wear increases with more or less than 15%, and the interval between contour lines is increased. Indicates that the value becomes narrower and the variation in the amount of wear increases.

Therefore, the cobalt powder addition amount range of 5 to 15% according to Example 1
In the above, the limit of the amount of nickel powder added is in the range of 5 to 23%, preferably in the range of 10 to 20%.

Example 3 (Influence of A-phase alloy powder addition amount) Composition of 15% Cr-12% Ni-6% Mo-6% W-remaining Fe Alloy iron powder (A phase) was changed by changing the addition amount of the sample. I checked the strength. The mixed powder is iron powder with 10% nickel powder and cobalt powder.
10%, 65% Mo alloy iron powder 10%, graphite powder 0.8%, and zinc stearate 0.5%, A phase alloy powder 5%, 10%
%, 15%, 20%, and 25% are added for convenience.

The sample was molded, sintered and lead infiltrated as in Example 1, and the test conditions were room temperature to 350 ° C.

The results are shown in the graph of FIG. 3, and generally, when the temperature exceeds 200 ° C., the radial crushing strength tends to suddenly decrease, but the decrease amount decreases when the A phase alloy powder addition amount is 10% or more.

However, the difference between 20% and 25% is small, and the compressibility deteriorates with increasing addition amount, so the maximum was made 20%.

Example 4 (Influence of Addition Amount of Hard Powder) The wear resistance of the samples having different compositions of 65% Mo alloy iron powder (B phase) and 35% Mo-10% Si alloy iron powder (C phase) was changed. Examined.

The compound powder is iron powder, nickel powder 10%, cobalt powder 10%,
The composition is 15% Cr-12% Ni-6% Mo-6% W-Alloy iron powder consisting of residual Fe (phase A) is 15%, graphite powder is 0.8%, and zinc stearate 0.5% is constant. % Mo-Fe alloy powder (B
Phase) and 35% Mo-10% Si-Fe alloy powder (C phase) at 5% and 1%, respectively.
A total of 10 kinds of mixed powders containing 0%, 15%, and 20% were molded, sintered, and lead infiltrated in the same manner as in Example 1 to obtain a sample, and the wear amount was measured in the same manner as in Example 2.

The graph of FIG. 4 shows the measurement results, and it can be seen that the amount of wear is significantly reduced by adding 5% or less. But 15
% And 20% are small, and an increase in the addition amount is disadvantageous in terms of compressibility and mold wear, and the strength of the sintered body tends to decrease, so the maximum was set to 20%.

Further, it can be seen that the hard powders have the same effect even if they are used alone or when they are mixed.

Example 5 (Comparison of wear resistance between conventional material and invention material) The wear resistance of the invention material based on Examples 1 to 4 and the conventional material of JP-B-59-37342 was compared.

The raw material powder compounding ratio of the inventive material is as shown in Table II. The used raw material powder, molding, sintering and lead infiltration were performed in the same manner as the test of Example 4, and the valve seat made of these materials was used as the test material. .

The description of the material according to the third aspect is omitted because it is within the characteristic range of the material used in the first aspect and the second aspect.

Of these samples, a micrograph of the first aspect of the first invention is shown in FIG. 6 as an example of the metal structure.

As is clear from the micrograph of FIG. 6, Fe-C-
Ni-Co solid solution white background and black background sorbite or bainite mottled texture base has a structure in which neutral phase A phase and white lumpy hard phase are dispersed, and the hardness of each phase is micro Vickers hardness. Then, the solid solution phase was 200 to 300, the sorbite or bainite phase was 300 to 430, the A phase was 340 to 500, and the hard phase was 1000 to 1560.

In addition, the weight of conventional materials is 73% iron powder, 1% copper powder, and 1 graphite powder.
%, Fe-15% Cr-10% Ni-5% Mo-5% W alloy powder 20
%, And 65% Mo alloy iron powder 5% with zinc stearate.
The mixed powder added with 5% was compression-molded into a predetermined ring shape, and then sintered at a temperature of 1140 ° C. for 30 minutes in a reducing gas atmosphere to prepare a material having a sintered density of 6.8 g / cm ³ .

Next, using a valve seat made of each material as a test material, the same simulated engine tester was used for the test of Example 2, and a graph comparing the amount of wear after testing for 30 hours at a predetermined valve seat temperature is shown. Shown in FIG. Incidentally, in this graph, the present invention material A, B, C,
D is as follows.

A: 1st invention (1st aspect) material B: 1st invention (2nd aspect) material C: Material in which the invention material of the said 1st aspect was lead infiltrated D: Infiltration of the invention material of said 2nd aspect by lead As can be seen from the graph of FIG. 5, the valve seat material according to the present invention has a small amount of wear and is particularly excellent at high temperatures.

Also, lead infiltrated materials show even better results.

<< Effects >> As described in detail above, the sintered alloy according to the present invention has considerably higher material strength at high temperatures than conventional sintered alloys and exhibits excellent wear resistance from low temperatures to high temperatures. It shows good results under severe operating conditions.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of the addition amount of Co powder, FIG. 2 is a graph showing the effect of the addition amount of Ni powder, FIG. 3 is a graph showing the effect of the addition amount of A phase alloy powder, and FIG. A graph showing the effect of the addition amount of powder B phase and hard powder C phase, FIG. 5 is a graph comparing the valve seat wear amounts of the conventional material and the material of the present invention, and FIG. 6 is the sintered alloy according to the material of the present invention. It is a microscope structure photograph which shows a metal structure.

Claims (2)

[Claims] 1. The total composition is C0.2-0.8%, Si3.3 by weight ratio.
% Or less, Cr1-4%, Ni6-26%, Mo1.8-13%, W0.2-
2%, Co5-15%, balance of Fe, and its structure is Fe-
In a matrix in which at least one of a sorbite phase and a bainite phase is scattered in a C-Ni-Co solid solution phase, the A phase having the following composition, which is rich in heat and corrosion resistance, is 10 to 20%, and the B phase is rich in wear resistance.
A high temperature wear-resistant sintered alloy in which at least one of a phase and a C phase is dispersed in a total amount of 5 to 15%. Phase B: 50-70Mo-Fe Phase C: 4-22Si-33-36Mo-Fe 2. The high temperature wear-resistant sintered alloy according to claim 1, wherein lead is infiltrated into the pores of the sintered alloy.