JPH01152247A - Sintered alloy having wear resistance at high temperature - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an iron-based sintered alloy suitable for valve seat materials for internal combustion engines for automobiles.

[Prior Art] Many sintered alloys have been developed for valve seats for automobile engines in response to lead-free Kallin.

For example, the valve seat for unleaded gasoline (Japanese Patent Publication No. 55-36242), which was developed and put into practical use by the present applicant, is an example of this. Impregnated with 10% or more lead, it is different from the conventional material Cr-MO-
Chinoku Special Publication 1979-179, impregnated with lead in V series sintered steel
Compared to No. 68), the wear resistance is further improved.

[Problems to be solved by the invention] However, in recent years, as the operating conditions of automobile engines have become more severe due to higher power performance, even the above-mentioned sintered alloys are insufficient. There was a desire to improve the material to a material with higher strength.

[Object of the invention] The present invention is directed to the above-mentioned conventional sintered alloy (Japanese Patent Publication No. 55-36
No. 242), and the object is to provide a sintered material with high material strength and excellent high-temperature wear resistance at a low cost.

<Structure of the Invention> [Means for Solving the Problems] In order to achieve the above object, the present invention has a matrix having a structure in which nickel is dispersed in a base made of a conventional sintered alloy composition. The material is impregnated with lead, and the optimum base material density and amount of lead impregnation are limited.More specifically, the overall composition is as follows: C: 0.35 to 1.1% by weight.

Ni: 4.6-25.8%.

MO: 0.3-2.7%.

CO; a4 to a7%.

Pb: 5-16%.

and the remainder essentially consists of Fe, The base composition is also in weight ratio, C: 0.45-1.15%.

Ni: 5.5-27.2%.

Mo: Q4-2.8%.

CO: 4.1-7.1%.

and the remainder substantially consists of Fe, and an austenite structure is dispersed in a mixed structure of a sorbite structure and a bainite structure, the pores contain lead, and the overall density is 7.6C.
I/cj or more, and the density of the sintered alloy excluding Pbff1 is 6.9 to 7.2q/cTl? It is characterized by being

First, the method for manufacturing the sintered alloy of the present invention will be briefly explained.
The powder used as raw materials is the same as in Japanese Patent Publication No. 55-36242, Ni0.5-3%, MOo, 5-3%, CO5,5.
-7.5% Fe balance is mixed with N1 powder, or the alloyed iron powder is mixed with Ni powder, graphite powder, and a lubricant such as zinc stearate.

Molding and sintering are normal methods, and the density of the sintered body is a9~
Set it to be 7.20/ci.

This sintered body is immersed in a molten lead bath to impregnate the pores with lead.

The numerical range constituting the sintered alloy of the present invention thus obtained will be explained next.

The composition of the basic alloyed iron powder is the same as the base composition of the conventional material, and each composition range is as described in Japanese Patent Publication No. 55-36242.

That is, Ni and MO are components that mainly contribute to improving the strength, and if they are less than 0.5%, they are insufficient, while if they are added in an amount of 3% or more, they are not cost effective. Moreover, when MO is added in excess, oxidation resistance decreases.

If CO is less than 5.5%, high-temperature hardness is insufficient and wear is likely to occur, while if it is more than 7.5%, the raw material powder becomes hard and compression molding becomes difficult.

C is added in the form of graphite powder, and the amount of carbon in the sintered body base is in the range of 0.6 to 1.2%; if it is less than this, sufficient hardness cannot be obtained, and if it is too much, the cementite structure will deteriorate. It becomes easy to precipitate and the base material becomes brittle.

Further, the structure of the matrix generally exhibits a mixed structure of a sorbite structure and a bainite structure, but when the zero point is close to the upper limit, the bainite structure comes to occupy most of the structure.

Next, the idea of adding Ni to the above alloy and dispersing it in the form of an austenitic structure is that the static mechanical strength is considerably improved, the strength loss at high temperatures is reduced, and the dispersed austenitic structure is difficult to repeat. This is based on the knowledge that it is effective in improving fatigue strength.

Ni is added in the form of carbonyl nickel powder, and after sintering, a spotted austenite structure is formed in the matrix. N
The amount of i powder added is in the range of 5 to 25% by weight, and 5%
If it is less than 25%, there will be little improvement in wear resistance and strength.
Even if it is added in excess of this amount, it will not be cost effective and will tend to deteriorate both wear resistance and strength.

The density of the above N1-Mo-CO-C based sintered steel is 6.9~
7.2 g/cm? is optimal. 6.9g/ci?
If the density is lower than 7.20/cj, it will easily wear out, and if the density is higher than 7.20/cj, the molding pressure will be high, which is disadvantageous in terms of workability and mold wear.In addition, the decrease in the amount of pores will lead to lead infiltration, which will be described later. becomes worse.

Regarding the infiltration and concealment of lead, the density after infiltration is 7.6 g/+a in the above-mentioned sintered density range. When impregnated to the above level, good wear resistance is exhibited. In other words, the amount of Pb is sintered density 6.9g
, /Cm' has a weight ratio of 9% or more and a sintered density of 7.
20/ctn' base material, the weight ratio is 5% or more. The upper limit of the infiltration density does not exceed a2q/cj because the sintered density range is limited.

Further, the amount of Pb is also the same, and is a maximum of 16% by weight in a base material with a sintered density of 69 g/cm'.

Expressing the above structure in terms of composition range, the overall composition is C: 0.35 to 1.1% by weight.

Ni: 4.6-25.8%.

MO: Q3~2.7%.

CO: a4 to a7%.

Pb: 5-16%.

Fe: remainder; In addition, the base composition is the same in terms of weight ratio, C: 045-1.15%.

Ni: 5.5-27.2%.

Mo: Q4-2.8%.

CO: 4.1-7.1%.

Fe: remainder.

Incidentally, there is a sintered alloy (Japanese Patent Publication No. 42991/1983) having a composition range similar to the above-mentioned base composition.

However, in this sintered alloy, 8 to 16% of Ni is dissolved in the matrix, whereas in the material of the present invention, a portion is dissolved in the matrix and the majority is dispersed in the matrix in the form of an austenite phase. , and the present invention material are different in that they contain a predetermined amount of Pb.

[Example] (Test-1) First, Ni: 1.5%, MO: 1.5% in weight ratio.

Atomized alloy iron powder containing 65% Go and having a particle size of 100 mesh or less and carbonyl nickel powder for forming an austenite structure were prepared.

Next, a sample was prepared by mixing the atomized alloy iron powder with 1% by weight of graphite powder and 0.8% of zinc stearate as a lubricant, and roughly adding 5.10, 15% of the above carbonyl nickel powder. , 20.25 and 30% by weight were prepared, and the sintered density was 7.0g/an? After adjusting the molding density so as to give a predetermined shape, sintering was performed in an ammonia decomposition gas atmosphere furnace at a temperature of 1160° C. for 30 minutes to obtain each sintered body.

Next, each sintered body was immersed in a molten lead bath at 550°C,
Lead was infiltrated into the pores in the sintered body by applying a pressure of 8 atmospheres.

The microscopic structure of these samples is a mixed structure of a bainite structure and a small amount of sorbite structure as a base, and the sample to which carbonyl nickel is added has a white austenite structure dispersed therein. Additionally, lead is observed within the pores.

Next, the radial crushing strength of each sample at room temperature and the amount of wear of each valve seat were compared using a simulated engine test machine using valve seats made of these materials as test materials.

This wear tester has a mechanism in which the camshaft is driven by a motor while heating the valve and valve seat to a predetermined temperature with LPG combustion gas, and the temperature, rotation speed, valve spring pressure, etc. can be adjusted arbitrarily. It can be set up and subjected to severe tests in a short period of time.

In addition, the material of the valve to be the mating material is 2l-4N (21%C
Using r-4%Ni heat resistant w4), the temperature of the valve seat was set to 300.
℃, and the amount of wear on the valve seat was measured after continuous operation for 30 hours.

Figure 1 shows the measurement results of radial crushing stress and valve seat wear.

show. The effect of the radial crushing strength was recognized when the addition of Ni powder was 5% or more, reached the maximum value at 10 to 20%, and then gradually decreased again.

The amount of wear on the valve seat shows a similar tendency, with the least amount of wear at 15 to 25%, and a slight tendency for wear to increase when it exceeds 25%.

Therefore, the lower limit of the amount of Ni powder added is 5%, and the upper limit is 25%.
%. As a result, the composition of the sintered body was 0.00% by weight.
45-1.15%, Nr5.5-27.2%, MOQ4
-2.8%, CO4, 1-7.1%, and the balance Fe.

(Test-2) Next, the relationship between the sintered density, the amount of lead infiltration, and the amount of wear was investigated.

The sample used was a mixed powder with a Ni powder addition of 10% from Test-1, and the sintered density was 67, a9, and 7.0 g/cn.
? After adjusting the molding density and molding into a predetermined shape, and sintering in the same manner as Test-1, lead infiltration was performed for each density of the sintered body by changing the immersion time and pressure in the molten lead bath. Samples with different amounts of lead infiltration were made.

Valve seats made of these materials were used as test materials and the amount of wear of each valve seat was compared using a simulated engine test machine as in Test-1. The results and the density and pb analysis values of each sample are shown in Table 1. Further, from Table 1, the relationship between sintered density, sample density, and Pb amount is shown in FIG.

In Figure 2, the circle mark indicates Q4mm with relatively little wear.
Hereinafter, the mark X represents a sample exceeding Q4mm. In addition, the area where the wear amount is 04 mm or less is indicated by diagonal lines, and the density of the sintered body in this area is 6.9 to 7.2 Ω/cn+, and the density of the lead-infiltrated sample is 7.6 g/d or more. , and P
b4 is in the range of 5% or more and 16% or less in total composition.

Table 1 Sample Sintered density Sample density Pb amount Wear amount number (g
/cm3) ((1/cm3) (%) (m
m) 1 6.7 8.26 19 0.45
2 6.7 8.01 16 0.453
6.7 7.44 10 0.704
B, 9 8.20 16 0.305 6.
9 7.92 13 0.356 B, 9
7.62 9 0. ．． 107 7.2
8.03 10 0.258 7.2 7
゜75 7 0.309 7.2 7.6
0 5 0.3510 7.2 7.40
3 0.50 test-3) The amount of Ni powder added was 15%, and a valve seat was prepared in the same manner as test-1 except for that, and a test material was used.

In addition, as a comparison material, a sample manufactured without adding Ni powder was also prepared, and the amount of wear caused by the temperature of the valve seat was compared using a simulated engine test machine. The relationship between temperature and radial crushing strength was also measured. The results are shown in FIG.

The invention material has a small amount of decrease in wear resistance and radial crushing strength even at high temperatures.

(Example) Next, the results of a bench durability test using a 4-cylinder 2000cc gasoline engine are shown in FIG.

The rotation speed is 6000 rpm, 100 hours and 200
It shows the amount of valve seat wear after hours of operation.

The samples used were the present invention material produced in the same manner as in Test-3 and the conventional material.

As is clear from the figure, the sample of the present invention has less wear and -
It's far superior.

[Effects of the Invention] As detailed above, the sintered alloy according to the present invention has considerably higher material strength than conventional materials, as is clear from the experimental results, and has excellent wear resistance from low to high temperatures. show,
This is useful when the operating conditions of an internal combustion engine are severe.

Furthermore, since no intermetallic compounds or expensive raw materials are used, it can be manufactured relatively inexpensively using normal manufacturing methods.

[Brief explanation of the drawing]

Figure 1 is a graph showing the effect of the amount of Ni powder added, Figure 2 is a graph showing the density range of the sintered body and the optimal amount of lead infiltration, and Figure 3 is a graph showing the effect of the amount of Ni powder added.
The figure is a graph showing the radial crushing strength and wear resistance at high temperatures of the conventional material and the present invention material, and FIG. 4 is a graph comparing the valve seat wear amount of the conventional material and the present invention material in an engine durability test. Patent applicant Nissan Motor Co., Ltd. Hitachi Powder Metallurgy Co., Ltd.

Claims (1)

[Claims] 1. Overall composition in weight ratio: C: 0.35-1.1%, Ni: 4.6-25.8%, Mo: 0.3-2.7%, Co: 3.4 to 6.7%, Pb: 5 to 16%, and the balance substantially consists of Fe, and the base composition is also in weight ratio: C: 0.45 to 1.15%, Ni: 5.5 ~27.2%, Mo: 0.4-2.8%, Co: 4.1-7.1%, and the remainder substantially consists of Fe, and is in a mixed structure of sorbite structure and bainite structure or in a bainite structure The austenite structure is dispersed in the pores, the pores contain lead, the overall density is 7.6 g/cm^3 or more, and the density of the sintered alloy excluding the amount of Pb is 6.9 to 7.2 g/cm. A high-temperature wear-resistant sintered alloy characterized by ^3.