JPH0250904A - Wear resistant sintered body - Google Patents

Abstract

PURPOSE:To obtain a ferrous sintered member having excellent wear resistance in a wide temp. range by impregnating LiF as lubricant into voids in sintered body composed of mixed material of fine powder-state ferrous alloy, metal for forming hard carbide and carbon. CONSTITUTION:Into the fine powder of low alloy iron containing 1-25wt.% one or more kinds among hard carbide forming elements of Cr, Mo, V, W, etc., 1-25wt.% fine powder of one or more kinds of Ni, Co and Si and 0.5-2.0wt.% carbon fine powder are added and further, zinc stearate as the lubricant is added at about 0.6% and mixed and pressurized and compacted in a metallic mold. This green compact is taken out from the metallic mold and sintered, and after making the sintered body having 5-15vol.% void ratio, this is submerged into molten LiF and impregnated into the void. This LiF is acted as the lubricant, and high hardness wear resistant sintered body caused by metallic carbide is obtd. and the ferrous sintered member having excellent wear resistance in wide temp. range and suiting to valve seat material for interval combustion engine is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a wear-resistant sintered body, and for example, to a wear-resistant sintered body suitable as a valve seat for an internal combustion engine.

Conventional technology With the increase in the output of internal combustion engines and the shift to unleaded gasoline for automobiles, valve seats are required to have even higher wear resistance. Thermal and mechanical loads tend to further increase due to the use of feeders, and attempts have been made to meet these demands by making valve seats made of sintered alloy instead of melted material.

In other words, in order to improve the wear resistance, high-temperature strength, and oxidation resistance of the valve seat, alloying elements such as chromium, nickel, cobalt, and molybdenum are added to the iron-based sintered alloy, and hard particles are dispersed to improve the material. Enhancements are being made.

However, when the temperature conditions vary widely from low to high temperatures depending on the load condition, such as in internal combustion engines,
It is difficult to provide good wear resistance in all temperature ranges. For example, in low temperature ranges, the lubrication effect due to the formation of oxide film cannot be expected as in high temperature ranges, so the valve and valve seat are Generally, the wear resistance is inferior to that when used in a high temperature range, such as metal contact.

In view of the above circumstances, the present invention focuses on the pores of an iron-based sintered alloy and impregnates the pores with a lubricating substance to improve the wear resistance particularly in the low temperature range. This led to the development of a gold valve seat.

It is known that the pores of an iron-based sintered alloy are impregnated with wax or the like to improve machinability and wear resistance, and one of the applicants has also impregnated a sintered alloy with an organic compound or an organometallic compound. The present invention proposes a sintered metal for a valve seat and a method for manufacturing the same (Japanese Patent Application No. 118001/1983 Sintered metal for an internal combustion engine valve seat and a method for manufacturing the same).

The impregnating substance in the invention of the earlier application has a melting point of 120 to 25
0°C, so that the valve seat does not melt when it is press-fitted into the cylinder head, and it melts at the temperature of the valve seat during internal combustion engine operation to recover the pores in the sintered alloy and prevents the pores from forming during operation. The appearance of the resulting oxide film is to increase the hardness and reduce the coefficient of friction, thereby improving the wear resistance of the valve seat. Valve Sea I・ based on the invention of this earlier application shows excellent wear resistance, but as a result of repeated studies by the present inventor, the following problems still remain when the heating temperature becomes particularly high. It turned out that

In other words, the valve seat (especially the exhaust valve seat) is constantly exposed to high-temperature gas, so even if the average temperature of the valve seat I- is below the melting point of the organic impregnating substance, the surface portion will momentarily become extremely high temperature. As a result, the impregnating substance may undergo evaporative decomposition and the impregnating effect may be lost.

In addition, if the average temperature of the valve seat is above the melting point of the organic impregnating material and lower than the temperature at which the valve seat base material forms an oxide film (approximately 200 to 350'C), the lubricating effect of the organic impregnating material or the friction caused by the oxide film may occur. There is a problem in that neither of the coefficient reduction effects can be fully expected.

OBJECT OF THE INVENTION The object of the present invention is to provide a wear-resistant sintered body that exhibits excellent wear resistance regardless of the heating temperature during use.

21. Constitution of the Invention The present invention relates to a wear-resistant sintered body having a structure in which the pores of a sintered alloy are impregnated with a lubricating fluoride having a high melting point.

The sintered alloy constituting the wear-resistant sintered body is preferably an iron-based sintered alloy that has a wear resistance of its own. By adding alloying elements to the matrix or dispersing hard phase particles as necessary, the chemical composition of the iron-based sintered alloy can be reduced to 0.
5 to 2% by weight (hereinafter, "weight%" is simply expressed as "%").

For other percentages, indicate accordingly. ), contains 1 to 25% in total of one or more of the carbide-forming elements chromium, molybdenum, vanadium, and tungsten, and 1 to 15% in total of one or more of nickel, cobalt, and silicon as necessary. It can be included. The porosity is preferably 5 to 15% by volume.

Carbon combines with chromium, molybdenum, vanadium, and tungsten to form carbides and improve wear resistance. Therefore, the amount of carbon is necessarily determined as an appropriate amount depending on the type and amount of these elements in the sintered material and whether they are added as alloying elements or as hard phase particles, and the above range of carbide-forming element amounts is determined. In this case, it is 0.5 to 2%. Carbon content is 0.
If it is less than 5%, the amount of carbide produced will not be sufficient and wear resistance will decrease due to the production of soft ferrite, which is not preferable. On the other hand, if it exceeds 2%, the material becomes too hard and brittle, which is undesirable, so the carbon content should be 0.5 to 2%.
It is better to set it as %.

Carbide-forming elements such as chromium, molybdenum, vanadium, and tungsten all combine with carbon to form carbides, thereby improving wear resistance.

Although this improvement effect varies in degree, it is common to all of the above elements, so any element may be added, or several types may be added in combination.

If the amount is less than 1%, the amount of carbide produced will not be sufficient and the wear resistance will decrease due to the formation of soft ferrite, and if it exceeds 25%, the material will become too hard and the cost will increase, which is not preferable. Therefore, the total amount of carbide-forming elements is preferably 1 to 25%.

In addition, one or more of nickel, cobalt, and silicon may be added in a total amount of 1 to 15%, if necessary, for the purpose of improving strength or stabilizing the structure.

If the amount is less than 1%, the effect will not be sufficient, and if it is added in excess of 15%, the effect will not be commensurate with the amount, and the cost will increase, which is undesirable, so these elements are added. In some cases, the amount is preferably 1 to 15%.

The lubricating substance to be impregnated has excellent lubricity, and the usage conditions for wear-resistant sintered bodies, such as valve seats, especially in the case of exhaust valve seats, are approximately 350° from room temperature.
The lubricating properties shall not deteriorate in the operating temperature range of C and in an atmosphere containing carbon oxide, carbon dioxide water, etc., and shall not disappear due to decomposition, evaporation, etc.

An example of an impregnating substance having such properties is lithium fluoride. The melting point of lithium fluoride is 842°C,
Since it is higher than the press-fitting temperature of the valve seat, it will not melt during press-fitting, and since it is higher than the operating temperature of the internal combustion engine, there is no risk of thermal deterioration, decomposition, or disappearance.

Regarding the amount of lithium fluoride impregnated, the amount of impregnation almost matches the pore volume of the sintered alloy. Generally, the number of pores in a sintered alloy can be varied from a few percent to several tens of percent depending on the compacting pressure, sintering temperature, sintering time, etc. of the raw material powder, but in the present invention, the compacting pressure and sintering temperature can be controlled. It is preferable that the volume of the pores is 5 to 15% by volume.

If the pore volume, and therefore the amount of impregnation, is too small than this range, the effect of impregnation will not be significant, while if it is too large, the strength of the impregnated sintered alloy itself will decrease, which is not preferable. Note that it is desirable that the purity of lithium fluoride is 90% or more.

E, Example The present invention will be explained in detail below.

5% of the particle size distribution with a peak at 150-200 meshes
Carbonyl nickel powder, metallic molybdenum powder and graphite powder under a 325 mesh sieve, and ferromolybdenum powder with a particle size distribution with a peak at 150 to 200 mesh are added to the molybdenum-containing iron powder at 10%, 5%, 1.2%, and 10%, respectively. % (weight ratio), and 0.6% zinc stearate as a lubricant to improve mold release during mold molding.
% and mixed. This mixed powder was filled into a cylindrical mold with an outer diameter of 46 mmφ and an inner diameter of 35 mm, and the molding pressure was 6 mm using a press.
．． Add 5 tons/ci, mold, and 650°C after cutting.
The material was heated at 1140° C. for 1 hour to dewax, and then heated and sintered at 1140° C. for 1 hour to prepare a valve seat sample material. Let this sample material be No. 1.

A pure iron powder with a particle size distribution having a peak at 150 to 200 meshes, an iron-based alloy powder of 2% nickel, 0.5% molybdenum, 0.2% manganese, and the balance iron with the same particle size distribution, 325
Nickel powder under mesh sieve and graphite powder, 150
An alloy powder of 55% chromium, 10% cobalt, 20% molybdenum, 1.2% carbon, balance iron with a particle size distribution peaking at ~200 meshes, the same as a ferromolybdenum powder with a particle size distribution of <63% molybdenum, and the same <12. Iron-based alloy powder with 5% chromium and the balance iron, and zinc stearate as a lubricant,
In this order: 41.7%, 41%, 1%, 1.3%, 5%,
They were blended and mixed at a ratio (weight ratio) of 5% and 0.5%.

Using this mixed powder, a valve seat sample material was prepared in the same manner as in the above-mentioned No. 1 month. Let this sample material be No. 2.

The analytical values of the above sample material were as shown in Table 1 below.

Table 1 (%) These sample materials were immersed in a bath of lithium fluoride (purity of 98% or more) heated and melted at 950'C, and heated to I Torr.
After degassing under reduced pressure for 30 minutes, the pressure was increased to 5 kg/cnl for 30 minutes using argon gas as an inert gas to impregnate lithium fluoride. The porosity of the sample materials was 9% by volume, and the amount of lithium fluoride impregnated was 9% by volume, which was almost the same as the porosity.

The following individual wear test was conducted using a test piece prepared by applying the above impregnation treatment and processed to a specified size, and a comparison test piece prepared by processing the sample material before impregnation to a specified size. were conducted to evaluate suitability as a valve seat and investigate the effect of impregnation.

FIG. 1 is an enlarged cross-sectional view of a valve seat used in the test, and the valve seat 1 is constructed by impregnating the pores of an iron-based sintered alloy 1a with lithium fluoride 1b. In the figure, 1C is the contact surface of the valve with the valve face.

The unit wear tester used is a model of an automobile engine, and its outline is shown in Figure 4.

The valve seat 1 is press-fitted into a valve seat holder 3 provided on a cylinder head 2, and is fixed to the cylinder head 2 via the valve seat holder 3. cylinder head 2
A valve drive unit body 4 is fixed to the lower part of the valve drive unit body 4, and a valve guide 5 is attached to the valve drive unit body 4. In the valve 10, the valve face is the valve seat 1.
The rod portion (valve stem) 10a is vertically movably inserted into the valve guide 5 so as to contact the chamfered surface (1c in FIG. 1). A camshaft 9 is rotatably supported by a bearing 8.8 provided on the valve drive unit main body 4. The lower end portion of the valve stem 10a is accommodated in the tappet 6A that presses against the cam piece 9a of the camshaft 9, and is held tightly at the step near the tip of the valve stem 10a, receiving and supporting the coil springs 7A and 7B. Both are fitted so that the retainer 6C surrounds the Kotsukuro B.The retainer 6C has a coil spring 7A,
It is fixed to the valve stem 10a via the bolt B by the urging force on the 7th. In addition, the tip of the valve stem 10a is pressed by the urging force of the coil springs 7A and 7B.
press against. The pressure contact between the tappet 6A and the cam piece 9a is achieved by the urging force of the coil springs 7A and 7B located between the retainer 6C and the valve drive unit main body 4.

With this structure, when the camshaft 9 is rotated by a drive device (not shown), the valve 10 moves up and down via the tappet 6A, and the valve face is aligned with the chamfered surface of the valve seat 1 (1c in FIG. 1). ) begins to hit shockingly repeatedly. This impact load is determined by appropriately selecting the strength of the coil springs 7A and 7B, the shape of the cam piece 9a, and the rotation speed of the camshaft 9.

A gas burner 11 is disposed above the valve 10, and a thermocouple 13 is inserted into a hole drilled in the valve seat holder 3 so that its hot junction contacts the valve seat 1, thereby increasing the temperature of the valve seat 1. Detected. A control circuit (not shown) adjusts the amount of compressed air blown from the nozzle 4 to the cylinder 2 to maintain the valve seat 1 at a predetermined temperature.

Further, the surface temperature of the valve 10 is measured by a radiation thermometer 12, and the gas burner 11 is controlled by a control circuit (not shown).
Adjust the amount of propane gas supplied to valve 1.
This is to maintain the surface temperature of 0 at a predetermined temperature.

The test was conducted under the following second condition assuming the usage conditions of the exhaust valve seat.
The test was carried out under the conditions shown in the table.

Table 2 Also, the amount of wear on the valve seat was determined as follows. At the end of the test for a predetermined period of time, replace the valve with a new, unused valve, that is, the reference valve, measure the change in the position of the reference valve relative to the position of the valve before the test (amount of sinking), and use this measured value as the valve. It was defined as the amount of wear on the seat. By doing this, only the amount of wear on the valve seat can be determined without including the amount of wear on the valve due to the test in the measured value.

The test results were as shown in Figure 2. In the same figure,
'L depending on whether or not the sample material number is impregnated with lithium fluoride.
They are distinguished by the numerals ``iF'' and ``none''.

From FIG. 2, it can be seen that the amount of wear on the valve seat 1 is significantly reduced at each temperature due to the impregnation with lithium fluoride.

Next, the valve seat test product No. 2 L i F, No. 2 None, prepared from the sample material No. 2,
Furthermore, a valve seat test product (No. 2stZn) was prepared by impregnating sample material No. 2 with zinc stearate.
A test was conducted for up to 25 hours. Valve seat test crystal No. 2stZn was obtained from the above-mentioned patent application No. 11/1984.
This is a comparison test product based on the invention of No. 8001. The test machine used was the test machine shown in Figure 4, and the valve surface temperature was 55.
The conditions were 0°C and a valve seat temperature of 250°C.

The test results were as shown in Figure 3. As in FIG. 2, the effect of impregnation on improving wear resistance is clearly recognized. The valve seat test product No. 2L i F (Example) had a slightly greater amount of wear than the comparative test product No. 2stZn up to the test time of 10 hours.

However, if the exam time exceeds 10 hours, No, 2stZ
For n, the increase in wear amount is accelerated. On the other hand, No.
, 2 Li F, the increase in wear amount gradually decreases as the test time passes, and when the test time exceeds 10 hours, the relationship between the two is reversed, and when the test time is 25 hours, No., 2.
It is the abbreviation A of stZn. It is thought that if the test time is further increased, the difference in the amount of wear between the two will become even larger.

From the results shown in FIG. 3, it can be seen that the valve seat in which the iron-based sintered alloy is impregnated with lithium fluoride can withstand long-term use under severe temperature conditions and has significantly improved durability. In addition, in a similar test for the specimen +AN01, results showing the same tendency as above were obtained, except that the absolute value of the wear amount of each test specimen was small.

In addition to the embodiments described above, various modifications are possible based on the technical idea of the present invention. For example, the chemical composition of the iron-based sintered alloy may be any suitable chemical composition that does not impair (or improve) wear resistance and mechanical strength. In addition to lithium fluoride, impregnating materials include alkali metal or alkaline earth metal fluorides that have good lubricity and a satisfactorily high melting point. For example, sodium fluoride (melting point 992°C), calcium fluoride (melting point 1360°C)
A 38:62 mixture of barium fluoride and barium fluoride (decomposition starts around the melting point of 1280°C to 11000°C) can be used. Although the above-mentioned embodiment is an example of a valve seat of an internal combustion engine, the present invention is also applicable to other sliding members such as bearings used under high loads.

In this case, as the sintered alloy, in addition to the iron-based sintered alloy, a copper-based sintered alloy used as a bearing material can be used.

Effects of the Invention In the wear-resistant sintered body according to the present invention, the pores of the sintered alloy are impregnated with a lubricating fluoride having a high melting point. Therefore, its lubricating effect does not deteriorate during use. As a result, 200-35
It exhibits excellent wear resistance over a wide temperature range from low temperatures of 0°C or lower to high temperatures, and can withstand long-term use under harsh conditions.

[Brief explanation of the drawing]

The drawings all show examples of the present invention, and FIG. 1 is an enlarged sectional view of a valve seat, FIGS. 2 and 3 are graphs showing the results of wear tests, and FIG. 4 is a single wear test. FIG. In addition, in the symbols shown in the drawings, 1... Valve seat 1a... Iron-based sintered alloy 1b... Lithium chloride 1c... Chamfered surface (contact surface with bulb) 6A... Tachent 7A, 7B... Coil spring 9...・・・
...Camshaft 9a...Cam piece 10...Valve 10a...Valve stem 11...
. . . Gas burner 12 . . . Radiation thermometer 13 . . . Thermocouple.

Claims (1)

[Claims] 1. A wear-resistant sintered body having a structure in which the pores of a sintered alloy are impregnated with a high melting point lubricating fluoride.