JPS5857505B2 - Greta japonica - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a composite material comprising an iron-based sintered alloy and an organometallic compound suitable for use as an exhaust valve seat for internal combustion engines that use unleaded gasoline or LPG (liquefied propane gas) as fuel, and a method for producing the same. Pertains to.

Exhaust valve seats of internal combustion engines that use unleaded gasoline or LPG as fuel undergo wear called so-called valve reset.

In other words, when leaded gasoline is used as fuel, the alkyne lead in the fuel produces lead compounds such as lead oxide, lead sulfate, or lead halides during combustion, and these are energized on the contact surfaces of valves and valve seats and become solid. Wear on valves and valve seats has rarely been seen as a problem because they act as lubricants and impact buffers, but when unleaded gasoline or LPG is used as fuel, lead compounds that have these functions are Since this does not occur, wear becomes severe, and furthermore, peeling due to fatigue failure occurs locally on the contact surface of the valve seat.

This is a phenomenon known as pitting wear, which impairs the airtightness between the valve and the valve seat, and eventually causes combustion gas to blow through, damaging the valve and rendering it inoperable. Even.

On the other hand, after the valve seat is press-fitted into the cylinder head, the working surface is machined coaxially with the valve guide in order to protrude from the valve, so it is required to have good machinability.

As mentioned above, the main properties required for valve seat materials are wear resistance, pitting resistance, and rigidity, but wear resistance and machinability are generally contradictory properties, and one should not be considered one. One thing that gets better tends to make the other worse.

To date, high-alloy heat-resistant steel, heat-resistant cast steel with a large amount of carbide precipitated, and a sintered alloy of high-base metal have been proposed as valve seat materials for internal combustion engines that use unleaded gasoline or LPG as fuel. No material has been found that satisfies all aspects.

In particular, sintered alloys have the disadvantage that due to the inherent pores, the cutting process involves intermittent cutting, which tends to damage the cutting edge of the tool, resulting in extremely short tool life and poor machining accuracy.

However, when iron-based sintered alloys are used as exhaust valve seats, oxides mainly composed of Fe 304 are formed in the pores during use, forming an oxide film on the surface, which reduces the apparent hardness. The oxide film increases and the friction coefficient decreases, and since the formed oxide film continues to the inside of the pores in contact with the surface, it is difficult to peel off, and the wear resistance is improved.

Therefore, sealing by infiltrating PB, Cu, or their alloys is effective for improving machinability, but it is inconvenient from the viewpoint of wear resistance, and since the infiltration temperature is around 100°C, It has the disadvantage of high cost.

Currently, iron-based sintered alloys in which hard powders such as metallic molybdenum, ferromolybdenum, and Cr-W-Co-C alloys are dispersed in Fe base materials have been proposed as valve seat materials, but the wear resistance is not satisfactory. Also, machinability is poor and pitting resistance is also poor.

In particular, materials containing both ferrochrome powder and ferromolybdenum powder have poor pitting resistance.

The present invention provides a low-cost composite material for valve seats that eliminates the drawbacks of conventional materials, has excellent wear resistance, good machinability, and excellent pitting resistance, and a method for manufacturing the same. be.

That is, the alloy powder used as a raw material for the composite material according to the present invention consists of the components Fe-C-Cr-Mo-Co, and since a ferroalloy that is inexpensive and has a low melting point can be used as a raw material for melting, it can be melted using ordinary cast steel melting. The composite material of the present invention can be melted in a melting furnace lined with a metal lining, and can be manufactured at low cost because it is easy to crush. The properties are also good.

The manufacturing procedure of the composite material of the present invention will be described below.

1.5-5.0%C, 15-40%Cr, 10-30%
An alloy with a composition consisting of Mo, 10% or less Co, and the balance substantially Fe is melted in a melting furnace with a conventional basic lining, cast into a mold to form an ingot, and after cleaning the surface. Grind into a powder of 100 mesh or less.

This alloy powder has a ratio of 8 to 20, Ni powder has a ratio of 0.5 to 5.0,
Graphite powder 0.6 to 1.5, one or two molybdenum disulfide or tungsten disulfide powder 0.2 to 2.0
%, the metallic manganese powder is mixed with ferromanganese powder so that the Mn content is 0.5 to 3.0, and the balance is Fe powder, and an appropriate amount of lubricant is added, mixed and molded, and the obtained green compact is obtained. is sintered at a temperature of 111,100 to 1,150°C, heated during or after cooling, and maintained at a temperature of 600 to 800°C to form a pearlite structure.

Thus metal sulfides and Fe-C-Cr-Mo
-C.

It has a hardness of HMV 800 to 1400, and has a density of 6, which has a structure in which fine particles (hereinafter referred to as hard phase) that maintain the shape of the raw material alloy powder are finely and uniformly distributed in a pearlite base. .3~7.1tjf/cc
Obtain valve seat material.

Next, this is immersed in an organometallic compound bath having a melting point of 100 to 250°C, and the pores of the sintered material are filled with the organometallic compound using a vacuum or pressure method to form a valve seat.

Next, the reason for limiting the composition range of the alloy powder used in the present invention will be described.

C forms carbides with Fe, Cr, Mo, and Co in the alloy powder, and the alloy powder has HMV 800~ in the pearlite base.
It is necessary to disperse into a hard phase with a hardness of 1400 and contribute to wear resistance, and it is also necessary to facilitate pulverization during powder production. The amount is small and the hardness is insufficient, making it difficult to crush.

When the coefficient exceeds 5.0, the crushability is good, but the hard phase cracks and easily falls off during use as an exhaust valve seat.

Cr, Mo, and Co are necessary as carbide-forming elements, and also partially diffuse into the base to strengthen the base around the hard phase and improve wear resistance and pitting resistance.

When the Cr value is less than 15, the hardness of the hard phase is low and the wear resistance is insufficient, and when it exceeds 40, machinability is impaired.

In addition, metal chromium, which has a high melting point, is required as a raw material when melting the alloy, which causes high costs.

Like Cr, Mo is a carbide-forming element, and if the coefficient is less than 10, the wear resistance is insufficient, and even if it exceeds 309 J, the effect of improving the wear resistance is not significant.

Co improves the sinterability between the alloy powder and the matrix.

It is especially effective when the amount of Cr and Mo is large, but 10%
Since no significant effect is observed even if the amount exceeds 10%, it is set at 10% or less from an economical standpoint.

This alloy can be easily melted in a melting furnace with a basic lining. After melting, it is cast into a mold to make an ingot. After cleaning the surface by shot blasting, etc., it is coarsely crushed in a show crusher, and then crushed in a vibrating ball mill. Grind it into a powder of less than a pound.

Alloys within the above composition range can be easily pulverized.

Next, the blending ratio of each raw material powder in producing the composite material of the present invention will be described.

Good properties can be obtained when the blending ratio of the alloy powder is in the range of 8 to 20%.

If it is less than 8%, wear resistance will be insufficient, and if it exceeds 20%, cracks will easily occur in the green compact during molding, and the life of the mold will be shortened, as well as poor rigidity.

The most preferable range is 10-15.

Ni powder is solid dissolved in the base to strengthen it and improve wear resistance and pitting resistance, and is also blended in the form of fine carbonyl nickel powder to uniformly diffuse into the base for the purpose of dimensional adjustment. If it is less than 0.5, the effect is small, 5.0%
If it exceeds this, the fluidity of the mixed powder will deteriorate, impairing the moldability and making it difficult to form the base into pearlite.

Mn is mixed in the form of metallic manganese powder or ferromanganese powder in an Mn amount of 0.5 to 3.0, but its purpose is to strengthen the base, similar to that of Ni, and also to produce manganese sulfide during sintering. It's about letting people know.

If the coefficient is less than 0.5, the reinforcement of the matrix is insufficient, and if it exceeds 3.0, the matrix is hardened and machinability is impaired.

Graphite powder is blended to adjust the C content of the base, but if the blended amount is less than 0.61, the base structure will have a large amount of ferrite, resulting in insufficient wear resistance. When this value is exceeded, the amount of pro-eutectoid cement precipitated increases and becomes brittle.

Molybdenum disulfide and tungsten disulfide decompose during sintering, Mo and W partially form a solid solution in the base to strengthen it, and a portion forms carbide and contributes to improving wear resistance, while S, Mn ，
It reacts with Fe and Ni to form sulfides, which are dispersed in the matrix and improve machinability.

The blending amount is desirably 0.5 to 2.0% of one or both of molybdenum disulfide and tungsten disulfide.If it is less than 0.5%, the effect of improving stiffness is small, and if it exceeds 2.0%, sulfide If the amount is too large, the strength will be significantly lowered and the moldability will be deteriorated.

The best effect is obtained when molybdenum disulfide is used alone.

When Mo and W are blended in the form of single metals or ferroalloys, diffusion becomes insufficient at the sintering temperature (1100 to 1150'C), resulting in poor rigidity.

Furthermore, if S is blended as simple sulfur, it will vaporize and dissipate during sintering, resulting in a low yield and large variations in the amount of S, as well as significantly shortening the life of the sintering furnace.

The composition range of the sintered alloy constituting the composite material of the present invention is limited as follows, as the composition of the alloy powder used and the blending ratio of each raw material powder are limited due to the above-mentioned reasons. .

That is, 0.6-2.3%C, 1.2-8. O%Cr
, 2.0 ql) or less Co, 0.5 to 5.0% N
i, 0.5-3.0%MnO. 1~0.6%S
, the amount of Mo supplied from the above alloy powder is 0.8 to 6.
04Mo, and the type or two of Mo and W supplied from one or two of molybdenum disulfide powder and tungsten disulfide powder, which are blended as sulfur additives, totaling 0.3 to 1.48% ( However, Mo is 1.2 or less, W
(0.37% or more), and the remainder consists essentially of Fe.

However, considering that unlike other elements, the yield during sintering is generally not 100%, the content range of C and S is 0.6 to 2.3 for C and 0.6 to 2.3 for S. 1 to 0 and 6 sections.

Add an appropriate amount of lubricant to the mixed powder blended as above and mold it in a mold at a molding pressure of 4 to 7 tons/cd.
C. for 20-60 minutes to sinter.

At temperatures below 1,100'C, diffusion is insufficient, resulting in insufficient strength and wear resistance, and at temperatures above 1,150'C, diffusion from the hard phase into the base 1 due to the Kirkendall effect.
The hardness of the hard phase decreases as it progresses only in the direction, and the hard phase eventually disappears, forming pores at that location and reducing wear resistance.
Furthermore, the hardness of the base increases, impairing machinability, and the expansion of the sintered material increases, resulting in poor dimensional accuracy.

Next, during cooling after sintering or after cooling, heat to 600 to 8
The purpose of maintaining the temperature at 00°C and using pearlite as the base is to improve machinability and to prevent pitting due to fatigue.

In other words, structures containing austenite, free ferrite, martensite, etc., have insufficient fatigue strength, and are susceptible to pitting due to fatigue fracture at the contact surface due to repeated impact loads and repeated heating and cooling during use. The presence of ferrite tends to cause chatter during cutting, and the precipitation of hypereutectoid cementite makes the material brittle, which is undesirable.

The most preferred matrix structure is granular pearlite.

In this way, a sintered alloy material having a density of 6.3 to 7.1 g/cc and a structure in which metal sulfide and a hard phase having a hardness of HMV 800 to 1400 are dispersed in a pearlite matrix is obtained.

If the density is less than 6.3S%c, the wear resistance is insufficient,
If it exceeds 7.1@/cc, high molding pressure is required during molding, so it is set at 6.3 to 7.1 f/cc.

A particularly preferred range is 6.5 to 6.8 t/cc.

Next, the above-mentioned material is immersed in a molten organometallic compound having a melting point of ioo to 250[deg.] C., and the pores of the material are filled with the organometallic compound by vacuum, pressure, or a combination of both.

In addition to preventing interrupted cutting, the organometallic compound also acts as a lubricant between the tool and the workpiece.

If the melting point is lower than 1ooc, it will liquefy during cutting and the effect of improving machinability will not be obtained, and if it exceeds 250℃, high temperature is required for infiltration, which is undesirable. Difficult to recover pores.

As the organometallic compound, organic compounds of low melting point metals such as Zn and PB are suitable.

When the exhaust valve seat according to the present invention is exposed to high temperatures during use, the organometallic compound filled in the pores near the contact surface easily vaporizes and recovers the pores, and the surface and the inside of the pores in contact with the surface are easily vaporized and recovered. An oxide film mainly composed of Fe3O4 is formed on the surface, improving wear resistance.

Moreover, since the oxide film is continuous within the pores, it is difficult to peel off and is stable.

The structure around the contact surface of the exhaust valve seat according to the present invention is modeled and shown in FIG.

a shows a state before use, with a hard phase 2 made of Fe-C-Cr)-Mo-Co alloy in a base 1 having a pearlite structure.
and metal sulfide 3 are distributed, and the pores are filled with organometallic compound 5.

In b, after a short period of operation, the organometallic compound near the contact surface has disappeared and the pores 4 have been recovered.

In C, after a long period of operation, an oxide 6 mainly composed of Fe3O4 is formed on the surface and in the recovered pores.

The exhaust valve seat material according to the present invention has a hard phase dispersed in the matrix,
Excellent wear resistance is maintained by the metal sulfide and the oxide film formed during operation.

Next, examples will be explained.

Example 1 High carbon ferrochrome, ferromolyftene, steel scrap, graphite layer, and metallic cobalt were melted in a magnesia-lined high-frequency induction furnace as raw materials, cast into a mold to make an ingot, and the surface was cleaned by shot blasting. After that, it was coarsely crushed in a show crusher, finely crushed in a vibrating ball mill, and passed through a vibrating sieve to obtain an alloy powder of 11,100 mesh.

The composition of the alloy powder is shown in Table 1.

Next, compounding, molding, sintering, heat treatment, and infiltration with organometallic compounds were carried out under the conditions shown in Table 2 to produce a cylindrical exhaust valve seat material with an outer diameter of 37cm, an inner diameter of 30rrrrrL, and a height of 7.5M. was produced.

The table also shows the characteristics of the material before and after infiltration with organometallic compounds.

The chemical composition (analytical value) of the sintered alloy constituting the exhaust valve seat material is as shown in Table 2-2.

Exhaust valve seats were made for samples 3.5 and 8 of these,
Water-cooled 4-cylinder 4-stroke, OHC type, displacement 1.60
A 100 or 200 hour durability test was carried out using an actual machine installed in a 0cc engine using unleaded gasoline as fuel at 6000 rpm and full load to measure the amount of wear on the exhaust valve seat and check for pitting on the contact surface. Observed.

The amount of wear on the valve seat was expressed as the amount of valve depression (M) when the valve was closed.

0.8%C, 0.3%Mo, 0.1%V as contrast materials,
A material consisting of 2.5*Cr, 0.07% Ni, balance Fe, hardness HRA 58, density 6.8 sintered alloy infiltrated with PB (referred to as contrast material A) and special heat-resistant steel ( Comparative material B) was tested under the same conditions.

The test results are shown in Table 3.

The exhaust valve seat according to the present invention has a clearly smaller amount of wear than the comparative material, and no or only slight pitting is observed, making it an extremely excellent material for exhaust valve seats. I understand that.

Example 2 The same material 1 as the valve seat material used in the example work was made into a chuck 4.
The material was mounted on a lathe by the method shown in FIG. 2, and the end face of the material was chamfered at 45° to conduct a machinability test.

The machinability was evaluated based on the wear dimension (M) of the cutting edge of the cutting tool 3 after cutting (1ffi).

The test conditions were a cutting speed of 58 m/min and a feed rate of 0.05 r.
rary/rey, tool material TH-03, chip shape 5
NP-432, bite holder N141VI-33.

The contrast material was a material that was not infiltrated with the organometallic sample 5 (5
’ ) were also tested.

The test results are shown in Figure 3.

Note that the tool material used in this test was not suitable for sample B, so it was excluded from the figure.

It can be seen that the valve seat material according to the present invention has significantly better rigidity than the control material.

As explained in detail above, the composite material for exhaust valve seats according to the present invention can be used in internal combustion engines that use unleaded gasoline or LPG as fuel, and has excellent wear resistance, pitting resistance, and It will be understood that it has good rigidity and can be manufactured at a low cost because it uses an easily pulverized alloy powder with a low melting point and is infiltrated with an organic metal that has an extremely low melting point.

Incidentally, for the purpose of further improving the pitting resistance of the exhaust valve seat material according to the present invention, it is effective to add V and Nb as base toughening elements.

In this case, it is preferable to limit the amount of each addition to 2 parts or less.

Addition in excess of this will impair rigidity. When Co is added in an amount of 5 to 15%, the wear resistance is slightly improved, but on the other hand, it has the effect of promoting the diffusion of C and promoting decarburization, so addition of a large amount should be avoided.

In addition, pitting resistance is improved by making the shape of the pores spherical, so Fe containing 0.3 to 0.6% P
It is also effective to use the powder in an amount of P in the range of 0.25% or less to form a part of the powder into a liquid phase.

[Brief explanation of drawings]

Fig. 1 is a tissue diagram for explaining the structure of the valve seat material of the present invention near the rotary surface, where a is the state before use, b is the state after short-time operation, and C is the state after long-time operation. shows. 1 is the base, 2 is the hard phase, 3 is the metal sulfide, 4 is the vacancy, 5
is an organometallic compound, 6 is an oxide, and Figure 2 is a cross-sectional view to explain the machinability test method, where 1 is a test piece, 2 is a cutting part, 3Vi is a tool, and 4 is a chuck. , the arrow indicates the feeding direction of the tool. FIG. 3 is a graph showing the results of the machinability test.

Claims (1)

[Claims] 1 0.6-2.3% C11, 2-8.0% Cr,
Co less than 2.0%, 0.5-5.0%Ni, 0
．． 5-3. O4Mn, OJ~0.6%S, 0.8~6.0% Mo as Mo supplied from raw material alloy powder
, and M supplied from one or two of molybdenum disulfide powder and tungsten disulfide powder as sulfur additives.
One or two of o and W in total is 0.3 to 1.48
% (However, Mo is 1.2% or less, W is 0.37% or more), the balance is substantially Fe, and F'e
Metal sulfide and 1
．． 5-5.0% C115-40%Cr, 10-30
%Mo, 10% or less Co, and the balance is formed from raw material powder consisting essentially of Fe, and has a HMv of 800 to 14
The pores of the sintered alloy, which has a structure in which a hard phase having a hardness of 0.00 and a density of 6.3 to 7.1 f/cc are finely dispersed, form an organic metal having a melting point of 100 to 250°C. A composite material for exhaust valve seats that is filled with a compound and has excellent wear resistance and rigidity. 2 1.5-5.0L1) C, 15-40% Cr, 10
~30% Mo, 10% or less Co, remainder substantially Fe
Alloy powder consisting of 8-20%, Ni powder 0.5-5.0%
%, graphite powder 0.6 to 1.5 ratio, one or two of molyfden disulfide powder and tungsten disulfide powder is 0 in total
．． 5 to 2.0%, ferromanganese powder or metallic manganese powder with Mn content of 0.5 to 3.0 Tozanbe Fe powder is compression molded, sintered at 1100 to 1150°C, and 600 to 800% The composite for an exhaust valve seat according to claim 1, characterized in that after the base is made into pearlite by heat treatment to maintain it at °C, the pores are filled with a molten organometallic compound having a melting point of 100 to 250 °C. Method of manufacturing the material.