JPS61139644A - Sintered iron alloy for valve seat - Google Patents

Abstract

PURPOSE:To obtain the titled sintered iron alloy having the well-balanced its own wear resistance and attacking action on an opposite member by dispersing the rigid particles of an alloy consisting of Co, Cr, Mo and C in an iron matrix contg. C or further contg. Ni. CONSTITUTION:The sintered iron alloy for a valve seat is obtd. by dispersing rigid particles of an alloy consisting of, by weight, 0.5-3.0% C, 5-20% Mo, 10-40% Cr and the balance Co in an iron matrix consisting essentially of pearlite. The iron alloy has a composition consisting of 1.9-21.1% Co, 0.5-10% Cr, 0.15-5% Mo, 0.8-2.8% C and the balance Fe or further contg. 1-10% Ni. Pb may be infiltrated into the iron alloy by 1-20wt% of the total amount. The iron alloy has the improved wear resistance and the weakened attacking action on an opposite member as compared with a conventional seat material, so an engine valve not subjected to filling or other processing for improving the wear resistance can be used stably.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to improving the performance of a sintered alloy for valve seats of internal combustion engines, and more specifically, it improves its own wear resistance and reduces its aggressiveness against mating valves. Concerning weakened iron-based sintered alloys.

[Prior art]

Iron-based sintered alloys containing alloying elements such as Cr, Ni, Co, and Mo are increasingly being used for valve seats of internal combustion engines in order to improve wear resistance at high temperatures.

By the way, the selection of the material for the valve seat should be determined in relation to the mating component, that is, the engine valve.If this selection is incorrect, it will not only weaken its own wear resistance, but also increase its aggressiveness against the mating component. This will have an undesirable effect on the entire valve mechanism. For example, conventionally,
Engine valves that are coated with metal such as stellite are often used to increase wear resistance, but in recent years,
There is a movement to abolish valve sales due to demands for cost reduction.

Against this background, if conventional valve seats that have been added with intermetallic compounds such as ferromolybdenum or composite carbides to have extremely high wear resistance are used as they are, engine valve wear will increase. This results in

[Problem that the invention seeks to solve]

The present invention applies to general-purpose engine valves (for example, JI88tJH31,
8 (manufactured by JH3), it will wear out the opponent,
Alternatively, it is an attempt to avoid a significant increase in self-wear, and an attempt is made to provide an iron-based sintered alloy for valve seats that has an appropriate balance between wear resistance and attack resistance. .

[Means for solving the problem] The iron-based sintered alloy for valve seats of the present invention contains carbon (q: '0.5 by weight) in an iron (Fe) base mainly composed of pearlite.
~&0%, molybdenum (MO) = 5 to 20%, chromium (Cr): 10 to 40%, and the remainder cobalt (Co). Hard particles are dispersed, and the overall composition is Co: 1.
9~21.11゜Cr: α5~l0IG, MO: α25
~sj, C: 0.8-2.8%, Ni if desired
1 to 10 cm, the balance being Fe and unavoidable impurities, and if desired, lead (pb) in a total weight ratio of 1 to 20 cm.
It is characterized by being infiltrated with.

[For production]

The above CO-based alloy hard particles have a particle size of 30 to 150 μm. The reason why this is dispersed in the Fe base containing C is to appropriately increase the wear resistance of the valve seat, and some of the CO in the alloy diffuses into the base and around the particles. It has the effect of forming a layer and increasing the bonding force between the particles and the base, thereby preventing the particles from falling off. The mixing ratio of such hard particles is determined based on the composition of the Fe base and the overall composition, and is in the range of about 5 to 25 inches.

On the other hand, C contained in the Fe base forms a solid solution with Fe in the base to form pearlite, increasing the hardness of the sintered alloy and improving wear resistance. The lubricating effect is exerted by being present in the .

However, if α is less than 81 g, the above effect will not appear, and if it is more than 2.0 g, free graphite will increase and the strength of the base will decrease. Therefore 0.8 to 2.0. The total composition is α8 to 2.
．． A value of 8 or better is preferable. If the valve seat is particularly required to have wear resistance, Ni is added as a base component. Ni is dissolved in the base and helps strengthen the base, but if the coefficient is less than 1, the effect will not be exhibited, and if it is more than 10, the base will become soft and the wear resistance will decrease, so 1q' to 10 is preferred.

Next, the reasons for limiting the components contained in the hard particles will be described.

Or combines with carbon to form carbide, and a part of it also forms an alloy with CO, which has the effect of improving the hardness of hard particles, but at 109g or less, □ does not have the above effect. ′
If it is insufficient, and if the number exceeds 40%, some of the Cr that maintains the equilibrium within the particle will diffuse out of the particle, and the particle
It will pickle and become brittle. In addition, the carbide in the particles will be eaten more and the aggressiveness towards the other member will be strengthened, so the
0 I was disappointed.

MO combines with carbon to form carbide, and some of it becomes solid solution to increase the hardness of the hard particles, but if it is less than 5 inches, this effect will not appear, and if it is more than 201, it will become too hard and attack the mating member. So I set it to 5 to 20 inches.

C combines with Cr and Mo to form carbides and increases the hardness of hard particles, but this effect does not appear below ttS*;
Since the amount of carbide becomes too large and becomes brittle when the amount is 15 or more, it is set to 15 to 311i.

The total composition of the iron-based sintered alloy consisting of the base and hard particles as described above is C: [L8 to 2.8%, Co: 1.9 to 21%.
11g, Cr: Q, 5-10 S, Mo: 1
25-5%, 1-10% Ni if desired, balance F
e and become unavoidable impurities.

If the operating conditions are severe, if the iron-based sintered alloy with the above structure is roughly infiltrated with Pb, a black oxide layer will be formed on the surface of the alloy, and its lubricating action will cause the valve seat to bond with the mating material. Improves wear resistance between valves. However, if the impregnation amount is less than 1 part, the effect will be small, and if it exceeds 20 parts, the skeleton will be weakened and the wear resistance will decrease, so 1 to 20 parts is preferable.

Such a sintered alloy of the present invention contains graphite powder of 18 to 2.0 parts, CO-based alloy of 5 to 25 parts, optionally 1 to 10 parts of Ni, 0.5 to 1 part of zinc stearate, and the balance. After blending and mixing the reduced iron powder, it is filled into a mold and molded at a molding pressure of 6 to 7 t/J, and then heated at 1100°C to 1250'C for 30 minutes in a reducing atmosphere.
It is obtained by sintering for 60 minutes. If necessary, the sintered body is brought into contact with a Pb lump and heated in a reducing atmosphere at 1000 to 1100°C for 30 to 60 minutes to infiltrate and disperse 1 to 20 inches of Pb into the sintered body.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Example 1 As shown in Table 1, -! i25 mesh graphite powder has a coefficient of 1.0 and a weight ratio of 159G Cr%, Cr%, O1,
So that the 1100 mesh CO-based alloy powder consisting of 8 mo C and the balance CO is 8%, and the zinc stearate is α8%.
The remaining 1100 mesh reduced iron powder was blended and mixed, the mixture was filled into a mold and compression molded using a pressure cuff ton/cd, and then the powder compact was heated to 1150 mesh in ammonia gas.
It was heated and sintered at °C for 60 minutes.

Thereafter, the sintered body obtained as described above was processed into a valve seat, and the valve seat was made into a valve seat with a displacement of 2000cc 14
It was press-fitted and assembled as an exhaust valve seat into the aluminum alloy cylinder head of a cylinder engine and subjected to a bench durability test.

The bench durability test was conducted using leaded gasoline at 6600 r, p.
m, continued for 200 hours at full load. At this time, a general-purpose valve (JISStJH3) without a metal plate was used as the mating valve. After the test, the increase in the contact surface width of the valve seat and the amount of wear on the mating valve were measured, and the results are listed in the table below along with the hardness and density of the sintered body. The table also includes the results of Examples 2 to 5 and Comparative Examples 1 to 2, which will be described later.

Examples 2 to 5 Valve seats were manufactured in the same manner as in Example 1, with the compositions changed as shown in the table, and were subjected to the same bench durability test as in Example 1. Regarding Example 3.4, the sintered body was brought into contact with a Pb lump and heated for 10 minutes in an ammonia decomposition gas atmosphere.
Pb was infiltrated by heating at 50'CX for 30 minutes. Also, as in Example 1, zinc stearate was included in addition to the listed components.

Comparative example 1 The valve seat was manufactured using cast iron FC50.

It was subjected to the same bench durability test as in Example 1.

Comparative Example 2 A valve seat was manufactured using JIS heat-resistant steel material 5UH4B, and subjected to the same bench durability test as in Example 1.

From the table above, the sintered alloys of Examples 1 to 5, which fall within the scope of the present invention, have a small amount of wear and a small increase in the valve contact surface width, and have excellent wear resistance. It is clear that the attack on the component is low.

Among them, Examples 2, 4, and 5 have Ni added instead of reducing the number of hard particles compared to Example 3, and have higher wear resistance than Example 3, and the amount of valve wear is also reduced. I got an excellent effect.

Furthermore, in Examples 3 and 4, the hardness itself was significantly increased depending on the composition or blending amount of the hard particles, but P
b Due to the effect of infiltration, the amount of valve wear is not much different from other examples.

On the other hand, Comparative Examples 1 and 2 have low wear resistance and a large amount of valve wear.

Examples 6 to 10, Comparative Examples 3 to 4 Sintered bodies having the compositions shown in Table 2 were manufactured and subjected to the bench durability test as described above. As a result, it was found that even when hard particles containing Ni were used, the effects of the present invention appeared.

〔Effect of the invention〕

As described above in detail, the iron-based sintered alloy for valve seats according to the present invention is produced by dispersing hard alloy particles in an Fe base containing C and optionally Ni, and infiltrating Pb if desired. This not only improves its own abrasion resistance, but also weakens the aggressiveness of the mating member compared to conventional sheet materials, thereby reducing the wear of the member.
This has made it possible to stably use engine valves that have not been subjected to wear-resistant treatments such as fillers.

Claims (2)

[Claims] (1) 0.5 to 30% carbon (C) and molybdenum (Mo) by weight in an iron (Fe) base mainly composed of pearlite.
Hard particles consisting of 5% to 20% chromium (Cr), 10% to 40% chromium (Cr), and the balance cobalt (Co) are dispersed, and the overall composition is as follows:
Co1.9-21.1%, Cr0.5-10%, Mo0
．． 25-5%, C0.8-2.8%, optionally Ni1
An iron-based sintered alloy for valve seats, characterized in that the iron-based sintered alloy is comprised of ~10%, the balance being Fe and unavoidable impurities. (2) 0.5 to 30% carbon (C) and molybdenum (Mo) by weight in an iron (Fe) base mainly composed of pearlite.
Hard particles consisting of 5% to 20% chromium (Cr), 10% to 40% chromium (Cr), and the balance cobalt (Co) are dispersed, and lead is infiltrated, resulting in an overall composition of 1.9% to 21.1% Co, 0.5% Cr.
~10%, Mo0.25~5%, Pb1~20%, C0
．． 8-2.8%, Ni 1-10% if desired, balance Fe
and unavoidable impurities.