JPH0152475B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing wear-resistant members for internal combustion engines, and specifically relates to piston rings and cylinder liners that are susceptible to sliding wear, camshafts, tappets, rocker arms that are prone to pitting, Alternatively, it is used for valves, valve seats, etc. that are prone to wear due to knocking.

These parts that require wear resistance are subject to various conditions such as sliding conditions, temperature, impact, load, and corrosive atmosphere, and it is necessary to select materials according to the conditions. One way is to increase the hardness of the surface that is subject to wear.

The reason for this is that the presence of a hard material on the surface reduces the substantial contact area associated with plastic deformation between the surfaces, thereby reducing the amount of wear.
On the other hand, materials with high hardness usually have high strength and are resistant to fatigue, and have excellent wear resistance against pitting and knocking.

However, even when such high-hardness materials are used, abnormal wear such as scuffing will occur if the lubrication conditions are not met, and means for adding lubrication conditions, such as self-lubricating particles such as graphite, may be used. This involves the use of materials and the provision of minute irregularities as a surface finish. Therefore, there are inevitably limitations on workability and basic materials, as well as compatibility with the mating material that is subject to wear, so generally cast iron and sintered alloys are used, and chrome plating is used. Surface coating, typically thermal spraying, and heat treatment, typically nitrocarburizing and hardening.

However, cast iron and sintered alloys are inferior in strength to steel, and there are manufacturing limitations when attempting to obtain even higher hardness. On the other hand, the surface coating is matte,
There is a limit to the adhesion strength of thermal spraying, and methods using heat treatment have limitations due to cracking and other reasons.

In particular, thermal spray coatings can be formed by mixing highly hard particles such as chromium oxide, chromium carbide, tungsten carbide, alumina, etc. with iron or other metals to form coatings that are exposed to significant sliding wear such as piston rings. However, the strength of the coating is low due to the presence of oxide and carbide particles and pores, and the coating strength is low for cams and cam followers that are subject to high surface pressure, valves that are subject to impact, etc. Not only do carbide and oxide particles easily fall off the valve seat, but the coating peels off from the base material, making it unusable.

On the other hand, for example, for valves and valve seats, a method of overlaying or welding stellite (for example, Utility Model Application Publication No. 55-59110) has been used, and although a highly hard surface is obtained, the stellite itself is expensive. Not only that, but also uneven build-up and weld cracks occur, the hardness is too high relative to the other material, the valve seat, and the material has a uniform surface, so it has poor lubricity. . On the other hand, those in which a sintered alloy is arranged here (for example, Utility Model Publication No. 52-137208, Japanese Patent Application Publication No. 137208,
55-8497), but piston rings and valves made using this method not only cannot sufficiently compensate for the relative hardness difference with respect to the cylinder liner and valve seat, but also have poor surface pressure strength and The bonding strength with the base material is insufficient. Another method, as in JP-A No. 52-44706, involves spraying powder onto the sintered alloy base material and melting it, but this method not only does not provide a thick build-up layer, but also , the shape of the build-up layer is difficult to control, similar to those that are thermally sprayed.

In this way, piston rings, cylinder liners,
At present, there is no material that takes into account relative wear such as camshafts, tappets, rocker arms, valves, and valve seats that are completely satisfactory.

The present invention has been made in view of the above, and provides a method for manufacturing a wear-resistant member for internal combustion engines, which has high hardness, product stability, productivity, and lubricity, and allows adjustment to the mating material. be. That is, 5 to 40% by volume of ceramic powder is mixed with iron-based powder, the mixed powder is compacted into a desired shape, and then sintered at the sintering temperature of iron-based powder. Next, the sintered alloy is placed on the surface of a base material of steel or cast iron, and a high-density heat source is applied from the surface of the sintered alloy to heat it, and the sintered alloy is remelted at the same time. , a method for manufacturing a wear-resistant member for an internal combustion engine, characterized in that a wear-resistant layer is formed on the surface of a base material.

Because the sintered alloy used in the present invention contains high-melting point ceramic particles, the high-melting point ceramic particles alone do not melt even during remelting in the above manufacturing process, and remain as individual particles even after remelting and cooling. Exists. Therefore, the high melting point ceramic particles are interposed on the surface of the sliding surface and exert a bearing effect on the sliding surface. To achieve this, the high melting point ceramic particles need to be uniformly dispersed from the time they are included in the sintered alloy, but they must also be dispersed in a volume percentage of 5 to 40%.
%. The reason for this is that if the amount is less than 5% by volume, the amount of high melting point ceramic particles interposed on the sliding surface will be too small, and the bearing effect will not be exhibited, and conversely, the sliding surface will be formed by base parts other than the high melting point ceramic particles. As wear progresses, high melting point ceramic particles fall off, causing abrasion wear. On the other hand, if it exceeds 40% by volume, a sintered alloy containing many high-melting point ceramic particles can only be obtained by a special method such as hot isostatic pressing, and the formability may be extremely poor. Furthermore, as mentioned above, the high melting point ceramic particles remain alone even after the sintered alloy is remelted, so the larger the amount, the weaker the strength, and easily cracks and peels. The following must be selected.

Furthermore, while these high melting point ceramic particles have a bearing effect on the sliding surface, they must also be supported by the surrounding base, so their size is also 5 to 5.
Must be in the range of 50μ. In other words, if the diameter is less than 5μ, the high melting point ceramic particles will easily fall off when the base is deformed due to the contact pressure with the mating member between the sliding surfaces. If the particles get hot, not only will abrasive wear occur at the inevitable initial wear stage, but the strength will drop significantly due to coarse particles dispersing in the structure, and the size of the high melting point ceramic particles requires an average particle size of 5 to 50μ.

Such high melting point ceramics are particles that do not decompose even at remelting temperatures, and are selected based on their bonding properties with the surrounding iron base metal and their sliding properties.
The melting point is above ℃. oxides, carbides, nitrides,
It is selected from silicides and borides. On the other hand, lasers, electron beams, and
Each plasma has an output of about 1.5 to 10 K.W., and the energy beam diameter is selected in the range of about 0.1 to 2 mm, so remelting can be done according to the thickness of the sintered alloy and the cooling efficiency of the base metal. It is possible to adjust the scanning speed of the energy beam so that the maximum temperature in the layer does not exceed the melting and decomposition temperature of the ceramic particles. However, if the volume of the sintered alloy to be remelted and the base metal is one-fifth or more of the base metal volume, a high output heat source is required, so it is necessary to forcefully cool the base metal. be. Furthermore, since there is a limit to the forced cooling of the base material, the volume of the sintered alloy to be remelted must be one-fourth or less of the base material.

This sintered alloy needs to have excellent bonding properties to ceramic particles and to the base material,
Furthermore, since it forms a part of the sliding surface after being remelted, it must have a certain degree of wear resistance and strength to support the ceramic particles. For this purpose, an iron-based alloy powder containing Fe as the main component is selected. In other words, because they are similar materials to the base material steel or cast iron, they are easily alloyed by remelting and have a high degree of bonding, but they also generally have no affinity for ceramic particles, which are carbides and oxides. Defects are less likely to occur at grain boundaries.

At least % by weight of this iron-based alloy powder
It is necessary to contain 0.2 to 3.0% of C. The reason for this is that when a sliding surface is formed after the iron-based alloy is remelted, if the C content is less than 0.2%, the amount of ferrite in the base will be large and hardness will not be obtained, and the rigidity to support the ceramic particles will not be obtained. If the C content exceeds 3.0%, ledebrite formation of the matrix progresses and becomes brittle, resulting in deterioration of strength and machinability, so it is preferable to select a C content of 0.2 to 3.0%.
Furthermore, for items used in high-temperature conditions such as diesel engines, exhaust valves, and valve seats, a total of 3 to 12% of one or more of Cr, Mo, and Ni is added to improve heat resistance and corrosion resistance. On the other hand, it is also possible to increase the amount of C and obtain the effect of corrosion resistance due to the generation of ledebrite structure.

On the other hand, in the case of mixing and sintering ceramic particles and powder mainly composed of Fe, the ceramic particles are uniformly dispersed, and the sintering brings each particle tightly together. Since the particles are coupled to the energy beam, there is no scattering of particles even when irradiated with an energy beam. Furthermore, the vacancies in the sintered alloy are also released upon remelting, so there is no decrease in strength due to the presence of vacancies. In addition, since sintered alloys have excellent formability, wear-resistant parts can be completed by simply forming sintered alloys that fit into key points of the base material and remelting them, increasing productivity. In addition to being superior, sintered alloys can have a large wall thickness, and it is easy to obtain a thick layer of several millimeters.

The base material is selected from ordinary steel and cast iron, and steel is more preferably used. This is because graphite in cast iron causes the generation of gases such as Co ₂ when remelted, and in cast iron that contains large amounts of Mn and Si, these Mn and Si can cause embrittlement of the matrix in the bonding layer with the sintered alloy. This is because there is a possibility that it may occur. Regarding the steel base material, heat-resistant steel is used for valves and valve seats that require particular heat resistance, hardened steel is suitable for cylinder liners and cam followers that require strength, and piston rings that require corrosion resistance are used. In other cases, high Cr steel or stainless steel is suitable.

In addition, a heat-affected layer is formed in this base metal due to remelting, but this has a hardness higher than that of a normal quenched structure, and is similar to a remelted layer that has become relatively brittle due to remelting and rapid cooling. It has the effect of supporting the base materials, especially when the remelted layer is thin.

In this way, in the present invention, wear resistance is mainly achieved by the bearing effect of ceramic particles, so the amount of ceramic particles relative to the mating material is
A relative sliding member is achieved by selecting the size, and material selection is wide.

In the present invention, when the sintered alloy is remelted, if there are many pores in the sintered alloy, air bubbles will remain in the remelted alloy layer. It is desirable to do so. In particular, powder mixed with ceramic particles having a relatively large particle size as in the present invention has poor compressibility and is difficult to obtain a high-density sintered body, so it is necessary to remelt it in a vacuum or undergo a sealing process. It is desirable to do so.

Claims (1)

[Claims] 1. Ceramic powder is added to 5 to 10% of iron-based powder.
40% by volume is mixed, the mixed powder is compacted into a desired shape, and then sintered at the sintering temperature of iron-based powder to form a sintered alloy. The sintered alloy is placed on the surface of the material, and a high-density heat source is applied from the surface of the sintered alloy to heat it, remelting the sintered alloy and at the same time remelting a part of the base material. Therefore, a method for producing a wear-resistant member for an internal combustion engine is provided, which comprises obtaining a wear-resistant layer on the surface of a base material.