KR100701812B1 - Material for sliding parts having self-lubricity and wire material for piston ring - Google Patents

Abstract

The present invention is C 0.4% by mass or more, less than 1.5% by mass, Si 0.1-3.0% by mass, Mn 0.1-3.0% by mass, Cr 0-0.5% by mass, Ni 0.05-3.0% by mass, Al 0.3-2.0% by mass, Mo, Average particle diameter of graphite observed from the surface of the graphite, consisting of a steel containing 0.3 to 20% by mass and 0.05 to 3.0% by mass of Cu in a total amount (Mo + W + V) of at least one selected from the group consisting of W and V It relates to the material for sliding parts which is 3 micrometers or less. Such steel is used as a wire rod for piston rings. In such steels, preferably, the area ratio of graphite observed in the tissue surface is 1% or more, and the average particle diameter of graphite observed in the tissue surface is 3 µm or less. S may be 0.3% or less and Ca may be contained 0.01% or less, and nitriding treatment is preferably used.

Material for sliding parts, wire rod for piston ring, graphite distribution situation, nitriding treatment, forging ratio, parallelism.

Description

Material for sliding parts and piston ring wires {Material for sliding parts having self-lubricity and wire material for piston ring}             

The present invention is a conventional sliding bearing (rolling bearing), roller bearing (roller bearing), ball bearing (ball bearing), gears, molds, piston rings, cylinder liners and vanes (vain) mounted on an internal combustion engine, such as automobile engines, etc. It relates to a material used for such sliding parts.

Conventionally, materials having excellent wear resistance are used for sliding parts such as cylinder liners and vanes. Among these, the piston ring used for an internal combustion engine, especially an automobile engine, has shifted to what is called the steel piston ring used by processing a steel wire in a ring form from the conventional cast iron. That is, the strand obtained by performing hot processing such as forging and hot rolling on an ingot having a predetermined composition is further formed into a steel wire suitable for the cross-sectional shape of the piston ring by drawing or the like. Piston rings are generally manufactured by adjusting and bending them into a ring of constant curvature.

In this regard, at present, it is common that three top rings, a second ring and an oil ring are mounted on one piston on the combustion chamber side, but domestically, the top ring and the oil ring corresponding to the severe part are made of steel. High functionalization by is penetrating. Against this backdrop, the recent research results of post-internal combustion engines such as electric vehicles have become more visible, and efforts have been made to improve the internal combustion engines more. Since it has been found that a diesel vehicle having a higher internal pressure than a vehicle has a small environmental burden, there is a demand for an improvement in sliding performance that can cope with a more severe diesel engine.

In addition, in recent years, a scalpel is also applied to the internal phenomenon of the engine, and it is pointed out that the wear of the second ring, which is made of cast iron, is the most severe among the three rings. [Non-Patent Document 1; Hideki Saito and two others, "A Study on the Wear of Diesel Engines under Severe Driving Conditions," Japanese Society of Mechanical Engineers Kyushu Branch, 2011 Research Presentation Lecture (1999) (Internet <URL: http: //www.ns.kogakuin.ac .jp / ~ wwa1013 / EGR / nagasaki / nagasaki.html>].

Another reason for the transition to steelization is that the reduction of frictional force loss due to the thinning of the ring structure to cope with the improvement of the environmental performance of the engine, accompanied by the need to improve the mechanical strength or wear resistance The improvement is in the background. Also, from the viewpoint of technology transfer, ease of expansion, and surface treatment of the ring manufacturing process, environmental regulations for Cr plating, which is the mainstream in cast iron, are becoming more stringent. Can be mentioned.

In the steel piston ring, a method of imparting wear resistance and sintering resistance by applying a surface treatment such as nitriding treatment to a contact surface with a cylinder liner has been proposed [Patent Document 1; Japanese Laid-Open Patent Publication No. Hei 10-030726, a method of improving wear resistance without surface treatment is also proposed (Patent Document 2; Japanese Patent Publication No. 58-046542].

Although steel piston rings are overwhelmingly superior to cast iron rings in mechanical properties and wear resistance, they are inferior in tack resistance. In particular, steel piston rings are one of the reasons why steel is not advanced in the second ring. As described in Patent Literature 1, such a problem is a situation in which a surface treatment such as nitriding treatment is used on a contact surface with a cylinder liner, and the correspondence is advanced. However, room for improvement remains in view of the cost of surface treatment and the prevention of aluminum adhesion occurring on the contact surface with the piston.

In addition, there are also attempts to solve without surface treatment, and Patent Document 2 or the like proposes a Cr addition region of 10% or more mainly as a component design for increasing Cr-based carbide in steel, which is excellent in terms of performance and cost. do. However, although the wear resistance is remarkably improved by increasing the carbide, the effect of improving the quench resistance is marginal, and there is a fear of deterioration in manufacturability such as deterioration of machinability. For this reason, although surface treatment, such as PVD, is given, the cost increase cannot be avoided.

Moreover, even when using light oil as fuel or using gasoline, the amount of sulfur (S) contained may be large depending on the quality. When a fuel with a high S content is used, SO ₄ ^2- is generated by the sulfur (S) contained and the piston ring is exposed to a sulfuric acid dew point environment. Therefore, sulfuric acid corrosion resistance is also required, and strict characteristics not conventionally required from the viewpoint of corrosion resistance are also required.

In view of the above problems, the present invention is applied to a sliding part material having excellent abrasion resistance by improving quenching resistance and using a nitriding treatment, and excellent in sulfuric acid corrosion resistance and manufacturability in addition to sliding characteristics. It is an object to provide a wire rod for a piston ring having a low coefficient of friction.

The present inventors investigated and examined the sliding behavior of various applied sliding parts, especially the sliding part exposed to the sliding environment under fluid lubrication represented by the piston ring in detail. As a result, the present invention has been found by finding the most suitable morphology for improving the adhesion resistance and lowering of the friction coefficient, and also finding the component composition effective for achieving such a structure while considering sulfuric acid corrosion resistance.

Therefore, according to the first aspect of the present invention, C 0.4% by mass or more and less than 1.5% by mass, Si 0.1 to 3.0% by mass, Mn 0.1 to 3.0% by mass, Cr 0 to 0.5% by mass, Ni 0.05 to 3.0% by mass, Al 0.3 And at least one member selected from the group consisting of 2.0 to 2.0 mass%, Mo, W, and V, and a steel containing 0.3 to 20 mass% and 0.05 to 3.0 mass% of Cu in a total amount (Mo + W + V). The material for sliding parts which has self-lubricating property whose average particle diameter of graphite observed to is 3 micrometers or less is provided.

According to the suitable form of such a sliding part material, the area ratio which graphite observes in a tissue cross section occupies 1% or more, and the average particle diameter of graphite observed in a tissue surface is 3 micrometers or less. Moreover, it is preferable that V carbide is not observed in a tissue cross section.

Also preferably, at least one member selected from the group consisting of Mo and W is 0.3 to 5.0% in total and V is less than 0.1%. A suitable amount of Al is 0.7 to 2.0%. It is preferable that the said steel contains Mo 1.5-3.0% and Co 10% or less. Moreover, it is preferable that sulfur (S) and Ca amount of the said steel are 0.3% or less of S, 0.01% or less of Ca, and it is preferable to nitrate the said steel and to use it as a material for sliding parts.

According to the second aspect of the present invention, C 0.4% by mass or more and less than 1.5% by mass, Si 0.1 to 3.0% by mass, Mn 0.1 to 3.0% by mass, Cr 0 to 0.5% by mass, Ni 0.05 to 3.0% by mass, Al 0.3 to 2.0 At least one selected from the group consisting of% by mass, Mo, W, and V, including 0.3 to 20% by mass and 0.05 to 3.0% by mass of Cu in the total amount (Mo + W + V), and the average of the graphite observed in the structure There is provided a wire rod for a piston ring made of steel having a particle diameter of 3 mu m or less. In a piston ring made of such a wire rod, the parallel state where the distribution state of the sulfide inclusions observed in the tissue cross section parallel to the outer circumferential surface is formed by the straight lines passing over the maximum diameter of each sulfide inclusion. It is 30 degrees or less as a degree. Preferably, the area ratio of graphite observed in the structure cross section of the piston ring wire rod is 1% or more, and the average particle diameter of graphite observed in the structure surface is 3 μm or less.

The wire rod for the piston ring preferably contains 10% or less of Co, contains 0.3% or less of S, 0.01% or less of Ca, and is preferably subjected to nitriding treatment.

An important feature of the present invention is to realize a steel structure in which graphite is precipitated at a fine and appropriate ratio as a means most suitable for improving its wear resistance and lowering of the friction coefficient with respect to the sliding part represented by the piston ring. That is, the objective is to improve the durability performance by taking into consideration the specificity of the friction behavior between the piston ring / cylinder and supplementing it, and also in the case of a non-surface treatment material or a nitriding treatment material which is advantageous in terms of surface treatment cost. Sufficient effects are achieved with respect to the reduction of the sintering resistance and the friction coefficient, which are each insufficient as the technique.

In addition, in order to hold the graphite precipitated structure of the present invention as an industrial implementation means thereof, it is possible to finely precipitate graphite rapidly, and to find a component composition that is effective in improving workability and machinability. The addition of a single addition or a complex addition of sulfur (S) and Ca also has a great feature in that a further improvement of these effects can be achieved.

First, the graphite precipitation structure of this invention is demonstrated.

In sliding parts, the mainstream is a fluid lubrication design in which a fluid film, such as oil or water, is constantly formed between its typically severely rubbing machine elements. This fluid film formation utilizes the buoyancy generated in the fluid in relative motion like an airplane, and when the viscosity and the relative velocity of the fluid increase, the fluid film between the sliding parts becomes thicker. Protect the

However, in the internal combustion engine, since most engines are currently reciprocating, in the vicinity of the top and bottom dead centers, the relative speed becomes zero between the piston rings / cylinders, which tears the fluid membrane and causes wear and burning. Interfere with normal driving. In addition, since the aim of improving the performance of the piston ring is to increase the so-called oil scraping action that prevents oil from entering the combustion chamber, the maintenance of the fluid film is increasingly difficult.

Nevertheless, various fluid lubrication modes operate in such a sliding motion, and the present inventors have tried to solve the problem by reviewing and utilizing these modes. That is, there are three (1) wedge action, (2) stretching action, and (3) squeeze action in the fluid lubrication mode, and the squeeze action of (3) has a function that works even if the relative velocity becomes zero. In this regard, for example, a plate-like solid is caused to slide on a substrate while interposing a fluid. In this case, the pressure distribution generated on the surface of the plate opposed to the substrate has a boundary condition where the pressure is zero at the edge of the plate, and in order to maintain lubrication, that is, to generate a positive pressure distribution, the pressure distribution is It must be a convex function above and can be described under the following conditions.

In Equation 1 above,

P represents pressure,

x represents the sliding direction,

y represents the distance in the direction perpendicular to the sliding direction.

In addition, the Reinolds equation which is the basic equation of fluid lubrication is represented as follows.

In Equation 2 above,

ρ represents the density of the fluid,

h represents the thickness of the fluid film,

η represents the viscosity coefficient,

t represents time,

u represents the relative velocity.

Therefore, the requirements for generating a positive pressure in the fluid membrane by the equations (1) and (2) are expressed as follows.

Three terms occur in Equation 3, wherein the first and second terms include the relative speed u, and correspond to the wedge action and the elastic action described above. And the third term which does not contain u is the term which shows the squeeze action which remains in possibility of functioning even if the relative speed becomes 0 between piston rings / cylinders.

Explaining what physical meaning that such a third term becomes negative means that when the density of the fluid is constant, the film thickness of the fluid film is drastically reduced in time, and as a result, positive pressure is generated in the fluid film. In reality, in order to cause this phenomenon, it is necessary to squeeze the fluid film by rapidly applying a vertical load on the sliding plate to the substrate. As a result, the fluid membrane is squeezed out, but at the same time, a high positive pressure is generated so that the solids hardly come into contact with each other, that is, a squeeze action can be expected.

Here, the inventors have found that in order to amplify such an effect, it becomes even higher by forming a plurality of hole-like structures on its sliding surface. That is, if a large number of fine pores are provided on the sliding surface, even if the fluid film having a relative velocity of 0 is torn, the fluid in the pores will be squeezed out of the surface of the fluid quickly in the next time period. It is possible to obtain a squeeze action by reducing the large film thickness of the fluid. Thereby, seizure in the vicinity of the top and bottom dead center of the reciprocating motion can be suppressed, and the friction coefficient can be reduced.

The graphite precipitated structure of the present invention is determined by paying attention to such action and effect. That is, the graphite structure of the present invention first acts as a lubricating phase which itself has a solid lubricating action, and at the same time, it is the squeeze effect of improving oil film retention as pores when the graphite is dropped. This squeeze action is as described above that the oil film is stably formed against the pressure fluctuation, and the effect thereof is increased by arranging holes in the surface as the shape of the sliding surface. In order to achieve this effect, graphite precipitation is effective, and in addition to conventional sliding bearings, roller bearings and ball bearing members, as well as shim faces of piston rings, cylinder liners, valve lifters with large fluctuations in pressure, various cams, gears, The present invention is also effective for sliding parts that are difficult to form a continuous fluid lubricating film such as a mold member or a sliding bearing such as a cutting knife.

Moreover, the graphite precipitation structure of this invention is effective also in preventing the adhesion wear with the piston made of aluminum which has become a problem recently when applied to such a piston ring. That is, since aluminum hardly has a solid solution to carbon, adhesion reaction is suppressed.

As mentioned above, although the material for sliding parts of this invention disperse | distributes graphite to a tissue surface, it is important to make the average particle diameter of graphite observed here be 3 micrometers or less. This is because when the average particle diameter exceeds 3 µm, the graphite periphery breaks during the sliding thereof, and the fragments thereof may enter the sliding surface. Moreover, in order to acquire the effect by the graphite dispersion | distribution of this invention, it is preferable to make the area ratio which the graphite observed from a structure surface occupy 1% or more. For graphite having a relatively large particle diameter of 1 µm or more, it is more preferable that the average particle diameter thereof is 5 µm or less or less than 5% in the area ratio thereof.

Since the lubrication effect by the formation of pores causes a decrease in the fluid film by the above-mentioned action, and one loses the effect, it is not treated as a mainstream fluid lubrication design. However, especially in the reciprocating motion which is difficult to form a continuous fluid lubricating film such as an internal combustion engine, the means of the present invention are effective, for example, the upper and lower dead centers near the top and bottom dead center where the fluid film is broken due to the relative velocity approaching zero, Graphite precipitation is powerful in an environment that causes abnormal frictional behavior, such as between piston rings / cylinders, where the lubricating oil transitions into a lubricious environment.

It is important to implement a lubrication design that can maintain the fluid film only under conditions in which structural failure of the fluid film temporarily occurs, such as a piston ring or a cylinder liner. Nevertheless, since the possibility of solid contact is increased when the engine speed or the structure of the sliding parts are changed, such abnormal sliding parts can be applied to a wider sliding condition by applying a material that precipitates graphite with solid lubrication such as graphite steel. It becomes possible.

Hereinafter, the component composition of the steel which comprises the sliding component of this invention is demonstrated.

The graphite steel itself has been reported in the past, and these are alloys mainly containing Si and Ni, but require dozens of hours or more for the graphite precipitation treatment to maintain a temperature of 600 ° C or higher. Therefore, the present invention is characterized in that cementite is easily decomposed in order to complete the precipitation of graphite at several hours, and an appropriate amount of Al is added in addition to Ni.

In general, carbon in iron is preliminarily precipitated as graphite, and once precipitated as metastable cementite. For this reason, in graphite precipitation process, it is necessary to disintegrate cementite and change it into stable graphite. In conventional graphite steels, decomposition of cementite is less likely to proceed, requiring a very long time. Therefore, in the present invention, by suppressing an element that prevents the decomposition of cementite such as Cr, for the purpose of designing a component that is decomposed soon even if metastable cementite is precipitated, substantially no cementite is produced, and graphite is suddenly produced. It can be precipitated as.

In addition, Al has a high diffusion rate in iron, and the addition of Al increases the diffusion rate of the pores, thereby shortening the time for forming the aggregate of pores that become the precipitation place of the graphite. By using these two effects in combination, in the present invention, graphite precipitation can be performed in a short time. It is also easy to deposit graphite only on the surface by carburizing treatment or the like.

In addition, Al is an element having nitriding hardenability and is suitable for alloy design of nitride hardened steel. Similarly, although Cr is an element used as a nitride hardening element, Cr not only suppresses the formation of graphite, which is the underlying technology of the present invention, but also significantly reduces sulfuric acid corrosion resistance, and thus avoids its use. Therefore, Al used by this invention is an important containing element.

In addition, if a defect such as graphite, for example, having a particle diameter of 10 µm or more is present in the nitride layer, for example, when nitriding treatment is applied to graphite steel in the related art, a drawback that the nitride layer is weak is pointed out. There was a difficulty in precipitation. Therefore, in this invention, in order to hold | maintain also as this nitrided steel, effort was made also to refine | miniaturize the graphite which precipitates.

Regarding the miniaturization of such precipitated graphite, there are three methods of (1) miniaturization by work deformation, (2) addition of inclusions such as Al ₂ O ₃ , or (3) BN, TiC, etc. as precipitation nuclei. Can be mentioned. However, (1) has a process limitation, (2) has a difficulty in manufacturing a dispersion, and (3) has a difficulty in manufacturing a high C steel because it is an effect achieved by controlling a trace component. Regarding these, for example, Japanese Unexamined Patent Application Publication No. Hei 11-246940 discloses a method of dispersing TiC, and reference such as Takashi Iwamoto et al. 84 (1998) p. 57 discloses a method of depositing graphite using BN as a nucleus, but since they precipitate a second phase having a high diffusion rate at a high temperature of 1000 ° C. or higher, it is possible to maintain fine uniformity of graphite. It is difficult, and it is difficult to apply to high alloys with severe segregation of ingredients.

Accordingly, the present inventors have studied various things to achieve such a finer graphite, and found that the Cu-Al metal precipitated phase in the structure works effectively. This is a phenomenon in which the above-mentioned second phase acts as a nucleus of the precipitated graphite, but since such a Cu-Al phase is precipitated at a low temperature of 800 ° C. or lower, fine graphite structure can be stably and quickly formed. In the present invention, specifically, the addition of Cu and Al at a level at which embrittlement does not occur can form a graphite structure with little strength degradation and functioning as a lubricating phase. In addition, Cu contributes to the improvement of sulfuric acid corrosion resistance.

The lubrication technique by dispersion of graphite is conventionally proposed in the field of cast iron, but since its use environment is severed every year for sliding parts in each field, the change is made from cast iron to the surface treatment material of steel. have. However, even so, for example, in the case of the cylinder block of an internal combustion engine, although most of it is aluminumized, the inner wall of the cylinder liner part still uses the cast iron which crystallized graphite for the said effect. to be. The sliding part of the present invention is intended to be established as a steel material including the characteristics of cast iron in order to combine not only the sliding characteristics but also the strength, abrasion resistance, and sulfuric acid corrosion resistance required by harsh environment. It is characterized by the alloy design. Hereinafter, the component composition will be described.

C is an important element in which part is dissolved in the matrix to give strength, part forms carbide, and the remainder forms graphite to increase wear resistance and quench resistance. This requires at least 0.4%. However, when it becomes 1.5% or more, melting | fusing point will fall and it becomes difficult to homogenize the structure by the diffusion annealing process for solidification segregation removal which heats an ingot for about several ten hours at 1200 degreeC. Therefore, C is made into 0.4% or more and less than 1.5%. Preferably it is 0.5% or more and less than 1.3%.

Although Si is normally added as a deoxidizer, since it is added here as an acceleration | stimulation element of graphite precipitation, since it also has the effect of improving sulfuric acid corrosion resistance, 0.1% was made into a minimum. On the other hand, it also influences the tempering softening behavior of the steel, and particularly, the influence of Si is important in low alloy steels. In order to prevent tempering softening and to increase the heat resistance, the amount of Si is preferably 1.0% or more. However, since the A ₁ point increase if excessively added, the upper limit of Si is defined as 3.0%. Therefore, Si is made into 0.1 to 3.0%. Preferably it is 0.5 to 3.0%, More preferably, it is 1.0 to 3.0%.

Mn, like Si, is used as a deoxidizer, and at least 0.1% is required, but excessive addition damages the precipitation of graphite. For this reason, the upper limit was set at 3.0%. Therefore, Mn is made into 0.1 to 3.0%.

Cr is an effective nitriding hardening element, but it is necessary to regulate it to 0.5% or less because it is an element that suppresses the decomposition of metastable cementite, strongly inhibits precipitation of graphite, and significantly reduces sulfuric acid corrosion resistance. . Therefore, in this invention, it is 0 to 0.5%, Preferably you may be 0 to 0.3%.

Ni is an element which promotes the formation of graphite and is also an element that is beneficial in suppressing the red brittleness of Cu-added steel, but on the other hand, Ni is an element that suppresses the workability in the annealing state because it increases the solid solution of C in Fe. . Therefore, it was made into 0.05 to 3.0%. Preferably, it is 0.6 to 1.5%.

Al is an element that raises the nitride hardness like Cr, but in the present invention, Al is added to secure the nitride hardness as much as Cr is not increased. In addition, it is characterized by the fact that it is a graphite-forming element, an element which helps to diffuse pores, and also becomes a nucleus of graphite precipitation as Cu-Al phase together with Cu, and is effective in causing rapid and fine precipitation. It is necessary to add more than%. Here, Al also raises the A ₁ point like Si, so it is defined as 2.0% or less. Therefore, in the present invention, it is limited to the addition range of 0.3 to 2.0%. Preferably it is 0.7-2.0%.

Mo is a carbide forming element which does not inhibit graphitization as compared with Cr, or is an element that imparts heat resistance. Carbide restrains a matrix in the thermoforming process performed after a bending process in a piston ring manufacturing process, for example, and functions to improve dimensional stability. However, excessive Mo addition, like Cr, inhibits the decomposition of cementite.

Even so, Mo has little influence of the above suppression, on the other hand, greatly contributes to the improvement of heat resistance, and contributes to the dimensional stability during heat treatment. In particular, in the manufacturing process of the piston ring, since the heat treatment step is applied in a thin wire state, the importance of such characteristics is high, and since it is effective in suppressing the nonuniformity of the globules, it is added at least 0.3%. On the other hand, since the precipitation of graphite is suppressed as the amount thereof increases, the upper limit thereof is made 20%. Here, since V and W have the same effect as Mo, in the present invention, one or more selected from the group consisting of Mo, W and V can be 0.3 to 20% in total amount.

However, even when V is added, it is preferable that V carbide is not observed from the surface of the structure because graphite precipitation is significantly suppressed when V carbide is generated. Or it is preferable that (Mo + W) by the complex or single addition of Mo and W is 0.3 to 5.0%, and V is less than 0.1%. In addition, Mo promotes the squeeze action of graphite and helps to form a fluid film under high pressure, thereby increasing the quench resistance and reducing the dynamic friction coefficient. Moreover, since the effect also improves sulfuric acid corrosion resistance, it is preferable that Mo addition amount is 1.5 to 3.0%.

Cu is an important element in the present invention together with Al because it is effective in depositing a metal phase of Cu—Al and forming a fine graphite structure stably and quickly. It also has the effect of improving sulfuric acid corrosion resistance. Therefore, mutual content adjustments relating to the amount of Al are required, and in order to obtain such an effect, it is necessary to add 0.05% or more, preferably 0.2% or more. On the other hand, when Cu is added excessively, the hardness at the time of annealing becomes high, and since workability is suppressed, it is necessary to be 3.0% or less. Therefore, in the present invention, the composition range is 0.05 to 3.0%, preferably 0.2 to 3.0%.

In addition, as a technique for improving lubricity, in the case of an internal combustion engine, sulfur (S) is conventionally known as a technique for organicizing and being added as an extreme pressure additive in engine oil to prevent seizure. On the other hand, the present inventors present sulfides (sulfides) such as MnS in steel, thereby forming an in-situ sulfide film on the new surface formed by the frictional heat generation of the sulfur (S) in the friction surface, which improves the lubricating performance. We found that it worked. According to this means, since the lubricating material is interspersed in the material, it is not necessary to add a large amount of lubricating material in order to improve the lubrication performance necessary locally, and since the efficacy is not lost during oil change like the extreme pressure additive, It can be expected to function semi-permanently.

In addition, the conventional means for increasing the Cr-based carbide in steel with respect to the piston ring, in other words, has a small contact area with the cylinder liner, increases the wear resistance at the piston ring side with high sliding energy per unit area, and balances the cylinder liner. The purpose is to take. Thereby, although sintering resistance becomes high, it is an object to promote abrasion on the cylinder liner side by the situation which arises by the nonuniformity of a contact essentially, and to increase a contact area and to avoid abnormal raise of local pressure. In short, it is a technique for improving the initial fusion of the piston ring, and has a small function as a wear characteristic requiring durability such as adhesion wear.

Moreover, excessive abrasion resistance may cause an attack on the cylinder liner side, and if it proceeds to an extreme, it may increase the blowby rate associated with the exhaust gas amount by increasing the clearance, but sulfur Since the effect of (S) improves the wear resistance by lowering the friction coefficient without promoting wear of the material, the effect of sustaining a situation where the change in clearance is small even when the engine is running is high.

Therefore, in the sliding part material of this invention, sinter resistance can further be improved by adding an appropriate amount of sulfur (S). In other words, sulfur (S) is mostly associated with Mn to form MnS, which acts on a lubricant such as engine oil to exert a lubricating effect, thereby lowering the coefficient of friction and improving the wear resistance.

Here, sintering is a phenomenon in which the friction surfaces are fixed because the temperature of the friction surfaces rises by frictional heating and the movement of atoms between the friction surface materials is caused by thermal vibration, and the friction surface temperature is the friction energy (= friction coefficient × surface pressure × Of the sliding speed). For this reason, when a friction coefficient decreases, it will become difficult to raise a temperature and sinter resistance will improve. The content of sulfur (S) is effective in order to obtain such an effect, but if it is excessively added, the mechanical properties deteriorate. For example, since the breakage is feared in the drawing process of steel wire for a piston ring made of steel, the upper limit is 0.3. It is preferable to set it as%. The content is preferably 0.01 to 0.3%, more preferably 0.03 to 0.3%.

In addition, the inventors of the present invention also found that it is preferable to increase the forging ratio performed in the manufacturing process in terms of mechanical properties in order to obtain a material containing sulfur (S) up to 0.3%. In other words, it is effective for improving the mechanical properties as a sliding part, and especially in steel piston rings obtained by bending steel wires, it is also an effective means for suppressing breakage and damage in the bending process.

In addition, the forging ratio in this case is defined as the reduction rate to the piston ring product starting from the ingot in the piston ring manufacturing step. In other words, the cross section perpendicular to the direction in which the steel is cut and extended, that is, the ingot cross-sectional area before forging and / or the cross-sectional area of the product after bending, as compared with the small ball surface in the final piston ring product. . However, the reduction rate from the steel wire by the bending process to the piston ring product is negligible in achieving the effect of the present invention, and can be evaluated by (ingot cross-sectional area before forging) / (steel wire cross-section before bending (after post-stretch)). have. The higher the number of such forging ratios, the more forging is being performed.

In steels containing sulfides such as MnS, in the casting state of the starting structure, many spherical or fusiform sulfides exist at the grain boundary triple point of the solidified cell structure, and the orientation thereof is a random structure, but forging is performed. As the ratio increases, the orientation of the sulfide changes, improving the mechanical properties.

By increasing the forging ratio, the orientation of the sulfide in the longitudinal direction of the steel wire is increased, that is, since the sulfide is elongated in a form corresponding to the circumferential stress mainly acting on the piston ring, the deterioration of mechanical properties is virtually eliminated. This effect is particularly pronounced with respect to elongated sulfides, i.e. sulfides having an aspect ratio (maximum diameter / minimum diameter) of 3 or more, that is to say, in particular, if the orientation of sulfides having an aspect ratio of 3 or more is poor in the main direction, due to deterioration of mechanical properties. It leads.

Specifically, the distribution state of the sulfide inclusions, particularly the sulfide inclusions having an aspect ratio of 3 or more, observed on a surface parallel to the outer circumferential surface of the piston ring is a straight line passing over the maximum diameter of each sulfide inclusion. By setting it as 30 degrees or less by the parallel degree (an angle of an acute angle) to achieve, it can be made into the material for sliding components especially effective as a wire rod for piston rings, For example, it is preferable to achieve such a forging ratio 500 or more. .

Fig. 5 shows a sketch of the microstructure of a steel microscope subjected to forging ratio 1 (as-cast state) and 500 forging at a magnification of 400 times in a non-corrosive (corrosion-free) state, and the sulfide inclusions at this time. The schematic diagram which carried out the parallelism measurement is shown. Two arbitrary sulfide inclusions having an aspect ratio of 3 or more are selected, and the angles of the acute angles formed by the straight lines A and B passing through their respective maximum diameters are measured, and all of them are measured within the observation field of view. This measurement is measured over at least 10 fields of view, and the maximum of these angles is defined as parallelism. When there is no intersection in the visual field (for example, FIG. 5-forging ratio 500), the A 'line parallel to the A line may be measured as the auxiliary line. In addition, the definition which considers one sulfide inclusion as one is made into what seems to be connected by 400 times optical microscope observation, and uses the straight line which passes through the maximum diameter as a measuring line.

In Fig. 5, it is understood that the forging ratio 1 is 1, but there are sulfide-based inclusions having a relationship of more than 30 degrees, but the forging ratio 500 is all 30 degrees or less. Specifically, the number 30 ° is a fracture mechanics number. 6 shows G. R. Irwin, Analysis of Stresses and Strains Near the End of a Crack Transversing a Plate, Trans. ASME, Ser. E, J. Appl. Mech., Vol. 24, No. 3 (1957), pp. It is a figure which shows how the change of a stress intensity | strength coefficient appears when an angle generate | occur | produces in a stress direction and a crack propagation direction computed analytically in [361-364], and is represented by Formula (4).

In Equation 4 above,

K _I is the stress intensity factor that becomes the driving force for crack propagation,

β is the angle between the stress direction and the crack direction,

σ is the stress,

π is the circumference

a is the crack length.

Cracks tend to progress when present in the direction perpendicular to the stress (β = 90 °), and when cracks exist along the stress direction (β = 0 °), the cracks do not progress and cracks tend to progress (i.e., Sudden increase in stress intensity factor is greater than 30 °. Considering that inclusions can be regarded as cracks because of lack of mechanical bonding, it can be seen that it is important to control the nonuniformity of orientation of inclusion distributions to 30 ° or less. And it turns out that it is important to have this orientation regarding the elongated inclusions.

Since sulfur (S) is a representative element that degrades the mechanical properties of steel, it is preferable to carry out its strength measures as a piston ring made of steel. For example, Japanese Patent Laid-Open Publication No. 07-258792, which is capable of adding 1% of sulfur (S), also targets cylinder liners that cannot be sufficiently forged. Is targeted at cast steel. In reality, it is the plastic working techniques such as drawing, rolling, and bending that are cost-effective to make the piston ring still. In other words, when using this process to finish steel containing 1% sulfur (S) with a wire for piston rings, there may be a breakage in the drawing process because the material strength required for its plastic working is insufficient. It is hard to reach completion as a piston ring made of steel certainly.

As described above, in the present invention, in order to further improve its quench resistance, it is preferable to use a material for sliding parts containing 0.3% or less of sulfur (S), and in particular, a material for sliding parts having a very high forging ratio. It is an effective means for the wire rod for the piston ring to be established as.

In order to further enhance the effect of S, it is effective to add Ca together with sulfur (S). Since Ca is inherent in MnS, it tends to flow out to a sintered surface. Moreover, since there is a strong reducing effect, the lubricity is improved in that oxide formation on the sintered surface is prevented and sulfide is facilitated. However, when Ca is excessively added, the hot workability is impaired, so 0.01% or less is preferable. It is preferably 0.0001% to 0.01%, more preferably 0.0005% to 0.01% to obtain the above effect.

Moreover, addition of S and Ca is effective also in the improvement of cutting property and grinding property besides ignition resistance. In particular, since the dispersion of MnS and the precipitation of graphite improve the machinability of the steel, the piston ring having an improved oil scraping function is particularly improved in that the formation of a corner portion having a small radius of curvature, which is difficult to form during grinding, can be easily performed by cutting. Makes the production easier.

In addition, the material for sliding parts and the wire for piston rings of the present invention may also contain Co for the effect of improving corrosion resistance, particularly sulfuric acid corrosion resistance. Or like Mo, it has the effect of promoting the squeeze action by graphite, assisting in the formation of a fluid film under high pressure, increasing adhesion resistance, and lowering the coefficient of kinetic friction. In this case, although it is preferably 0.5% or more, on the other hand, it is preferable to set it to 10% or less since it is not only an expensive element but further effects are not seen even if it is added excessively. More preferably, it is 2 to 5%.

The steel constituting the sliding part material and the piston ring wire of the present invention can be, for example, a steel whose balance is substantially Fe after satisfying the content of each element type described above. The element species of may be, for example, 10% or less in total or 5% or less in total. Regarding this, it is possible to apply one made of steel of residual Fe and unavoidable impurities.

The following elements may be included in the steel of the present invention as long as they are within the following ranges, and are preferred ranges.

P≤0.1%, Mg≤0.01%, B≤0.01%, Zr≤0.1%

Moreover, as preferable conditions of this invention, when the area ratio of the nonmetallic inclusion in a structure surface shall be 2.0% or less, it will prevent fracture | rupture at the time of the drawing process processed with steel wires, and the formation of the break | wound at the time of forming the said wire rod in coil form. Effective in It is especially preferable as a range which is effective for manufacture of the piston ring accompanying manufacture and processing of a thin wire material, and a manufacture with high operation rate is possible.

The nitriding treatment is an effect added to the present invention, and is effective in improving better adhesion resistance and wear resistance. However, in the present invention, excellent adhesion resistance is achieved with or without surface treatment. You may combine other surface treatment. In addition, taking the piston ring as an example, such surface treatment is performed on the contact surface between the piston ring / cylinder liner, which is a conventional main sliding surface, and cannot be prevented from adhering wear because it is not performed on the friction surface with the piston. However, the material of the present invention exhibits sufficient adhesion resistance even without surface treatment, and also suppresses the adhesion reaction, making the material particularly effective for piston rings.

In addition, since the graphite phase is present in the material of the present invention, for example, a so-called intercalation process in which a separate molecule or ion is inserted between molecular layers of the layered molecular structure of graphite by being immersed in a CuCl ₂ solution. It can be carried out, it is possible to further improve the sliding characteristics. In addition, since the graphite after the insertion treatment may also be a polymer polymerization catalyst, the lubrication treatment by the polymer coating (polymer coating treatment) is carried out, or only the insertion treatment is performed in advance so that the lubricating oil can be easily polymerized. It can be made into a sliding part that maintains the state of self-lubrication by causing.

BRIEF DESCRIPTION OF THE DRAWINGS It is a micro structure | tissue photograph which shows the distribution situation of the graphite observed in the structure cross section of the material (sample No. 3) of the example of this invention.

FIG. 2 is a microstructure photograph showing the distribution of graphite observed in the tissue cross section (separate field of view) of the same material as that shown in FIG.

3 is a microstructure photograph showing a distribution state of graphite observed in a tissue cross section of a material (Sample No. 14) of a comparative example.

FIG. 4 is a microstructure photograph showing the distribution of graphite observed in the tissue cross section (separate field of view) of the same material as that shown in FIG.

5 is a schematic view and a schematic view of a microstructure photograph illustrating a parallel view of sulfide inclusions.

It is a figure explaining the influence of the angle which a stress direction and a crack propagation direction make on a stress expansion coefficient.

It is a schematic diagram explaining the ultrahigh pressure friction wear test method.

It is a schematic diagram explaining the reciprocating wear test method.

FIG. 9 is a Stribeck diagram showing the relationship between the inverse of the load and the dynamic friction coefficient, and illustrates the lubrication state.

Hereinafter, the effect of this invention is demonstrated by a specific example.

Example 1

By high frequency induction melting in the air, ingots (cross-sectional dimensions 220 mm x 220 mm) of each sample were adjusted to the compositions of the balance Fe and inevitable impurities shown in Table 1. Sample Nos. 1 to 6 are examples satisfying the present invention, and Sample Nos. 16 is a comparative example. In addition, sample No. 16 is JIS-SUS440B equivalent material, and is a piston ring material currently used.

First, this ingot was subjected to hot working to obtain a linear material having a cross-sectional dimension of 9 mm x 9 mm (forging ratio: about 598). In addition, although sample No. 13 can be cast, a test piece could not be produced because the steel material was destroyed in a subsequent hot working step.

Subsequently, predetermined annealing treatment and tempering treatment were performed after the annealing treatment, and the hardness was adjusted to about 45 HRC. And the surface of the structure of the linear raw material after such hard film processing and tempering was observed in the non-corrosive state, and the distribution situation (average particle diameter, the area ratio which occupies for a structure) of graphite was investigated. The distribution status was investigated using image analysis from an image of 10 fields observed with a 1000 times optical microscope. In addition, the diameter of the circle | round | yen used the diameter of the round shape used as the area of the measured graphite. In the distribution of graphite of steel Nos. 1 to 6 of the present invention, the average particle diameter thereof was about 0.3 to 2 µm, and the area ratio was about 0.5 to 5%.

1 to 4 are micrographs showing the distribution of graphite in samples No. 3 and No. 14. Fine graphite precipitates in the matrix structure of Sample No. 3, but the graphite of Sample No. 14 has large particles. This is a fine graphite distribution because a fine Cu-Al phase is precipitated prior to graphite precipitation and graphite is precipitated in the case of containing a proper amount of Cu and Al, but if Cu or Al is insufficient, its mechanism does not work. Because of this, graphite is precipitated into large particles. Other samples are also included and Table 2 shows the distribution of graphite. No graphite was observed in the structures of samples No. 11, No. 12, No. 15, and No. 16.

This sample was subjected to ion nitriding treatment under a condition of 530 ° C for 5 hours at H ₂ : N ₂ = 1: 1 to obtain an evaluation sample for tack resistance and wear resistance. The test method according to the evaluation of ignition resistance was performed under the following conditions using the ultrahigh-pressure friction wear tester shown in FIG. 7, and the sintering start was carried out at the time when the rotational torque of the counterpart rose sharply and scuffing the load at this time It evaluated as a scuffing load. In addition, the dynamic friction coefficient was calculated from the rotational torque of the counterpart when the load was 10 MPa. In Fig. 7, reference numeral 1 represents a sample, 2 represents a counterpart, and F represents a load.

Sliding surface shape; 5mm × 5mm square

Frictional speed; 2 m / s

Friction surface pressure; Initial pressure 1.5MPa,

             0.5 MPa every minute

lubricant; Motor oil # 30

        Dropwise at initial pressure (10 cm3 / min), then stop supply

Counterpart; JIS FC250 (Rat Cast Iron) (Hardness: 10HRB)

Abrasion resistance was evaluated by a reciprocating wear test. This is to measure a wear width at this time by rubbing a separately prepared test piece having a diameter of 8 mm and a length of 20 mm with a counterpart material (FC250) having a diameter of 20 mm by reciprocating motion. A schematic diagram of the test method is shown in FIG. 8, and other test conditions are described below. Shown in In FIG. 8, the code | symbol 1 represents a sample, 2 represents a counterpart, F represents a load, and OIL represents lubricating oil, respectively.

Compressive load; 500N

Sliding distance per stroke; 130 mm

Maximum sliding speed; 0.5 m / s

Lubricating oil (supplied by dropwise addition); Motor oil # 30                 

Counterpart; JIS FC250 (Rat Cast Iron) (Hardness: 10OHRB)

The measurement results of the scuffing load, dynamic friction coefficient, and wear width are described in Table 2 together with the nitride hardness.

Sample number Graphite distribution situation Presence of V carbide Nitriding Hardness (HV) Scuffing Load (MPa) Dynamic friction coefficient Wear width (mm) Remarks Average particle diameter (μm) Area rate (%) One 0.4 0.8 none 853 12.5 0.11 0.55 The present invention 2 0.5 0.9 has exist 890 11.5 0.12 0.65 The present invention 3 0.8 3.5 none 930 10.5 0.07 0.5 The present invention 4 0.7 2.6 none 910 13.5 0.08 0.55 The present invention 5 1.9 4.1 none 950 10.5 0.07 0.51 The present invention 6 0.7 1.9 none 895 12.6 0.06 0.51 The present invention 11 Not observed 0 none 445 6.5 Not measurable 1.53 Comparative example 12 Not observed 0 none 773 7.0 Not measurable 0.71 Comparative example 14 6.2 5.8 none 723 6.0 Not measurable 0.64 Comparative example 15 Not observed 0 none 563 7.0 Not measurable 1.62 Comparative example 16 Not observed 0 none 1032 7.5 Not measurable 0.53 Comparative example

From Table 2, all of the samples No. 1 to No. 6 which satisfy the present invention have a high scuffing load and a narrow wear width, and thus are excellent in wear resistance and wear resistance. Further, Samples No. 3 to No. 6 had low values of dynamic friction coefficient and exhibited extremely excellent characteristics as sliding members. On the other hand, all the comparative samples which do not satisfy the graphite distribution of this invention are inferior in tack resistance. The lack of wear resistance of samples No. 11 and No. 15 is due to the low content of either Cr or Al, which is an element having nitride hardening ability, and low nitride hardness.

Moreover, about the sample produced in Example 1, the ignition test was performed on the same conditions, without performing the nitriding process. The results are shown in Table 3. The adhesion resistance of samples No. 1 to No. 6 satisfying the graphite distribution of the present invention is exhibited regardless of the presence or absence of surface treatment, and even if graphite is present, the scuffing load of comparative sample No. 14 having large particles is low. . As a result of observing the dynamic friction surface after the test of the sample No. 14, it is considered that the graphite peripheral portion is damaged, and such debris enters the friction surface and the sliding characteristics deteriorate.

Sample number Graphite distribution situation Scuffing Load (MPa) Remarks Average particle diameter (μm) Area rate (%) One 0.4 0.8 11.5 The present invention 2 0.5 0.9 10.5 The present invention 3 0.8 3.5 11.0 The present invention 4 0.7 2.6 13.0 The present invention 5 1.9 4.1 12.0 The present invention 6 0.7 1.9 11.5 The present invention 11 Not observed 0 6.5 Comparative example 14 6.2 5.8 6.0 Comparative example

Example 2

Sample No. 1 and Sample No. 15 according to the composition of Table 1 were hot rolled into a coil having a diameter of 5.5 mm, and then finished in a flat shape having a cross-sectional dimension of 1.5 mm x 3.1 mm by drawing-cold rolling. Sample No. 1 can be processed without a problem, but Sample No. 15 was broken in the drawing process due to poor cold workability. As a result of image analysis of the area ratio of nonmetallic inclusions in both tissue surfaces in a billet state before drawing, in a tissue surface perpendicular to the direction of drawing and rolling to be performed later, Sample No. 1 was 1.86% and Sample No. 15 is 2.23%, and the cause of breakage is that in addition to the high sulfur (S) content, the nonmetallic inclusions have an area ratio of more than 2.0%.

Example 3

Samples No. 1 to No. 6, No. 11, and No. 12 according to the composition of Table 1 were finished in a flat shape having a cross-sectional dimension of 1.5 mm x 3.1 mm in the step shown in Example 2, and the dura mater was treated at 1000 ° C. Tempering was carried out for 30 minutes so that the hardness was about 510 HV. Thereafter, the grinding wheel was cut 10 times at a rotational speed of 10, OOOrpm and at a feed rate of 1 mm / sec, and the burr occurrence frequency was examined. Table 4 lists the frequency of occurrence.

Sample number Burr Frequency Remarks One 0 The present invention 2 0 The present invention 3 0 The present invention 4 0 The present invention 5 0 The present invention 6 7 The present invention 11 8 Comparative example 12 10 Comparative example

Burr generation was confirmed in samples No. 11 and No. 12, but samples No. 1 to No. 5 to which sulfur (S) was added did not show burr generation, and sulfur (S) of the present invention was added. It can be seen that the effect on Gabor reduction is great. Thereby, especially the manufacturability in manufacture of a piston ring also improves.

Example 4

Using the ingot of the same composition as the sample No. 1 of Table 1 previously prepared separately, the wire rod of 3.0 mm x 3.0 mm of cross-sectional dimension was produced in the hot working process changed to forging ratio 1-10,000. And parallelizing the sulfide-based inclusions (aspect ratio ≥ 3) in the tissue surface parallel to the whole body and the length direction of the wire rod which becomes the outer circumferential surface when such a piston ring is made even by hardening and tempering of the film to 400HV. Was measured according to the above tips.

Then, a three-point bending test with a span of 30 mm was performed on the wire rod after such hardness adjustment, and the broken and broken ones were evaluated as A and B as being broken up to 10 mm in displacement. This is to determine whether or not moldability of the wire rod subjected to the dura mating treatment and tempering is possible when forming a piston ring having a predetermined curvature by a roller bending method. These results are shown in Table 5.

Sample number Forging Parallelism (°) Presence or failure 1-1 One 84.5 B 1-2 10 45.2 B 1-3 500 27.8 A 1-4 2000 11.5 A 1-5 10000 3.5 A

The high forging ratio and the parallelism of the sulfide inclusions are 30 ° or less, which is excellent in mechanical properties and effective in suppressing breakage that is a concern during bending from the wire rod to the ring shape. In addition, the parallelism or the aspect ratio of the sulfide-based inclusions observed in the tissue surface parallel to its outer circumferential surface when the wire rod having excellent bending workability was bent to form a piston ring was not substantially changed as in the wire rod.

The parallelism of the sulfide inclusions observed in such a wire state is also reflected in the piston ring state after the bending process. Also, regarding the lack of fatigue failure that is concerned when such a piston ring having a small cross-sectional area is mounted on an engine, the form of sulfide inclusions having a degree of parallelism of 30 ° or less is effective for improving mechanical properties, and is particularly preferable for wire rods for piston rings. Means.

Example 5

By high frequency induction melting in the air, ingots (section dimensions of 220 mm x 220 mm) of Nos. 21 to No. 23 satisfying the present invention adjusted to the composition of the balance Fe and inevitable impurities shown in Table 6 were obtained. Compared with sample No. 21, sample No. 22 contains much Mo, and sample No. 23 contains much Co.

Sample number Chemical composition (mass%) C Si Mn P S Ni Cr Mo Co Cu Al Fe 21 0.86 1.75 0.30 0.008 0.020 0.30 0.001 0.98 0.01 0.82 1.22 Residual amount 22 0.86 1.69 0.30 0.010 0.022 0.30 0.001 1.97 0.01 0.76 1.20 Residual amount 23 0.86 1.68 0.31 0.008 0.022 0.31 0.001 0.99 3.99 0.87 1.18 Residual amount

First, this ingot was subjected to hot working to obtain a linear material having a cross-sectional dimension of 9 mm x 9 mm (forging ratio: about 598). Subsequently, predetermined annealing treatment and tempering treatment were performed after the annealing treatment, and the hardness was adjusted to about 40 HRC. And the surface of the structure of the linear raw material after such a film | membrane process and tempering was observed in the non-corrosive state, and the distribution situation (average particle diameter, the area ratio which occupies for structure) of graphite was investigated. The distribution situation was investigated using image analysis from 10 images observed with the 1000-times optical microscope.

Sample number Average Particle Diameter of Graphite (μm) Area fraction of graphite in the whole tissue surface (%) Area percentage of graphite of 1 µm or more occupying the whole surface of the tissue Average Particle Diameter of Graphite of 1 µm or More (µm) 21 0.55 1.69 0.41 1.15 22 0.50 2.05 0.14 1.20 23 0.75 3.50 0.70 1.33

Graphite precipitation of all the samples No. 21-No. 23 was fine. Table 7 describes the distribution of graphite. The average particle diameter of graphite was 1 탆 or less, and the area ratio was 1 to 4%. In addition, the graphite with a comparatively large particle | grain of 1 micrometer or more is 1-1.5 micrometers in average particle diameter in all the samples, and it is less than 1% by area ratio. And in each sample, it turns out that the ratio of the area which the comparatively large particle | grains of 1 micrometer or more occupy for the whole graphite area is one quarter or less, and it turns out that fine graphite occupies most of the precipitated graphite.

And this sample was made into the evaluation test piece of the dynamic friction coefficient. The evaluation method of the dynamic friction coefficient is similarly performed using the ultra-high pressure friction wear tester shown in FIG. 7, except that the friction speed is different from that shown in FIG. Every time it increased by, it calculated from the torque and load which generate | occur | produce in a counterpart material. 9 shows the relationship between the inverse of the load and the dynamic friction coefficient.

Sliding surface shape; 5mm × 5mm square

Frictional speed; 1 m / sec friction surface pressure; Initial pressure 1.5MPa,

          0.5 MPa every minute

lubricant; Motor oil # 30

        Always dropwise at 10 cm3 / min

Counterpart; FC25O (JIS rat cast iron)

Fig. 9 is a curve referred to as a stribeck curve, in which the "load characteristics" indicating the load conditions applied to the friction sliding portion are shown on the horizontal axis, and the coefficient of friction is shown on the vertical axis. Thereby, a lubrication state can be known. In the case of this embodiment, at the point where the frictional velocity is constant at 1 m / sec, the horizontal axis can be expressed as the inverse of the load. In each curve of FIG. 9, the right side (low load side: the range shown by an arrow) is the area | region where the lubricating film is not broken but a fluid lubrication is performed, rather than the plot (extreme value) with the lowest friction coefficient, and the left side (high load side) A fluid film is torn and a region in which solid lubrication is mixed with fluid lubrication due to contact between solids. Therefore, as the plot (extreme value) with the lowest coefficient of friction shifts to the left side of the graph, it indicates that the fluid film can be lubricated without tearing even at a higher load.

From the result of FIG. 9, in the sample No. 22 which has more Mo content compared with the sample No. 21, the fluid film | membrane is hold | maintained also on the higher load side. And in sample No.23 with high Co content, it turns out that the fluid film is hold | maintained also at the higher load side. This indicates that Mo and Co have the squeeze action promoting effect described above.

In addition, the leftmost plot of each curve corresponds to the load at which the test was stopped because sintering occurred. In the samples No. 22 and No. 23, the above plot is shifted to the left side (high load side) by addition of Mo and Co, and it is observed that even in the quench resistance. The coefficient of dynamic friction is also lowered as a whole, and the addition of Mo and Co improves the favorable sliding characteristics due to graphite precipitation.

According to the present invention, it is possible to apply to various sliding parts by providing self-lubricating property in that it is excellent in wear resistance even without surface treatment, and has a low coefficient of friction and low energy loss due to friction. In addition, the shape adjustment of such sulfide inclusions is also carried out, which is particularly effective as a piston ring, reduces the aggression of the cylinder liner and the piston, and contributes greatly to the improvement of the environmental performance and durability of the internal combustion engine. In addition, it is excellent in machinability such as machinability in the manufacturing process, and can reduce manufacturing cost and lead time, making it an excellent sliding part material for both performance and manufacturing. It is a good technique.

The material of the present invention is used in sliding parts such as piston rings, cylinder liners and vanes mounted on internal combustion engines such as sliding bearings, roller bearings, ball bearings, gears, molds, automobile engines and the like.

Claims (16)

C 0.4 mass% or more and less than 1.5 mass%, Si 0.1-3.0 mass%, Mn 0.1-3.0 mass%, Cr 0-0.5 mass%, Ni 0.05-3.0 mass%, Al 0.3-2.0 mass%, Mo, W, and V At least one member selected from the group consisting of steel containing 0.3 to 20% by mass and 0.05 to 3.0% by mass of Cu in a total amount (Mo + W + V), and the average particle of graphite observed in the structure A material for self-lubricating sliding parts having a diameter of 3 µm or less. The material for self-lubricating sliding parts according to claim 1, wherein the area ratio of graphite observed in the tissue surface is 1% or more and less than 5%, and the average particle diameter of graphite observed in the tissue surface is 3 µm or less. The material for self-lubricating sliding parts according to claim 1 or 2, wherein V carbide is not observed in the tissue surface. The sliding component for self-lubricating component according to claim 1 or 2, wherein at least one member selected from the group consisting of Mo and W is 0.3 to 5.0 mass% in total amount (Mo + W), and V is less than 0.1 mass%. material. The material for self-lubricating sliding parts of Claim 1 or 2 which consists of steel which contains 0.7-2.0 mass% of Al. The material for self-lubricating sliding parts of Claim 1 or 2 which consists of steel containing 1.5-3.0 mass% of Mo. The material for self-lubricating sliding parts of Claim 1 which consists of steel containing 10 mass% or less of Co. The material for self-lubricating sliding parts of Claim 1 or 7 which consists of steel containing 0.3 mass% or less of S. The material for self-lubricating sliding parts of Claim 8 which consists of steel containing Ca 0.01 mass% or less. The material for self-lubricating sliding parts as described in any one of Claims 1, 2, and 7 used by performing nitriding treatment. C 0.4 mass% or more and less than 1.5 mass%, Si 0.1-3.0 mass%, Mn 0.1-3.0 mass%, Cr 0-0.5 mass%, Ni 0.05-3.0 mass%, Al 0.3-2.0 mass%, Mo, W, and V At least one selected from the group consisting of a steel containing 0.3 to 20% by mass and 0.05 to 3.0% by mass of Cu in a total amount (Mo + W + V), the average particle diameter of graphite observed in the tissue surface is 3 As a wire rod for a piston ring of not more than μm, The parallelism of the distribution of sulfide inclusions observed on the outer peripheral surface of the piston ring with the tissue surface parallel to the straight lines passing over the maximum diameter of each sulfide inclusion. A wire rod for piston rings that is 30 ° or less as a working angle. The wire rod for piston rings according to claim 11, wherein an area ratio of graphite observed in the tissue surface is 1% or more and less than 5%, and an average particle diameter of graphite observed in the tissue surface is 3 µm or less. Wire rod for piston rings of Claim 11 which consists of steel containing 10 mass% or less of Co. The piston rod wire rod according to claim 11 or 13, which is made of a steel containing S at most 0.3 mass%. The wire rod for piston rings according to claim 14, which is made of steel containing Ca at 0.01 mass% or less. The wire rod for piston rings according to any one of claims 11 to 13, which is subjected to nitriding treatment.

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