JP4953377B2 - Cast iron containing A-type graphite, casting method of cast iron containing A-type graphite, and cylinder liner using the cast iron containing A-type graphite - Google Patents

Description

  The present invention relates to a cast iron containing A-type graphite, a casting method for cast iron containing the A-type graphite, and a cylinder liner using the cast iron containing the A-type graphite.

  Cast iron has historically been known as an iron alloy that basically contains carbon, silicon, manganese, phosphorus, and sulfur components. And cast iron is classified into flake graphite cast iron (gray cast iron), spheroidal graphite cast iron, etc. according to the presence state of carbon in the structure, and has been used properly according to the use.

  In particular, flake graphite cast iron has been used to form a cylinder liner of an internal combustion engine typified by an automobile engine because of its excellent balance between strength and vibration damping characteristics. The cylinder liner is provided on the inner peripheral wall surface of the cylinder of the internal combustion engine. The cylinder liner is required to be in sliding contact with the piston and the piston ring and maintain a certain airtightness. Therefore, the surface finish accuracy of a cylinder liner is important in addition to various properties such as strength, wear resistance, and seizure resistance in a high-temperature environment formed by continuous vaporization and explosion of fuel such as gasoline. Become.

  As cast iron considering wear resistance and seizure resistance in a high temperature environment, special cast iron having A-type graphite in the structure and containing Cr, B, P, etc. as wear resistance improving elements is generally used. In Patent Document 1, the chemical composition is expressed by weight%, C: 3.3 to 3.7%, Si: 1.8 to 2.4%, and Mn: 0.5 to 1.0. %, P: 0.1 to 0.4%, Cr: 0.15 to 0.5%, Cu: 0.4 to 1.0%, Mo: 0.2 to 0.8%, B: 0.0. There is disclosed a cast iron composition of 02-0.06% and the balance substantially consisting of Fe.

  For example, the surface finishing accuracy should be considered that the cutting performance is determined by the cast iron structure in consideration of performing grinding or honing as a processing method. If the cutting performance is inferior, the surface to be processed is formed rough. This cast iron structure can be different depending on the casting method. For example, as cast iron casting methods for cylinder liners, gravity casting methods using sand molds and centrifugal casting methods using molds tend to be frequently used, and it is important to select a casting method according to the selected cast iron composition It becomes. It should be noted that it is natural that the roughness of the surface to be processed is greatly affected by the grinding conditions or the honing conditions.

  And most of the cast iron materials conventionally used as a cylinder liner are manufactured by the centrifugal casting method. As a result, compared to the gravity casting method, the distance between graphite is shortened because carbon is thin and dispersed as a number of flake graphite in the crystal structure, and the frequency of missing graphite phases increases during grinding or honing. The tendency of the inner peripheral surface of the cylinder liner after processing to become rough was remarkable. Although this casting method is referred to in Patent Document 2, it is a problem to be considered according to the cast iron composition, and is a factor that needs to be examined according to the adopted cast iron composition.

  Therefore, in order to solve the above-mentioned problems that have existed in the past, the inventors of the present invention, as disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 9-209072), have a chemical composition of wt% and C: 2.9-3. 5%, Si: 2.0 to 2.5%, Mn: 0.5 to 1.0%, P: 0.1 to 0.3%, S: 0.01 to 0.13%, Cu: 0 0.3 to 0.6%, Cr: 0.1 to 0.3%, the balance is made of Fe and inevitable impurities, the microstructure is the area ratio, the ferrite phase is 3% or less, and the steadite phase is 1 % Of pearlite base containing 10 to 18% of graphite phase, and providing a wear-resistant cast iron characterized in that the base hardness is HV330 or higher, satisfying the characteristics as a sliding member, and processed surface Has been made smoother than before. That is, by defining the cast iron structure and the base hardness within a predetermined range, the sliding member satisfies the characteristics such as wear resistance and strength, and improves the processing performance when the honing is performed. Remarkable effects have been demonstrated by reducing the surface roughness.

JP-A-6-49583 Japanese Patent Publication No. 58-36664 Japanese Patent Laid-Open No. 9-209072

  However, it is also true that there is a certain quality variation in general industrial products that exist in the world. That is, while pursuing industrial productivity with cast iron having the composition disclosed in Patent Document 3, the cast iron obtained may be greatly affected by fluctuations in the composition of the molten metal and the casting conditions during casting. When the structure is viewed by area ratio, it cannot be a pearlite base containing 3% or less of the ferrite phase, 1% or more of the steadite phase, and 10 to 18% of the graphite phase, and as a result, good processing performance may not be obtained. It was.

  From the above, the present inventors have superior cutting performance (hereinafter including honing performance and grinding performance) compared with the cast iron material disclosed in Patent Document 3, and higher yield. It is an object of the present invention to provide a cast iron material that is particularly suitable for cylinder liner applications.

  Thus, as a result of intensive studies, the present inventors have come up with the idea that the above problem can be solved by adopting cast iron having the composition shown below.

Cast iron containing A-type graphite according to the present invention: A cast iron containing A-type graphite according to the present invention is a cast iron containing A-type graphite having a non-directional and non-directional and uniformly distributed form. , Carbon is 2.9 mass% to 3.6 mass%, silicon is 2.0 mass% to 2.5 mass%, manganese is 0.5 mass% to 1.0 mass%, and phosphorus is 0.03 mass%. ~ 0.3 mass%, sulfur 0.01 mass% to 0.13 mass%, copper 0.03 mass% to 0.6 mass%, chromium 0.03 mass% to 0.3 mass%, tin Is 0.001 mass% to 0.3 mass% and / or antimony is 0.001 mass% to 0.2 mass%, with the balance comprising a chemical composition consisting of iron and inevitable impurities It is.

  And it is also preferable that the cast iron containing A-type graphite according to the present invention has a composition containing 0.1% by mass to 0.6% by mass of molybdenum.

  Furthermore, the cast iron containing A-type graphite according to the present invention has a cast structure of 100 area% of the entire observation area of the metal structure that can be observed with a metal microscope, and the area occupied by the ferrite phase is 1.5 area%. Hereinafter, it is preferable to provide a pearlite base having an area occupied by the steadite phase of 0.05 area% or more and an area occupied by the graphite phase of 10 area% to 18 area%.

  Moreover, it is preferable that the cast iron containing A-type graphite according to the present invention has a Vickers hardness of 250HV0.1 or more.

Casting method of cast iron containing A-type graphite according to the present invention: The cast iron containing A-type graphite according to the present invention has a casting method of 2.9 mass% to 3.6 mass% carbon and 2.0 mass% silicon. ~ 2.5 mass%, manganese 0.5 mass% to 1.0 mass%, phosphorus 0.03 mass% to 0.3 mass%, sulfur 0.01 mass% to 0.13 mass%, copper Is 0.03 mass% to 0.3 mass%, chromium is 0.03 mass% to 0.3 mass%, tin is 0.001 mass% to 0.3 mass%, and / or antimony is 0.001 mass%. It is characterized by preparing a molten metal having a chemical composition consisting of iron and inevitable impurities, and casting the molten metal in a mold using a gravity casting method or a centrifugal casting method. Is.

Cylinder liner according to the present invention: A cylinder liner according to the present invention is provided on an inner wall portion of a cylinder that accommodates a piston of an internal combustion engine, and is formed using cast iron containing A-type graphite according to the present invention described above. It is characterized by this.

  The cast iron containing A-type graphite according to the present invention has the above-described cast iron composition, so that it has wear resistance required as a sliding member, and at the same time, exhibits good cutting performance exceeding conventional wear-resistant cast iron. become. Moreover, in the production of cast iron containing A-type graphite according to the present invention, the same level of wear resistance and cutting performance are exhibited no matter which of the gravity casting method and the centrifugal casting method is used as the casting method. It becomes like this. Therefore, the selection range of the casting method is widened, which is preferable. The cast iron containing A-type graphite according to the present invention is suitable for a cylinder liner provided on an inner wall portion of a cylinder that accommodates a piston of an internal combustion engine, and can provide a high-quality cylinder liner.

  Hereinafter, embodiments relating to each of the cast iron containing A-type graphite according to the present invention, the method for producing the cast iron containing the A-type graphite, and the cylinder liner according to the present invention will be described in detail, and then examples relating to the present invention will be described.

Form of cast iron containing A-type graphite according to the present invention as seen from the composition: Cast iron containing A-type graphite according to the present invention is characterized in that it is a composition in which copper and chromium are added to a normal cast iron composition. Have. Here, “cast iron containing A-type graphite” means that the graphite does not have directionality in the cast structure and is distributed in a disorderly and even manner, and the size of the graphite is maintained appropriately. By making the base pearlite, it becomes so-called tough cast iron, and exhibits good wear resistance and good scuff resistance required for the sliding member. Further, when the cast iron containing A-type graphite according to the present invention is viewed from a structural aspect, the ferrite phase and the steadite phase are controlled to a certain level or less. It should be noted that there is no misunderstanding, but the “cast iron containing A-type graphite” in the present invention clearly indicates that the graphite forms observable in the cast iron structure are not all A-type graphite shapes. It is a term used for this purpose. That is, the cast iron containing A-type graphite according to the present invention includes not only A-type graphite but also a certain amount of B-type graphite, D-type graphite, E-type graphite and the like. Hereinafter, each component contained in the composition will be described.

  The carbon content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 2.9 mass% to 3.6 mass%. In order to obtain the target graphite structure, the control of the carbon content is important and must be within an appropriate range. When the carbon content is less than 2.9%, the amount of graphite precipitated in the cast iron structure decreases. Therefore, an appropriate sliding performance with the piston surface that slides in contact with the cylinder liner cannot be obtained, and good wear resistance and good scuff resistance cannot be obtained. At this time, the graphite phase in the cast iron structure is observed as an area ratio of less than 10 area%, and a preferable cast structure described later cannot be obtained. On the other hand, if the carbon content exceeds 3.6%, it becomes a hypereutectic region in the iron-carbon phase diagram, the precipitation amount of graphite in the cast iron structure becomes excessive, and the accompanying precipitation of ferrite occurs. Become prominent. As a result, even if it is excellent in wear resistance and scuff resistance, it becomes a brittle structure and it is impossible to obtain a strength that can withstand use in an internal combustion engine. And the graphite phase in this cast iron structure will be observed as the area ratio exceeds 18 area%, and the preferable cast structure mentioned later cannot be obtained.

  The silicon content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 2.0 mass% to 2.5 mass%. The silicon content described here is closely related to the carbon content described above. That is, silicon functions as a carbonization promoter for promoting graphitization of carbon in the process of solidifying from molten metal to cast iron. In general, if the amount of carbon is constant, the greater the amount of silicon, the more likely it is to become gray cast iron. Therefore, the meaning of limiting the numerical value of the silicon content range is also based on the above-described carbon content range. Here, when the silicon content is less than 2.0%, it is difficult for A-type graphite to precipitate in the cast iron structure, and the level of wear resistance required for a sliding member such as a cylinder liner of an internal combustion engine and Scuff resistance is impaired. On the other hand, when the silicon content exceeds 2.5%, free ferrite increases and soft cast iron is formed, which is not preferable because the base is softened and the strength is insufficient. At this time, the area ratio of the ferrite phase in the cast iron structure is observed as exceeding 1.5 area%.

  The manganese content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 0.5 mass% to 1.0 mass%. Manganese in the cast iron composition is a so-called pearlite stabilizing element, which suppresses the precipitation of ferrite and makes it easy to obtain a refined pearlite structure. Moreover, the said manganese functions as a component which suppresses the production | generation of graphite, when silicon content is high. However, considering the above silicon content level, in the case of manganese in cast iron containing A-type graphite according to the present invention, ferrite precipitation to make the area ratio of the ferrite phase in the cast iron structure 1.5 area% or less It functions as a free-cutting element as well as a restraining function. That is, the manganese mentioned here combines sulfur and manganese described later to form manganese sulfide (MnS), and improves the machinability of cast iron containing A-type graphite according to the present invention. Therefore, when the manganese content is less than 0.5% by mass, the effect of improving the machinability becomes insufficient. On the other hand, even if the manganese content exceeds 1.0% by mass, the stabilization effect of pearlite is saturated, and resources are wasted.

  The phosphorus content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 0.03% by mass to 0.3% by mass. This phosphorus becomes cementite in which iron phosphide is mixed in the cast iron structure, and functions to form a so-called steadite (iron phosphide eutectic) phase. This steadite phase is very hard and brittle, but if an appropriate amount of steadite phase is present in the cast iron structure, the wear resistance is significantly improved and at the same time good machinability is obtained, but if it becomes excessive, The finishing accuracy of the surface to be processed after cutting becomes a problem. Therefore, when the phosphorus content is less than 0.03% by mass, the wear resistance and scuff resistance cannot be improved, and good machinability cannot be obtained. On the other hand, when the phosphorus content exceeds 0.3% by mass, good machinability cannot be obtained even though the wear resistance and scuff resistance can be improved. In such a case, the area ratio of the steadite phase is observed as exceeding 0.05 area% in the cast iron composition.

  The sulfur content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 0.01% by mass to 0.13% by mass. Considering the relationship between manganese and sulfur, 1.7 × [sulfur (mass%)] + 0.2 mass% ≦ [manganese (mass%) ≦ 1.7 × [sulfur (mass%)] + 0.3 mass %, The sulfur graphitization inhibiting action can be prevented, and manganese sulfide (MnS) can be formed to improve machinability. Here, the said manganese content is the range of 0.5 mass%-1.0 mass%, and sulfur content is 0.01 mass%-0.13 mass%. Accordingly, all of the sulfur components are combined with the above-described manganese to form manganese sulfide (MnS), and act to improve the machinability of cast iron containing A-type graphite according to the present invention. However, when the sulfur content of the cast iron containing A-type graphite according to the present invention is less than 0.01%, the formation of manganese sulfide (MnS) is small and the machinability is not improved. Cast iron products with poor toughness are obtained because iron is formed into white cast iron. On the other hand, when the sulfur content exceeds 0.13%, sulfur itself serves to suppress the solubility of carbon in the molten metal and promote the formation of graphite, but tends to be white cast iron and is A-type. It becomes difficult to obtain graphite.

  In the case of cast iron containing A-type graphite according to the present invention, tin and antimony described below are pearlite stabilizing components and components that perform a common function. Therefore, within the content range described below, one of tin and antimony may be used, or these may be used in combination. Hereinafter, description will be made separately for tin and antimony.

  The tin content is preferably in the range of 0.001% by mass to 0.3% by mass. Tin is a graphitization-inhibiting element in the cast iron structure, and fulfills a pearlite stabilization function that facilitates the formation of a pearlite matrix with excellent wear resistance. Therefore, when the tin content of the cast iron containing A-type graphite according to the present invention is less than 0.001% by mass, the pearlite stabilizing function cannot be achieved. On the other hand, even if the tin content of the cast iron containing A-type graphite according to the present invention exceeds 0.3% by mass, the pearlite stabilization function is not improved further, and the effect is saturated. It is a waste of resources.

  The antimony content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 0.001% by mass to 0.2% by mass. Antimony is a graphitization-inhibiting element in the cast iron structure and, like the above-mentioned tin, fulfills a pearlite stabilizing function that facilitates the formation of a pearlite base having excellent wear resistance. That is, antimony contributes to the improvement of the hardness of cast iron containing A-type graphite obtained for refining the graphite size in the pearlite matrix. When the antimony content of the cast iron containing A-type graphite according to the present invention is less than 0.001% by mass, the pearlite stabilization function cannot be achieved. Even if the antimony content of the cast iron containing A-type graphite according to the present invention exceeds 0.2% by mass, the pearlite stabilizing function is not further improved and the effect is saturated.

  The copper content of the cast iron containing A-type graphite according to the present invention is preferably in the range of 0.03% by mass to 0.6% by mass. Copper does not inhibit carbon graphitization in the cast iron structure and functions as a pearlite stabilizer. However, the addition of the above-described antimony and / or tin makes pearlite stabilization more reliable and prevents the precipitation of free ferrite. As a result, copper is a component for improving wear resistance and a component for improving corrosion resistance, which increases the hardness of cast iron, and acts as a graphite-size forming component suitable for preventing processing defects in grinding or honing. This contributes to the formation of graphite that functions as a lubricant capable of improving the properties. Therefore, when the copper content is less than 0.03% by mass, none of the items of wear resistance, corrosion resistance, and machinability can be improved. On the other hand, when the copper content exceeds 0.6% by mass, the wear resistance, corrosion resistance, and machinability are not expected to increase and become saturated. Further, if the copper content is further increased excessively, the above-mentioned antimony and / or tin content in the range of graphitization inhibition is not preferable because precipitation of free ferrite cannot be effectively prevented and softening occurs.

  The chromium content of cast iron containing A-type graphite according to the present invention is preferably in the range of 0.03% by mass to 0.3% by mass. Chromium is a graphitization-inhibiting element in the cast iron structure and, like the above-described tin and antimony, fulfills a pearlite stabilizing function that facilitates the formation of a pearlite matrix having excellent wear resistance. Therefore, the cast iron containing A-type graphite according to the present invention contains chromium, so that it is possible to improve particularly the wear resistance and the corrosion resistance. When the chromium content is less than 0.03% by mass, it is meaningless to add since both wear resistance and corrosion resistance are not improved. On the other hand, when it adds so that the said chromium content may exceed 0.3 mass%, machinability will fall.

  Moreover, it is also preferable that the cast iron containing A-type graphite according to the present invention has a composition in which molybdenum is added in a range of 0.1 mass% to 0.6 mass%. This molybdenum is added as necessary, and is used for further improving the material strength as well as excellent machinability and wear resistance. That is, molybdenum is a graphitization inhibiting element, prevents the coarsening of the graphite size, disperses the graphite finely and evenly in the base to increase the strength, and is a pearlite base excellent in toughness and wear resistance. It fulfills the pearlite stabilization function that facilitates the formation of Therefore, when the molybdenum content is less than 0.1% by mass, neither toughness nor wear resistance can be improved. On the other hand, if the molybdenum content exceeds 0.6% by mass, a bainite structure is formed, the hardness becomes too high, and the machinability deteriorates, which is not preferable.

Form of cast iron containing A-type graphite according to the present invention as seen from the cast structure: By using the cast iron composition described above, flake graphite having an appropriate size and uniform distribution is formed in the structure, and a pearlite base Hardness can be suitably adjusted. The steadite phase in cast iron has been used to improve cutting performance, but on the other hand, when the steadite phase increases, the phenomenon of crack-type chips during cutting becomes prominent, resulting in finished accuracy. Has become a problem. However, in the case of cast iron containing A-type graphite according to the present invention, good wear resistance and good machinability can be obtained at the same time even if the amount of steadite phase required for improving machinability is reduced. It is characterized by the fact that it has become possible.

  By changing the manufacturing method using the cast iron composition according to the present invention, what has various cast iron structures can be obtained as a final cast iron product. Among them, cast iron containing A-type graphite having the observation structure described below has the best cutting properties and wear resistance, has a beautiful surface to be processed, and dramatically improves the finishing accuracy. In other words, the machinability referred to in the present invention is not only easy to cut and prolonging the life of the processing jig, but as long as the same processing jig and the same processing conditions are used, the workpiece subjected to the cutting processing is used. It should be clearly stated that this means that the surface finishing accuracy is good.

  That is, in the case of cast iron containing A-type graphite according to the present invention, the entire observation region area of the metal structure that can be observed with a metal microscope is 100% by area, and the occupied area of the ferrite phase is 1.5% by area or less. In the case where a pearlite base having a occupying area of 0.05 area% or more and a occupying area of graphite phase of 10 area% to 18 area% is provided, the best cutting ability and wear resistance are simultaneously exhibited. Here, when observing the structure of cast iron containing A-type graphite according to the present invention, the graphite shape is observed without etching and at a magnification of 100 times with a metal microscope. And when observing a ferrite phase and a steadite phase, predetermined | prescribed etching processes, such as using a night, are performed, and it observes 200 times with a metal microscope.

The base of cast iron containing this A-type graphite is a pearlite base. Here, perlite is a well-known term for those skilled in the art, but will be briefly described. The γ solid solution in the iron-carbon phase diagram is decomposed into an α solid solution (ferrite) and an iron carbon compound (Fe ₃ C: cementite) by the eutectoid transformation (A ₁ transformation), and both of these become thin layers. A striped pattern in which layers are alternately stacked is formed. The perlite base means that the entire organization is a perlite organization. Further, in the case of cast iron containing A-type graphite according to the present invention, the ferrite phase, steadite phase, and graphite phase are uniformly distributed in the pearlite matrix.

  In the case of cast iron containing A-type graphite according to the present invention, the entire observation region area of the metal structure that can be observed with a metal microscope is 100% by area, and the occupied area of the ferrite phase is preferably 1.5% by area or less. . The area occupied by the ferrite phase in this range is to reduce the ferrite phase lacking in wear resistance as much as possible to prevent the base strength from being lowered, and to prevent the occurrence of crack-type chips due to cutting or honing. In order to improve the finishing accuracy of the surface to be processed and obtain a smooth processed surface. Therefore, when the area occupied by the ferrite phase exceeds 1.5 area%, the finishing accuracy of the surface to be processed is deteriorated and a smooth processed surface cannot be obtained.

And the steadite phase of the cast iron containing A-type graphite according to the present invention has the entire area of the observation area of the metal structure observable with a metal microscope as 100 area%, and the occupied area is 0.05 area% or more. Is preferred. Steadite is a ternary eutectic structure of α iron, Fe ₃ C (cementite), and iron phosphide (Fe ₃ P), and has high hardness. As a result, if the steadite phase is precipitated in the pearlite base as less than 0.05 area%, crack type chip generation phenomenon occurs at the time of honing, and as a result, the finishing accuracy of the surface to be processed deteriorates, A smooth machined surface cannot be obtained.

  Further, the graphite phase of cast iron containing A-type graphite according to the present invention has an area occupied by the graphite phase of 10 area% to 18 area, where the entire observation area of the metal structure that can be observed with a metal microscope is 100 area%. % Is preferred. At this time, when the area occupied by the graphite phase is less than 10% by area, the lubricating function of the graphite phase as a sliding member is not exhibited, and the wear resistance and scuff resistance are poor. On the other hand, when the occupied area of the graphite phase exceeds 18%, the graphite size becomes coarse, the cast iron strength decreases, and the practicality as a structural member for a machine is lacking. The cast iron material and cylinder liner containing A-type graphite of the present invention contains 70% by area or more of A-type graphite when the amount of all flake graphite in the observation area is 100% by area, and the rest is B-type graphite. And D-type graphite. In the case of the centrifugal casting method, the total of A-type graphite and E-type graphite is preferably 70 area% or more.

  When the cast iron containing A-type graphite according to the present invention has the cast iron structure as described above, the Vickers hardness of pearlite base hardness is 250HV0.1 or more. From the viewpoint of wear resistance, the pearlite structure is superior to the ferrite structure. In general, the higher the hardness, the better the wear resistance, but from the viewpoint of more reliably preventing cracking chip generation during honing by making the lamellar structure of the pearlite structure coarse and not increasing the amount of ferrite. The base hardness is more preferably 300HV0.1 or more. In addition, although there is no restriction | limiting in particular regarding an upper limit here, it is preferable that Vickers hardness is 400HV0.1 or less. This is because when the Vickers hardness exceeds 400 HV0.1, the toughness required as a structural member for a machine is lowered, and the machinability, vibration damping characteristics, and the like are also deteriorated.

Form of Cast Iron Casting Method Containing A-Type Graphite According to the Present Invention: An embodiment of a casting method of cast iron containing A-type graphite according to the present invention will be described. The composition of the molten metal for obtaining the cast iron containing A-type graphite according to the present invention basically uses a molten metal having a composition whose Si is about 0.2% lower than the final cast iron-containing composition containing A-type graphite. . And inoculation (ferrosilicon alloy) for promoting graphitization is performed immediately before pouring. As a result, there is almost no component difference between the molten metal and the cast iron after solidification. That is, first, 2.9% to 3.6% by mass of carbon, 2.0% to 2.5% by mass of silicon, 0.5% to 1.0% by mass of manganese, and 0.8% of phosphorus. 05 mass% to 0.3 mass%, sulfur 0.01 mass% to 0.13 mass%, copper 0.03 mass% to 0.3 mass%, chromium 0.03 mass% to 0.3 mass% %, Tin is 0.001 mass% to 0.3 mass% and / or antimony is 0.001 mass% to 0.2 mass%, and the remainder is prepared from iron and inevitable impurities. There are no particular limitations on the method for adjusting the molten metal, the order of addition of various components into the molten metal, and the type of adjusting method, and any known method may be used. And the composition of this molten metal is computed from the ratio of the additional raw material at the time of preparing a molten metal.

  And when casting a molten metal in a casting_mold | template, either the gravity casting method or the centrifugal casting method may be used. However, when the centrifugal casting method is adopted for the molten metal having the above composition, if the surface temperature of the mold is less than 250 ° C., the cooling rate is too fast, graphitization is suppressed, and a good-sized A-type graphite is obtained. Since it becomes difficult to precipitate, it is not preferable. On the other hand, if the surface temperature of the mold exceeds 270 ° C., the cooling rate becomes too slow, the size of the precipitated graphite becomes coarse, and the base hardness decreases.

  In the centrifugal casting method, a coating mold mainly composed of diatomaceous earth is applied and formed on the inner surface of the mold. The coating thickness at this time is an important factor affecting the cooling rate and the mold life. When the coating mold thickness is less than 0.5 mm, the cooling rate is too fast, the chilling tendency of the cast product is increased, and the above-described cast structure cannot be obtained. On the other hand, if the coating thickness exceeds 1.5 mm, the cooling rate becomes too slow, the precipitated graphite size becomes coarse, the base hardness decreases, and the wear resistance required as a sliding member, etc. Necessary functions are not displayed.

Form of the cylinder liner according to the present invention: The cylinder liner according to the present invention is provided on the inner wall portion of the cylinder that accommodates the piston of the internal combustion engine, and is formed using the cast iron containing A-type graphite as described above. It is characterized by. By using cast iron containing the A-type graphite, the surface of the cylinder liner after honing can be finished beautifully and smoothly at an unprecedented level, and a high-quality cylinder for an internal combustion engine can be provided. Become.

  In this example, a molten metal having a composition almost the same as the final cast iron composition was prepared, and a cast iron for a cylinder liner was manufactured using a gravity casting method or a centrifugal casting method. Then, in order to evaluate the processing performance by honing the cast iron surface for cylinder liner after casting, the maximum height (Pt) of the cylinder liner surface after processing was measured based on JIS B0601 (2001). . In addition, the maximum height (Pt) at this time was measured using a stylus with a radius of curvature of 2 μm using a stylus-type surface roughness meter. In Table 1 below, it is possible to compare the cast iron composition and casting conditions of Examples (Sample 1 to Sample 17) and Comparative Examples (Sample C-1, Sample C-2, Sample C-3) described later. It summarizes and shows. Here, it should be clearly noted that the amounts of each component described as the cast iron composition in Table 1 are intentionally added and do not include trace components contained as inevitable impurities.

  And the result of having observed the cast structure of the cast iron for cylinder liners of the composition shown in Table 1 and measuring the surface roughness of the processed surface after honing was described later as Examples (Sample 1 to Sample 15). The comparative examples (Sample C-1, Sample C-2, Sample C-3) are shown in Table 2 below so that they can be compared. The honing conditions are listed below.

Honing condition Whetstone: Roughing process ... Diamond # 220
Finishing process: GC # 220
Plato: Soft grinding wheel
Stock allowance: Roughing process ... 0.02-0.03mm / diameter
Finishing process: 0.03-0.04mm / diameter
Prato 5 strokes
Grinding wheel extension method: mechanical

  Furthermore, in FIGS. 1-4, the typical metal-microscope observation image of the cast iron for cylinder liners provided with the cast iron structure | tissue containing the A-type graphite which concerns on this invention is shown. In FIG. 1, a cast structure in the case of no corrosion of cast iron for a cylinder liner manufactured by a sand mold using the gravity casting method of Sample 3 is shown as a metal microscope observation image at a magnification of 100 times. On the other hand, in FIG. 2, the cast structure in the case where the sample 3 was etched with a night was shown as a metal microscope observation image with a magnification of 200 times. FIG. 3 shows a cast structure for a cylinder liner manufactured by a mold using the centrifugal casting method of Sample 9 and a cast structure without etching as a metal microscope observation image at a magnification of 100 times. FIG. 4 shows a cast structure obtained when the sample 9 is etched by night as a metal microscope observation image with a magnification of 200 times. As can be seen from FIGS. 1 to 4, it can be seen that a good A-type graphite form is obtained.

Comparative example

  In this comparative example, similarly to the example, a molten metal having a composition almost the same as the final cast iron composition was prepared, and cast iron for cylinder liners was manufactured using a centrifugal casting method. The cast iron composition and casting conditions at this time are listed in Table 1 simultaneously with the examples. Then, the surface of the cast iron for cylinder liner after the casting is honed, and the maximum height (Pt) of the cylinder liner surface after processing is measured and used for comparison with the example in order to evaluate the processing performance. . Other honing processing conditions and the like are the same as in the example.

  Further, FIG. 5 shows an unetched cast structure of cast iron for cylinder liner manufactured by the centrifugal casting method of Sample C-1 as a metal microscope observation image at a magnification of 100 times. And in FIG. 6, the cast structure | tissue at the time of etching the sample C-1 with a night is shown as a metal-microscope observation image of 200-times multiplication factor. In FIGS. 5 and 6 as well, the graphite form is good A-type graphite.

<Contrast between Example and Comparative Example>
The examples and comparative examples described above will be described in comparison with each other. This comparison is made with reference to Table 2.

  Looking at the casting compositions of Sample 1 to Sample 17 in the examples of Table 1, all are 2.9% to 3.6% by mass of carbon, 2.0% to 2.5% by mass of silicon, manganese Is 0.5 mass% to 1.0 mass%, phosphorus is 0.05 mass% to 0.3 mass%, sulfur is 0.01 mass% to 0.13 mass%, and copper is 0.03 mass% to 0 mass%. .3% by mass, chromium by 0.03% by mass to 0.3% by mass, tin by 0.001% by mass to 0.3% by mass and / or antimony by 0.001% by mass to 0.2% by mass. The balance is in the range of iron and inevitable impurities. In contrast, Sample C-1, Sample C-2, and Sample C-3 of Comparative Example in Table 1 are not included in the composition range.

  The cast structures of Sample 1 to Sample 17 in the examples in Table 2 are 100% by area of the entire observation region area of the metal structure that can be observed by a metal microscope, and the area occupied by the ferrite phase is 1.5% by area or less. It can be seen that a pearlite base having an area occupied by the steadite phase of 0.05 area% or more and an area occupied by the graphite phase of 10 area% to 18 area% is provided. On the other hand, it can be seen that Sample C-1, Sample C-2, and Sample C-3 of Comparative Example in Table 1 do not satisfy the characteristics of the cast structure.

  Here, referring to Table 2, when the base hardness of the example (sample 1 to sample 17) and the comparative example (sample C-1, sample C-2, sample C-3) is seen, The sample has a Vickers hardness in the range of 254 to 350 at HV0.1. On the other hand, the Vickers hardness of the sample of the comparative example is in the range of 332 to 360. That is, in terms of Vickers hardness, it can be seen that the sample of the example has a wider range of hardness and a softer region. However, according to the research by the inventors, there is no significant difference in wear resistance between the example and the comparative example, and the level is equivalent.

  And with reference to Table 2, the surface roughness of the surface to be processed after the honing process of the example (sample 1 to sample 17) and the comparative example (sample C-1, sample C-2, sample C-3) (In Table 2, simply indicated as “surface roughness after honing”). As a result, the maximum height (Pt) of the comparative example is in the range of 6.1 μn to 6.3 μm, whereas the maximum height (Pt) of the example is in the range of 3.3 μm to 4.0 μm. It can be seen that the roughness of the surface to be processed after the honing process has been dramatically smoothed, and the finishing accuracy has been greatly improved. This is the same even if the sample of the comparative example using the centrifugal casting method and the samples 11 to 13 of the example using the centrifugal casting method are compared. Further, when the maximum height (Pt) of each of the samples 1 to 10, 14, and 15 of the example and the maximum height (Pt) of each of the samples 11 to 13 are compared, the present invention It is supported that cast iron containing A-type graphite exhibiting good honing performance can be obtained by using either the gravity casting method or the centrifugal casting method as a casting method in the case of using the molten metal having the composition according to the above.

  Furthermore, referring to Table 2, the surface roughness of the surface to be processed after the honing process of the example (sample 16 and sample 17) and the comparative example (sample C-1, sample C-2, sample C-3). (In Table 2, simply indicated as “surface roughness after honing”). Sample 16 and sample 17 corresponding to this example have a composition in which tin, antimony and molybdenum are used in combination as the cast iron composition. As a result, the base hardness is significantly harder than that of the sample of the comparative example. Therefore, it can be inferred that Sample 16 and Sample 17 are superior in wear resistance performance by adopting a cast iron composition in which tin, antimony and molybdenum are used in combination in the present invention, as compared with the sample of the comparative example. Moreover, when the roughness of the surface to be processed after the honing process of the example (sample 16 and sample 17) and the comparative example (sample C-1, sample C-2, sample C-3) is seen, the direction of the example Although it has hard physical properties, it can be seen that a dramatically smooth surface to be processed can be obtained, and the finishing accuracy has been dramatically improved as compared with the comparative example.

  The cast iron containing A-type graphite according to the present invention has the above-described cast iron composition, and has the wear resistance required as a sliding member, and at the same time exhibits a good cutting performance exceeding that of conventional wear-resistant cast iron. Since it has such characteristics, it is suitable for a cylinder liner provided on an inner wall portion of a cylinder that houses a piston of an internal combustion engine, and can provide a high-quality cylinder liner. The method for producing cast iron containing A-type graphite according to the present invention is characterized by a molten metal composition reflecting the cast iron composition of cast iron containing A-type graphite to be obtained. Since both the gravity casting method and the centrifugal casting method can be adopted as the casting method, there is an advantage that no new capital investment is required.

It is a metal-microscope observation image without the etching of the sample 3 (Example: gravity casting method). It is a metal-microscope observation image after the etching of the sample 3 (Example: Gravity casting method). It is a metal-microscope observation image without the etching of the sample 9 (Example: Centrifugal casting method). It is a metal-microscope observation image after the etching of the sample 9 (Example: Centrifugal casting method). It is a metal-microscope observation image without the etching of sample C-1 (comparative example: centrifugal casting method). It is a metal-microscope observation image after the etching of sample C-1 (comparative example: centrifugal casting method).

Claims (6)

A cast iron containing A-type graphite having a presence form in which graphite is not directional and is disordered and uniformly distributed,
Carbon is 2.9 mass% to 3.6 mass%, Silicon is 2.0 mass% to 2.5 mass%, Manganese is 0.5 mass% to 1.0 mass%, and Phosphorus is 0.03 mass% to 0.3 wt%, sulfur 0.01 wt% to 0.13 wt%, copper 0.03 wt% to 0.6 wt%, chromium 0.03 wt% to 0.3 wt%, tin A type characterized in that 0.001% by mass to 0.3% by mass and / or antimony is 0.001% by mass to 0.2% by mass and the balance has a chemical composition consisting of iron and inevitable impurities. Cast iron containing graphite. The cast iron containing A-type graphite according to claim 1, wherein molybdenum is contained in an amount of 0.1 mass% to 0.6 mass%. The observation area of the metal structure that can be observed with a metal microscope is 100% by area, the ferrite phase occupies 1.5 area% or less, the steadite phase occupies 0.05 area% or more, and the graphite phase occupies The cast iron containing A-type graphite according to claim 1 or 2, comprising a pearlite base having an area of 10 area% to 18 area%. The cast iron containing A-type graphite according to any one of claims 1 to 3, wherein the base has a Vickers hardness of 250HV0.1 or more. A casting method for cast iron containing the A-type graphite according to any one of claims 1 to 4,
Carbon is 2.9 mass% to 3.6 mass%, Silicon is 2.0 mass% to 2.5 mass%, Manganese is 0.5 mass% to 1.0 mass%, and Phosphorus is 0.03 mass% to 0.3 wt%, sulfur 0.01 wt% to 0.13 wt%, copper 0.03 wt% to 0.6 wt%, chromium 0.03 wt% to 0.3 wt%, tin 0.001% by mass to 0.3% by mass and / or antimony is 0.001% by mass to 0.2% by mass, and a molten metal having a chemical composition consisting of iron and inevitable impurities is prepared.
A casting method for cast iron containing A-type graphite, wherein the molten metal is cast into a mold using a gravity casting method or a centrifugal casting method. A cylinder liner provided on an inner wall portion of a cylinder for accommodating a piston of an internal combustion engine,
A cylinder liner formed by using cast iron containing the A-type graphite of claim 1.