JPH0135062B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cast iron sliding member that is required to have both wear resistance and scuffing resistance, such as a cylinder liner for an internal combustion engine, and a method for manufacturing the same. In recent years, the trend toward higher speeds and higher outputs in internal combustion engines has become more pronounced, and cylinder liner materials are required to have severe wear resistance and scuffing resistance. In order to meet these harsh demands, we have improved the material composition of cast iron, which has been mainly used as cylinder liners because it has graphite precipitated and has good wear resistance, and improved the inner periphery. Improvements in the surface properties of the surface, surface treatment of the inner peripheral sliding surface, etc. have been studied, but the current situation is that nothing satisfactory has been achieved yet. In other words, although some effects have been achieved in improving the composition of cast iron materials by strengthening the matrix through the addition of alloying elements and precipitating carbides, this is still insufficient, and improvements in the graphite structure have not yet been considered. Although increasing the graphite size and precipitating a large amount of graphite has a certain effect on improving scuffing resistance, it causes a decrease in strength and furthermore, a lack of wear resistance. Next, to improve the surface quality of the inner peripheral sliding surface of the cylinder liner, honing, which is currently widely used, is being considered, but honing may produce a degraded layer, or due to the graphite There is a limit to the ability of honing to significantly improve the surface properties of the sliding surface due to reasons such as the prevention of exposure to the sliding surface. Furthermore, surface treatment of the inner circumferential sliding surface has disadvantages in terms of environmental pollution caused by wastewater treatment, etc., and economic efficiency. In view of the above points, the present invention provides a cast iron material with excellent wear resistance and scuffing resistance by limiting the composition and structure of the cast iron material and subjecting the cast iron material to a prescribed heat treatment, and an economical production thereof. It seeks to provide law. That is, in the present invention, in addition to the main elements of carbon, silicon, manganese, phosphorus, and sulfur, at least one element selected from the group consisting of nickel and copper, which mainly strengthens the matrix, is added in a total of 0.05 to 1.0.
%, and at least one selected from the group consisting of chromium, molybdenum, niobium, titanium, vanadium, tungsten and boron, which mainly form carbides, in the case of 1 type, 0.05 to 1.0%, 2
If it is more than 1%, it is a sliding member made of cast iron containing 0.05 to 2% in total and containing graphite, (a)
The graphite size of the graphite is ASTM 4 to 6,
(b) 70% of the graphite is of ASTM classification A type.
and (c) has a graphite structure (a) to (c) in which the widths of the tip and center of the graphite are substantially the same, and is honed. It is characterized by the exposed graphite of cast iron on the sliding surface of the member. The method according to the present invention includes at least one component selected from the group consisting of nickel and copper in addition to the five main components of carbon, silicon, manganese, phosphorus and sulfur.
Species totaling 0.05-1.0%, and mainly chromium, molybdenum, niobium, titanium, forming carbides.
At least one selected from the group consisting of vanadium, tungsten and boron, in the case of one
0.05-1.0%, 0.05-2% in total if there are two or more types
ASTM in graphite containing and precipitating as-cast
Cast iron with a classification A type graphite occupation area ratio of 70% or more and a graphite size of 4 to 6 at a temperature of 1000℃ or higher and 1140℃
After heating and holding at the following temperature for more than 10 minutes, preferably less than 3 hours, the graphite size is changed so that the width of the graphite is substantially the same at the tip and the center while substantially maintaining the graphite size in the as-cast state. By letting
The aim is to produce cast iron with excellent wear resistance and scuffing resistance. The reasons for the limitations of the present invention will be described below. Nickel, copper, etc. form a solid solution in the matrix of cast iron, toughen the cast iron material, reduce the formation of a damaged layer due to honing, etc., and also contribute to wear resistance by toughening the material. If the total amount is less than 0.05%, no effect will be recognized, and if the total amount exceeds 1%, white ironization of cast iron, refinement of graphite structure, changes in matrix structure, etc. will occur. Next, chromium, molybdenum, niobium, titanium,
Vanadium, boron, tungsten, etc. are precipitated as carbides, and these carbides form the primary sliding surface on the sliding surface, which acts as a bearing effect and contributes to improving wear resistance and scuffing resistance. It also has the effect of dividing the process-affected layer caused by processing, etc., but if it is less than 0.05%, this effect is poor. When added alone, if it exceeds 1%, the cast iron becomes white iron, the graphite structure becomes finer, and a large amount of carbide precipitates, resulting in a decrease in strength and deterioration of workability. In addition, in the case of combined addition, even if the total amount exceeds 2%, it may cause white ironization of iron casting, refinement of graphite structure,
Furthermore, the strength decreases due to the precipitation of a large amount of carbides,
This leads to deterioration of workability. Therefore, chromium, molybdenum, niobium, titanium, and
At least one kind selected from vanadium, boron, tungsten, etc., in the case of one kind, from 0.05 to
1.0%, and in the case of two or more types, the total amount is limited to 0.05-2%. The graphite structure that precipitates in cast iron and appears on the sliding surfaces of sliding members has self-lubricating properties, so it not only contributes to improving scuffing resistance, but also reduces the fine sliding that occurs due to friction. It also has the effect of separating moving scratches. Furthermore, since the graphite portion is extremely soft compared to the matrix, it becomes a concave portion and acts as an oil pool, which is effective in improving wear resistance and scuffing resistance. The graphite shape that effectively exhibits this effect is ASTM classification type A, and moreover, the occupied area ratio of type A graphite in the precipitated graphite is
70% or more of the graphite size is 4 to 6. If the area ratio occupied by type A graphite in the precipitated graphite is less than 70%, the shape deteriorates and the area ratio occupied by fine graphite inevitably increases, which is not preferable. Furthermore, when the graphite size exceeds 6, the graphite becomes finer. The width of the graphite is not uniform, and there is a high probability that fine graphite will be covered with a damaged layer due to plastic flow that occurs near the machined surface during honing, and if graphite is not exposed on the sliding surface, it will have a self-lubricating effect. No oil pooling effect can be expected, leading to deterioration in scuffing resistance. On the other hand, if the graphite size is less than 4, the graphite becomes coarse, and although it is effective in improving scuffing resistance, the strength of the cast iron decreases. In the present invention, the content of carbon and silicon in cast iron is not particularly limited as it can be adjusted to obtain the above-mentioned structure, but in general, carbon and silicon are 2.5 to 4% and silicon 1.5 to 3%.
It is sufficient if it is within the range of . According to the manufacturing method of the present invention, the occupied area ratio of type A graphite of ASTM classification in all the graphite in which the graphite structure is precipitated in the as-cast state is 70% or more, and the graphite size is 4.
~6. In the as-cast state, in general cast iron having the above-mentioned graphite structure, the width of the precipitated flake graphite becomes smaller at the tip,
There is a high probability that the graphite will be covered with a damaged layer caused by honing, etc., and it is inevitable that the proportion of graphite exposed on the processed surface will decrease. This results in deterioration of wear resistance and scuffing resistance. In order to avoid such a phenomenon, an effective method for improving wear resistance and scuffing resistance is to make the tip of the flaky graphite have the same width as the center. Therefore, in the present invention, a cast iron material having the chemical composition and structure as described above is heat-treated at a temperature of 1000°C to 1140°C to obtain a so-called caterpillar-like graphite structure, which is effective in improving wear resistance and scuffing resistance. This is what we are trying to do. That is, the cast iron material related to the present invention
If the graphite is heated at a temperature of 1100°C to 1140°C for 10 minutes to 3 hours and then cooled, the relatively large flake graphite obtained in the as-cast state will hardly change the graphite size measured by the ASTM measurement method and become wormlike graphite. become.
Such graphite has a wide width, preferably 4 to 20
It is micron-sized and uniform, reducing the probability of being covered by a damaged layer caused by honing, etc., increasing the proportion of graphite exposed on the machined surface, and improving wear resistance and scuffing resistance. Theoretically, if the heating temperature is above the _A1 transformation point of cast iron and below the melting point, solid solution of graphite in the matrix will occur, but below 1000℃, the transformation of flaky graphite into caterpillar graphite is slow. When the temperature exceeds 1140℃, partial melting begins, so the heating temperature is 1000℃.
Limited to above ℃ and below 1140℃. Heating retention time is 10
If the heating time is less than 1 minute, uniform vermiform graphite cannot be obtained, and if it exceeds 3 hours, the heating time becomes economically disadvantageous, so the heating and holding time is limited to 10 minutes or more and 3 hours or less. For cooling after heating, a pearlite matrix requires furnace cooling or air cooling, and if a hardened matrix is desired, it is slowly cooled to the quenching temperature of cast iron, which is commonly used, and then oil or water cooled. It will be done. As shown in FIGS. 1 and 2, the caterpillar graphite cast iron obtained in this manner has rounded tips and is distributed as graphite over a wide range compared to normal flake graphite. These graphites are less likely to be covered with a process-affected layer even during honing processing, and as shown in Figure 3, approximately 60% of graphite is uniformly coated on the processed surface.
It is exposed in an amount of 2.5 cm/cm ² and has a beneficial effect on improving abrasion resistance and scuffing resistance. As described above, the cast iron material according to the present invention not only strengthens the matrix and precipitates carbides, but also has an area ratio of 70% or more of ASTM Class A graphite in all graphite, and has a graphite size of 4 to 6. Graphite, which stipulates that the dovetail width is substantially the same at the tip and center, is exposed on the inner circumferential surface of the honing process, and cast iron with a predetermined as-cast structure is heated to 1000℃.
By applying heat treatment at 1140℃ or less for 10 minutes to 3 hours, the shape of the graphite changes from flaky graphite to caterpillar graphite, meeting even harsher demands for abrasion resistance and scuffing resistance. The purpose is to provide cast iron materials that can be obtained. The effects will be explained below using examples. Example 1 Using pig iron, steel scrap, and ferroalloy as raw materials, chemical composition: 3.02%C, 1.78%Si, 0.74%Mn, 0.29%P,
Molten metal containing 0.036% S, 0.25% Cr, 0.48% Ni, and 0.31% Nb was melted in a high-frequency induction furnace and cast into a 20 mm round bar green sand mold. In the as-cast state, the ASTM classification type A graphite was approximately 78% and the graphite size was 6. This round bar was heat treated at 1130°C for 30 minutes and cooled in air. A micrograph of the obtained tissue is shown in FIG. The graphite size was 6. Example 2 Using pig iron, steel scrap, and ferroalloy as raw materials, chemical composition: 3.13%C, 2.18%Si, 0.74%Mn, 0.47%P,
0.061%S, 0.30%Cr, 0.49%Cu, 0.28%Nb,
0.12% V was melted in a high frequency induction furnace and cast into a 30㎓ round bar green sand mold. In the as-cast state, the ASTM classification type A graphite was approximately 86% and the graphite size was 5.
This round bar was heat treated at 1080°C for 1 hour and cooled in air. The graphite size was 5. The resulting structure is shown in FIG. The graphite shape is larger than in Example 1 because the diameter of the round bar in Example 2 is larger and the cooling rate is lower than in Example 1. Example 3 Using pig iron, steel scrap, and ferroalloy as raw materials, chemical composition: 3.08%C, 1.85%Si, 0.68%Mn, 0.25%P,
0.027%S, 0.22%Cr, 0.61%Cu, 0.26%Nb,
A 0.06% B molten metal was melted in a low frequency induction furnace, a cylinder liner was cast in a shell sand mold, and then heat treated at 1080°C for 1 hour and air cooled. In the as-cast condition, it was approximately 82% ASTM Classification Type A graphite. FIG. 3 shows a photograph of the inner circumferential surface of the cylinder after honing the inner circumferential surface of the cylinder liner. The graphite size was 4-5. Comparative Example 1 This is an as-cast material with the same chemical composition and the same casting conditions as in Example 1, and a micrograph of its microstructure is shown in FIG. The graphite size was 6. Comparative Example 2 This is an as-cast material with the same chemical composition and the same casting conditions as in Example 2, and a microscopic structure photograph thereof is shown in FIG. The graphite size was 5. Comparative Example 3 This is an as-cast cylinder liner material with the same chemical composition and the same casting conditions as in Example 3. Figure 6 shows a photograph of the inner peripheral surface of the cylinder liner after completion of processing.
The graphite size was 4-5. As can be seen from this photograph of the inner circumferential surface, the graphite is covered with a layer of damage caused by honing and is not exposed to the outside. Comparative Example 4 Using pig iron, steel scrap, and ferroalloy as raw materials, chemical composition: 3.18%C, 2.09%Si, 0.74%Mn, 0.22%P,
Molten metal containing 0.024% S and 0.31% Cr was melted in a high-frequency induction furnace and cast into a 20mm round bar mold. The graphite shape obtained is ASTM classification type D, and the graphite size is 7.
It was ~8. Thereafter, it was heat treated at 1130°C for 30 minutes and then air cooled. A microscopic photograph of the obtained tissue is shown in FIG. A scuffing resistance test was conducted on Examples 1 and 2 and Comparative Examples 1, 2, and 4 thus obtained. A schematic diagram of the test apparatus is shown in FIG. Mating material A
is hard chrome plated. Test piece B, counterpart material A
The surface was subjected to a finishing test by grinding to a surface roughness of 1 to 2 μRZ. The test was conducted in a dry manner without lubrication. The scuffing resistance was evaluated based on the load, friction speed, and friction distance until scuffing occurred in the test rotor shown in FIG. 8. The results are shown in Table 1.

[Table] From Table 1, it is clear that the scuffing resistance of the material of the present invention, in which the flaky graphite of the as-cast material was changed to caterpillar graphite by heat treatment, is improved compared to the comparative example. Also in the comparative example, ATSM classification A
It is clear that Comparative Examples 1 and 2 containing Type D graphite have better scuffing resistance than Comparative Example 4, which was made of cast iron containing ASTM Class D graphite and was heat treated under the same conditions as Example 1. In,
It is important for ASTM classification A type graphite to precipitate at least 70% of the precipitated graphite in terms of scuffing resistance, but it is important to make the graphite into worm-like graphite through the heat treatment according to the present invention. It is clear that it exhibits an excellent effect in improving scuffing properties. Next, using Example 3 and Comparative Example 3, an engine scuffing resistance test was conducted. The test conditions are shown below. Engine Water-cooled 4-cylinder 4-stroke diesel engine Displacement 2.96 Output 85PS-3600rpm Lubricating oil SAE#10 Lubricating oil temperature 110-115℃ Cooling water temperature 90-95℃ Operating method Break-in 30 minutes Full load 3600 rpm 2.5 hours Engine test completed Afterwards, the occurrence of scuffing in the test cylinder liner was visually inspected.
The number of cylinder liners used in the engine test was 20 in both Example 3 and Comparative Example 3, and the scuffing occurrence rate was 5% in Example 3 and 65% in Comparative Example 3.
It was hot. The engine test also revealed that the material of the present invention has excellent scuffing resistance. Further, using Example 3 and Comparative Example 3, a durability test using an engine was conducted. The test conditions are shown below. Engine Water-cooled 4-cylinder 4-stroke diesel engine Displacement 2.96 Output 85PS-3600rpm Lubricating oil SAE #30 Lubricating oil temperature 110-115℃ Cooling water temperature 90-95℃ Operating conditions Full load 3600rpm 300 hours Durability test results are displayed on the first compression ring When comparing the amount of wear of the cylinder liner at the dead center, Example 3 had a wear amount of 5 to 10 μm, and Comparative Example 3 had a wear amount of 10 to 15 μm. As described above, it is clear that the cast iron sliding member according to the present invention has improved scuffing resistance and wear resistance.

[Brief explanation of drawings]

1 and 2 are photographs of the graphite structure of Examples 1 and 2, respectively. FIG. 3 is a photograph of the graphite structure of the inner peripheral surface of the cylinder liner of Example 3. Graphite structure photographs of Comparative Examples 1 and 2, and FIG. 6 are graphite structure photographs of the inner peripheral surface of the cylinder liner of Comparative Example 3. The magnification is 50x in both cases. FIG. 7 is a photograph of the graphite structure of Comparative Example 4, and the magnification is 100 times. FIG. 8 is a schematic diagram of the scuffing resistance test, where A is a mating material coated with hard chrome, and B is a test cast iron rotor.

Claims (1)

[Claims] 1. In addition to the five main elements of carbon, silicon, manganese, phosphorus, and sulfur, at least one element selected from the group consisting of nickel and copper that mainly strengthens the matrix is added in a total of 0.05 to 1.0. %, and at least one selected from the group consisting of chromium, molybdenum, niobium, titanium, vanadium, tungsten, and boron, which mainly form carbides, in the case of one type, 0.05 to 1.0%, and in the case of two or more types. is a sliding member made of cast iron containing 0.05 to 2% in total and having graphite, (a) the graphite size is ASTM 4 to 6, and (b) the shape of the graphite is
ASTM classification type A accounts for more than 70%, and
(c) The sliding surface of the sliding member is honed and has the graphite structure (a) to (c) above, in which the width of the tip and the center of the graphite are substantially the same. A cast iron sliding member with excellent wear resistance and scuffing resistance, characterized in that the graphite is exposed. 2 In addition to the five main elements of carbon, silicon, manganese, phosphorus and sulfur, a total of 0.05 to 1.0% of at least one element selected from the group consisting of nickel and copper, which mainly strengthen the matrix, and mainly carbides. At least one selected from the group consisting of chromium, molybdenum, niobium, titanium, vanadium, tungsten, and boron to form, in the case of one type, 0.05 to 1.0%, and in the case of two or more types, 0.05 to 2% in total. %, the occupied area ratio of ASTM type A graphite in the as-cast graphite is 70% or more, and the graphite size is ASTM 4 to 6. Abrasion resistant, characterized in that the width of the graphite is changed so that the tip and center portions are substantially the same by cooling after heating and holding for 10 minutes or more, and substantially maintaining the graphite size in the as-cast state. , a method for manufacturing cast iron sliding members with excellent scuffing resistance.