Spheroidal graphite cast iron

Abstract

The present invention aims to provide spheroidal graphite cast iron that can achieve both strength and machinability. [Solution] The spheroidal graphite cast iron of the present invention consists of, by mass%, C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010-0.080%, Al: 0.050-0.120%, Ca: 0.0005-0.0080%, with the remainder being Fe and impurities. Spheroidal graphite cast iron can be used in hydraulic equipment, engine parts, undercarriage parts, cast iron pipes, cast iron shaped pipes, and drivetrain parts.

Description

Technical Field

[0001] The present invention relates to spheroidal graphite cast iron.

Background Art

[0002] Since spheroidal graphite cast iron has excellent mechanical strength, it is used in various machines, such as hydraulic equipment (hydraulic control valves, hydraulic pumps, etc.).

[0003] For example, in Patent Document 1, there is disclosed a spheroidal graphite cast iron containing, in mass %, C: 3.3% to 4.0%, Si: 2.1% to 2.7%, Mn: 0.20% to 0.50%, S: 0.0050% to 0.030%, Cu: 0.20% to 0.50%, Mg: 0.030% to 0.060%, with the balance being Fe and impurities, and having a tensile strength of 550 MPa or more and an elongation of 12% or more.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] Spheroidal graphite cast iron generally has excellent strength compared to flake graphite cast iron and vermicular cast iron, but is inferior in machinability using tools. Therefore, there is a demand for improving machinability.

[0006] An object of the present invention is to provide a spheroidal graphite cast iron capable of achieving both strength and machinability.

Means for Solving the Problems

[0007] The spheroidal graphite cast iron of the present invention is in mass %, C: 3.0 to 4.0%, Si: 1.5 to 3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010~0.080%, Al: 0.050~0.120%, Ca: 0.0005~0.0080%, The remainder consists of Fe and impurities.

[0008] In the cross-section of the spheroidal graphite cast iron, it is preferable that the pearlite content, expressed by the following formula, is less than 25%. Perlite ratio = {(Area of ​​perlite structure) / (Area of ​​perlite structure + Ferrite structure) (area of ​​weaving) × 100

[0009] In the cross-section of the spheroidal graphite cast iron, it is preferable that the pearlite ratio represented by the above formula is 25 to 70%.

[0010] In the cross-section of the spheroidal graphite cast iron, it is preferable that the pearlite ratio represented by the above formula exceeds 70%.

[0011] Furthermore, the hydraulic equipment, engine parts, or undercarriage parts of the present invention are It contains the spheroidal graphite cast iron described above.

[0012] Furthermore, the agricultural machinery or construction machinery of the present invention is It is equipped with the hydraulic equipment, engine parts, or undercarriage parts described above.

[0013] Furthermore, the method for producing spheroidal graphite cast iron according to the present invention is In mass%, C: 3.0~4.0%, Si: 1.5~3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010~0.080%, Al: 0.050 to 0.120%, Ca: 0.0005 to 0.0080%, The balance: Fe and impurities, including a step of casting a molten metal prepared so as to obtain a spheroidal graphite cast iron having a composition consisting of.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a spheroidal graphite cast iron capable of achieving both strength and machinability.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is an image showing a cross-section of a low pearlite ratio spheroidal graphite cast iron according to an embodiment of the present invention. [Figure 2] FIG. 2 is an image showing a cross-section of a medium pearlite ratio spheroidal graphite cast iron according to an embodiment of the present invention. [Figure 3] FIG. 3 is an image showing a cross-section of a high pearlite ratio spheroidal graphite cast iron according to an embodiment of the present invention. [Figure 4] FIG. 4 is a graph showing the machinability of a low pearlite ratio spheroidal graphite cast iron according to an embodiment of the present invention. [Figure 5] FIG. 5 is a graph showing the machinability of a medium pearlite ratio spheroidal graphite cast iron according to an embodiment of the present invention. [Figure 6] FIG. 6 is a graph showing the machinability of a high pearlite ratio spheroidal graphite cast iron according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail. Unless otherwise specified, “%” means “mass %”.

[0017] The spheroidal graphite cast iron according to the embodiment of the present invention contains, by mass%, C: 3.0% to 4.0%, Si: 1.5% to 3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010% to 0.080%, Al: 0.050% to 0.120%, with the remainder being Fe and impurities. The reasons for limiting the components will be explained below.

[0018] C: 3.0%~4.0% Carbon (C) is an element that forms the graphite structure, improving castability and causing pearlite precipitation. The lower limit of the C content is 3.0%, preferably 3.4%. The upper limit of the C content is 4.0%, preferably 3.8%. Including 3.0% or more C improves the ductility and toughness of spheroidal graphite cast iron. On the other hand, by keeping the C content at 4.0% or less, the graphite particle size can be adjusted to an appropriate size, ensuring a spheroidization rate and improving elongation and strength.

[0019] Si: 1.5%~3.0% Si plays a role in promoting the crystallization of graphite and increasing the fluidity of the molten metal. The lower limit of the Si content is 1.5%, preferably 1.7%. The upper limit of the Si content is 3.0% or less, preferably 2.5% or less. Including a Si content of 1.5% or more improves the strength of spheroidal graphite cast iron. Furthermore, by keeping the Si content at 3.0% or less, the strength of the spheroidal graphite cast iron is ensured, as is the low-temperature toughness of the ferrite structure.

[0020] Mn: 1.0% or less Mn is an element that is inevitably mixed in from the raw materials, but it is a stabilizing element for the pearlite structure. The lower limit of the Mn content is 0% (i.e., no Mn is present), and preferably it is 0.30% or more. The upper limit of the Mn content is 1.0% or less, and preferably it is 0.50%. By setting the Mn content to 1.0% or less, it has the effect of precipitating the pearlite structure. In addition, by setting the Mn content to 1.0% or less, machinability and toughness are improved.

[0021] P:0.10% or less P is an element that is inevitably present in the raw materials. The lower limit of the P content is 0% (i.e., no P is present). The upper limit of the P content is 0.10%, preferably 0.050%. By reducing the P content to 0.10% or less, the ductility is improved.

[0022] S: 0.020% or less S is a graphite spheroidizing inhibitory element that is inevitably mixed in from the raw materials. The lower limit of the S content is 0% (i.e., no S content), preferably 0.0050%. The upper limit of the S content is 0.020%, preferably 0.015%. By keeping the S content below 0.020%, the graphite becomes more easily spheroidized.

[0023] Cu: 1.0% or less Cu is a stabilizing element for the pearlite structure and has the effect of precipitating the pearlite structure. The lower limit of the Cu content is 0% (i.e., no Cu is present), and preferably 0.10%. The upper limit of the Cu content is 1.0%, and preferably 0.40%. As the Cu content increases, the pearlite ratio of the matrix structure increases, and the strength of the spheroidal graphite cast iron increases. By keeping the Cu content below 1.0%, the ductility and impact resistance of the spheroidal graphite cast iron are improved.

[0024] Mg: 0.010%~0.080% Mg is an element necessary for graphite spheroidization, and some of it constitutes an oxide. The lower limit of the Mg content is 0.010%, preferably 0.020%. The upper limit of the Mg content is 0.080%, preferably 0.050%. By including 0.010 mass% or more of Mg, the graphite can be made spherical, improving the strength and ductility of spheroidal graphite cast iron. Furthermore, by keeping the Mg content below 0.080%, the ductility and low-temperature toughness of spheroidal graphite cast iron can be improved.

[0025] Al: 0.050%~0.120% Al (Al) is an essential element for improving the machinability of spheroidal graphite cast iron. In spheroidal graphite cast iron, Al exists as so-called solAl, which is dissolved in the matrix, and as so-called InsolAl, which remains without dissolving in the matrix as Al oxide (Al2O3), forming complex oxides with Mg and Ca. The complex oxides of Al, Mg, and Ca lower the melting point of spheroidal graphite cast iron and can extend tool life by adhering to the tool during machining. Some of the Al is mixed in as an additive to the inoculant FeSi. The lower limit of the Al content is 0.050% or more, preferably 0.065%. The upper limit of the Al content is 0.120%, preferably 0.100%. Machinability can be improved by setting the Al content to 0.050% or more. On the other hand, if the Al content is too high, the spheroidal graphite cast iron becomes harder and its castability decreases. Furthermore, if the amount of Al is high, the Al that has dissolved on the surface of the spheroidal graphite cast iron will oxidize, inducing a wrinkled pattern. Therefore, the upper limit for Al should be as stated above.

[0026] solAl and InsolAl can be measured by the following analytical methods after collecting chips from spheroidal graphite cast iron, degreasing, washing, and acid decomposition. solAl can be analyzed based on the "Method for Determination of Acid-Soluble Aluminum" in JIS G1257-10-2. InsolAl can be measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) after melting the residue generated during the solAl pretreatment. The melting method can be carried out based on the residue treatment section of JIS G1257-10-1.

[0027] Ca: 0.0005~0.0080% Calcium (Ca) is an element that can be optionally included to improve the machinability of spheroidal graphite cast iron. The lower limit of the Ca content is 0.0005%, preferably 0.0030%. The upper limit of the Ca content is 0.0080%, preferably 0.0070%. By including Ca within the above ranges, the machinability of spheroidal graphite cast iron can be improved.

[0028] Remaining Fe and impurities The remainder consists of Fe and impurities. These impurities include those that are inevitably introduced during the melting process. For example, O and N can be cited as unavoidable impurities.

[0029] <Machinability> In this specification, machinability refers to the ease with which a workpiece can be cut. Specifically, "improved machinability" of spheroidal graphite cast iron means that the deterioration of the workpiece tools of machine tools such as lathes used when machining components made of spheroidal graphite cast iron is reduced.

[0030] <Microstructure of spheroidal graphite cast iron> The matrix structure of spheroidal graphite cast iron according to one embodiment of the present invention is a two-phase mixed structure in which ferrite and pearlite structures are distributed in a camouflage pattern. Alternatively, this matrix structure is a two-phase mixed structure in which ferrite structures are dispersed in an island-like manner within the pearlite structure (see Figures 1 to 3 described later), and has a pearlite ratio that will be explained later.

[0031] In the spheroidal graphite cast iron according to one embodiment of the present invention, the size of the pearlite and ferrite structures is not particularly limited. The maximum length of the pearlite structure in the metallographic photograph of the cast iron cross-section may be, for example, 200 μm or less, and the maximum length of the ferrite structure may be, for example, 150 μm or less.

[0032] <Perlite ratio> In this specification, the pearlite ratio is the percentage of the area of ​​the pearlite structure relative to the total area of ​​the ferrite and pearlite structures in the cross-section of spheroidal graphite cast iron. The area of ​​each structure can be calculated from a metallographic photograph of the cast iron cross-section by image processing. Specifically, the area of ​​the structure (pearlite structure + ferrite structure) extracted from the metallographic photograph of the cast iron cross-section, excluding the graphite, is determined by image processing. From this, the ferrite structure is further removed to extract the pearlite structure, and the area of ​​the pearlite structure is determined. The pearlite ratio is then calculated using the following formula. Perlite ratio = {(Area of ​​perlite tissue) / (Area of ​​perlite tissue + Area of ​​ferrite tissue)} × 100

[0033] The pearlite content of spheroidal graphite cast iron according to one embodiment of the present invention can be appropriately set depending on the application of the spheroidal graphite cast iron. Figure 1 is a metallographic image of spheroidal graphite cast iron with a pearlite content of 13.5%, Figure 2 is a metallographic image of spheroidal graphite cast iron with a pearlite content of 43.25%, and Figure 3 is a metallographic image of spheroidal graphite cast iron with a pearlite content of 91.25%.

[0034] When using the spheroidal graphite cast iron of the present invention in parts that require both strength and elongation (such as cast iron pipes and cast iron shaped pipes), the lower limit of the pearlite content is preferably 0%, more preferably 5%. The upper limit of the pearlite content is preferably less than 25%, more preferably 20%, even more preferably 15%, and most preferably 10%.

[0035] Furthermore, when using the spheroidal graphite cast iron of the present invention in parts requiring high strength (such as hydraulic equipment, engine parts, and suspension parts), the lower limit of the pearlite content is preferably 25%, more preferably 30%, and more preferably 40%. The upper limit of the pearlite content is preferably 70%, and more preferably 60%. Sufficient strength can be ensured if the pearlite content is 25% or higher, and machinability is further improved if it is 70% or lower.

[0036] Furthermore, when using the spheroidal graphite cast iron of the present invention in parts requiring even higher strength (such as hydraulic equipment, engine parts, and drivetrain parts), the lower limit of the pearlite content is preferably greater than 70%, more preferably 80%, and most preferably 90%. In addition, while the upper limit is not particularly limited in the above applications, it is preferably 99%, more preferably 97%, and most preferably 95%.

[0037] A method for producing spheroidal graphite cast iron according to one embodiment of the present invention includes the step of casting molten metal prepared to obtain spheroidal graphite cast iron having a composition containing C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010-0.080%, Al: 0.050-0.120%, Ca: 0.0005-0.0080%, with the remainder being Fe and impurities.

[0038] Methods for melting the raw materials into molten metal can include using electric furnaces, cupolas, or other melting furnaces.

[0039] In the manufacturing method according to the present invention, it is preferable to add a spheroidizing agent to the molten metal. Examples of spheroidizing agents include Mg or Fe-Si-Mg alloys.

[0040] In the manufacturing method according to the present invention, it is preferable to add an inoculant to the molten metal. An example of an inoculant is an Fe-Si alloy containing a small amount of one or more elements selected from the group consisting of Al, Ca, Ba, Zr, La, and Ce.

[0041] When adding an Al-containing inoculant at this time, it should be added so that the final Al content in the molten metal is 0.050-0.120%. When dissolving the raw materials to prepare the molten metal, an Al source may be added as a raw material to achieve an Al content of 0.050-0.120%, or an Al-containing substance may be added to the prepared molten metal to achieve an Al content of 0.050-0.120%. Furthermore, a combination of adding an Al source as a raw material and adding an Al-containing substance may be used to achieve an Al content of 0.050-0.120%.

[0042] Furthermore, when adding a calcium-containing inoculant, it should be added so that the final calcium content in the molten metal is 0.0005 to 0.0080%. When dissolving the raw materials to prepare the molten metal, a calcium source may be added as a raw material to achieve a calcium content of 0.0005 to 0.0080%, or a calcium-containing substance may be added to the prepared molten metal to achieve a calcium content of 0.0005 to 0.0080%. Moreover, a combination of adding a calcium source as a raw material and adding a calcium-containing substance may be used to achieve a calcium content of 0.0005 to 0.0080%.

[0043] As a manufacturing method for one embodiment of the present invention, gravity casting or centrifugal casting can be employed.

[0044] Furthermore, in the manufacturing method according to the present invention, the pearlite content of the spheroidal graphite cast iron produced can be adjusted by conventionally known methods. For example, this can be done by adjusting the content of Mn and Cu, or by performing pearlitizing heat treatment or ferriticizing heat treatment. In some cases, both can be performed to adjust the pearlite content.

[0045] Mn and Cu are stabilizers for the pearlite structure. Increasing their content tends to increase the pearlite ratio, while decreasing their content tends to decrease it. To achieve a pearlite ratio of less than 25%, for example, the Mn content should be around 0.35% and the Cu content 0.1% or less. To achieve a pearlite ratio of 25-70%, the Mn content should be around 0.45% and the Cu content 0.25%. To achieve a pearlite ratio of over 70%, for example, the Mn content should be around 0.45% and the Cu content 0.55%.

[0046] The spheroidal graphite cast iron according to the present invention has excellent strength and machinability, and can therefore be used in a wide range of applications. Examples include hydraulic equipment, engine parts, undercarriage parts, drivetrain parts, cast iron pipes, and cast iron shaped pipes.

[0047] Examples of hydraulic equipment include hydraulic control valves and hydraulic pumps. Examples of engine parts include crankcases, cylinder heads, crankshafts, connecting rods, and camshafts. Examples of suspension parts include steering knuckles and arms. Examples of drivetrain parts include differential cases and pressure plates.

[0048] Of the parts mentioned above, spheroidal graphite cast iron with a pearlite content of 25-70% is suitable for use in hydraulic control valves, hydraulic pumps, crankcases, cylinder heads, steering knuckles, and arms. Furthermore, spheroidal graphite cast iron with a pearlite content exceeding 70% is suitable for use in hydraulic control valves, hydraulic pumps, crankcases, cylinder heads, crankshafts, connecting rods, camshafts, differential cases, and pressure plates.

[0049] These hydraulic components, engine parts, undercarriage parts, and drivetrain parts are used, for example, in automobiles, agricultural machinery (tractors, combine harvesters, etc.), and construction machinery (backhoes, wheel loaders, etc.).

[0050] Examples of cast iron pipes include straight pipes used for water pipes, etc. Examples of cast iron shaped pipes include shaped pipes used for connecting pipes. When using the spheroidal graphite cast iron according to the present invention for shaped pipes, cast iron shaped pipes, etc., it is preferable to use spheroidal graphite cast iron with a pearlite content of less than 25%. This is because such spheroidal graphite cast iron has the strength and elongation to withstand water pressure and the load of roads. [Examples]

[0051] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0052] Test specimens were prepared from spheroidal graphite cast iron samples of Examples 1-6 and Comparative Examples 1-3, and round bars with a diameter of 80 mm and a length of 250 mm were manufactured. Examples 1-2 and Comparative Example 1 are test specimens with a low pearlite content (less than 25%), Examples 3-4 and Comparative Example 2 are test specimens with a medium pearlite content (25% to 70%), and Examples 5-6 and Comparative Example 3 are test specimens with a high pearlite content (greater than 70%). Comparative Example 1-3 is an aluminum-free test specimen.

[0053] <Examples 1, 3, 5> For Examples 1, 3, and 5, alloys of the specified composition were prepared and melted in an electric furnace to obtain molten metal. A Zr-containing Fe-Si alloy (inoculant) was added to this molten metal. Next, Al was added so that the Al content relative to the total molten metal was 0.050 to 0.120 mass%. The resulting molten metal was poured into a mold and test specimens were cast by gravity casting. The test specimens were spheroidal graphite cast iron with the following mass% composition: C: 3.0 to 4.0%, Si: 1.5 to 3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010 to 0.080%, Al: 0.050 to 0.120%, Ca: 0.0005 to 0.0040%, with the remainder being Fe and impurities. Table 1 shows the specific compositions of Examples 1, 3, and 5. In Table 1, T.Al represents the total amount of Al in the test specimen (the same applies hereafter). In Examples 1, 3, and 5, the perlite ratio was adjusted by adjusting the content of Mn and Mg, as shown in Table 1. Note that the Ca contained in Examples 1, 3, and 5 was inevitably introduced from the raw materials.

[0054] [Table 1]

[0055] <Examples 2, 4, 6> Examples 2, 4, and 6 were obtained by adding an Fe-Si-Mg-Ca alloy (spheroidizing agent) before adding the inoculant and performing spheroidizing treatment in the manufacturing methods of Examples 1, 3, and 5 above. As a result, test pieces of nodular graphite cast iron with the following composition in mass% were obtained: C: 3.0 - 4.0%, Si: 1.5 - 3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010 - 0.080%, Al: 0.050 - 0.120%, Ca: 0.0005 - 0.0080%, and the balance being Fe and impurities. The specific compositions of Examples 2, 4, and 6 are shown in Table 1. For Examples 2, 4, and 6, the pearlite ratio was adjusted as shown in Table 1 by adjusting the contents of Mn and Mg.

[0056] <Comparative Examples 1 - 3> Comparative Examples 1 - 3 were produced by not adding Al in the manufacturing methods of Examples 2, 4, and 6. As a result, test pieces of nodular graphite cast iron with the following composition in mass% were obtained: C: 3.0 - 4.0%, Si: 1.5 - 3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010 - 0.080%, Ca: 0.0005 - 0.0080%, and the balance being Fe and impurities. The specific compositions of Comparative Examples 1 - 3 are shown in Table 1. For Comparative Examples 1 - 3, the pearlite ratio was adjusted as shown in Table 1 by adjusting the contents of Mn and Mg.

[0057] For the obtained test pieces of Examples 1 - 6 and Comparative Examples 1 - 3, measurements and tests of the following items were carried out.

[0058] <Measurement of solAl and Insol> For solAl, chips of the test piece were collected, degreased, washed, acid-digested, and then analyzed based on the "Method for Determination of Acid-Soluble Aluminum" in JIS G1257 - 10 - 2. For InsolAl, the residue generated in the pretreatment of solAl was melted and measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). The melting method was carried out based on the residue treatment part of JIS G1257 - 10 - 1. The results are shown in Table 1.

[0059] Note that in Table 1, "T.Al" (Total Al amount) does not match the sum of "solAl" and "InsolAl". This may be due to errors caused by differences in analytical methods. T.Al was measured by emission spectrometry.

[0060] <Brinell hardness> The Brinell hardness (HBW 10 / 3000) was measured under the following conditions: test ball: cemented carbide grade, ball diameter: 10 mm, load: 29.42 kN. Specifically, the Brinell hardness was calculated from the surface area of ​​the indentation created when the test ball was pressed into the test specimen and the applied load. Measurements were performed on the outer circumference and the center in the thickness direction of each test specimen, and the average was used as the measurement result.

[0061] <Perlite ratio> Metallographic photographs were taken of the outer circumference and the center of the thickness of each specimen, and the procedure described above was followed. Perlite ratio = {(Area of ​​perlite tissue) / (Area of ​​perlite tissue + Area of ​​ferrite tissue)} × 100 The pearlite ratio was measured using the following method, and the average was used as the measurement result. The calculated pearlite ratio is shown in Figures 1 to 3, which also show the metallographic images of Examples 1-3.

[0062] <Tensile strength> Tensile strength was measured in accordance with JIS Z 2241.

[0063] <Machinability> The machinability of the test specimen was evaluated as a measure of tool life on a CNC lathe. The specific machining conditions were as follows: tool: K-grade cemented carbide with TiAlN coating, throwaway insert; machining speed: 300 m / min; feed rate: 0.1 mm / rev; depth of cut: 1 mm. Tool life was defined as the time until the relief wear area of ​​the tool reached 0.3 mm.

[0064] <Result> The results of the above measurements and tests are shown in Table 1, and the metallographic images of Examples 1-3 are shown in Figures 1-3. Figures 4-6 are bar graphs showing the evaluation of machinability. Note that in Table 1, examples and comparative examples with similar pearlite content are rearranged to allow for comparison.

[0065] Referring to Figures 1 to 3, it can be seen that the test specimens of Examples 1-3 have a two-phase mixed structure in which the ferrite structure is dispersed in an island-like manner within the pearlite structure.

[0066] Then, we compared Examples 1-2, which had a low perlite content (less than 25%), with Comparative Example 1; Examples 3-4, which had a moderate perlite content (25% to 70%), with Comparative Example 2; and Examples 5-6, which had a high perlite content (greater than 70%), with Comparative Example 3.

[0067] As a result, when comparing samples with similar pearlite content, no significant difference was observed in hardness, and they had equivalent strength. Furthermore, the tensile strength of the example was higher than that of the comparative example. On the other hand, as can be seen from Figures 4 to 6, the tool life of the example was more than twice that of the comparative example, indicating superior machinability. Therefore, when the pearlite content is similar, the spheroidal graphite cast iron according to the present invention possesses machinability while having equivalent or greater strength and tensile strength compared to the comparative example.

[0068] The fact that the examples exhibit strength and tensile strength equivalent to or greater than the comparative examples is thought to be due to solid solution strengthening by Al. Furthermore, the superior machinability of the examples compared to the comparative examples is thought to be due to InsolAl existing as Al oxide and lowering its melting point by forming a complex oxide with Mg and Ca, thereby adhering to the tool during machining and protecting it, as well as the solAl in the matrix forming an oxide film on the surface, which also protects the tool.

[0069] The above description is for the purpose of explaining the present invention and should not be interpreted as limiting or restricting the scope of the invention described in the claims. Furthermore, it goes without saying that the configuration of each part of the present invention is not limited to the above embodiments and can be modified in various ways within the technical scope described in the claims.

Claims

1. In mass percent, C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010-0.080%, Al: 0.050-0.120%, Ca: 0.0005-0.0080%, The remainder consists of Fe and impurities. Spheroidal graphite cast iron.

2. In the cross-section of the aforementioned spheroidal graphite cast iron, the pearlite content, expressed by the following formula, is less than 25%. The spheroidal graphite cast iron according to claim 1. Perlite ratio = {(Area of ​​perlite structure) / (Area of ​​perlite structure + Ferrite structure) (area of ​​weaving) × 100

3. In the cross-section of the aforementioned spheroidal graphite cast iron, the pearlite content, expressed by the following formula, is 25 to 70%. The spheroidal graphite cast iron according to claim 1. Perlite ratio = {(Area of ​​perlite tissue) / (Area of ​​perlite tissue + Area of ​​ferrite tissue)} × 100

4. The spheroidal graphite cast iron according to claim 1, wherein the pearlite content expressed by the following formula is greater than 70% in the cross-section of the spheroidal graphite cast iron. Perlite ratio = {(Area of ​​perlite tissue) / (Area of ​​perlite tissue + Area of ​​ferrite tissue)} × 100

5. The spheroidal graphite cast iron comprises the spheroidal graphite cast iron according to any one of claims 1 to 4. Hydraulic equipment, engine parts, or suspension parts.

6. The hydraulic equipment, engine parts, or undercarriage parts described in claim 5 are provided. Agricultural machinery or construction machinery.

7. The spheroidal graphite cast iron comprises the spheroidal graphite cast iron described in claim 1 or claim 2. Cast iron pipe or cast iron shaped pipe.

8. The spheroidal graphite cast iron comprises the spheroidal graphite cast iron described in claim 1 or claim 4. Drivetrain components.

9. In mass percent, C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 1.0% or less, P: 0.10% or less, S: 0.020% or less, Cu: 1.0% or less, Mg: 0.010-0.080%, Al: 0.050-0.120%, Ca: 0.0005-0.0080%, Remainder: Fe and impurities, The process includes casting a molten metal prepared to obtain spheroidal graphite cast iron having a composition consisting of the following: A method for manufacturing spheroidal graphite cast iron.

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