Austenitic casting material and ferrous casting

Abstract

This austenitic casting material contains 0.1 to 3.5 mass% C, 0.01 to 4.5 mass% Si, 0.01 to 4.5 mass% Mn, 10.0 to 50.0 mass% Ni, 0.001 to1.0 mass% N, 0 to10.0 mass% Co, and 0.0001 to 0.050 mass% Mg, the balance being Fe and unavoidable elements.

Description

Austenitic casting materials and iron castings

[0001] The present invention relates to an austenitic casting material and an iron casting.

[0002] The abstract of Patent Document 1 describes the provision of a spheroidal graphite cast iron having excellent gas defect resistance with few gas defects such as pinholes caused by free N, and having mechanical properties and machinability equivalent to or better than those of conventional spheroidal graphite cast iron. The abstract also describes the provision of a spheroidal graphite cast iron having excellent gas defect resistance, consisting, by mass, of 3.3 to 4% C, 2 to 3% Si, 0.05% or less P, 0.02% or less S, 0.8% or less Mn, 0.8% or less Cu (excluding 0), 0.02 to 0.06% Mg, 0.01 to 0.04% Ti, 0.001 to 0.01% V, 0.001 to 0.01% Nb, 0.004 to 0.008% N, and the remainder being substantially Fe and unavoidable impurities.

[0003] International Publication No. 2017 / 56522

[0004] Provided is an austenitic casting material that can suppress the generation of gas defects and exhibit good damping characteristics.

[0005] One aspect of the present invention is an austenitic casting material containing 0.10 mass % to 3.50 mass % C, 0.01 mass % to 4.50 mass % Si, 0.01 mass % to 4.50 mass % Mn, 10.0 mass % to 50.0 mass % Ni, 0.001 mass % to 1.000 mass % N, 0 mass % to 10.00 mass % Co, 0.0001 mass % to 0.0500 mass % Mg, and the balance being Fe and unavoidable elements.

[0006] In the above-described embodiment, by setting the lower limit of the Mg content to 0.0001% by mass, magnesium nitride can be formed by combining with N, for example, mixed into the molten metal of the casting material (hereinafter referred to as the "molten metal") from the atmosphere. This allows the N mixed into the molten metal to be fixed as magnesium nitride. This reduces the probability of gas defects occurring due to N mixed into the molten metal when the molten metal solidifies. Furthermore, by setting the upper limit of the Mg content to 0.0500% by mass, the graphite crystallized during solidification of the molten metal is easily flaked, thereby preventing the graphite from becoming worm-like or spheroidal. This prevents a decrease in the damping ratio of the iron casting obtained by solidifying the molten metal. Therefore, a casting material can be provided that can suppress the occurrence of gas defects and exhibit good damping characteristics.

[0007] The Mg content is preferably 0.0005% by mass or more and 0.0500% by mass or less. By setting the lower limit of the Mg content to 0.0005% by mass, the probability of gas defects occurring can be further reduced. Furthermore, even if gas defects occur inside the iron casting, the region where the gas defects occur can be reduced to a region close to the casting surface. Therefore, the machining allowance required to remove gas defects scattered directly below the casting surface can be reduced.

[0008] The Mg content is preferably 0.0005% by mass or more and 0.0350% by mass or less. By setting the upper limit of the Mg content to 0.0350% by mass, the decrease in the damping ratio of the iron casting can be further suppressed.

[0009] The Mg content is more preferably 0.0050 mass% or more and 0.0500 mass% or less. The Mg content is more preferably 0.0050 mass% or more and 0.0350 mass% or less. The Ni content is preferably 20.0 mass% or more and 45.0 mass% or less. The C content is preferably 1.00 mass% or more and 3.50 mass% or less. The Si content is preferably 0.10 mass% or more and 4.00 mass% or less. The Mn content is preferably 0.10 mass% or more and 3.50 mass% or less. The Co content is preferably 0.10 mass% or more and 8.50 mass% or less.

[0010] Another aspect of the present invention is an iron casting cast using the above-mentioned casting material.

[0011] Fig. 1 is a diagram showing the composition, depth of gas defects, and damping ratio of iron castings cast using an austenitic casting material in Examples and Comparative Examples. Fig. 2 is a diagram showing the depth of gas defects in a Y-section test piece in Comparative Example 1.

[0012] Hereinafter, with reference to the accompanying drawings, embodiments of an austenitic casting material and an iron casting according to the present disclosure will be described. The present invention is not limited to the following embodiments, and includes those defined in the claims. In the following description, unless otherwise specified, terms such as "first" and "second" are used merely to distinguish components from one another, and do not represent a specific order or sequence.

[0013] The iron casting according to the embodiment of the present invention is obtained by casting using an austenitic casting material. "Austenitic casting material" refers to a material in which the main structure of the matrix (iron matrix structure excluding graphite) of the iron casting at room temperature is austenitic. For example, the proportion of austenitic phase in the matrix of the iron casting is 50% or more. The proportion of austenitic phase in the matrix of the iron casting is preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, even more preferably 90% or more, and even more preferably 95% or more.

[0014] In this disclosure, "casting" includes casting by various casting methods such as sand casting, metal mold casting, die casting, and lost wax casting. Furthermore, the "mass %" of an element refers to the percentage of the mass of the element relative to the mass of the austenitic casting material. For example, the expression "an element of A mass % to B mass %" means that the mass % of the element is A mass % to B mass %. For example, the expression "an element of 0 mass % to B mass %" means that the element is not included or that the mass % of the element is B mass % or less. The "balance" refers to components other than the listed elements that make up the austenitic casting material.

[0015] <First Form of Casting Material> A first form of an austenitic casting material (hereinafter referred to as "the material") contains 10.0 mass % or more and 50.0 mass % or less of Ni, 0.001 mass % or more and 1.000 mass % or less of N, 0.0001 mass % or more and 0.0500 mass % or less of Mg, and the balance being Fe and unavoidable elements.

[0016] (Ni: Nickel) A first embodiment of the present material contains 10.0% by mass or more and 50.0% by mass or less of Ni. In the first embodiment of the present material, by setting the Ni content to 10.0% by mass or more and 50.0% by mass or less, Ni is segregated around the graphite. In other words, by concentrating Ni in the region around the graphite, austenite is stabilized. By setting the lower limit of the Ni content to 10.0% by mass, austenite can be stabilized and martensite formation can be suppressed. Therefore, a decrease in the ductility of the iron casting can be suppressed and the machinability of the iron casting can be improved. Furthermore, by setting the upper limit of the Ni content to 50.0% by mass, an increase in the linear expansion coefficient can be suppressed. The same applies to the following embodiments of the present material.

[0017] In the first embodiment of this material, the lower limit of the Ni content is preferably 11.0 mass%, more preferably 12.0 mass%, more preferably 13.0 mass%, more preferably 14.0 mass%, more preferably 15.0 mass%, more preferably 16.0 mass%, more preferably 17.0 mass%, more preferably 18.0 mass%, more preferably 19.0 mass%, more preferably 20.0 mass%, more preferably 21.0 mass%, more preferably 22.0 mass%, more preferably 23.0 mass%, and more preferably 24.0 mass%. More preferably, the content is 25.0% by mass, more preferably 25.5% by mass, more preferably 26.0% by mass, more preferably 27.0% by mass, more preferably 28.0% by mass, more preferably 28.5% by mass, more preferably 29.0% by mass, more preferably 30.0% by mass, more preferably 30.5% by mass, more preferably 31.0% by mass, more preferably 31.5% by mass, more preferably 32.0% by mass, more preferably 32.5% by mass, and even more preferably 33.0% by mass. The same applies to the following embodiments of the material.

[0018] In the first embodiment of this material, the upper limit of the Ni content is preferably 49.0 mass%, more preferably 48.0 mass%, more preferably 47.0 mass%, more preferably 46.0 mass%, more preferably 45.0 mass%, more preferably 44.0 mass%, more preferably 43.0 mass%, more preferably 42.0 mass%, more preferably 41.5 mass%, more preferably 41.0 mass%, more preferably 40.5 mass%, and even more preferably 40.0 mass%, relative to the above-mentioned lower limits. The same applies to the following embodiments of this material.

[0019] (N: Nitrogen) A first embodiment of the material contains 0.001% by mass or more and 1.000% by mass or less of N. In the first embodiment of the material, by setting the lower limit of the N content to 0.001% by mass, the mechanical properties of the iron casting can be improved by solid-solution strengthening of the iron matrix structure. Furthermore, by setting the upper limit of the N content to 1.000% by mass, the probability of gas defects such as pinholes and blowholes occurring when the material is cast can be reduced. The same applies to the following embodiments of the material.

[0020] In the first embodiment of the material, the lower limit of the N content is preferably 0.004 mass%, more preferably 0.007 mass%, more preferably 0.010 mass%, and even more preferably 0.011 mass%, as in the following embodiments of the material.

[0021] In the first embodiment of the material, the upper limit of the N content is preferably 0.800% by mass, more preferably 0.600% by mass, more preferably 0.400% by mass, more preferably 0.200% by mass, more preferably 0.100% by mass, more preferably 0.070% by mass, and even more preferably 0.040% by mass, relative to each of the above lower limits. The same applies to the following embodiments of the material.

[0022] (Mg: Magnesium) The first embodiment of the material contains 0.0001% by mass or more and 0.0500% by mass or less of Mg. In the first embodiment of the material, for example, N dissolved in the molten metal is prone to gas defects due to a decrease in solubility as the temperature decreases and solidification progresses. Gas defects are particularly likely to occur near the casting surface, where the solidification crystal growth rate is rapid. In the first embodiment of the material, by setting the lower limit of the Mg content to 0.0001% by mass, for example, magnesium nitride can be formed by combining with N mixed into the molten metal from the atmosphere, etc. This allows N mixed into the molten metal to be fixed as magnesium nitride. This reduces the probability of gas defects occurring due to N mixed into the molten metal during solidification. Furthermore, by setting the upper limit of the Mg content to 0.0500% by mass, the graphite crystallized during solidification of the molten metal is more likely to become flaked, preventing the graphite from becoming worm-like or spheroidal. Therefore, it is possible to suppress a decrease in the damping ratio of the iron casting obtained by solidifying this molten metal. Therefore, it is possible to provide a casting material that can suppress the occurrence of gas defects and exhibit good damping characteristics. The same applies to the following embodiments of this material.

[0023] In the first embodiment of the material, the lower limit of the Mg content is preferably 0.0004 mass%, more preferably 0.0007 mass%, more preferably 0.0010 mass%, more preferably 0.0014 mass%, more preferably 0.0018 mass%, more preferably 0.0022 mass%, more preferably 0.0026 mass%, more preferably 0.0030 mass%, more preferably 0.0034 mass%, more preferably 0.0038 mass%, more preferably 0.0045 mass%, and more preferably 0.0050 mass%. , more preferably 0.0055% by mass, more preferably 0.0060% by mass, more preferably 0.0065% by mass, more preferably 0.0070% by mass, more preferably 0.0073% by mass, more preferably 0.0078% by mass, more preferably 0.0083% by mass, more preferably 0.0088% by mass, more preferably 0.0095% by mass, more preferably 0.0100% by mass, more preferably 0.0120% by mass, more preferably 0.0150% by mass, and even more preferably 0.0175% by mass. The same applies to the following embodiments of the material.

[0024] In the first embodiment of this material, the upper limit of the Mg content is preferably 0.0475% by mass, more preferably 0.0450% by mass, more preferably 0.0425% by mass, more preferably 0.0400% by mass, more preferably 0.0375% by mass, more preferably 0.0350% by mass, more preferably 0.0325% by mass, more preferably 0.0300% by mass, more preferably 0.0275% by mass, more preferably 0.0250% by mass, more preferably 0.0225% by mass, and even more preferably 0.0200% by mass, relative to the respective lower limits. The same applies to the following embodiments of this material.

[0025] (Fe: iron, inevitable elements) The balance in the first embodiment of this material is Fe and inevitable elements. Examples of inevitable elements contained in the balance include P (phosphorus), Cu (copper), Cr (chromium), Mo (molybdenum), V (vanadium), As (arsenic), Sn (tin), Ca (calcium), Nb (niobium), B (boron), Pb (lead), Sb (antimony), W (tungsten), Te (tellurium), Bi (bismuth), and Zn (zinc). The content of inevitable elements is, for example, preferably 10.0% by mass or less in total, more preferably 5.0% by mass or less in total, more preferably 3.0% by mass or less in total, and even more preferably 1.0% by mass or less in total. The same applies to the following embodiments of this material.

[0026] <Second Form of Casting Material> A second form of the present material contains 0.10 mass % to 3.50 mass % C, 10.0 mass % to 50.0 mass % Ni, 0.001 mass % to 1.000 mass % N, and 0.0001 mass % to 0.0500 mass % Mg, with the balance being Fe and unavoidable elements.

[0027] (C: Carbon) A second embodiment of the present material contains 0.10% by mass or more and 3.50% by mass or less of C. In the second embodiment of the present material, by setting the lower limit of the C content to 0.10% by mass, the liquidus temperature of the material can be lowered. This improves the flowability of the material. Furthermore, by setting the lower limit of the C content to 0.10% by mass, the amount of graphite crystallization or precipitation can be increased. This improves the machinability of the iron casting. Furthermore, by setting the upper limit of the C content to 3.50% by mass, graphite flotation can be suppressed. This prevents a decrease in the strength and ductility of the iron casting. Furthermore, by setting the upper limit of the C content to 3.50% by mass and the upper limit of the Ni content, which acts as a graphitization-promoting element, to 50.0% by mass, excessive graphitization of C can be suppressed. This prevents the formation of coarse graphite. This improves the elongation of the iron casting. Furthermore, by setting the upper limit of the C content to 3.50 mass%, it is possible to suppress the occurrence of gas defects caused by CO gas. Furthermore, by setting the C content to 0.10 mass% or more and 3.50 mass% or less, it is possible to improve the damping ratio of the iron casting due to frictional heat generated between the crystallized graphite and the iron matrix interface and internal friction loss of the graphite itself. The same applies to the following embodiments of this material.

[0028] In a second embodiment of the material, the lower limit of the C content is preferably 0.15% by mass, more preferably 0.20% by mass, more preferably 0.40% by mass, more preferably 0.70% by mass, more preferably 1.00% by mass, more preferably 1.25% by mass, more preferably 1.50% by mass, and even more preferably 1.75% by mass. Setting the lower limit of the C content to 0.70% by mass increases the tendency of graphite crystallizing during solidification to form a eutectic structure, thereby increasing the amount of expansion of graphite and suppressing the occurrence of shrinkage cavities. The same applies to the following embodiments of the material.

[0029] In a second embodiment of this material, the upper limit of the C content is preferably 3.30% by mass, more preferably 3.20% by mass, more preferably 3.15% by mass, more preferably 3.10% by mass, more preferably 3.00% by mass, more preferably 2.95% by mass, more preferably 2.90% by mass, more preferably 2.85% by mass, more preferably 2.80% by mass, more preferably 2.75% by mass, more preferably 2.70% by mass, more preferably 2.65% by mass, more preferably 2.60% by mass, more preferably 2.55% by mass, more preferably 2.50% by mass, more preferably 2.45% by mass, and even more preferably 2.40% by mass, relative to the respective lower limits. The same applies to the following embodiments of this material.

[0030] <Third Form of Casting Material> A third form of the present material contains 0.10 mass % to 3.50 mass % C, 0.01 mass % to 4.50 mass % Si, 10.0 mass % to 50.0 mass % Ni, 0.001 mass % to 1.000 mass % N, and 0.0001 mass % to 0.0500 mass % Mg, with the balance being Fe and unavoidable elements.

[0031] (Si: Silicon) A third embodiment of the present material contains 0.01% by mass or more and 4.50% by mass or less of Si. In this third embodiment of the present material, the Ni content is set to 10.0% by mass or more and 50.0% by mass or less, and the Si content is set to 0.01% by mass or more and 4.50% by mass or less, thereby causing Ni to segregate around the graphite, and as a result, causing Si to segregate in the final solidification region. In other words, by concentrating Ni in the region around the graphite, austenite is stabilized, and Si is concentrated in the final solidification region, which is the residual liquid side. Setting the lower limit of the Si content to 0.01% by mass facilitates lowering the liquidus temperature of the present material. This facilitates improving the fluidity of the present material. Furthermore, setting the lower limit of the Si content to 0.01% by mass facilitates increasing the ratio of the Si content to the C content. This inhibits the formation of CO gas. This reduces gas defects on the surface of the iron casting. In addition, by setting the lower limit of the Si content to 0.01 mass%, the N mixed into the molten metal can be converted into silicon nitride (Si ３ N ４ ) can be fixed as 0.01% by mass or more. Therefore, when the molten metal solidifies, the probability of gas defects occurring due to N mixed in the molten metal can be reduced. Furthermore, by setting the upper limit of the Si content to 4.50% by mass, the amount of Si dissolved in the Fe (iron matrix) can be reduced. This can suppress an increase in the linear expansion coefficient. Furthermore, by setting the upper limit of the Si content, which acts as a graphitization-promoting element, to 4.50% by mass, excessive graphitization of C can be suppressed. This can suppress the generation of coarse graphite. Therefore, the elongation of the iron casting can be improved. Furthermore, by setting the content of Si, which has a graphitization effect similar to that of C, to 0.01% by mass or more and 4.50% by mass or less, the damping ratio of the iron casting can be improved due to frictional heat generation between the interface between the crystallized graphite and the iron matrix and internal friction loss of the graphite itself. The same applies to the following embodiments of this material.

[0032] In a third embodiment of the material, the lower limit of the Si content is preferably 0.05% by mass, more preferably 0.10% by mass, more preferably 0.15% by mass, more preferably 0.18% by mass, more preferably 0.20% by mass, more preferably 0.25% by mass, more preferably 0.50% by mass, more preferably 0.75% by mass, more preferably 1.00% by mass, more preferably 1.20% by mass, more preferably 1.30% by mass, and even more preferably 1.40% by mass. The same applies to the following embodiments of the material.

[0033] In a third embodiment of this material, the upper limit of the Si content is preferably 4.30 mass%, more preferably 4.10 mass%, more preferably 3.90 mass%, more preferably 3.70 mass%, more preferably 3.50 mass%, more preferably 3.30 mass%, more preferably 3.10 mass%, more preferably 2.90 mass%, more preferably 2.70 mass%, more preferably 2.50 mass%, more preferably 2.30 mass%, and even more preferably 2.10 mass%, relative to the above-mentioned lower limits. The same applies to the following embodiments of this material.

[0034] <Fourth form of casting material> A fourth form of the present material contains 0.10 mass % to 3.50 mass % C, 0.01 mass % to 4.50 mass % Si, 0.01 mass % to 4.50 mass % Mn, 10.0 mass % to 50.0 mass % Ni, 0.001 mass % to 1.000 mass % N, and 0.0001 mass % to 0.0500 mass % Mg, with the balance being Fe and unavoidable elements.

[0035] (Mn: Manganese) A fourth embodiment of the present material contains 0.01% by mass or more and 4.50% by mass or less of Mn. In this fourth embodiment of the present material, by setting the Mn content to 0.01% by mass or more and 4.50% by mass or less, a synergistic effect with Ni stabilizes austenite and suppresses the formation of martensite. This improves the machinability of the iron casting. By setting the lower limit of the Mn content to 0.01% by mass, austenite can be stabilized even at room temperature. Furthermore, by setting the upper limit of the Mn content to 4.50% by mass, the amount of Mn dissolved in the Fe (iron matrix) can be reduced. This suppresses an increase in the linear expansion coefficient. Furthermore, by setting the upper limit of the Mn content to 4.50% by mass, MnO suspended in the molten metal can be prevented from reacting with C in the molten metal to generate CO gas. This suppresses the generation of gas defects due to CO gas. The same applies to the following embodiments of the present material.

[0036] In the fourth embodiment of the material, the lower limit of the Mn content is preferably 0.05 mass%, more preferably 0.07 mass%, more preferably 0.08 mass%, more preferably 0.09 mass%, more preferably 0.10 mass%, and even more preferably 0.13 mass%. The same applies to the following embodiments of the material.

[0037] In a fourth embodiment of the material, the upper limit of the Mn content is preferably 4.00% by mass, more preferably 3.50% by mass, more preferably 3.20% by mass, more preferably 3.00% by mass, more preferably 2.50% by mass, more preferably 2.00% by mass, more preferably 1.50% by mass, more preferably 1.00% by mass, more preferably 0.75% by mass, more preferably 0.50% by mass, and even more preferably 0.25% by mass, relative to the respective lower limits. The same applies to the following embodiments of the material.

[0038] <Fifth Form of Casting Material> A fifth form of the present material contains 0.10 mass % to 3.50 mass % C, 0.01 mass % to 4.50 mass % Si, 0.01 mass % to 4.50 mass % Mn, 10.0 mass % to 50.0 mass % Ni, 0.001 mass % to 1.000 mass % N, 0.10 mass % to 10.00 mass % Co, and 0.0001 mass % to 0.0500 mass % Mg, with the balance being Fe and unavoidable elements.

[0039] (Co: Cobalt) A fifth embodiment of the present material contains 0.10% by mass or more and 10.00% by mass or less of Co. In the fifth embodiment of the present material, by setting the Co content to 0.10% by mass or more and 10.00% by mass or less, the linear expansion coefficient can be further reduced by a synergistic effect with Ni. By setting the lower limit of the Co content to 0.10% by mass, the minimum value of the linear expansion coefficient can be reduced by a synergistic effect with Ni. Furthermore, by setting the upper limit of the Co content to 10.00% by mass, it is possible to suppress an increase in the linear expansion coefficient after reaching a minimum value due to excessive addition of Co.

[0040] In the fifth form of this material, the lower limit of the Co content is preferably 0.50 mass%, more preferably 1.00 mass%, more preferably 1.50 mass%, more preferably 2.00 mass%, more preferably 2.50 mass%, more preferably 3.00 mass%, more preferably 3.50 mass%, more preferably 3.80 mass%, and even more preferably 4.00 mass%.

[0041] In the fifth embodiment of this material, the upper limit of the Co content is preferably 9.50 mass%, more preferably 9.00 mass%, more preferably 8.50 mass%, more preferably 8.00 mass%, more preferably 7.50 mass%, more preferably 7.00 mass%, more preferably 6.50 mass%, more preferably 6.25 mass%, more preferably 6.00 mass%, and even more preferably 5.50 mass%, relative to the respective lower limits. Furthermore, the Co content is preferably 4.00 mass% to 5.50 mass% when the Ni content is 31.0 mass% to 34.0 mass%. Furthermore, when the lower limit of the Ni content is 28.5 mass%, the Co content is preferably 5.00 mass% to 8.00 mass%. By setting the lower and upper limits of the Co content as described above, the linear expansion coefficient is more easily reduced due to the synergistic effect with Ni.

[0042] Casting using this material in the above-described form can suppress the generation of gas defects and provide iron castings with excellent damping properties. An example of a casting method using this material involves first melting raw materials (iron scrap, returned materials, etc.) in a melting furnace (such as a high-frequency induction furnace) and adjusting the components to produce a molten metal of the desired composition. Next, this molten metal is poured into a predetermined mold (such as a sand mold or metal mold) and solidified by cooling to room temperature within the mold. Finally, the mold is demolded to obtain the iron casting. Iron castings cast using this material are suitable for a wide variety of applications requiring high vibration absorption. Examples of applications for this iron casting include machine tool beds, columns and spindle peripherals, bases for semiconductor manufacturing equipment, and surface plates for precision measuring instruments, as well as components and components for various machines, devices, and equipment that require high damping performance.

[0043] <Examples and Comparative Examples> Figure 1 shows the composition, gas defect depth, and damping ratio of examples and comparative examples of iron castings cast using the present material. Figure 2 shows the depth of gas defects in a Y-section test piece of Comparative Example 1. In Figure 1, the C (carbon) content (mass%) is a value measured by combustion-infrared absorption spectroscopy using an "EMIA-Expert" material carbon / sulfur analyzer manufactured by Horiba, Ltd. The Si (silicon), Ni (nickel), Co (cobalt), and Mg (magnesium) contents (mass%) are values ​​measured by inductively coupled plasma optical emission spectroscopy using an "SPS3520UV" optical emission spectrometer manufactured by Hitachi High-Tech Science Corporation. The contents (mass%) of other elements are values ​​measured by optical emission spectroscopy using a "PDA-8000" optical emission spectrometer manufactured by Shimadzu Corporation. The gas defect depth (mm) is the maximum distance measured from the surface (casting surface) of the iron casting to the deepest of multiple gas defects scattered in the depth direction (perpendicular to the casting surface) when gas defects are present inside the iron casting. Specifically, it indicates the maximum distance measured from the surface to the deepest of multiple gas defects scattered in the depth direction using a Y-section test specimen taken from a Y-section B test piece in accordance with JIS G 5502 (spheroidal graphite cast iron). For example, the gas defect depth in Comparative Example 1 is 6.35 mm, which is the value measured at the distance indicated by the symbol D in the Y-section test specimen shown in Figure 2. In Figure 1, the gas defect depth of 0 mm indicates that no gas defect formation was confirmed in the Y-section test specimen. The damping ratio (%) was determined by analyzing the natural frequency components of the mode (mode 1) having the lowest natural frequency among the multiple vibration modes obtained by a hammering test using a rectangular parallelepiped test piece measuring 20 x 20 x 100 mm taken from the above-mentioned Y-type B test material.In the hammering test, an acceleration sensor (NP-3211 manufactured by Ono Sokki) was attached to the test piece, and the test piece was struck using an impulse hammer (GK-3100 manufactured by Ono Sokki). The signals obtained from the acceleration sensor and the impulse hammer were input into an FFT analyzer (DS3100 manufactured by Ono Sokki) and analyzed using analysis software (DS-0320 manufactured by Ono Sokki).

[0044] Comparison of Examples 1 to 17 with Comparative Example 1 As shown in FIG. 1 , the Mg content in Examples 1 to 17 is 0.0001% by mass or more, while the Mg content in Comparative Example 1 is 0% by mass (less than 0.0001% by mass). As shown in FIG. 1 , the depth of gas defects in Examples 1 to 17 is smaller than that in Comparative Example 1. Specifically, the depth of gas defects in Comparative Example 1 is 6.35 mm, while the depth of gas defects in Examples 1 to 17 is 4.97 mm or less. Thus, by setting the Mg content to 0.0001% by mass or more in Examples 1 to 17, the region where gas defects occur can be reduced to a region close to the casting surface. Therefore, the machining allowance required to remove gas defects scattered directly below the casting surface can be reduced.

[0045] (Comparison between Examples 1 to 17 and Comparative Example 2) As shown in FIG. 1 , the Mg contents of Examples 1 to 17 are 0.0500 mass% or less, while the Mg content of Comparative Example 2 is 0.0590 mass% (exceeding 0.0500 mass%). As shown in FIG. 1 , Examples 1 to 17 have higher damping ratios than Comparative Example 2. Specifically, the damping ratio of Comparative Example 2 is 0.085%, while the damping ratios of Examples 1 to 17 are 0.114% or more. Thus, in Examples 1 to 17, by setting the Mg content to 0.0500 mass% or less, it is possible to suppress a decrease in the damping ratio.

[0046] (Comparison of Examples 4 to 15 with Examples 1 to 3) As shown in FIG. 1 , the Mg content in Examples 4 to 15 is 0.0050% by mass or more, while the Mg content in Examples 1 to 3 is 0.0038% by mass or less (less than 0.0050% by mass). As shown in FIG. 1 , no gas defect formation was observed in Examples 4 to 15. Thus, in Examples 4 to 15, by increasing the Mg content to 0.0050% by mass or more, the occurrence of gas defects can be suppressed. Therefore, it is possible to provide iron castings that are close to the finished product, i.e., near-net-shape. This reduces the cost of materials used in casting and the cost of processing after casting.

[0047] (Comparison between Examples 4 to 15 and Example 16) As shown in FIG. 1 , the C content in Examples 4 to 15 is 3.15% by mass or less, while the C content in Example 16 is 3.19% by mass (exceeding 3.15% by mass). Furthermore, the Si content in Examples 4 to 15 is 0.18% by mass or more, while the Si content in Example 16 is 0.15% by mass (less than 0.18% by mass). As shown in FIG. 1 , no gas defect formation was observed in Examples 4 to 15. Thus, in Examples 4 to 15, by setting the Mg content to 0.0050% by mass or more, the C content to 3.15% by mass or less, and the Si content to 0.18% by mass or more, the occurrence of gas defects can be suppressed. Therefore, it is possible to provide iron castings in a state close to the finished product, i.e., near-net-shape. This reduces the cost of materials used in casting and the cost of post-casting processing.

[0048] (Comparison between Examples 4 to 15 and Example 17) As shown in FIG. 1 , the Ni content in Examples 4 to 15 is 41.0 mass% or less, while the Ni content in Example 17 is 41.4 mass% (exceeding 41.0 mass%). Furthermore, the Co content in Examples 4 to 15 is 0.10 mass% or more, while the Co content in Example 17 is 0 mass% (less than 0.10 mass%). As shown in FIG. 1 , no gas defect formation was observed in Examples 4 to 15. Thus, in Examples 4 to 15, by setting the Mg content to 0.0050 mass% or more, the Ni content to 41.0 mass% or less, and the Co content to 0.10 mass% or more, the occurrence of gas defects can be suppressed. Therefore, it is possible to provide iron castings in a state close to the finished product, i.e., near-net-shape. This reduces the cost of materials used in casting and the cost of post-casting processing.

Claims

1. An austenitic casting material comprising: 0.10 mass% or more and 3.50 mass% or less of C; 0.01 mass% or more and 4.50 mass% or less of Si; 0.01 mass% or more and 4.50 mass% or less of Mn; 10.0 mass% or more and 50.0 mass% or less of Ni; 0.001 mass% or more and 1.000 mass% or less of N; 0 mass% or more and 10.00 mass% or less of Co; and 0.0001 mass% or more and 0.0500 mass% or less of Mg, with the remainder being Fe and unavoidable elements.

2. The casting material according to claim 1, wherein the Mg content is 0.0005 mass% or more and 0.0500 mass% or less.

3. The casting material according to claim 2, wherein the Mg content is 0.0005 mass% or more and 0.0350 mass% or less.

4. The casting material according to claim 2, wherein the Mg content is 0.0050 mass% or more and 0.0500 mass% or less.

5. The casting material according to claim 4, wherein the Mg content is 0.0050 mass% or more and 0.0350 mass% or less.

6. A casting material according to any one of claims 1 to 5, wherein the Ni content is 20.0 mass% or more and 45.0 mass% or less.

7. The casting material according to claim 6, wherein the C content is 1.00 mass % or more and 3.50 mass % or less.

8. The casting material according to claim 7, wherein the Si content is 0.10 mass% or more and 4.00 mass% or less.

9. The casting material according to claim 8, wherein the Mn content is 0.10 mass % or more and 3.50 mass % or less.

10. The casting material according to claim 9, wherein the Co content is 0.10 mass % or more and 8.50 mass % or less.

11. An iron casting cast using the casting material according to claim 10.

12. An austenitic casting material comprising: 0 mass% or more and 3.50 mass% or less of C; 0 mass% or more and 4.50 mass% or less of Si; 0.01 mass% or more and 4.50 mass% or less of Mn; 10.0 mass% or more and 50.0 mass% or less of Ni; 0.001 mass% or more and 1.000 mass% or less of N; 0 mass% or more and 10.00 mass% or less of Co; and 0.0001 mass% or more and 0.0500 mass% or less of Mg, with the remainder being Fe and unavoidable elements.

13. An iron casting cast using the casting material according to claim 12.

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