JP2008303434A - High strength spheroidal graphite iron casting having excellent wear resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength spheroidal graphite iron castings, which have as-cast: high strength satisfying the tensile strength of >900 MPa; and high ductility satisfying the high ductility of ≥3%, further which have excellent wear resistance, and in which chilling in a thin part with a thickness of ≤10 mm is prevented. <P>SOLUTION: The high strength spheroidal graphite iron castings have a composition comprising, by mass, 3 to 4% C, 1.8 to 3.5% Si, 0.2 to 2% Mn, 0.003 to 0.03% S, 0.05 to 1% Nb, 1.4 to 4% Cu and 0.015 to 0.07% Mg, further comprising one or two selected from 0.05 to 0.4% Mo and 0.05 to 0.6% V, or further comprising ≤0.5% Ni, and the balance Fe with inevitable impurities. In this way, the high strength spheroidal graphite iron castings combining the tensile strength of >900 MPa and the tensile strength of ≥3% as-cast, further having excellent wear resistance, and free from the generation of chilling in a thin part can be obtained. It is preferable that, as the impurities, the content of P be regulated to <0.04%, and the content of Cr be regulated to <0.1%. Further, <0.03% Ti and <0.1% W are allowable, and also, <0.05% Al, <0.05% REM, <0.002% Ca, <0.002% Ba and <0.02% Bi are allowable. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spheroidal graphite cast iron casting suitable for machine structural parts, structural members for civil engineering, and the like, and particularly to a high-strength spheroidal graphite cast iron product having excellent ductility and wear resistance.

  Spheroidal graphite cast iron has good castability and high strength, and is widely used as a substitute for forged steel and cast steel, especially for civil engineering and construction materials and machine structural parts. From the viewpoints of weight reduction of structural members for civil engineering and construction and mechanical parts in recent years, improvement of lifespan, and economic efficiency, they are strengthened and have excellent wear resistance for structural members for civil engineering and construction and mechanical structural parts. In addition, inexpensive cast iron products tend to be used. Therefore, there is a demand for a high-strength spheroidal graphite cast iron product having high strength exceeding tensile strength: 900 MPa and excellent wear resistance in an as-cast state without performing heat treatment.

In response to such a request, for example, Patent Document 1 includes C: 3.20 to 4.00%, Si: 2.00 to 3.20%, Mn: 0.05 to 3.00% by weight ratio, and appropriate amounts of P, S, and Mg. There is proposed a spheroidal graphite cast iron product including and adjusted to Cu, further containing Cu: 0.40 to 2.00%, rare earth: 0.005 to 0.300%, and the balance being Fe. Spheroidal graphite cast iron manufactured by the technique described in Patent Document 1 contains high strength with a tensile strength of 700 N / mm ² or more and high ductility of 2% or more by containing Cu and a rare earth element in combination. Can be secured.

Patent Document 2 includes C: 3.2 to 3.9%, Si: 2.0 to 2.6%, Mn: 0.6% or less, P, S, and Mg are adjusted to appropriate amounts, and Cu: 2.4 to Spheroidal graphite cast iron containing 3.3%, Sn: 0.01 to 0.05%, and remaining Fe has been proposed. Spheroidal graphite cast iron produced by the technique described in Patent Document 2, by composite containing Cu and Sn, tensile strength: 900 N / mm ² near or with 900 N / mm ² or more high strength, elongation : High ductility of 4% or more can be secured.

  Patent Document 3 includes, by weight%, C: 3.0 to 4.5%, Si: 1.6 to 2.5%, Mn: 0.2 to 0.5%, and P, S, and Mg adjusted to appropriate amounts, Zr: High strength spheroidal graphite cast iron containing 0.0005 to 0.09%, one or two of Sn and Cu, 0.03 to 0.11% in terms of Sn, and the balance consisting of Fe and inevitable impurities has been proposed. Yes. The spheroidal graphite cast iron product produced by the technique described in Patent Document 3 is said to have a tensile strength of 900 MPa or more as it is as cast and has good machinability.

Patent Document 4 includes, by weight ratio, C: 3.20 to 4.00%, Si: 2.00 to 3.20%, Mn: 0.30 to 2.50%, and P, S, and Mg adjusted to appropriate amounts. Cu: 0.30 to 3.50%, rare earth element: 0.005 to 0.30%, promotes cooling of the molten metal consisting of the remaining Fe, cast iron products, and petals with ferrite or ferrite and pearlite around graphite And a spheroidal graphite cast iron product having an as-cast tensile strength of 800 N / mm ² or more, preferably 900 to 1000 N / mm ² and an elongation of 2% or more, preferably 3% or more. A method for producing a spheroidal graphite cast iron product has been proposed.

  Patent Document 5 includes, by weight%, C: 2.0 to 4.0%, Si: 1.5 to 4.5%, Mn: 2.0% or less, and P, S, and Mg adjusted to appropriate amounts, and Cu : 1.8-4.0%, or even Sn: 0.08% or less, and / or Mo: 0.5% or less, Ni: 0.5% or less, one or two of them, the balance consisting of Fe and inevitable impurities, high Strength spheroidal graphite cast iron has been proposed. Spheroidal graphite cast iron products produced by the technique described in Patent Document 5 have a high tensile strength of 800 MPa or more, as-cast, can remarkably suppress water embrittlement, and machinability. Is going to improve.

In Patent Document 6, Mg is appropriate in terms of weight ratio: C: 3.0 to 4.0%, Si: 1.6 to 3.3%, Mn: 0.2 to 1.0%, Ni: 0.5 to 2.0%, Mo: 0.2 to 1.5% A high-strength ductile containing Cu: 1.0 to 3.0%, V: 0.03 to 0.2%, the balance being Fe and unavoidable impurities, and the base structure being pearlite or pearlite and bainite. Cast iron has been proposed. A high-strength spheroidal graphite cast iron product manufactured by the technique described in Patent Document 6 is said to have a tensile strength exceeding 1000 MPa and an elongation of 2% or more.
JP 2000-26932 A JP 2001-131678 A JP 2002-275575 A JP 2002-317219 A Japanese Patent Laid-Open No. 2003-13170 JP 2004-99923 A

However, the techniques described in Patent Documents 1, 2, 4, and 5 have a problem that wear resistance is inferior, although a certain level of high strength is obtained, and are required as civil engineering building members and machine structural parts. However, there was a problem that it was not possible to meet the demand for improved wear resistance of 1.3 times or more that of conventional products. Further, in recent years, there has been a demand for thinner and lighter castings. In particular, cast iron products having a thin portion with a thickness of 10 mm or less are likely to be whitened in the thin portion. In particular, cast iron products containing a large amount of alloy elements such as V, Cr, Mo and Zr in order to improve wear resistance have a problem that whitening cannot be prevented. In addition, the spheroidal graphite cast iron products manufactured by the techniques described in Patent Documents 3 and 6 can ensure a high strength of tensile strength: 900 N / mm ² or more, but there is no confirmation of wear resistance. It is unclear whether it has excellent wear resistance, and in the case of a cast iron product having a thin part with a thickness of 10 mm or less, it contains Zr, Sn or Mo, V. There was a problem that whitening of the thin-walled portion could not be prevented.

  The present invention solves the above-mentioned problems of the prior art, and as-cast, has a tensile strength of over 900 MPa, an elongation of over 3.0%, and a superior wear resistance. An object of the present invention is to provide a high-strength spheroidal graphite cast iron product that can prevent whitening in a thin portion having a thickness of 10 mm or less. Here, “excellent wear resistance” means having a wear resistance 1.3 times or more that of a conventional product (equivalent to FCD800). The target strength and ductility here refer to the strength and ductility when the molten metal is poured into a sand-type Y-shaped keel block (thickness of parallel part 25 mm) and a tensile test is performed as-cast.

  It has been conventionally known that cast iron products having high strength are easily whitened. In particular, when a large amount of carbide-forming elements such as Cr, Mo, V, and W are added to improve wear resistance, whitening occurs more significantly, especially when the thickness is 10 mm or less. Become. When whitening occurs, the strength of the cast iron product decreases to about 1/2 to 1/3, and the ductility is almost lost. Incidentally, “whitening” refers to a phenomenon in which brittle eutectic carbides (redebrite) crystallize and cast iron products become hard and brittle. A cast iron product that has turned white appears to glow white when broken.

  In order to achieve the above-mentioned object, the present invention first made extensive studies on various factors that affect the strength and wear resistance of an as-cast spheroidal graphite cast iron product. As a result, in order to combine the as-cast spheroidal graphite cast iron products with high strength exceeding 900MPa and excellent wear resistance, a high-strength base structure must be used. It came to mind that it is important to disperse many fine and extremely hard carbides. Further, it was also found that it is important that the elements constituting the harder carbide do not dissolve in the matrix and promote whitening. According to further studies by the present inventors, in order to obtain a high-strength base structure, the inclusion of Cu and the inclusion of Nb as an element constituting a hard carbide are effective, respectively. It was found that if it exists, it will not dissolve in the base, and whitening will be suppressed. Furthermore, the present inventors have obtained a novel finding that, by containing a small amount of Mo and / or V together with Nb, a decrease in strength is suppressed even when the thickness of the cast iron product is increased, and the wear resistance is further improved. According to the study by the present inventors, this is because a part of Mo and V is solid-solved in MC carbide to further harden the carbide, and also solid-dissolves in the base to strengthen the base, and Nb This is because it becomes hard carbide without dissolving in the base, and absorbs excess Mo and V from the molten metal to form MC carbide, contributing to improvement of wear resistance and suppression of whitening. Conceivable.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: 3-4%, Si: 1.8-3.5%, Mn: 0.2-2%, S: 0.003-0.03%, Nb: 0.05-1%, Cu: 1.4-4%, Mg : Containing 0.015-0.07%, Mo: 0.05-0.4%, V: containing one or two selected from 0.05-0.6%, having a composition consisting of the balance Fe and inevitable impurities, A high-strength spheroidal graphite cast iron product characterized by excellent wear resistance.
(2) In (1), the composition contains, in mass%, one or two selected from Mo: 0.05 to 0.4% and V: 0.05 to 0.6% in total of 0.8% or less. A high-strength spheroidal graphite cast iron product characterized by having a composition.
(3) A high-strength spheroidal graphite cast iron product according to (1) or (2), further comprising Ni: 0.5% or less by mass% in addition to the above composition.
(4) A high-strength spheroidal graphite cast iron product according to any one of (1) to (3), wherein the inevitable impurities are adjusted to P less than 0.04% and Cr less than 0.1%.

  According to the present invention, a civil engineering / architectural member that has an as-cast high tensile strength exceeding about 900 MPa, high ductility, and excellent wear resistance, and does not cause whitening even in a thin portion. And high-strength spheroidal graphite cast iron products for machine structural parts can be easily manufactured, and it has remarkable industrial effects. Further, the cast iron product according to the present invention is subjected to tempering treatment for stress relaxation, or is subjected to quenching tempering treatment or austempering treatment so that the base structure is martensite (tempered martensite) or bainite (austenite + It is also possible to use it after adjusting to bainitic ferrite. Further, the cast iron product according to the present invention is a high strength and high ductility cast iron product that has no whitening even in a thin portion and has excellent wear resistance. It also has an effect that it can be applied to a landscape member, a manhole cover, a stop for civil engineering, and various other thin wear-resistant cast iron members.

First, the reasons for limiting the composition of the spheroidal graphite cast iron product of the present invention will be described. Hereinafter, the mass% in the composition is simply expressed as%.
C: 3-4%
C is an important element that affects the amount of spheroidal graphite crystallization, the amount of layered cementite in pearlite and the amount of MC carbide precipitated, and the fluidity and whitening of the molten metal. When the C content is less than 3%, the amount of graphite is particularly insufficient, whitening is promoted, fluidity is insufficient, and it becomes difficult to obtain a spheroidal graphite cast iron that ensures desired high strength and high ductility. On the other hand, if the content exceeds 4%, the amount of graphite becomes excessive and the strength decreases. For this reason, C was limited to 3-4%. In addition, Preferably, it is 3.2 to 4.0%.

Si: 1.8-3.5%
Si is an element that affects the fluidity and whitening of the molten metal, and in the present invention, it needs to be contained in an amount of 1.8% or more. If Si is less than 1.8%, the fluidity is lowered, making it difficult to fill the thin portion with molten metal, and whitening also occurs. On the other hand, if the content exceeds 3.5%, ferrite tends to precipitate in the matrix, making it difficult to increase the strength. For this reason, Si was limited to the range of 1.8 to 3.5%. In addition, Preferably, it is 2.1 to 3.0%.

Mn: 0.2-2%
Mn is a useful element that dissolves in the base and contributes to increasing the strength of the base. In order to obtain such an effect, the content of 0.2% or more is required. If Mn is less than 0.2%, the strength decreases, and the desired high strength cannot be ensured. On the other hand, if Mn content exceeds 2%, Mn segregates at the grain boundary of the solidification cell, and the material becomes brittle. For this reason, Mn was limited to the range of 0.2 to 2%. In addition, Preferably, it is 0.5 to 1.8%.

S: 0.003-0.03%
S is an element having an action of suppressing whitening by forming a compound with Mg, REM, Ca and the like to form a nucleus of graphite. In order to acquire such an effect, it contains 0.003% or more in this invention. On the other hand, a content exceeding 0.03% lowers the graphite shape. For this reason, S was limited to the range of 0.003 to 0.03%. In addition, Preferably it is 0.005-0.02%.

Nb: 0.05-1%
Nb forms hard MC-type carbides and contributes effectively to improving wear resistance, and also refines the solidified structure and contributes to high strength. Nb is a white glaze produced by V, Mo, etc. Since it also has an action to suppress crystallization, it is an extremely important element in the present invention. Such an effect is recognized when the content is 0.05% or more. However, when the content exceeds 1%, the MC carbide is coarsened and the strength is reduced. For this reason, Nb was limited to the range of 0.05 to 1%. In addition, Preferably, it is 0.1 to 0.8%.

Cu: 1.4-4%
Cu is an important element in the present invention that has the effect of densifying the pearlite structure and increasing the strength of the matrix. In order to obtain such an effect, the content of 1.4% or more is required. If it is less than 1.4%, the above effects cannot be expected. On the other hand, if the content exceeds 4%, Cu is segregated in large quantities at the grain boundaries of the solidification cell, leading to a decrease in strength. For this reason, Cu was limited to the range of 1.4 to 4%. In addition, Preferably it is 1.5 to 3.8%.

Mg: 0.015-0.07%
Mg has a function of spheroidizing graphite, and is an essential element in spheroidal graphite cast iron. In order to secure such an effect, it is necessary to contain 0.015% or more of Mg. If the Mg content is less than 0.015%, worm-like graphite appears and the strength decreases. On the other hand, if the content exceeds 0.07%, Mg oxide generates a large amount of dross and increases surface defects. For this reason, Mg was limited to the range of 0.015 to 0.07%.

Further, since excessive Mg content promotes whitening, it is preferable to contain about 0.015 to 0.04% in a casting having a thin portion with a thickness of 10 mm or less. Further, in the case of a casting having a wall thickness exceeding 25 mm, the content is preferably about 0.02 to 0.05%. Further, in the case of a casting having a thickness exceeding 100 mm, the content is preferably about 0.03 to 0.07%.
One or two selected from Mo: 0.05 to 0.4%, V: 0.05 to 0.6%
Both Mo and V are dissolved in MC carbide to strengthen the MC carbide, and further have the effect of increasing the strength by solid solution in the matrix, and are important elements in the present invention. Contains one or two. The remainder of Mo and V, which cannot be completely dissolved in MC carbide, also has a function of forming a solid solution in the matrix to densify and strengthen the pearlite structure. Due to the effects of Mo and V and the action of Cu described above, a cast iron product having both excellent wear resistance and high strength can be obtained. In order to obtain such an effect, it is necessary to contain one or two of Mo: 0.05% or more and V: 0.05% or more. If Mo is less than 0.05% and V is less than 0.05%, the above effects cannot be secured. On the other hand, when a large amount of V exceeds 0.6%, MC carbide is coarsened, and crystallization of the carbide cannot be suppressed as it is as cast, so that strength and ductility are lowered. In addition, when a large amount of Mo exceeds 0.4%, shrinkage nests (zaku nests) tend to appear and the soundness of cast iron products is reduced. For this reason, Mo was limited to 0.05 to 0.4%, and V was limited to 0.05 to 0.6%. In addition, when Mo and V are contained in combination, the wear resistance and strength are remarkably improved particularly in cast iron products having a thickness exceeding 30 mm. When Mo and V are contained in combination, it is preferably limited to 0.8% or less in total. This is because when the contents of Mo and V exceed 0.8% in total, crystallization of carbides becomes remarkable.

Although the above-described components are basic components, in the present invention, in addition to the basic composition described above, Ni of 0.5% or less can be contained as required.
Ni: 0.5% or less
Ni is an element having an action of promoting precipitation of pearlite, and can be contained as necessary. In order to obtain such an effect, the content is preferably 0.1% or more, but the content exceeding 0.5% inhibits the homogenization of the structure, such as partially depositing bainite as it is, and has characteristics. There is an adverse effect such as causing variation. For this reason, it is preferable to limit Ni to 0.5% or less.

The balance other than the above components is Fe and inevitable impurities. In addition, as an inevitable impurity element, it is preferable to adjust to P: less than 0.04% and Cr: less than 0.1%.
P is an element that has an effect of increasing the number of nests or segregating at the grain boundaries of the solidification cell to embrittle the material. In the present invention, P is preferably reduced as much as possible. Above 0.04%, the above-mentioned adverse effects become significant. For this reason, it is preferable to adjust P to less than 0.04%. More preferably, it is 0.03% or less.

  Cr is an element that promotes whitening and is preferably reduced in order to suppress whitening. If Cr is less than 0.1%, the adverse effect is small and acceptable. For this reason, it is preferable to adjust to Cr: less than 0.1%. In order to keep Cr within the above-mentioned range, it is important to use a melted raw material that does not contain a large amount of this element. Do not need. More preferably, Cr is less than 0.05%.

As inevitable impurities other than P and Cr, Ti: less than 0.03% and W: less than 0.1% are acceptable.
Ti and W are both elements that promote whitening, and the content of these elements is preferably low in order to suppress whitening. If Ti: less than 0.03% and W: less than 0.1%, the adverse effect is small and acceptable. For this reason, it is preferable to adjust to Ti: less than 0.03% and W: less than 0.1%. In order to make Ti and W within the above ranges, it is important to use a melting raw material that does not contain a large amount of these elements. Does not require careful selection. More preferably, Ti is less than 0.02% and W is less than 0.04%.

Inevitable impurities, Al, REM, Ca, Ba, Bi, Al: less than 0.05%, REM: less than 0.05%, Ca: less than 0.002%, Ba: less than 0.002%, Bi: less than 0.02% are acceptable it can.
Al, REM, and Ca are usually contained in Fe-Si-Mg alloys and Si-Mg alloys that are used as graphite spheroids, and REM, Ca, Al, Ba, and Bi are usually used as inoculums. It is contained in the Fe-Si alloy and Ca-Si alloy used. For this reason, Al, REM, Ca, Ba, and Bi are impurities inevitably contained in the spheroidal graphite cast iron. However, if Al is contained in an amount of 0.05% or more, it adversely affects the spheroidization of graphite and causes a decrease in strength. Moreover, when 0.05% or more of REM is contained, whitening is promoted. For this reason, it is preferable to adjust to Al: less than 0.05% and REM: less than 0.05%. If Ca is contained in an amount of 0.002% or more and Ba is contained in an amount of 0.002% or more, dross increases and the occurrence of surface defects increases. For this reason, it is preferable to adjust to Ca: less than 0.002% and Ba: less than 0.002%. Further, when Bi is contained in an amount of 0.02% or more, it may adversely affect the spheroidization of graphite and may cause carbides to crystallize. For this reason, Bi is preferably adjusted to less than 0.02%.

There is N as an inevitable impurity other than the above-described impurities, but in the case of a normal molten metal melting method, the N content is about 0.002 to 0.01%. If the content is within this range, there is no particular adverse effect.
The spheroidal graphite cast iron product of the present invention has the above-described composition, as-cast, spheroidized graphite, and the base is preferably a densified layered pearlite, and remains as-cast. Tensile strength: High strength exceeding 900 MPa, Elongation: High ductility of 3% or more, and excellent wear resistance 1.3 times or more of conventional materials (FCD800 equivalent), and wall thickness of 10 mm or less It has a feature that can prevent whitening of thin-walled parts.

Next, a preferred method for producing the spheroidal graphite cast iron product of the present invention will be described.
Melting the mother molten metal by a conventional cast iron melting method such as a high-frequency furnace, adding a graphite spheroidizing agent such as a conventional Mg-containing alloy to the mother molten metal by a plunger method, etc. After the graphite spheroidization treatment by the sandwich method or the like, the composition is further inoculated with an inoculant such as an ordinary Fe-Si alloy or Ca-Si alloy to form the above-described composition. It is preferable to pour (cast) into a conventional mold such as a mold. In the present invention, inoculation is a commonly used method, a method performed simultaneously with the spheroidizing process of graphite, a method performed at the time of transfer to a ladle, a method added to a pouring stream when pouring into a mold, a runner, etc. Any of the methods performed in the mold (in-mold inoculation) may be used. Here, it goes without saying that the “inoculation” is more effective if it is performed immediately before pouring into the mold.

  Mg-containing alloy as a graphite spheroidizing agent is an alloy containing Si, Mg, Ca, REM, Al, etc., for example, by mass%, Si: 45%, Mg: 5%, Ca: 2%, REM: 2% Al: An alloy containing 0.5% and the balance being Fe can be exemplified, but it goes without saying that the present invention is not limited to this. Moreover, although the Fe-Si alloy which is an inoculum can illustrate the alloy which is Si: 75% and remainder Fe, for example, in this invention, it is not limited to this. Needless to say, inoculating agents such as Si alloys containing Ba, Li, Ca, Al, Bi, S and the like which are commercially available other than Fe-Si alloys may be used.

  The present invention will be further described below based on examples.

Example 1
An alloying element was added to the molten mother metal melted using a high-frequency furnace so that the alloy composition shown in Table 1 was obtained. The maximum temperature of the molten metal after addition of the alloy elements was 1490 to 1580 ° C. When the molten metal after addition of the alloy elements is transferred to the ladle, a commercially available Mg-containing alloy (Fe-45 mass% Si-5 mass% Mg-2 mass% Ca-2 mass% REM-0.5 mass% Al alloy) The graphite was spheroidized by the sandwich method. Subsequently, it was inoculated with an Fe-75% Si alloy. Immediately after inoculation, a sample for chemical analysis was collected, and immediately the molten metal was poured into a sand mold (casting) to form a Y-shaped keel block (parallel part thickness 25 mm) and a plate casting (thickness 5 mm x width 30 mm). . The casting temperature was 1360 ° C to 1500 ° C.

After casting, the mold was brushed after standing for 12 hours or more, and test pieces were collected from the Y-type keel block in an as-cast state and subjected to a tensile test and a wear test. Moreover, the whitening test was implemented using the plate-shaped casting in an as-cast state. The test method was as follows.
(1) Tensile test Take a JIS 14A tensile test piece (parallel part diameter: 10mmφ x GL50mm) from a Y-type keel block and perform a tensile test at room temperature (25 ° C) in accordance with the provisions of JIS Z 2241. The tensile strength TS and the elongation El were measured.

(2) Wear test A wear test piece (disk-shaped test piece: outer diameter φ60 mm × thickness 10 mm) was collected from the Y-type keel block. The abrasion test was a two-spin rolling method. The mating material was a disk-shaped test piece made of S45C material (outer diameter φ190 mm × thickness 15 mm). In the wear test, the number of revolutions of the test piece was 700 rpm, the slip rate was 2%, the load was 75 kgf (735 N), and the test time was 60 min. The weight of the test piece was measured before and after the wear test, and the wear loss (wear amount) of the test piece was measured. The wear resistance of each cast iron product was evaluated by the ratio to the wear amount of the conventional example (cast iron product No. 10), wear ratio = (wear amount of the conventional example) / (wear amount of each cast iron product (test piece)). . Higher wear ratio means better wear resistance.

(3) Whitening test The tip of an as-cast plate-like casting (thickness 5 mm) was broken with a hammer, and the fracture surface was visually observed to check for whitening. The case where the fractured surface appears to glitter whitely was rated as “whitened” and the others were evaluated as “no whitened” and evaluated as ◯.
The obtained results are shown in Table 2.

  All examples of the present invention have high tensile strength TS: 950 MPa or more and elongation El: 3.0% or more, and high wear resistance 1.3 times or more of the conventional example (cast iron product No. 10). It is a spheroidal graphite cast iron product that has excellent properties and exhibits excellent properties in that it is not whitened even in a thin portion having a thickness of 5 mm. On the other hand, the comparative example which is out of the scope of the present invention is not able to ensure the desired high strength and high ductility characteristics, whether the tensile strength is less than 900 MPa or the elongation is less than 3.0%, and the meat Thickness: Whitening was observed at a thin part of 5 mm. In the comparative example (cast iron product No. 11) containing Mo: 0.47%, V: 0.18% and not containing Nb, no improvement in wear resistance was observed, and whitening was observed in the thin part. In addition, the comparative example (cast iron product No. 12) containing V as 0.80%, which is out of the range of the present invention, has a tensile strength of less than 900 MPa and an elongation of less than 3.0%. Ductility was not secured, and whitening was observed in the thin wall portion. In addition, the comparative example (cast iron product No. 13) containing 0.28% Cr exceeding the impurity level has a tensile strength of less than 900 MPa and an elongation of less than 3.0%, ensuring the desired high strength and high ductility. In addition, whitening was observed in the thin part. In addition, the comparative example (cast iron product No. 14) containing 1.5% with the Nb content outside the range of the present invention has a tensile strength of less than 900 MPa and an elongation of less than 3.0%. Ductility was not secured, and whitening was observed in the thin wall portion. Further, the comparative example (cast iron product No. 15) in which the Cu content falls outside the scope of the present invention has a tensile strength of less than 900 MPa, and cannot secure a desired high strength.

Claims (4)

% By mass
C: 3-4%, Si: 1.8-3.5%,
Mn: 0.2-2%, S: 0.003-0.03%,
Nb: 0.05 to 1%, Cu: 1.4 to 4%,
Mg: 0.015-0.07%
In addition, it contains one or two selected from Mo: 0.05 to 0.4% and V: 0.05 to 0.6%, and has a composition comprising the remaining Fe and inevitable impurities, and is excellent in wear resistance. A high-strength spheroidal graphite cast iron product.   The composition is a composition containing, in mass%, one or two selected from Mo: 0.05 to 0.4% and V: 0.05 to 0.6% in total of 0.8% or less. The high-strength spheroidal graphite cast iron product according to claim 1.   The high-strength spheroidal graphite cast iron product according to claim 1 or 2, wherein in addition to the composition, the composition further contains Ni: 0.5% or less by mass%.   The high-strength spheroidal graphite cast iron product according to any one of claims 1 to 3, wherein P is adjusted to less than 0.04% and Cr is adjusted to less than 0.1% as the inevitable impurities.