KR101708583B1 - Method for spheroidizing molten metal of spheroidal graphite cast iron - Google Patents

Abstract

(RE rare earth element) containing 30 to 80 wt% of Si, Mg, either Ce of 80 to 100 wt% of purity or La of 80 to 100 wt% of purity, Ca, and a graphite spheroidizing agent containing Al use. 0.001 to 0.009 wt% of RE, 0.001 to 0.02 wt% of Ca, and 0.001 to 0.02 wt% of Al are added to the entire molten metal, and the graphite spheroidizing agent is added to the molten metal in an amount of 0.03 to 0.07 wt% % Of Mg is included in the total amount of Mg. Deterioration of the crystallization of chunky graphite and deterioration of mechanical properties in the afterglow products of the spheroidal graphite cast iron can be suppressed inexpensively.

Description

METHOD FOR SPHEROIDIZING MOLTEN METAL OF SPHEROIDAL GRAPHITE CAST IRON BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a method for treating graphite spheroidization of molten metal of spheroidal graphite cast iron.

Spheroidal graphite cast iron is excellent in mechanical properties (Young's modulus, tensile strength, elongation), in which graphite is spheroidized under casting conditions. The spheroidization of graphite is carried out by adding a graphite spheroidizing agent in the beads. The graphite spheroidizing agent includes Mg, a rare earth element (hereinafter abbreviated as " RE "), Ca, Al and the like.

(Hereinafter referred to as " thicker portions " thereof) in which the cooling rate is slowed, chunky graphite, which is an abnormal graphite structure, is crystallized in the metal structure of the spheroidal graphite cast iron . The Young's modulus, the tensile strength and the elongation of the cast iron material are remarkably lowered by the crystallization of the chunky graphite.

JP-A-2007-182620 discloses an example of a graphite spheroidizing agent intended to suppress the generation of chunky graphite. There is no definite teaching of the proper amount of addition to the molten metal in this document.

An object of the present invention is to provide a graphite spheroidizing treatment method capable of more reliably suppressing crystallization of chunky graphite in a thick portion of spheroidal graphite cast iron.

In the graphite spheroidizing treatment method according to one embodiment of the present invention, the graphite spheroidizing agent to be used is one of 30 to 80 wt% of Si, Mg, Ce of 80 to 100 wt% of purity or La of 80 to 100 wt% of purity (Rare earth element), Ca, and Al. Usually, the remaining amount of the graphite spheroidizing agent other than the above element is iron and inevitable impurities. The graphite spheroidizing agent may further include S as an optional adopted element. Wherein the graphite spheroidizing agent is added in an amount of 0.001 to 0.009 wt% of RE, 0.001 to 0.02 wt% of Ca and 0.001 to 0.02 wt% of Al relative to the entire molten metal and 0.03 to 0.07 wt% Mg is added to the molten metal.

According to the above embodiment, since the content of RE, Ca, and Al, which exhibits graphitizing action and promotes the crystallization of chunky graphite, is optimized while being reduced, the thickening of the spheroidal graphite cast iron, specifically, it is possible to suppress the crystallization of chunky graphite in the thick portion which is not less than 1000 ks (i.e., 1000 seconds).

Further, according to the above embodiment, since the amount of Ca and Al promoting the generation of slag and dross is optimized while being reduced, a pure melt can be obtained and a product having few defects such as slag inclusion and pin holes can be obtained have.

Further, according to the above embodiment, since the amount of RE that is expensive and unstable in price stability is reduced, the material cost can be reduced and the sensitivity to price fluctuation can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an optical microscope photograph showing an example of a structure of sound ductile iron. FIG.
2 is an optical microscope photograph showing an example of a structure in which chunky graphite is crystallized.
3 is a schematic view illustrating graphite spheroidizing treatment by a stationary injection method;
4 is a schematic view for explaining graphite spheroidizing treatment by a wire feeder method;

Hereinafter, the graphite spheroidization treatment method according to the embodiment of the present invention will be described.

The shape of the product to which the graphite spheroidization treatment method according to the embodiment is applied is not particularly limited. However, the above-mentioned graphite spheroidization treatment method achieves a particularly excellent tissue improving effect when the process coagulation time is within a range of 1.0 ks or more, for example, 1.0 to 100 ks or when the product maximum thickness is 100 to 500 mm .

The graphite spheronizing agent used in one embodiment of the graphite spheroidization treatment method of the present invention is a graphite spheroidizing agent which is composed of 30 to 80 wt% of Si (silicon), Mg (magnesium), RE (rare earth element), Ca Al (aluminum). Further, in the present embodiment, the graphite spheroidizing agent is added to the molten metal so as to satisfy the following two conditions. The first condition is that 0.001 to 0.009 wt% of RE, 0.001 to 0.02 wt% of Ca, 0.001 to 0.02 wt% of Al, and 0.001 to 0.02 wt% of Al are added to the molten metal of the respective elements (the ratio of the added weight of each element to the total weight of the molten metal) %, And the second condition is that the molten metal after the graphite spheroidization treatment contains 0.03 to 0.07 wt% of Mg.

The graphite spheroidizing agent may further contain S, The portion of the graphite spheroidizing agent other than the above-mentioned elements typically includes Fe (iron) and inevitable impurities.

The Mg added to the molten metal is related to nucleation of graphite, but a part of Mg does not become a graphite nucleus but becomes a composite compound with an oxide, RE or the like and becomes slag. As a result, an amount of Mg in which the graphite spheroidizing effect is maintained, specifically, 0.03 to 0.07 wt% of Mg is retained in the molten metal after the spheroidizing treatment of graphite (that is, just before injection into the mold) Is added to the molten metal.

If the Mg content in the molten metal after the graphite spheroidization treatment is less than 0.03 wt%, the graphite shape deteriorates due to insufficient deoxidization effect by Mg and Mg deficiency as a raw material of graphite nuclei. When the Mg content exceeds 0.07 wt%, explosive graphite is produced In any case, the deterioration of the graphite shape deteriorates the mechanical properties. The value of the amount of Mg is general in the production of spheroidal graphite cast iron.

The relationship between the amount of Mg added to the molten metal and the Mg content in the molten metal after graphitization is well known in the art. For example, when 1.5 wt% of a spheroidizing agent containing 5 wt% of Mg is added to the molten metal (that is, when 0.075% of Mg is added to the molten metal), the Mg content (analytical value) in the molten metal after graphitization is 0.035 To 0.055 wt%. It is also well known that the yield of Mg decreases as the amount of Mg added increases. Therefore, it is easy for those skilled in the art to determine the amount of Mg added to the molten metal in which 0.03 to 0.07 wt% of Mg remains in the molten metal after the graphite spheroidizing treatment.

As the RE, it is preferable to add only Ce (cerium) or La (lanthanum) alone, not as a form of alloy or mixture of REs. By adding Ce alone or La alone alone in an appropriate amount, excellent mechanical properties can be obtained. When only Ce is used as RE, the purity of Ce is preferably 80 to 100 wt%. When only La is used as RE, the purity of La is preferably 80 to 100 wt%. However, the above-mentioned composition rule does not exclude that La, which can not be completely separated from Ce, is included as an inevitable impurity in RE to be added, for example, when RE to be added is Ce.

Further, when RE is used as a component of the graphite spheroidizing agent, it is generally used in the form of an alloy of Ce: La = 2: 1 (Mish Metal). On the contrary, in the present embodiment, such micro metal is further refined to add Ce or La of high purity alone.

As described above, 0.001 to 0.009 wt% of RE (Ce or La) is preferably added to the molten metal. If the addition amount of RE is less than 0.001 wt%, the neutralization ability of the graphite nodularization inhibiting element is insufficient and the graphite shape deteriorates. When the RE addition amount exceeds 0.009 wt%, chunky graphite is largely crystallized and mechanical properties are lowered in any case. Further, it is more preferable to add RE (Ce or La) in an amount of 0.002 to 0.005 wt% to the molten metal in order to make the graphite shape more robust.

(RE / S) of the addition amount of RE to the addition amount of S (sulfur) is 0.06 to 1.60 (S: 0.005 to 0.030% by weight, RE: 0.002 to 0.008 wt%). According to this, a good-shaped graphite shape can be obtained more reliably. It has been conventionally reported that RE / S = 2.0 to 5.0 in a thin-walled product is preferable in obtaining a good-shaped graphite shape.

S also depends on the melting furnace and the melting method, but may be relatively contained in the molten metal of the cast iron (raw iron). As described above, actively adding S is a case where the molten metal (raw water) is sufficiently desulfurized. When a relatively large amount of S is contained in the raw water, S may not be added positively, or S may be added in an amount equivalent to the amount of S originally contained in the raw water.

As described above, it is preferable to add 0.001 to 0.020 wt% of Ca and 0.001 to 0.020 wt% of Al to the molten metal. When the addition amount of Ca or the addition amount of Al is less than 0.001 wt%, graphite nucleation is not sufficiently performed. If the amount of Ca added or the content of Al exceeds 0.020 wt%, chunky graphite is crystallized and slag and dross are easily produced, and slag inclusion and pinhole defects may occur in the product.

For reference, an example of a good graphite shape in a casting with a process solidification time of 2.5 ks is shown in the photograph of Fig. 1, and an example of a bad graphite shape is shown in the photograph of Fig. In the photograph of FIG. 2, particularly, the crystallization of chunky graphite is confirmed on the left side in particular. In the example of Fig. 1, the addition amounts of RE, Ca and Al are optimized based on the above, and in the example of Fig. 2, Ca and Al are excessive.

The above-mentioned graphitizing agent can be applied to all known graphite spheroidizing methods such as (but not limited to) a stationary injection method (sandwich method), a tundish method, a wire feeder method and the like.

Fig. 3 shows a schematic view of the stationary injection method. In the commonly used stationary injection method, the graphite spheroidizing agent SA is filled in the reaction groove (pocket) at the bottom of the reel L and completely covered with the cover CA (iron piece, Fe-Si, etc.). The raw RM of 1,400 to 1,500 ° C is sprinkled on these rollers, and the graphite is spheroidized by the reaction between the graphite spheroidizing agent and the molten metal. When the amount of Mg added is large, the reaction is aggravated. In this case, Ca is added in an optimum range to make the reaction gentle.

An example of a suitable composition of the graphite spheroidizing agent in the case of performing the stationary injection method is as follows.

Si: 30 to 80 wt%

Mg: 3 to 8 wt%

RE: 0.1 to 0.6 wt% (RE includes any one of Ce of 80 to 100 wt% of purity or 80 to 100 wt% of purity of purity), preferably 0.2 to 0.5 wt%

Ca: 0.1 to 1.3 wt%

Al: 0.1 to 2.0 wt%

Residual portion: Fe and inevitable impurities (may contain S)

As for the graphite spheroidizing agent used in the stationary injection method, for example, in the case of a small casting of 10 to 500 kg, a granular material having a grain size of 1 to 5 mm is used so that there is no residual material, It is preferable to use a massive material having a particle diameter of 5 to 70 mm to suppress fading as much as possible.

Fig. 4 shows a schematic view of the wire feeder method. In the state that the cover of the reed L is opened, the raw water of 1400 to 1500 占 폚 is sprinkled on the reed, and the cover is closed. In this state, a wire W of a predetermined length is fed to the molten metal MM at a feed rate controlled by a feeder (not shown) (see arrows in the figure). As the wire, a graphite spheroidizing agent having a particle diameter of 0.1 to 1 mm, for example, enclosed in an inner cavity of a hollow iron-cladding material may be used.

An example of a suitable composition of the graphite spheroidizing treatment agent (which is enclosed in the wire) in the case of performing the wire feeder method is as follows.

Si: 30 to 80 wt%

Mg: 9 to 25 wt%

RE: 0.3 to 1.8 wt% (RE includes any one of Ce of 80 to 100 wt% of purity or 80 to 100 wt% of purity of purity)

Ca: 0.1 to 6.0 wt%

Al: 0.1 to 6.0 wt%

In this case as well, the graphite spheroidizing treatment agent may further contain S.

Since the price per wire is high, a graphite spheroidizing agent having a high concentration of each element is enclosed in the wire to obtain a desired composition in a small amount.

Generally, a spheroidal graphite cast iron product having a good mechanical property is obtained by injecting a molten metal subjected to spheroidizing treatment of graphite into a casting mold at 1300 to 1400 DEG C, but in the case of a casting product having a process coagulation time exceeding 1 ks , It is preferable to set the injection temperature to be lower than this, for example, 1270 to 1370 캜.

Further, even in the case of using the above-mentioned graphite spheroidizing agent, the mechanical properties can be further improved by inoculation after the graphite spheroidizing treatment. For example, using an inoculant having a composition of Fe- (30 to 75 wt%) Si- (0 to 3.0 wt%) Ca- (0 to 3.0 wt%) Al- (0 to 1.0 wt% The inoculant may be added one to five times in an amount of 0.01 to 0.20 wt% (inoculum weight / weight of the molten metal) per dose. Such inoculation may be performed not only in the padding before pouring into the mold, but also at the time of pouring the pour into the mold such as inoculation of the injection container or inoculation.

Example

Hereinafter, results of experiments conducted to confirm the effect of the graphite spheroidizing treatment will be described.

A mold for casting a 100 mm-thick test piece designed to have a process coagulation time of 1.0 ks was prepared.

A granular graphitizing agent having the following composition was prepared.

Si: 75 wt%

Mg: 5.1 wt%,

Ca: 0.7 wt% or 2.0 wt%

Al: 0.7 wt% or 2.0 wt%

RE: 0.15 wt%, 0.3 wt%, 0.6 wt% or 1.3 wt%

S: 0.33 wt%, 0.67 wt% or 2.0 wt%

Balance part: Fe and inevitable impurities

By the stationary injection method shown in Fig. 3, the aforementioned graphite spheroidizing agent was added to 30 kg of the raw pot. By adding about 1.5 wt% of a sphering agent to the molten metal, the amount of each element added to the molten metal was set as follows.

Mg: 0.075 wt%

Ca: 0.01 wt% or 0.03 wt%

Al: 0.01 wt% or 0.03 wt%

RE: 0.002 wt%, 0.004 wt%, 0.008 wt% or 0.019 wt%

S: 0.005 wt%, 0.010 wt% or 0.030 wt%

As a result of adding the above amount of Mg, the amount of Mg contained in the molten metal after graphitization was about 0.045 wt%.

In addition, the following elements were contained in the molten metal (raw water).

C: 3.5 to 3.7%,

2.4 to 2.6% of Si,

Mn: 0.5 to 0.6%

After the graphite spheroidizing treatment, the casting was performed quickly (so fast that fading did not occur). However, in the samples of Nos. 26 to 29, after the graphite spheroidizing treatment, before the injection into the mold, inoculation by the above-mentioned inoculant is performed twice in the reed, and then the sample is rapidly ) Were cast. The component values of the samples Nos. 26 to 29 are before the inoculation after the graphite spheroidization treatment.

After casting the test piece, the test piece was processed into a predetermined shape and subjected to a tensile test to measure the tensile strength and elongation. Further, the hardness of the test piece was measured, the structure was observed by an optical microscope, and the graphitization degree of graphite was measured. All of the above tests were carried out in accordance with the Japanese Industrial Standards for Ductile Iron (JIS G5502).

The results of the test are shown in Table 1.

In Table 1, " o " in the second column from the left indicates the following four conditions

(Condition 1) RE contains only either Ce or La

(Condition 2) RE addition amount is within the range of 0.001 to 0.009 wt%

(Condition 3) Ca addition amount is in the range of 0.001 to 0.02 wt%

(Condition 4) Al content is in the range of 0.001 to 0.02 wt%

Are satisfied at the same time.

Also, the samples to which "? &Quot; is applied all have a RE / S range of 0.06 to 1.60.

In Table 1, in Samples Nos. 10 to 16, the above-mentioned Mish Metal is used as RE.

As shown in Table 1, the tensile strength was lower than 450 MPa when the amount of RE after graphitization was 0.019 wt%, but it was 450 MPa or higher in other conditions. With respect to elongation, it was confirmed that even when the amount of RE was small, the amount of addition of Ca and Al was 0.03%, and that the tendency was lowered when Ce and La were used as alloys.

Samples 26 to 29, which were inoculated twice with the inoculation agent, showed no decrease in tensile strength, and a high elongation was obtained.

As a standard of the quality of the castings, reference values of mechanical properties applicable to those having a main thickness of 60 to 200 mm of the cast iron articles in FCD400-15A and FCD500-7A described in JIS G5502, Table 3 "Mechanical Properties of the seal material having a main body" . The reference value is a tensile strength of 420 N / mm 2 (= 420 MPa) or more and an elongation of 5% or more in FCD 400 - 15 A, a tensile strength of 370 N / mm 2 (= 370 MPa) And hardness HB 130 to 230, respectively. It is preferable that the reference value exemplified here is satisfied with sufficient margin.

In Table 1, samples having "? &Quot; in the second column from the left indicate high nucleation rate and elongation, indicating that good quality is obtained.

Claims (9)

A spheroidization treatment method for spheroidizing graphite by adding a graphite spheroidizing agent to a molten metal,
Wherein the graphite spheroidizing agent comprises 0.1 to 0.6 wt% of RE, wherein the graphite spheroidizing agent contains either Si in an amount of 30 to 80 wt%, Mg in an amount of 3 to 8 wt%, Ce in a purity of 80 to 100 wt%, or La in a purity of 80 to 100 wt% (Rare earth element), 0.1 to 1.3 wt% of Ca and 0.1 to 2.0 wt% of Al, the balance being Fe and inevitable impurities,
0.001 to 0.009 wt% of RE, 0.001 to 0.02 wt% of Ca, and 0.001 to 0.02 wt% of Al are added to the entire molten metal and the graphite spheroidizing agent is added to the molten metal in an amount of 0.03 to 0.07 wt% % Of Mg is included in the spheroidizing treatment. A spheroidization treatment method for spheroidizing graphite by adding a graphite spheroidizing agent to a molten metal,
Wherein the graphite spheroidizing agent comprises 0.3 to 1.8 wt% of RE, wherein the graphite spheroidizing agent contains either Si in an amount of 30 to 80 wt%, Mg in an amount of 9 to 25 wt%, Ce in a purity of 80 to 100 wt%, or La in a purity of 80 to 100 wt% (Rare earth element), 0.1 to 6.0 wt% of Ca and 0.1 to 6.0 wt% of Al, the balance being Fe and inevitable impurities,
0.001 to 0.009 wt% of RE, 0.001 to 0.02 wt% of Ca, and 0.001 to 0.02 wt% of Al are added to the entire molten metal and the graphite spheroidizing agent is added to the molten metal in an amount of 0.03 to 0.07 wt% % Of Mg is included in the spheroidizing treatment. The method according to any one of claims 1 to 3, wherein the graphite spheroidizing agent further comprises S, the amount of RE added to the molten metal is 0.002 to 0.008 wt%, the amount of RE added to the molten metal is the amount of S added to the molten metal Of the graphite spheroidizing agent is 0.06 to 1.60. The spheroidizing treatment method according to claim 1, wherein the graphite spheroidizing agent is added to the molten metal by a sandwich method. The spheroidization treatment method according to claim 2, wherein the graphite spheroidizing agent is added to the molten metal by a wire feeder method. The spheroidizing treatment method according to claim 4, wherein the graphite spheroidizing agent is granular particles having a particle size of 1 to 5 mm. The method of claim 4, wherein the graphite spheroidizing agent is a mass having a length of 5 to 70 mm. The spheroidization treatment method according to claim 5, wherein the graphite spheroidizing agent is a wire shape continuously containing graphite spheroidizing agent particles having a particle diameter of 0.1 to 1.0 mm. The spheroidization treatment method according to claim 1 or 2, wherein the spheroidizing treatment temperature is 1400 to 1500 占 폚 and the pouring temperature to the mold is 1270 to 1370 占 폚.

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