KR20180008612A - How to melt cast iron - Google Patents

Abstract

The cast iron molten metal treatment method is characterized in that it comprises 15 to 80% by weight of Si as an inoculating agent, one of La with a purity of 80 to 100% by weight as a RE, 80 to 100% by weight of purity with Ca, The balance Fe and inevitable impurities, and the inoculant is used in an amount of 0.001 to 0.009% by weight of La or Ce, 0.001 to 0.02% by weight of Ca, 0.001 to 0.02% by weight of Ca, To 0.001 to 0.02% by weight based on the total weight of the cast iron.

Description

How to melt cast iron

The present invention relates to a method of processing molten iron (including both spheroidal graphite cast iron and flake graphite cast iron). This molten metal treatment method particularly includes an inoculation treatment effective for improving the mechanical properties of the secondary cast iron (spheroidal graphite cast iron, cast graphite cast iron).

In the casting of spheroidal graphite cast iron and cast graphite cast iron, the casting process is performed on the molten metal at the time of tapping from the melting furnace to the ladle, from the ladle to the casting mold, etc., and the mechanical properties (tensile strength and elongation) Improvement is generally made.

In the case of the cast iron cast iron after the sintering, since the process coagulation time in which the crystallization of graphite takes place is prolonged, abnormal graphite or coarse graphite tends to be precipitated in the metal structure. The elongation of graphite or coarse graphite deteriorates the tensile strength of the cast iron. In the ferritic spheroidal graphite cast iron, the elongation of the material remarkably decreases due to crystallization of abnormal graphite or coarse graphite.

The crystallization of abnormal graphite and coarse graphite can be avoided by increasing the number of eutectic cells by performing an appropriate inoculation process. As the number of process cells increases, the number of graphite particles and the graphite spheroidization ratio increase in spheroidal graphite cast iron, and the formation of fine A-type graphite in graphite cast iron is promoted, and in any case, the mechanical properties are improved.

In casting a relatively thin cast iron product, Ca (calcium), Al (aluminum), Ba (barium), Bi (bismuth) and the like are added to Fe-Si It is well known that inoculation treatment is carried out using the inoculant.

As described above, when casting a cast iron article of a deep-fried product, the process coagulation time is prolonged. Therefore, when a general inoculant containing Ca, Al, Ba, Bi and the like having not only an effect of increasing the number of process cells but also an effect of promoting graphitization is used in the casting of the cast iron product of the afterglow, Quot; Chunky graphite ") or coarse graphite may be extracted. That is, at the time of casting a cast iron product of a deep-fried product, it is necessary to suppress the graphitization more than necessary while increasing the number of process cells. Therefore, it is considered that it is preferable to use a rare earth element as the graphite nucleus generating material.

In casting a piece of cast iron graphite cast iron product, there is not known a method of treating a molten iron using an inoculant containing a rare earth element which can sufficiently satisfy the above requirements. Patent Document 1 (International Publication WO2015 / 034062A1) discloses a method of spheroidizing a molten metal when producing a spheroidal graphite cast iron product of a beef. The method disclosed here has room for improvement in the efficiency of micronization of graphite.

International Publication WO2015 / 034062A1

An object of the present invention is to provide a molten metal treatment method, in particular, a method of inoculating, which can suppress crystallization of abnormal graphite and coarse graphite and suppress deterioration of mechanical properties.

In order to achieve the above object, in the present invention, the amount of RE (rare earth, rare earth element), Ca (calcium), and Al (aluminum) It suppresses abnormal graphite and coarse graphite which are crystallized by the action.

In the inoculation method according to one embodiment of the present invention, a graphite inoculant (hereinafter simply referred to as "inoculation agent") is prepared by mixing 15 to 80% of Si, either La (lanthanum) or Ce (cerium) And an inoculant containing Al and the balance of Fe (iron) and inevitable impurities is used, and the inoculant is added in an amount of 0.001 to 0.009% of RE (La or Ce) as an additive amount of each component element to the molten metal, 0.001 to 0.02% of Ca, and 0.001 to 0.02% of Al are added to the molten metal. In the present specification, the percentage indicating the content or addition amount means all percent by weight unless otherwise specified.

RE, Ca, and Al exhibit graphitizing action in the case of a cast iron having a process solidification time of 1.0 ks or more, thereby promoting crystallization of abnormal graphite or coarse graphite. However, by optimizing the amount of RE, Ca and Al to be added and using La or Ce alone as RE as described above, crystallization of abnormal graphite and coarse graphite can be suppressed.

When the addition amount of Ca and Al is excessive, not only the crystallization of abnormal graphite or coarse graphite is promoted, but also the generation of slag and dross is promoted. However, by optimizing the amount of addition of Ca and Al as described above, a clear melt can be obtained, and it is possible to suppress occurrence of slag inclusion or defects such as pinholes in the product.

Further, by suppressing the addition amount of RE, which is expensive and unstable in price stability, to be as low as described above, the material cost can be reduced and the sensitivity to price fluctuation can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photograph of an organization chart of a spheroidal graphite cast iron according to an embodiment of the present invention. FIG.
2 is a photograph of the organization chart of the spheroidal graphite cast iron of the conventional example.
3 is a photograph of the organization chart of the piecemeal graphite cast iron of the embodiment of the present invention.
Fig. 4 is a photograph of the organization chart of the conventional piece-shaped graphite cast iron.
5 is a schematic view showing a runner box method.
6 is a schematic diagram showing the sandwich method.
7 is a schematic view showing a wire processing method.
Figure 8 is a schematic diagram showing multiple runner box inoculation and in-mold inoculation.
Fig. 9 is a schematic view showing a combination of a main stream flow inoculum and a runner box inoculation. Fig.

A preferred embodiment of the present invention will be described below.

By using the molten metal treating method according to the embodiment of the present invention, particularly the casting method, it is possible to suppress the crystallization of chunky graphite, which is abnormal graphite, in castings whose shape is spherical spheroidal graphite cast iron and whose process solidification time is 1.0 ks or more.

The inoculant used is composed of 15 to 80% of Si and either of La or Ce as RE, Ca and Al, and the balance Fe and inevitable impurities.

The inoculant can be produced by dissolving RE, Ca and Al in a predetermined amount (detailed later) in a Fe-Si alloy (silicon iron) molten metal, solidifying the molten metal, and crushing and granulating the molten metal.

The content of Si in the inoculant is set to 15 to 80%, as is clear from the known Fe-Si state diagram (for example, ASM HANDBOOK (trademark or registered trademark), Volume 3 etc.) The amount of Si is increased. Further, when the Si content is 80% or more, other component elements are difficult to penetrate. Further, it is more preferable that the content of Si in the inoculation agent is set to 15 to 25% or 50 to 60% in order to increase the amount of the solvent.

RE is not only in the form of a mixture of a plurality of REs (for example, an alloy of Ce: La = 2: 1 called "mischmetal") or a mixture thereof but only Ce (cerium) or La (lanthanum) alone . By adding Ce alone or La alone alone in a proper amount, excellent mechanical properties can be obtained. When Ce alone is used as RE, the purity of Ce is preferably 80 to 100% by weight. When only La is used as RE, the purity of La is preferably 80 to 100% by weight. The above-mentioned composition rule does not exclude that, for example, when RE to be added is Ce, La which can not be completely separated from Ce in the RE to be added is included as an inevitable impurity.

The addition amount of RE to the molten metal is preferably 0.001 to 0.009%. If the addition amount of RE is less than 0.001%, there is a problem that the number of process cells in the cast iron graphite cast iron decreases, and in the cast iron spheroidal graphite, the neutralization ability of the graphite iron nuggets is insufficient and the graphite shape deteriorates. When the addition amount of RE exceeds 0.009%, there is no great adverse effect on the cast graphite cast iron, but in the spheroid graphite cast iron, there is a problem that much chunky graphite, which is abnormal graphite, is extracted. If the graphite shape is deteriorated, it may cause deterioration of mechanical properties.

The amount of Ca added to the molten metal is preferably 0.001 to 0.020%, and the amount of Al to be added to the molten metal is preferably 0.001 to 0.020%. When the addition amount of Ca and Al is less than 0.001, nucleation of graphite is not sufficiently performed. If the added amount of Ca and Al exceeds 0.020%, abnormal graphite or coarse graphite tends to be easily poured, and slag and dross are easily generated, and slag inclusion and pinhole defects may occur in the product.

The inoculant described above can be used for inoculation in a furnace immediately before the raw water is tapped and all known inoculation methods such as a sandwich method, a runner box method, a main bath flow inoculation method, an inmold method, a wire treatment method, It can also be used for.

The composition of the inoculant which can be suitably used in the sandwich method, the runner box method, the main-stream flow inoculation method and the in-mold method is shown below.

Si: 30 to 80%

RE: 0.1 to 0.6% (purity 80 to 100% by weight La or Ce)

Ca: 0.1 to 1.3%

Al: 0.1 to 2.0%

The balance Fe and inevitable impurities

The composition of the inoculant which can be suitably used for the wire treatment method is shown below.

Si: 30 to 60%

RE: 0.3 to 1.8% (purity 80 to 100% by weight La or Ce)

Ca: 0.1 to 6.0%

Al: 0.1 to 6.0%

The balance Fe and inevitable impurities

By suppressing the concentration of Fe and Si in the above composition to a low level and increasing the concentration of other component elements, the feed amount of the wire can attain at least a sufficient inoculation effect, so that the inoculation treatment time can be shortened.

Whether the inoculation method is used or the inoculant of any composition is used, the amount of each component element added to the molten metal is set as described above.

Mg (magnesium) is not included in the inoculant according to the present embodiment. Therefore, in casting the nodular cast iron product, the spheroidizing treatment is carried out separately from the inoculating agent used in the inoculating treatment, prior to the inoculating treatment, by using a different sphericalizing agent. The spheronizing agent used in the spheronization treatment may be selected from known ones and used. However, the spheroidizing agent may be one which does not contain RE, Ca and Al, such as Fe-Si-Mg (e.g. Fe: Si: Mg = 45: 45: 10 or 30:30:20 or 45: : 30: 5, etc.) is preferably used from the viewpoint of minimizing the influence on the inoculation treatment.

It is known that the inoculation process can achieve a high effect by performing as close as possible at the time when the molten metal is poured into the mold. In this embodiment, Mg, which is an element contributing to spheroidization, is not included in the inoculant, The inoculation effect can be enhanced by carrying out the inoculation treatment immediately before pouring the mold after the spheroidizing treatment.

In casting a piece of graphite cast iron product, the above inoculant may be added to the molten metal.

Figure 6 shows a schematic diagram of the sandwich method. In the commonly used sandwich method, the inoculant is filled in the reaction groove (pocket) of the ladle bottom, and the raw water of 1400 to 1500 ° C is sprinkled on the ladle and inoculated.

In the molten process of the spheroidal graphite cast iron, the inoculant may be used as a cover agent for covering the surface of the spheroidizing agent filled in the reaction groove to mild the reaction of Mg. When the amount of Mg added is large, the reaction becomes severe, but the reaction can be tempered by adding Ca in a large amount within the above-mentioned optimum range (0.001 to 0.02 wt% with respect to the entire molten metal).

Fig. 7 shows a schematic view of the wire processing method. The inoculation process can be efficiently performed in a short time by the wire process.

Fig. 8 shows a schematic view of a combination of runner box inoculation and in-mold inoculation. It is also possible to perform only the runner box inoculation or the in-mold inoculation. Generally, by performing inoculation immediately before pouring into the casting mold, the mechanical properties of the casting can be further improved. Further, as shown in the schematic diagram of Fig. 9, the injection of the mainstream liquid and the runner box inoculation may be performed in combination.

It is also possible to use a combination of two or more of inoculation into molten metal in the ladle, runner box inoculation, in-mold inoculation and mainstream stream inoculation after the tapping from the melting furnace to the ladle to the completion of the pouring into the mold It is also preferable to inoculate the molten steel, and by doing so, the mechanical properties of the casting can be further improved. When a plurality of inoculations are to be carried out, the sum of the respective component elements relative to the molten metal is made to fall within the above-mentioned range.

It is preferable to pour a molten metal having been subjected to the inoculation treatment (in the case of the spheroidal graphite cast iron, in addition to the seeding treatment) to the casting mold at 1300 to 1400 DEG C, thereby obtaining a post casting having good mechanical properties. There is no particular limitation on the shape of the casting, but the inoculation method according to the above-described embodiment exhibits particularly excellent effects when the step coagulation time has a thickness of 1.0 ks or more. In the case where the casting is larger or thicker so that the process coagulation time becomes longer, the injection temperature is preferably set at 1280 to 1360 캜, which is slightly lower, to ensure good mechanical properties of the casting. Further, in the case of the spheroidal graphite cast iron, the spheroidizing treatment temperature is preferably 1400 to 1500 ° C.

Example

Casting tests were performed on cast iron graphite cast iron and spheroidal graphite cast iron cast iron products using inoculants as examples of the present invention and inoculants as comparative examples. In this experiment, a mold for casting a 100 mm-thick test piece designed to have a process coagulation time of 1.2 ks was used. If the process coagulation time is long, abnormal graphite and coarse graphite are easy to be extracted, so that it is suitable for verifying the effect of inoculation.

In the experiment, as described above, RE, Ca, and Al of a predetermined amount (detailed later) were dissolved in a Fe-50% Si alloy (silicon iron) molten metal and the molten metal was solidified, Inoculants were used. The inoculant was added to 30 kg of the raw tea by the runner box method so that the addition amount to the molten metal (raw tea) was as described in Nos. 1 to 20 of Table 1 below. When the spheroidal graphite cast iron was cast, a spheroidizing agent separate from the inoculant was placed at the bottom of the reaction groove of the ladle bottom, and spheroidizing treatment was performed together with inoculation. No.1 and 11 are not inoculated. The amount of Ca added was 0.003%, 0.012%, 0.03%, the content of Al was 0.003%, 0.012% and 0.03%, the amount of RE was 0.002%, 0.008%, 0.020% .

Graphite cast iron molten metal has a composition of 3.5 to 3.7% of C, 2.4 to 2.6% of Si and 0.5 to 1.0% of Mn, the composition of the cast iron graphite cast iron is 3.1 to 3.2% of C, 1.5 to 1.7% of Si, Mn: 0.8 to 0.9%.

The obtained test piece was subjected to a tensile test to measure the tensile strength and elongation at break, and the structure was observed.

Table 1 shows the test results.

Nos. 1 to 10 in Table 1 are spheroidal graphite cast iron, and Nos. 11 to 20 are graphite cast iron. Nos. 11 to 20 show the mechanical properties and conditions of cast iron graphite cast iron.

The following were confirmed for the tensile strength of the spheroidal graphite cast iron. In the case of non-inoculation (No.1), when RE is Ce + La (using mischmetal as RE) (No.2-4), and when RE is only La or Ce alone, RE addition is 0.02% Nos. 7 and 10) had a tensile strength of less than 450 MPa. However, in the other cases (Nos. 5, 6, 8 and 9), that is, in the examples, the tensile strength was 450 MPa or more.

The following were confirmed for the elongation of the spheroidal graphite cast iron. (No. 5, No. 6, No. 8, No. 9), that is, the case where the amount of RE, Ca, and Al was reduced 4, 7, and 10).

The following were confirmed as to the tensile strength of the cast iron graphite cast iron. All samples exhibited a tensile strength of more than 300 MPa. An increase in tensile strength was confirmed by inoculation. When RE, Ca, and Al were added in the same amounts, the addition of RE alone or Ce alone, as RE, exhibited a higher tensile strength than RE in which RE was added in the form of mischmetal. As a result of comparison between the addition of La alone as RE and the addition of RE, Ca and Al (No.15 and 16) in which the addition amount of RE, Ca and Al was lower than that of No.17 Showed high tensile strength. (No. 18, 19) in which the addition amount of RE, Ca and Al was lower than that in which RE, Ca, and Al were added (No. 20) Showed high tensile strength. With respect to the elongation of the cast iron graphite cast iron, there was hardly any difference due to inoculation, RE, Ca, and Al addition amount.

Fig. 1 is an embodiment of the spheroidal graphite cast iron of the present invention, and Fig. 2 is a photograph of the organization chart of spheroidal graphite cast iron of the prior art. Fig. 3 is an embodiment of the cast graphite cast iron of the present invention, and Fig. 4 is a photograph of the organization chart of the conventional cast iron graphite cast iron. By inoculation, the number of graphite particles in the spheroidal graphite cast iron increases, and the graphite structure of the cast graphite cast iron is refined. Improvement of the structure was confirmed by using the inoculant with the optimum amount of RE, Ca and Al.

Claims (10)

A method for producing an inoculant comprising 15 to 80% by weight of Si, 80 to 100% by weight of purity of 80 to 100% by weight of RE, 80 to 100% by weight of purity of RE, Ca and Al and the balance of Fe and inevitable impurities Wherein the inoculant is used in an amount of 0.001 to 0.009% by weight of La or Ce, 0.001 to 0.02% by weight of Ca and 0.001 to 0.02% by weight of Al relative to the molten iron of the cast iron To the molten metal so that the molten iron of the cast iron is inoculated. The method according to claim 1, wherein the inoculant has a content of Si of 30 to 80%, a purity of 80 to 100% by weight of La or a purity of 80 to 100% by weight of Ce in an amount of 0.1 to 0.6% by weight, 0.1 to 1.3% by weight, and the Al content is 0.1 to 2.0% by weight. The method according to claim 1, wherein the inoculating agent has a content of Si of 30 to 60%, a purity of 80 to 100% by weight of La or a purity of 80 to 100% by weight of Ce in an amount of 0.3 to 1.8% by weight, 0.1 to 6.0% by weight, and the Al content is 0.1 to 6.0% by weight. The method according to any one of claims 1 to 3, wherein the inoculating agent is a granular material having a particle size of 1 to 5 mm. The method according to any one of claims 1 to 3, wherein the inoculating agent is a massive mass having a length of 5 to 70 mm. 4. The method according to any one of claims 1 to 3, wherein the inoculant is made of cast iron having a particle diameter of 0.1 to 1.0 mm and supplied to the molten metal while the particles are continuously contained in the core portion of the wire. Method of molten metal treatment. The method according to any one of claims 1 to 6, further comprising performing graphite spheroidizing treatment using a different spheroidizing agent different from the inoculating agent, wherein the treatment temperature of the graphite spheroidizing treatment is in the range of 1400 to 1500 ° C, Wherein the casting temperature of the casting mold is in the range of 1270 to 1370 占 폚. The method according to any one of claims 1 to 6, wherein the inoculant according to any one of claims 1 to 6 is used for one casting, and after spheroidizing treatment and inoculation by the sandwich method, Or more of the inoculant is used. The method for treating molten iron according to claim 8, wherein the method for performing the multiple inoculation is a combination of a main-stream inoculation, an in-mold inoculation, and a runner box inoculation performed at the time of pouring into a mold. The method for processing molten iron according to any one of claims 1 to 9, wherein a spheroidizing treatment agent containing magnesium is used to conduct a spheroidizing treatment separately from the inoculating treatment by the inoculating agent.

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