WO2016186094A1

WO2016186094A1 - Method for processing molten cast iron

Info

Publication number: WO2016186094A1
Application number: PCT/JP2016/064548
Authority: WO
Inventors: 藤本　亮輔; 本間　周平
Original assignee: 東芝機械株式会社
Priority date: 2015-05-18
Filing date: 2016-05-17
Publication date: 2016-11-24
Also published as: US20180148805A1; CN107532225B; KR20180008612A; CN107532225A; JP6728150B2; DE112016002243T5; JPWO2016186094A1; KR102107888B1

Abstract

This method for processing molten cast iron uses an inoculant that includes: 15-80 wt% of Si; as a rare earth element, either La of 80-100 wt% purity or Ce of 80-100 wt% purity; Ca; and Al; the remainder consisting of Fe and unavoidable impurities. The method includes a molten cast iron inoculation process, in which the inoculant is added to molten cast iron such that the amounts of the constituent elements added in relation to the molten cast iron are 0.001-0.009 wt% La or Ce, 0.001-0.02 wt% Ca, and 0.001-0.02 wt% Al.

Description

Cast iron melt processing method

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

In casting of spheroidal graphite cast iron and flake graphite cast iron, mechanical properties (tensiles) of cast iron products are obtained by inoculating the molten metal at the time of pouring from the melting furnace to the ladle, pouring from the ladle to the mold, etc. Strength, elongation) is generally improved.

In thick cast iron products, the eutectic solidification time during which crystallization of graphite occurs becomes long, so abnormal graphite or coarse graphite tends to crystallize in the metal structure. Due to the crystallization of abnormal graphite or coarse graphite, the tensile strength of cast iron decreases. In ferritic spheroidal graphite cast iron, the elongation of the material is significantly reduced due to crystallization of abnormal graphite or coarse graphite.

Crystallization of abnormal graphite and coarse graphite can be avoided by increasing the number of eutectic cells by appropriate inoculation treatment. As the number of eutectic cells increases, the number of graphite grains and the graphite spheroidization ratio increase in spheroidal graphite cast iron, and the formation of fine A-type graphite is promoted in flake graphite cast iron. In either case, the mechanical properties are improved. Is done.

When casting cast iron products with relatively thin walls, Ca (calcium), Al (aluminum), Ba (barium), Bi (bismuth), etc. are added to Fe-Si (ferrosilicon) in a ladle or hanging weir. It is well known to inoculate using an inoculum.

As mentioned above, the eutectic solidification time becomes longer when casting thick cast iron products. For this reason, when a general inoculant containing Ca, Al, Ba, Bi, etc. having not only an eutectic cell increasing action but also a graphitization promoting action is used for casting thick cast iron products, abnormal graphite (spherical graphite) In the case of cast iron, “chunky graphite”) or coarse graphite may crystallize. In other words, when casting a thick cast iron product, it is necessary to suppress graphitization more than necessary while increasing the number of eutectic cells. For this reason, it is considered preferable to use rare earth elements as the graphite nucleation substance.

In the casting of thick flake graphite cast iron products, there is no known melt treatment method using an inoculum containing rare earth elements that can sufficiently satisfy the above requirements. Patent Document 1 (International Publication WO2015 / 034062A1) describes a spheroidizing method for molten metal when producing a thick spheroidal graphite cast iron product. The method disclosed here has room for further improvement in the refinement efficiency of graphite.

International Publication WO2015 / 034062A1

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

In order to achieve the above object, the present invention optimizes the amount of RE (rare earth, rare earth element), Ca (calcium), and Al (aluminum) added to the molten metal as a graphite nucleus compound in the inoculum. Suppresses abnormal graphite and coarse graphite that crystallize due to excessive graphitization.

In the inoculation method according to one embodiment of the present invention, as a graphite inoculum (hereinafter simply referred to as “inoculum”), 15 to 80% of Si and either La (lanthanum) or Ce (cerium), An inoculant containing Ca and Al, the balance being Fe (iron) and unavoidable impurities, was used, and the inoculant was added with each component element in the amount of RE (La or Ce): 0.001 to 0 0.009%, Ca: 0.001 to 0.02%, Al: 0.001 to 0.02%, and added to the molten metal. In the present specification, the percentages indicating the content or the addition amount all mean% by weight unless otherwise specified.

In thick cast iron with a eutectic solidification time of 1.0 ks or longer, RE, Ca, and Al exhibit graphitization and promote crystallization of abnormal graphite or coarse graphite. However, crystallization of abnormal graphite and coarse graphite can be suppressed by optimizing the addition amount of RE, Ca, and Al as described above and using La or Ce alone as RE.

If the added amount of Ca and Al is excessive, it not only promotes the crystallization of abnormal graphite or coarse graphite, but also promotes the formation of noro and dross. However, by optimizing the addition amount of Ca and Al as described above, a clean molten metal can be obtained, so that it is possible to suppress the occurrence of defects such as bite and pinholes in the product.

Also, by suppressing the amount of RE that is expensive and remains unstable in price stability as described above, the material cost can be reduced, and the sensitivity to price fluctuations can be reduced.

The structure figure photograph of the spheroidal graphite cast iron of the example of the present invention. Fig. 3 is a photograph of the structure of conventional spheroidal graphite cast iron. The structure figure photograph of flake graphite cast iron of the example of the present invention. Fig. 2 is a photograph of the structure of conventional flake graphite cast iron. Schematic which shows a hanging weir method. Schematic which shows the pouring method. Schematic which shows a wire processing method. Schematic which shows the hanging dam inoculation and in-mold inoculation implemented in combination. Schematic which shows the pouring flow inoculation and hanging dam inoculation implemented in combination.

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

In a cast product with eutectic solidification time of 1.0 ks or more with thick-walled spheroidal graphite cast iron, by using the molten metal treatment method according to the embodiment of the present invention, particularly the inoculation method, Crystallization can be suppressed.

The inoculum used contains 15 to 80% Si, either La or Ce as RE, Ca and Al, and the balance Fe and unavoidable impurities.

The inoculum can be prepared by dissolving a predetermined amount (details will be described later) of RE, Ca, and Al in a molten Fe—Si alloy (ferrosilicon), solidifying the molten metal, and then crushing it into granules. .

The content of Si in the inoculum is 15 to 80% within this range, as is clear from the known Fe-Si phase diagram (see, for example, ASM HANDBOOK (trademark or registered trademark), Volume3, etc.). This is because the amount of Si dissolved increases. Further, when the Si content is 80% or more, other component elements are difficult to dissolve. Further, the Si content in the inoculant is preferably 15 to 25% or 50 to 60% in order to increase the amount of penetration.

RE is not an alloy of multiple types of RE (for example, an alloy of Ce: La = 2: 1 called “Misch metal”) or a mixture, but only Ce (cerium) or La (lanthanum) is added alone. Is done. By adding an appropriate amount of Ce alone or La alone alone, excellent mechanical properties can be obtained. When only Ce 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. For example, when the RE to be added is Ce, La does not exclude the inclusion of La that cannot be separated from Ce as an unavoidable impurity.

The amount of RE added to the molten metal is preferably 0.001 to 0.009%. When the amount of RE added is less than 0.001%, there is a problem that the number of eutectic cells is reduced in flake graphite cast iron, and in the case of spheroidal graphite cast iron, the neutralization ability of the graphite spheroidization inhibiting element is insufficient. The problem that a shape deteriorates arises. When the amount of RE exceeds 0.009%, there is no significant adverse effect in flake graphite cast iron, but nodular graphite cast iron has a problem that a lot of chunky graphite, which is abnormal graphite, is crystallized. When the graphite shape is deteriorated, it causes a decrease in mechanical properties.

The addition amount of Ca to the molten metal is preferably 0.001 to 0.020%, and similarly, the addition amount of Al to the molten metal is preferably 0.001 to 0.020%. When the addition amount of Ca and Al is less than 0.001, graphite nucleation is not sufficiently performed. Also, if the addition amount of Ca and Al exceeds 0.020%, abnormal graphite or coarse graphite is likely to be crystallized, and noro and dross are likely to be generated, and the product may have a bite or pinhole defect. There is sex.

The above inoculum can be used when inoculating in the furnace just before the main hot water is discharged, and also the pouring method, hanging weir method, pouring flow inoculation method, in-mold method, wire treatment It can also be used for the implementation of all known methods of inoculation, such as the method.

The composition of the inoculum that can be suitably used for the pouring method, the hanging weir method, the pouring flow inoculation method, and the in-mold method is shown below.
Si: 30-80%
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%
Remaining Fe and inevitable impurities

The composition of the inoculum that can be suitably used for the wire treatment method is shown below.
Si: 30-60%
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%
Remaining Fe and inevitable impurities In the above composition, the concentration of Fe and Si is kept low, and the concentration of other component elements is increased so that a sufficient inoculation effect can be achieved even with a small amount of wire feed. Therefore, the inoculation processing time can be shortened.

Regardless of the inoculation method used or the inoculum of any composition, the amount of each element added to the molten metal is as described above.

The inoculum according to this embodiment does not contain Mg (magnesium). Therefore, when casting a spheroidal graphite cast iron product, the spheroidizing process is performed separately prior to the inoculation process using a spheroidizing agent different from the inoculum used for the inoculation process. The spheroidizing agent used for the spheroidizing treatment can be selected from known ones and used. However, the spheroidizing agent does not contain RE, Ca, or Al, such as Fe—Si—Mg (for example, Fe: Si: Mg = 45: 45: 10, or 30:30:20, or 45:30 in weight ratio). : Etc.) is preferable from the viewpoint of minimizing the influence on the inoculation process.

It is known that a high effect can be obtained by performing the inoculation process as close as possible to the time when the molten metal is poured into the mold. In this embodiment, Mg, which is an element contributing to spheroidization, is included in the inoculum. Instead, the spheroidization treatment is performed with a separate spheronizing agent, and the inoculation effect can be enhanced by performing the inoculation treatment immediately after pouring into the mold after the spheronization treatment.

When casting flake graphite cast iron products, the above inoculum may be added to the molten metal.

Fig. 6 shows a schematic diagram of the pouring method. When used in the generally used pouring method, the reaction groove (pocket) at the bottom of the ladle is filled with the inoculant, and the hot water at 1400-1500 ° C is poured into the ladle and inoculated. .

In the melt treatment of spheroidal graphite cast iron, the above-mentioned inoculating agent can be disposed so as to cover the surface of the spheroidizing agent filled in the reaction groove, and can also be used as a cover agent that moderates the Mg reaction. When the amount of Mg added is large, the reaction becomes violent, but the reaction can be moderated by adding a large amount of Ca within the above optimum range (0.001 to 0.02 wt% with respect to the entire molten metal).

Fig. 7 shows a schematic diagram 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 diagram in which the hanging weir inoculation and in-mold inoculation are performed in combination. It is also possible to carry out only the weir inoculation or in-mold inoculation. Generally, the mechanical properties of the casting can be further improved by inoculating immediately before pouring the mold. Moreover, as shown in the schematic diagram of FIG. 9, the pouring flow inoculation and the hanging weir inoculation may be performed in combination.

In addition, after pouring from the melting furnace to the ladle and until the pouring of the mold is completed, there are two types: inoculation of the molten metal in the ladle, hanging weir inoculation, in-mold inoculation and pouring flow inoculation It is also preferable to inoculate the molten metal a plurality of times by combining the above, and by doing so, the mechanical properties of the casting can be further improved. In addition, when performing inoculation several times, it is made for the sum total of each component element with respect to a molten metal to be in the range mentioned above.

It is preferable to pour the molten metal that has been subjected to the above inoculation treatment (in the case of spheroidal graphite cast iron in addition to the inoculation treatment) into a mold at 1300 to 1400 ° C., so that good mechanical properties can be obtained. A thick casting having the thickness is obtained. Although there is no restriction | limiting in particular about the shape of a casting, The inoculation method which concerns on embodiment mentioned above shows a particularly outstanding effect, when it has thickness that eutectic solidification time will be 1.0 ks or more. If the casting is larger or thicker and the eutectic solidification time is longer, the casting temperature is preferably slightly lower, from 1280 to 1360 ° C., in order to ensure good mechanical properties of the casting. In the case of spheroidal graphite cast iron, the spheroidizing temperature is preferably 1400 to 1500 ° C.

Casting experiments were conducted on flake graphite cast iron products and spheroidal graphite cast iron products using the inoculant as an example of the present invention and the inoculant as a comparative example, respectively. In this experiment, a mold for casting a test piece having a thickness of 100 mm designed to have a eutectic solidification time of 1.2 ks was used. Thus, when eutectic solidification time is long, abnormal graphite and coarse graphite are likely to be crystallized, which is suitable for verifying the effect of inoculation.

In the experiment, as described above, a predetermined amount (details will be described later) of RE, Ca, and Al is dissolved in a molten Fe-50% Si alloy (ferrosilicon), and the molten metal is solidified and then crushed into granules. The inoculum prepared by doing was used. The amount of this inoculum added to the molten metal (Motoyu) with respect to 30 kg of Motoyu is No. 1 in Table 1 below. They were added using the hanging weir method as described in 1 to 20 respectively. When casting a spheroidal graphite cast iron product, a spheroidizing agent different from the inoculant was placed at the bottom of the reaction groove at the bottom of the ladle, and the spheroidizing treatment was performed together with the inoculation. No. 1 and 11 are no inoculation. In the test piece with inoculation, the addition amount of Ca is 0.003%, 0.012%, or 0.03%, and the addition amount of Al is 0.003%, 0.012%, or 0.03%. In any case, the amount of RE added was 0.002%, 0.008%, or 0.020%.

The composition of the spheroidal graphite cast iron melt is C: 3.5 to 3.7%, Si: 2.4 to 2.6%, and Mn: 0.5 to 1.0%. C: 3.1-3.2%, Si: 1.5-1.7%, Mn: 0.8-0.9%.

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.

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

The following was confirmed for the tensile strength of spheroidal graphite cast iron. The amount of RE added is 0.02% even when there is no inoculation (No. 1), when RE is Ce + La (using misch metal as RE) (No. 2-4), and when RE is La alone or Ce alone In the case of (No. 7, 10), the tensile strength was less than 450 MPa. However, in other cases (No. 5, 6, 8, 9), that is, in the examples, the tensile strength was 450 MPa or more.

The following was confirmed for the elongation of spheroidal graphite cast iron. In the case where La is added alone or Ce is added alone as RE, and the addition amount of RE, Ca, Al is kept low (No. 5, 6, 8, 9), that is, the examples are comparative examples (No. 1). , 2-4, 7, 10).

Regarding the tensile strength of flake graphite cast iron, the following was confirmed. All samples showed a tensile strength of 300 MPa or more. An increase in tensile strength was observed by inoculation. Comparing RE, Ca, and Al with the same amount of addition, higher tensile strength is obtained when RE is added as La alone or Ce alone than RE is added in the form of misch metal. It was. Comparing those in which La was added alone as RE, the amount of RE, Ca, Al added was suppressed lower than that in which RE, Ca, and Al were added in a high amount (No. 17) (No. 15, 16) showed higher tensile strength. Comparing those in which Ce was added alone as RE, compared to those in which RE, Ca and Al were added in a high amount (No. 20), those in which RE, Ca and Al were added to a lower amount (No. 18, 19) showed higher tensile strength. As for the elongation of flake graphite cast iron, there was almost no difference depending on the presence or absence of inoculation and the addition amount of RE, Ca, and Al.

FIG. 1 is an example of the spheroidal graphite cast iron of the present invention, and FIG. 2 is a photograph of the structure of the conventional spheroidal graphite cast iron. FIG. 3 is an example of flake graphite cast iron according to the present invention, and FIG. 4 is a structural diagram photograph of flake graphite cast iron of a conventional example. By performing the inoculation, the number of graphite grains of spheroidal graphite cast iron is increased, and the graphite structure of flake graphite cast iron is refined. Improvement of tissue could be confirmed by using an inoculum with optimum amounts of RE, Ca, and Al.

Claims

As an inoculum, it contains 15 to 80% by weight of Si, RE has a purity of either 80 to 100% by weight of La or a purity of 80 to 100% by weight of Ce, Ca and Al, the balance being Fe and inevitable Using an inoculant composed of impurities, the inoculum contains La or Ce in an amount of 0.001 to 0.009% by weight, Ca in an amount of 0.001 to 0.02% by weight, A cast iron molten metal treatment method comprising inoculating the molten metal of the cast iron by adding Al to the molten metal in an amount of 0.001 to 0.02% by weight.
In the inoculum, the Si content is 30 to 80%, the purity is 80 to 100% by weight La or the purity is 80 to 100% by weight Ce is 0.1 to 0.6% by weight, and the Ca content is 0. The cast iron molten metal treatment method according to claim 1, wherein the cast iron melt has a content of 0.1 to 1.3% by weight and an Al content of 0.1 to 2.0% by weight.
In the inoculum, the Si content is 30 to 60%, the purity is 80 to 100% by weight La or the purity is 80 to 100% by weight Ce is 0.3 to 1.8% by weight, and the Ca content is 0. 2. The cast iron molten metal treatment method according to claim 1, wherein the molten iron has a content of 0.1 to 6.0% by weight and an Al content of 0.1 to 6.0% by weight.
The cast iron molten metal treatment method according to any one of claims 1 to 3, wherein the inoculum is granular with a particle diameter of 1 to 5 mm.
The cast iron molten metal treatment method according to any one of claims 1 to 3, wherein the inoculum is a lump having a length of 5 to 70 mm.
The inoculum comprises particles having a particle size of 0.1 to 1.0 mm, and is supplied to the molten metal in a state where the particles are continuously included in the core of the wire. The cast iron molten metal processing method as described in any one of Claims.
The method further includes performing a graphite spheroidizing treatment using another spheroidizing agent different from the inoculant, wherein the graphite spheroidizing treatment temperature is 1400-1500 ° C., and the pouring temperature of the mold is 1270-1370 ° C. The cast iron molten metal treatment method according to any one of claims 1 to 6, wherein
The inoculum according to any one of claims 1 to 6 is used for one casting, and after spheroidizing treatment and inoculation by a pouring method, any one of a ladle, a hanging weir, and a mold A cast iron melt treatment method in which the inoculum is further inoculated once or more at a place or more.
The cast iron molten metal treatment method according to claim 8, wherein as a method for inoculating a plurality of times, a pouring flow inoculation, an in-mold inoculation, and a hanging weir inoculation performed when pouring into a mold are combined.
The cast iron molten metal treatment method according to any one of claims 1 to 9, wherein a spheroidizing treatment is performed using a spheroidizing treatment agent containing magnesium separately from the inoculating treatment with the inoculating agent.