JP2626417B2 - Graphite spheroidizing alloy in mold and graphite spheroidizing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for loading a molten cast iron into a reaction chamber provided in the middle of a runner and melting the molten cast iron as it passes through the reaction chamber to form a graphite spheroid. The invention relates to a graphite spheroidizing alloy in a mold and a graphite spheroidizing method.

[0002]

2. Description of the Related Art Among the methods for producing spheroidal graphite cast iron, a method of spheroidizing graphite in a mold (commonly called an in-mold method) involves a method of forming a graphite spheroidized alloy in the middle of a runner of molten cast iron. Is provided, and the molten cast iron is passed through the reaction chamber. In this case, the casting speed and the pre-treatment rate are determined based on the melting coefficient (also referred to as the reaction coefficient) specific to the graphite spheroidizing alloy used. When the molten cast iron in a certain temperature range passes through the reaction chamber calculated by the S amount and the target residual Mg amount in the molten cast iron, the graphite spheroidizing alloy previously loaded in the reaction chamber is homogeneously melted, This is a graphite spheroidizing method for obtaining a spheroidal graphite cast iron having desired properties by leaving a predetermined amount of Mg in the entire product. Here, the above-mentioned dissolution coefficient is a coefficient unique to the chemical composition and particle size distribution of the graphite spheroidized alloy.

In this method of spheroidizing graphite in a mold, the molten spheroidized cast iron is cast into the mold immediately after the spheroidizing treatment. Compared to other required graphite spheroidization treatment methods,
Because it is not affected by the wear phenomenon (commonly called fading) due to the vaporization and oxidation or resulfurization of Mg, which is an element that mainly controls the graphite spheroidization phenomenon, rare earth elements and Ca, Al, It is generally known that spheroidal graphite cast iron having a fine graphite structure and a fine eutectic cell structure can be easily obtained by the inoculation effect of Si or the like.

[0004] In order to obtain such a fine graphite structure,
This is an important issue in the production of spheroidal graphite cast irons, such as improving the possibility of thinning spheroidal graphite cast iron castings, which are difficult to manufacture due to chilling, and improving mechanical properties such as impact resistance and cutting workability. Is required to further refine the graphite structure.

Conventionally, as a method for refining the graphite structure, it has been known to add Bi to molten cast iron.
That is, Bi is an element that basically prevents crystallization of graphite in cast iron, and in spheroidal graphite cast iron, is a graphite spheroidizing element. And an alloy containing Bi, which is known as an element for increasing the number of eutectic cells, and which contains Bi (JP-A-59-43843).
(Japanese Patent Application Laid-Open No. 58-45311) has also been proposed.

However, the former additive alloy is mainly used for pouring, but since Bi has a high vapor pressure, it is difficult to maintain the inoculation effect due to fading of Bi due to fading with time in the pouring method. , The amount of residual Bi is not stable, and the effect is unstable. In addition, in the latter addition method immediately before casting such as a pouring flow inoculation method using an inoculant or in a mold inoculation method, the amount of the inoculant to be added is limited due to the solubility limit of the added inoculant (usually 0). .2%), inevitably necessitates the inclusion of a large amount of Bi in the inoculant, but increasing the Bi content in the inoculant makes production of the inoculant difficult, as described later. In addition, casting defects due to non-metallic inclusions are liable to be empirically experienced in cast iron manufacturing technology. Furthermore, the amount of Bi dissolved in the molten cast iron is unstable with the above-mentioned addition means, and it is impossible to finely control the Bi content in the cast iron and ensure homogeneity.

[0007] Further, alloys containing only Bi in the graphite spheroidized alloy have been developed. However, as will be described later, the graphite spheroidized alloy in the mold has a specific melting coefficient, and therefore, its chemical composition. Due to strict restrictions on particle size and grain size, it is impossible to use the existing Bi-containing graphite spheroidized alloy as it is as a graphite spheroidized alloy in a mold.

[0008] The present invention has been made in view of the above circumstances,
Instability due to Bi fading can be eliminated, and the amount of Bi added can be strictly controlled.
Provided are a graphite spheroidizing alloy in a mold and a method for spheroidizing graphite, which can overcome the difficulty of adding Bi to the molten metal in the conventional method and can obtain a thinner spheroidal graphite cast iron without heat treatment. The purpose is to:

[0009]

Means and Action for Solving the Problems The present inventors have
As a result of intensive studies to achieve the above object, it was found that a graphite spheroidizing method in a mold was adopted as a graphite spheroidizing method. In this case, as a graphite spheroidizing alloy, Mg3 was used.
-8% by weight, rare earth element 0.4-9% by weight, Bi0.4
To 3% by weight, 40 to 50% by weight of Si, the balance being Fe and unavoidable impurities, and 0.5% by weight or less of Al;
Total oxygen content is refined to 0.1% by weight or less, 0.5-5m
It has been found that it is effective to use a material having a particle size range of m and to perform graphite spheroidizing treatment in a mold using a graphite spheroidizing alloy containing Bi in the above specified amount.

That is, in the graphite spheroidizing method in a mold, about 1
% Of the graphite spheroidized alloy is charged into the reaction chamber, which is about 2% less than the addition method using the inoculant alone described above.
It is worth up to 15 times the amount added. Therefore, the residual Bi in the cast iron
Since the Bi content in the additive that causes the amount to be unstable or heterogeneous can be lowered, the amount of residual Bi can be controlled in a narrower range than in the existing Bi addition method, If the amount of Bi corresponding to the target residual amount is contained in the graphite spheroidized alloy in the mold, the graphite spheroidized alloy is uniformly dissolved in the cast iron melt together with Mg when the graphite spheroidized alloy is melted. It has been found that the target amount of residual Bi can be more stably and surely obtained as compared with the addition of Bi by the method described above.

Therefore, in addition to the feature that the graphite spheroidizing treatment in the mold inherently has the feature of miniaturizing the graphite structure according to the present invention, the feature of the system is the prevention of Bi wear and the target residual Bi. By utilizing the method for high-precision control of the amount, it is possible to obtain a spheroidal graphite cast iron having a finer graphite structure which was impossible with the conventional graphite spheroidizing method in a mold or the existing Bi addition method. It has become.

On the other hand, in the production of thin-walled spheroidal graphite cast iron, rapid cooling of the molten cast iron promotes crystallization of redebrite by metastable solidification, and a hard and brittle chill structure remains to produce a sound cast iron. It is well known that it is difficult to obtain, and it is generally known that increasing the number of graphite particles is an effective means for preventing the crystallization of redebrite. Spheroidal graphite cast iron is more stable than the conventional method, because it has a fine graphite structure reliably, by the present invention, it was found that thin-walled spheroidal graphite cast iron that was impossible in the conventional method is possible, The present invention has been accomplished.

Accordingly, the present invention provides a method for (1) loading a molten cast iron into a reaction chamber provided in the middle of a runner, melting the molten cast iron when passing through the reaction chamber, and subjecting the molten cast iron to spheroidizing graphite. A graphite spheroidizing alloy in a mold used,
Mg 3 to 8% by weight, rare earth element 0.4 to 9% by weight, Bi
0.4-3% by weight, Si 40-50% by weight, balance Fe
And 0.5% by weight of Al
Thereafter, the total oxygen content is refined to 0.1% by weight or less,
A graphite spheroidizing alloy in a mold characterized by having a particle size range of ５5 mm, and (2) a reaction chamber loaded with a graphite spheroidizing alloy in the middle of a runner is provided. In passing through the graphite spheroidizing treatment alloy, the molten cast iron is subjected to graphite spheroidizing treatment, and the graphite spheroidized cast iron melt is cast into a mold. Mg alloy
3 to 8% by weight, rare earth element 0.4 to 9% by weight, Bi0.
4 to 3% by weight, 40 to 50% by weight of Si, the balance being Fe and unavoidable impurities, and refined to 0.5% by weight or less of Al and 0.1% by weight or less of total oxygen.
Provided is a graphite spheroidizing method using a particle having a particle size range of 5 mm.

Hereinafter, the present invention will be described in more detail. The graphite spheroidizing alloy in a mold according to the present invention has a F
e, Si as a main component, and Mg, a rare earth element, and Bi in the specific amounts described above.

Here, M in the graphite spheroidized alloy in the mold is
g is an element serving as a reference for the dissolution coefficient used in the design of the reaction chamber in the spheroidizing treatment in a mold. If the content of Mg is less than 3% by weight, the amount of the graphite spheroidizing alloy increases and the surface area of the reaction chamber increases. As a result, the weight of the reaction chamber that does not become a cast product increases, and the casting yield (product weight / cast weight) decreases, which is extremely uneconomical and impractical.
On the other hand, if the Mg content is more than 8% by weight, the dissolution rate increases, the surface area of the reaction chamber decreases, and the amount of residual Mg becomes unstable. Backfire) is also large and extremely dangerous. For this reason, it is necessary that the Mg content in the alloy according to the present invention be 3 to 8% by weight.

It is generally said that the Bi content is effective for reducing the graphite of ordinary spheroidal graphite cast iron having a wall thickness of up to 30 mm. In view of the residual Bi amount of 0.002 to 0.007% by weight (however, in the case of a large thick casting, the addition may be performed about three times as much), it is effective to set the amount to 0.4 to 3% by weight. .

On the other hand, rare earth elements such as Ce are not necessarily indispensable elements for the graphite spheroidizing alloy in the mold.
i is Fe and S which occupy most of the graphite spheroidized alloy.
not alloyed with i (or alloying unknown), M
Since g and Ce are easily alloyed, they are indispensable elements for the graphite spheroidizing alloy of the present invention for stably containing a required amount of Bi, and are 0.4% by weight or more. Need to be added. Further, in the production temperature range of 1200 to 1400 ° C. of the graphite spheroidized alloy, Bi and Ce
In order to form a stable eutectic of Ce and Ce ₃ Bi, it is effective to define the maximum content of Ce to be three times the content of Bi, and to set the maximum content to 9% by weight.

A in the graphite spheroidized alloy in the mold of the present invention
It is necessary that the amount of l be 0.5% by weight or less. That is, about 1-2% of Al is usually contained in Fe-Si, which accounts for about 60% of the raw material used for producing the graphite spheroidized alloy.
Although contained, in the in-mold graphite spheroidization method, the spheroidized cast iron melt is cast into the mold without being subjected to slagging treatment. Therefore, casting defects (eg, dross defects and pinhole defects) caused by Al Is liable to occur and should be reduced as much as possible, but there is no problem if it is 0.5% by weight or less.

Further, as described above, in the graphite spheroidizing method in a mold, a casting method of a reaction chamber or the like is determined by a melting coefficient specific to the graphite spheroidizing alloy used therein. On the other hand, oxygen present in the graphite spheroidized alloy is mainly composed of Si,
Active elements such as Al, Mg, Ce, and Ca constitute oxides. The amount of the oxides affects the solubility of the graphite spheroidized alloy, and accordingly, the amount of oxides, that is, the amount of oxygen contained in the alloy. Is a factor that determines the alloy-specific melting coefficient. From this point, it is necessary that the total oxygen content in the alloy of the present invention be 0.1% by weight or less. It is difficult to maintain the total amount of oxygen in the graphite spheroidized alloy produced and controlled in the atmosphere at a constant level, but the total oxygen content is limited to a certain level or less by deoxidation scouring. can do.

In addition to the above-described alloying elements, the factor determining the melting coefficient specific to the graphite spheroidized alloy in the mold is also an important factor in the range of the particle size of the alloy. That is, in the graphite spheroidizing treatment in the mold, it is assumed that the molten cast iron flowing into the reaction chamber uniformly contains an alloy element such as Mg by melting the graphite spheroidizing alloy in the reaction chamber at a constant speed. Therefore, if the grain size range of the alloy is not constant, the bulk density of the alloy will fluctuate, and therefore, the penetration amount of the alloy element will not be kept constant due to the fluctuation of the total contact surface area with the molten cast iron. Therefore, the graphite spheroidizing alloy in the mold must be manufactured in a limited particle size range. In this regard, the graphite spheroidizing alloy in the mold according to the present invention has a particle size range of 0.5 to 5 mm. Things.

The alloy for spheroidizing graphite in a mold of the present invention has the composition and form as described above. May be contained for the purpose of providing at least one of Ca, Ba and Zr. However, since these elements easily combine with oxygen in the molten cast iron and easily form nonmetallic inclusions such as slag, and consequently induce casting defects caused by them, the total content of these elements Must be limited to a maximum of 1%. In this case, if the total content is 0.2% or less, the required inoculation effect is not expected sufficiently, so the addition amount of these elements is preferably 1% or less, particularly preferably 0.2 to 1%.

The graphite spheroidizing alloy of the present invention is used for the graphite spheroidizing treatment in a mold, and a known method can be used as a method of using the alloy and the method of the graphite spheroidizing treatment in a mold.

[0023]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

EXAMPLES, COMPARATIVE EXAMPLES Various in-mold graphite spheroidized alloys having the compositions shown in Table 1 were prepared. Here, B in the table
i1, Bi2, Bi3 are examples of Bi-containing alloys according to the present invention, and STD is a conventional graphite-in-mold spheroidizing alloy used for comparison. In order to compare only the effect of Bi, other graphite spheroids (Mg, rare earth element (RE), Ca) were set to almost the same level, and the grain size of all the alloys was 1 to 4 mm (4 mm to 10% by weight, 1 mm or less 1
0% by weight or less).

[0025]

[Table 1]

Next, graphite spheroidizing treatment was performed on the cast iron melt using the above alloy, and the treated cast iron melt was cast into the mold. Here, the outline of the apparatus is as shown in FIG.
In order to obtain cast test pieces A to D having the dimensions shown in FIG.
~ D were deployed as shown in FIG. In this case, test piece A
D is 7.5, 15, 30, and 50 mm for investigating the wall thickness sensitivity of the cast iron melt treated in the same manner. The dimensions of the mold are designed according to the basic formula of a casting method generally used for the graphite spheroidizing treatment in the mold, and the same amount of each of the alloys shown in Table 1 is added to the reaction chamber in FIG. Levels (0.4, 0.8, 1.2% by weight based on total cast weight) were loaded. The mold was an inorganic self-hardening mold (CO
Type ₂ ) was used.

As the molten cast iron, high-purity pig iron, electrolytic iron, and metallic silicon are used to have almost the same chemical composition (target C:
(3.8% by weight, Si: 2.0% by weight), and about 15% of molten cast iron melted in a high-frequency induction furnace.
After the temperature was raised to 50 ° C., the energization was stopped, and when the temperature dropped to about 1452 ° C., the molten metal was poured into the mold. The casting speed was almost the same, the temperature and the passing speed of the molten cast iron passing through the reaction chamber in the mold were kept under constant conditions, and the obtained cast iron structure was evaluated only by the influence of the chemical composition of each alloy in Table 1. Conditions.

In FIGS. 1 and 2, black circles indicate a temperature sensor arrangement site, white circles indicate a thermocouple arrangement site, and E indicates an analysis chill plate.

FIGS. 3 to 5 show the contents of Mg, Bi, and Si in the cast iron which has been subjected to graphite spheroidizing treatment in the mold with each of the alloys shown in Table 1, respectively. Each element increases at a substantially constant rate as the addition amount increases. In particular, for Bi, the Bi addition amount and the contained Bi amount show a good correspondence, and this indicates that the Bi in the mold made of the alloy of the present invention. Shows that Bi was added stably and uniformly.

Reference photographs 1 to 16 show metallographic micrographs (nital corrosion) of the thick portions of the spheroidal graphite cast iron test pieces A to D cast into the molds A to D in the above experiment.

FIGS. 6 to 8 show that the thick portions of the test pieces A to D are converted into the cooling rate of the molten cast iron, while
Image analysis of the structure photograph of No. 16 and measurement of the graphite spheroidization ratio, the number of graphite particles, and the ferrite area ratio were performed to obtain a cast iron structure of each alloy of Table 1 at a constant cooling rate (that is, a constant thickness portion). The result of having analyzed the influence quantitatively is shown. From the results, it can be seen that the graphite particle diameter is reduced and the number of particles is increased with the increase of Bi addition amount (that is, Bi content) in each thick part. In the matrix structure, the ferrite area ratio is remarkably increased except for the minimum thickness portion where pearlitization is promoted. In particular, it can be seen that the presence of Bi appears as a large difference with the conventional in-mold spheroidizing alloy.

That is, although the number of graphite particles is not much different in a thick portion having a low cooling rate, the effect of preventing diffusion of carbon atoms of Bi maintains a higher graphite spheroidization ratio than that of a conventional alloy due to the effect of preventing the diffusion of carbon atoms of Bi. This indicates that the anti-fading effect is excellent. On the other hand, in the thin part where the effect of fading is less than the effect of the cooling rate, although there is no difference in the graphite spheroidization rate compared with the conventional alloy,
Both the number of graphite particles and the area ratio of ferrite show a large increase. This indicates that the graphite spheroidizing treatment in the mold with the alloy of the present invention can provide a thinner ductile cast iron without a chill than that of the conventional alloy. In addition, a good correspondence between the Bi content, the number of graphite grains, and the area ratio of ferrite is also shown for the intermediate thick portions other than the above, and the Bi content in the alloy according to the present invention is adjusted to achieve the desired purpose. This shows that a ductile cast iron structure can be obtained, which can be stably obtained only by subjecting the alloy according to the present invention to spheroidizing graphite in a mold.

FIGS. 9 and 10 show the mechanical properties of each of the test pieces A to D obtained in this experiment. The tensile strength of each specimen tends to increase as the cooling rate increases (that is, becomes thinner). However, the sample of the alloy containing Bi according to the present invention is treated with a conventional alloy. In comparison, the tensile strength is large, and especially in the thin portion, the value is almost twice. The other elongation also shows an increasing tendency in each sample as the thickness becomes thinner, but the sample of the alloy according to the present invention has a thickness of 1.5 to 1.5 in comparison with the one treated with the conventional alloy at the same thickness.
It shows an excellent elongation of twice. That is, it can be seen that the spheroidal graphite cast iron treated with the alloy of the present invention is a spheroidal graphite cast iron having excellent mechanical properties showing higher strength and higher toughness than that of the conventional alloy.

It should be noted that, among the samples treated with Bi3 having the highest Bi content, the elongation percentage at the thinnest portion is different from the results of other samples and shows a decreasing tendency, but this indicates that the Bi content is excessive. Therefore, it is considered that a segregated portion of Bi is generated in the cast iron. This means that Bi is contained in the cast iron to increase the number of graphite grains and obtain a thinner cast iron or to obtain a cast iron having the above-mentioned excellent mechanical properties. Strictly needs to be managed.

According to the above experimental results, the graphite spheroidizing treatment in the mold using the Bi-containing graphite spheroidizing alloy in the present invention can be carried out by the ordinary pouring treatment using a Bi-containing graphite spheroidizing alloy or the treatment using a Bi-containing inoculant. Makes it possible to incorporate a wider range and a more accurate amount of Bi into the cast iron, which has been difficult, and the cast iron obtained according to the present invention can easily obtain a fine graphite structure among existing methods. It was recognized that a finer graphite structure and excellent mechanical properties could be obtained as compared with cast iron obtained by a known conventional in-mold graphite spheroidizing method.

[0036]

According to the present invention, it is possible to obtain a spheroidal graphite cast iron having a finer graphite structure and excellent physical properties, which can be contained in cast iron by controlling the amount of Bi strictly. In addition, a thinner spheroidal graphite cast iron can be easily and reliably obtained without heat treatment.

[Brief description of the drawings]

FIG. 1 is a schematic view of a graphite spheroidizing apparatus used in Examples and Comparative Examples of the present invention.

FIG. 2 is a side view of a spheroidal graphite cast iron test piece obtained by the same apparatus.

FIG. 3 is a graph showing the relationship between the amount of Mg added and the amount of residual Mg in various mold spheroidizing alloys.

FIG. 4 is a graph showing the relationship between the amount of Bi added and the amount of residual Bi in various mold spheroidizing alloys.

FIG. 5 Target Si by graphite spheroidizing alloy in various molds
4 is a graph showing a relationship between the residual amount and the residual amount.

FIG. 6 is a graph showing a relationship between a graphite spheroidizing rate and a cooling rate of each thick portion treated with a graphite spheroidizing alloy in various molds.

FIG. 7 is a graph showing the relationship between the number of graphite particles in each thick portion treated with various alloy spheroidizing alloys in a mold and the cooling rate.

FIG. 8 is a graph showing the relationship between the ferrite ratio and the cooling rate of each thick portion treated with the graphite spheroidizing alloy in various molds.

FIG. 9 is a graph showing the relationship between the tensile strength and the cooling rate of each thick portion treated with a graphite spheroidizing alloy in various molds.

FIG. 10 is a graph showing the relationship between the elongation percentage and the cooling rate of each thick portion treated with various types of graphite spheroidizing alloys in a mold.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takeo Oguchi 2-6-1 Otemachi, Chiyoda-ku, Tokyo Shin-Etsu Chemical Co., Ltd. (56) References JP-A-59-43843 (JP, A) Kai 58-45311 (JP, A)

Claims (3)

(57) [Claims] 1. A graphite spheroid in a mold which is charged into a reaction chamber provided in the middle of a runner, melts when the molten cast iron passes through the reaction chamber, and is used for spheroidizing the molten cast iron. A treated alloy comprising 3 to 8% by weight of Mg, 0.4 to 9% by weight of a rare earth element, 0.4 to 3% by weight of Bi,
40 to 50% by weight, with the balance being Fe and unavoidable impurities, Al being 0.5% by weight or less, and total oxygen content of 0.1%
A spheroidized graphite alloy in a mold characterized by being refined to not more than% by weight and having a particle size range of 0.5 to 5 mm. 2. At least one of Ca, Ba and Zr
The alloy for spheroidizing graphite in a mold according to claim 1, wherein the alloy contains 0.2 to 1% of a total element content. 3. A reaction chamber loaded with a graphite spheroidizing alloy is provided in the middle of the runner, and when the molten cast iron passes through the reaction chamber, the graphite spheroidizing alloy is melted to form the graphite spheroid. In the graphite spheroidizing method, the molten cast iron that has been subjected to the graphite spheroidizing treatment is cast into a mold.
As the graphite spheroidized alloy, Mg 3 to 8% by weight, rare earth element 0.4 to 9% by weight, Bi 0.4 to 3% by weight, S
i is 40 to 50% by weight, the balance being Fe and unavoidable impurities, Al is 0.5% by weight or less, and the total oxygen content is 0.
A graphite spheroidizing method comprising using a material refined to 1% by weight or less and having a particle size range of 0.5 to 5 mm.