JP2006122917A - Method for casting cast iron and cast iron product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for casting cast iron by which a cast iron product equivalent to a plurality of kinds can be obtained from the same die. <P>SOLUTION: The method for casting cast iron is characterized in that when the molten metal of an iron alloy is poured into a cavity inside a die and a cast iron product with a desired shape is cast, the cast iron product obtained by solidification of the molten metal of the iron alloy poured into the die is cooled, and when the temperature of the cast iron product reaches a prescribed temperature higher than room temperature, the die is opened and the cast iron product is discharged, and the cast iron product discharged from the die is annealed at a cooling rate slower than the cooling rate in the die. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cast iron method and a cast iron product, and more particularly to a cast iron method and a cast iron product in which a molten iron alloy is poured into a cavity in a mold to cast a cast iron product having a desired shape.

A cast iron product made of spheroidal graphite cast iron having a large amount of ferrite and excellent toughness is known, for example, in Patent Document 1 below. Since such cast iron products have toughness, they are used in a wide range of applications such as automobile parts.
In casting of cast iron products made of such spheroidal graphite cast iron, a sand mold formed using sand coated with a resin binder (binder) is used.
However, in casting using a sand mold, sand processing equipment such as sand collection, cooling, transport, kneading and remanufacturing is required as well as a sand mold making machine.
Moreover, cast iron products the iron alloy melt obtained by pouring the sand mold, in a state diagram of the iron alloy, A ₁ transformation temperature or less of that and austenite phase at a temperature below the austenite phase crystallizes is transformed into pearlite Since it is taken out after being cooled in the sand mold to near room temperature, the time from pouring into the sand mold until taking it out is remarkably long, and its productivity is becoming a problem.
On the other hand, in order to improve the productivity of the cast iron products, cast iron products obtained by pouring the molten iron alloy into a mold made of a highly heat conductive material such as water-cooling structure or copper, A ₁ transformation temperature or less in the mold There is also known a cast iron method in which the steel is rapidly cooled to near room temperature.
Japanese Patent No. 2730959 (claims, page 3, left column)

Compared with the cast iron method using a sand mold, the cast iron method using a rapidly coolable mold can significantly shorten the time from pouring into the mold until the cast iron product is taken out from the mold.
Furthermore, since the mold can be reused, sand processing equipment can be dispensed with and the process can be simplified.
However, cast iron products obtained by pouring molten iron alloy into the mold are generally low strength flake graphite cast iron having undercooled eutectic graphite and low toughness with low ferrite content. Grade spheroidal graphite cast iron.
Heat treatment is indispensable for making such a cast iron product having a high ferrite content and excellent toughness. For this reason, even if it is the cast iron method using a metal mold | die, it is difficult to improve the productivity remarkably.
However, the cast iron method using a metal mold has many advantages such as significantly shortening the time required to take out a cast iron product from the metal mold and eliminating the need for a sand treatment facility.
Conventionally, a single type of cast iron product is cast from the same mold. However, if cast iron products corresponding to a plurality of types can be cast, efficiency such as reduction in the number of held molds can be achieved.
Accordingly, an object of the present invention is to provide a cast iron method capable of obtaining cast iron products corresponding to a plurality of types from the same mold, and a cast iron method capable of obtaining a cast iron product having a large amount of ferrite and excellent in toughness without performing heat treatment. And to provide cast iron products.

The present inventors first examined a cast iron method using a conventional mold. In the conventional cast iron method using a mold, a cast iron product taken out from the mold using a water-cooled structure or a mold made of a high heat conductive material such as copper in order to rapidly cool the molten iron alloy poured into the mold. Is sufficiently cooled.
For this reason, the present inventors consider that the cast iron product is excessively cooled in the mold in the conventional cast iron method, take out the high temperature cast iron product from the mold, and cool the high temperature cast iron product by air cooling. I tried to do that.
According to such an attempt, if the temperature of the cast iron product taken out from the mold is different, the quality of the cast iron product obtained after cooling by air cooling is different, and the higher the temperature of the cast iron product taken out from the mold is, The present inventors have found that the amount of ferrite is increased as compared with a cast iron product rapidly cooled to near room temperature in a conventional mold, and have reached the present invention.

That is, according to the present invention, when a molten iron alloy is poured into a cavity in a mold to cast a cast iron product having a desired shape, the molten iron alloy poured into the mold is obtained by solidification. When the cast iron product is cooled and the temperature of the cast iron product reaches a predetermined temperature higher than room temperature, the mold is opened and the cast iron product is taken out, and the cast iron product taken out from the mold is placed in the mold. The cast iron method is characterized in that it is gradually cooled at a cooling rate slower than the cooling rate.
In the present invention, the temperature at which the mold is opened to take out the cast iron product is equal to or lower than the eutectic temperature at which the austenite phase and graphite crystallize in the phase diagram of the iron alloy poured into the cavity, and the austenite phase. When the temperature is higher than the A ₁ transformation temperature at which the steel transforms into a pearlite phase, specifically 1147 to 727 ° C., a cast iron product having a large amount of ferrite and excellent in toughness can be obtained without heat treatment.
On the other hand, the temperature of the mold and mold opening takes out the cast iron products, in the state diagram of the iron alloy poured into the cavity, A ₁ transformation temperature of less than the temperature at which austenite phase is transformed into pearlite phase, specifically 727 ° C. By making it less than this, although the amount of ferrite decreases, a cast iron product excellent in tensile strength and proof stress can be obtained.
The present invention also relates to a cast iron product having an HRB hardness of 80 to 100 obtained by pouring a molten iron alloy into a cavity in a mold, and the ferrite content measured with a metallographic micrograph of the cast iron product. 70% or more, the number of graphite particles having a particle size of 5 μm or more is 900 pieces / mm ² or more, and among the graphite particles, the graphite spheroidization ratio occupied by the spherical graphite particles is 70% or more. It is also a featured cast iron product.

In the present invention, the cast iron product taken out from the mold and cooled to a predetermined temperature equal to or higher than room temperature is allowed to cool at room temperature, so that the cast iron product taken out from the mold can be made easier than the cooling rate in the mold Cools at a slow cooling rate.
The time when the mold is opened and the cast iron product is taken out can be easily managed by replacing the temperature of the cast iron product with the elapsed time from the pouring of the molten metal into the mold.
Further, it is preferable to use an iron-carbon alloy as the iron alloy to be used as the molten metal, and in particular, carbon (C) 3.1 to 3.9% by weight, silicon (Si) 2.0 to 3.0% by weight, manganese (Mn) 0.3 wt% or less, phosphorus (P) 0.03 wt% or less, chromium (Cr) 0.10 wt% or less, magnesium (Mg) 0.018 to 0.060 wt%, residual iron and impurities An iron alloy having a CE value (carbon equivalent) of 4.0 to 4.7% by weight can be suitably used.
When pouring such a molten metal into a mold, it is possible to refine the graphite by pouring and injecting 0.05 to 0.225 wt% of Fe—Si in Si amount.
As the mold used in the present invention, a gravity cast iron mold in which the molten metal poured from the gate is filled in the cavity by gravity can be suitably used. As this mold, by using a mold having cooling characteristics that can control the time of taking out the cast iron product in which the molten iron alloy is solidified, the take-out temperature of the cast iron product can be made constant. Quality cast iron products can be obtained. As such a mold, a mold made of steel (S45C) containing 0.45% by weight of carbon (C) can be suitably used.

According to the present invention, the cast iron product cooled to a predetermined temperature of room temperature or higher is taken out from the mold having a high cooling rate and gradually cooled at a cooling rate lower than the cooling rate in the die, thereby cooling. The same effect as when heat treatment is performed on the finished cast iron product can be obtained. For this reason, different types (characteristics) of cast products can be obtained by changing the temperature of the cast iron product taken out from the mold.
For example, the temperature of the mold and mold opening takes out the cast iron products, in the state diagram of iron alloy, the austenite phase is cooled to a temperature lower than the A ₁ transformation temperature to transform into pearlite phase, obtained by completion of the cooling Although the pearlite ratio of the cast iron product increases and the ferrite content decreases, a cast iron product excellent in tensile strength and proof stress can be obtained.
On the other hand, cast iron products in the mold, in the state diagram of iron alloy, the austenite phase and graphite are both and austenite phase at eutectic temperature below the crystallisation reaches the A ₁ transformation temperature above which the transformation to pearlite phase When the cast iron product is taken out from the mold and slowly cooled at a cooling rate slower than the cooling rate in the mold, the ferrite content and the graphite spheroidization rate can be improved, and the cast iron product exhibiting excellent toughness is subjected to heat treatment. Can be obtained without application. Presumably due to the possible slow cooling the cast iron products in the vicinity of A ₁ transformation temperature.

In the present invention, the cast iron product obtained by solidification of the molten iron alloy poured into the mold is cooled, and when the temperature reaches a predetermined temperature of room temperature or higher, the mold is opened to remove the cast iron product. It is important to take out and slowly cool at a cooling rate slower than the cooling rate in the mold.
Here, the cooling rate of the cast iron product taken out from the mold is cooled more than the cooling rate in the mold. The obtained cast product is equivalent to the cast product obtained by rapid cooling in the mold. Is.
The temperature at which the mold is opened and the cast iron product is taken out will be described with reference to the iron-carbon alloy phase diagram shown in FIG. In the phase diagram shown in FIG. 1, in an iron alloy melt containing 3.5% by weight of iron, solidification starts at about 1240 ° C., and an austenite (γ) phase in which carbon is dissolved in iron crystallizes. Solidification of the molten metal is completed at 1147 ° C., and the austenite phase and cementite (Fe ₃ C) or graphite and austenite phase are crystallized simultaneously in the solidified body.
When this solidified body is further cooled, the austenite phase is transformed into a pearlite phase at 738 to 727 ° C. or lower. In the present invention, it referred to the temperature at which the austenite phase is transformed into pearlite phase and the A ₁ transformation temperature.

The temperature at which the mold is opened and the cast iron product is taken out is equal to or lower than the eutectic temperature at which both the austenite phase and graphite crystallize in the phase diagram of the iron alloy shown in FIG. 1, and the austenite phase is transformed into a pearlite phase. ₍₁ ) When the cooling is completed by slowly cooling the casting product taken out of the mold at a temperature higher than the transformation temperature at a cooling rate slower than the cooling rate in the mold, the ferrite content and the graphite spheroidization ratio are large. A cast iron product exhibiting excellent toughness can be obtained without heat treatment.
Specifically, the take-out temperature at which the mold is opened and the cast iron product is taken out is preferably 1147 to 727 ° C, and particularly 1147 to 850 ° C. 70% or more is preferable.
When the temperature at which such cast iron product is taken out exceeds 1147 ° C., the molten metal tends to be incompletely solidified in the mold.
On the other hand, when the cast iron product is cooled to a temperature lower than the A ₁ transformation temperature, specifically 727 ° C., in the mold, the cast iron product obtained by slow cooling at a cooling rate slower than the cooling rate in the mold is Although the hardness increases and the ferrite content decreases, a cast iron product having excellent tensile strength and proof stress can be obtained.

In principle, it is best to judge the time of taking out the cast iron product from the mold based on the temperature of the cast iron product. However, it is difficult to directly measure the temperature of the cast iron product at every casting. For this reason, the relationship between the temperature of the cast iron product in the mold and the elapsed time since the molten metal was poured into the mold was measured, and the mold was determined based on the elapsed time since the molten metal was poured into the mold. It is easy to manage the timing of removing cast iron products from
In the present invention, an iron-carbon alloy is preferably used as the molten iron to be poured into the mold. In particular, 3.1% to 3.9% by weight of carbon (C) and 2.0% of silicon (Si) are used. -3.0% by weight, manganese (Mn) 0.3% by weight or less, phosphorus (P) 0.03% by weight or less, chromium (Cr) 0.10% by weight or less, magnesium (Mg) 0.018-0. An iron alloy composed of 060% by weight, residual iron and impurities and having a CE value (carbon equivalent) of 4.0 to 4.7% by weight can be suitably used.

Here, if the carbon (C) is less than 3.1% by weight, carbides are likely to precipitate, pearlite increases, and castability tends to decrease. On the other hand, when the carbon (C) exceeds 3.9% by weight, quiche graphite is precipitated, the graphite is unevenly deposited, and the chain graphite tends to be precipitated.
When silicon (Si) is less than 2.0% by weight, carbide tends to precipitate and tends to increase pearlite. On the other hand, when it exceeds 3.0% by weight, quiche graphite is precipitated, and graphite is unevenly deposited. The chain graphite tends to be easily deposited.
When manganese (Mn) exceeds 0.3% by weight, pearlite tends to increase. When phosphorus (P) exceeds 0.03% by weight, chromium (Cr) exceeds 0.10% by weight. Tends to become brittle due to steadite.
If the magnesium (Mg) is less than 0.018% by weight, the graphite tends not to spheroidize. On the other hand, if it exceeds 0.060% by weight, shrinkage cavities and carbides tend to precipitate.
On the other hand, when the CE value (carbon equivalent) is less than 4.0% by weight, carbides are likely to be precipitated, pearlite is increased, and castability tends to be lowered. On the other hand, when the CE value (carbon equivalent) exceeds 4.7% by weight, quiche graphite is precipitated, graphite is unevenly deposited, and chain graphite tends to be precipitated.
When pouring a molten metal having such a composition into a mold, it is possible to refine the graphite by pouring and injecting 0.05 to 0.225% by weight of Fe—Si. When the amount of Fe-Si poured is less than 0.05% by weight, the graphite tends to be difficult to be refined. Even if the amount exceeding 0.225% by weight is poured, The degree of refinement has reached saturation, and undissolved products tend to be generated.

As the mold used in the present invention, a gravity cast iron mold in which the molten metal poured from the gate is filled into the cavity by gravity can be suitably used because of its simple structure.
By the way, as a conventional mold for cast iron, a mold made of a water-cooled structure or a high heat conductive material such as copper is used. In such conventional cast iron mold is sufficiently cooled to a temperature lower than the A ₁ transformation temperature significantly faster cooling rate of the filled molten metal into the cavity, approximately 10 seconds after pouring the molten metal into a mold For this reason, it is difficult to control the timing of removing the cast iron product from the mold.
For this reason, as a metal mold used in the present invention, a cooling characteristic capable of controlling the take-out time of cast iron products in which a molten iron alloy is solidified, specifically, a water-cooled structure or a high heat conductive material such as copper is used. A mold having a cooling rate that is less than the cooling rate of a conventional mold is used.
As such a mold, a mold made of steel (S45C) containing 0.45% by weight of carbon (C) can be suitably used. This mold does not need to be provided with a water cooling structure. Therefore, the structure is simpler than the mold having the conventional water cooling structure, and the manufacturing cost is also reduced.
In addition, the mold agent used by the conventional metal mold | die can be used for the metal mold | die used by this invention.

In the present invention, it is important that after the cast iron product cooled to a predetermined temperature of room temperature or higher in the mold is opened and taken out, the cast iron product is gradually cooled at a cooling rate slower than the cooling rate in the mold. is there.
If the cooling rate of the cast iron product taken out from the mold is equal to or higher than the cooling rate of the cast iron product in the mold, the cooled cast iron product has a higher pearlite ratio and a reduced ferrite content. Become.
Such slow cooling can be achieved by allowing the cast iron product taken out from the mold to cool at room temperature.
In this way, it is considered that the cooling rate of the cast iron product in the mold having no water cooling structure can be made faster than the case where the cast iron product is allowed to cool at room temperature.
In the present invention, since the mold is opened at a predetermined temperature of room temperature or higher, the mold is opened in a short time after pouring, and a cast iron product in a high temperature state is taken out during cooling. For this reason, even in a mold that does not have a water cooling structure, the molten metal that has been poured is cooled in a state in which the solidification of the molten metal and the rise in the mold temperature caused by the cast iron product are suppressed. It has a heat capacity that can sufficiently absorb the amount of heat up to the extraction temperature at which the cast iron product is taken out.
In addition, heat transfer from the molten metal and cast iron product to the mold is better than heat transfer from the cast iron product to the air.
Therefore, the cooling rate of the cast iron product obtained by solidifying the molten metal poured into the mold in the cooled state is faster than when the cast iron product is allowed to cool at room temperature.
In addition, when the cooling rate of the cast iron product in the mold is equal to or less than that when the cast iron product is allowed to cool at room temperature, cold air is poured into the mold into which the molten metal has been poured and / or the mold from which the cast iron product has been taken out. Etc. may be used to perform forced cooling.

As described above, according to the cast iron method according to the present invention described above, a cast iron product made of spheroidal graphite cast iron having a large amount of ferrite and excellent toughness can be quickly obtained.
In particular, by setting the temperature of the cast iron product from which the mold is opened to take out the cast iron product to 1147 to 850 ° C., the ferrite content measured by the metallographic micrograph of the cast iron product is 70% or more, and the particle size A cast iron product can be obtained in which the number of graphite particles of 5 μm or more is 900 particles / mm ² or more, and among the graphite particles, the graphite spheroidization ratio occupied by the spherical graphite particles is 70% or more. This cast iron product corresponds to FCD450 and is used for automobile parts and the like.
Here, when the temperature of the cast iron product from which the mold is opened and the cast iron product is taken out is 727 ° C. to less than 850 ° C., the ferrite content measured by the metallographic micrograph of the cast iron product is 60 to 70%. In addition, it is possible to obtain a cast iron product in which the number of graphite particles having a particle size of 5 μm or more is 900 particles / mm ² or more and the graphite spheroidization ratio occupied by the spherical graphite particles is 70% or more. This cast iron product corresponds to FCD550.

As described later, when a cast iron product of about 2.5 kg corresponding to FCD450 is cast by the cast iron method according to the present invention using a mold of S45C material that does not have a water cooling structure, a molten metal is poured into the mold. Then, the mold can be opened in about 70 seconds, and the cast iron product can be taken out and allowed to cool.
In contrast, in order to obtain a cast iron product of about 2.5 kg corresponding to FCD450 by a conventional cast iron method using a water-cooled mold, it is necessary to take out the cooled cast iron product from the water-cooled mold. Although the time is about 10 seconds, it is necessary to heat-treat the extracted cast iron product, and this heat treatment requires about 45 minutes.
Further, when a cast iron product of about 2.5 kg corresponding to FCD450 is cast using a conventional sand mold, it takes about 45 minutes from pouring the molten metal into the sand mold and taking out the cooled cast iron product.

As described above, according to the cast iron method of the present invention, ferrite can be produced in a short time compared to the conventional cast iron method using a water-cooled structure or a mold made of a high heat conductive material such as copper or the cast iron method using a sand mold. A cast iron product made of spheroidal graphite cast iron having a large amount and excellent toughness can be obtained quickly.
Furthermore, in the present invention, compared with a conventional water-cooled structure or a mold made of a high heat conductive material such as copper, a mold in which the cooling rate of cast iron products in the mold is relaxed can be used. Since the special structure can be made unnecessary, an inexpensive mold with a simplified mold structure can be used, and the production cost of cast iron products can be reduced.
Further, according to the cast iron method according to the present invention, compared to the conventional cast iron method using a sand mold, a sand mold making machine, sand collection, cooling, transport, kneading remanufacturing and the like can be eliminated, Capital investment in cast iron plant can be reduced.

(1) Mold: As a mold for gravity cast iron, a mold made of steel (S45C) with 0.45% by weight of carbon (C) was prepared. This mold was not provided with a water cooling structure.
A cast iron product that can be cast iron with such a mold is a cylindrical member that constitutes a master cylinder having a weight of 2.5 kg and a diameter of 40 mm and a length of 170 mm.
(2) Molten metal: 3.1 to 3.9% by weight of carbon (C), 2.0 to 3.0% by weight of silicon (Si), 0.3% by weight or less of manganese (Mn), 0.8% of phosphorus (P). 03 wt% or less, chromium (Cr) 0.10 wt% or less, magnesium (Mg) 0.018 to 0.060 wt%, trace amount of sulfur (S), copper (Cu), and CE value (carbon equivalent) ) 4.0 to 4.7% by weight of an iron alloy was melted to form a molten metal. The solidification completion temperature of this iron alloy is 1145 ° C., and the A ₁ transformation temperature is 730 to 727 ° C.
(3) Cooling curve of the cast iron product in the mold The molten metal was poured into the pouring gate of the prepared mold, and at that time, 0.20% by weight of Fe—Si in terms of Si amount was poured and inoculated.
In addition, after casting the cast product by pouring the molten metal into this mold four times, the temperature of the cast iron product in the mold is measured by a thermocouple inserted into the mold gate. A cooling curve was determined. The results are shown as a graph in FIG.
The graph shown in FIG. 2 shows the relationship between the elapsed time from the start of pouring molten metal into the mold gate and the temperature of the cast iron product.
As is apparent from the graph shown in FIG. 2, the molten metal poured from the pouring gate of the mold solidifies after 40 seconds from the start of pouring, and the cast iron product in the mold is linear with respect to the elapsed time up to about 600 ° C. it indicates that an manner being cooled, the cast iron product in the mold, also in the a ₁ transformation temperature near the iron alloy is cooled immediately after the melt has solidified substantially equal cooling rate.
When the cooling rate in the mold of the cast iron product is determined from the slope of the cooling curve until the cast iron product is cooled to 600 ° C., 4.5 ° C./second (up to 800 ° C.) to 1.17 ° C. / Sec (800 to 600 ° C.).

After casting was performed four times by pouring molten metal into the mold created in Example 1 to cast a cast product, 3.47% by weight of carbon (C) and silicon (Si) were added to the mold gate. 2.71 wt%, manganese (Mn) 0.21 wt% or less, phosphorus (P) 0.02 wt%, chromium (Cr) 0.04 wt%, sulfur (S) 0.007 wt%, magnesium (Mg ) A molten metal obtained by melting an iron alloy composed of 0.023 wt%, copper (Cu) 0.04 wt% and having a CE value (carbon equivalent) of 4.37 wt% was poured. At that time, molten iron was inoculated with 0.20% by weight of Fe-Si. The eutectic temperature at which both the austenite phase and graphite of the molten metal infused with Fe—Si crystallize is 1148 ° C., and the A ₁ transformation temperature at which the austenite phase transforms into a pearlite phase is 727 ° C.

After 109 seconds from the start of pouring the molten metal into the mold spout, the mold was opened and the cast iron product was taken out and air-cooled at room temperature. The temperature at which the cast iron product is taken out from the mold is 930 ° C. from the graph shown in FIG. Moreover, the cooling rate of the cast iron product in air cooling is 2.17 ° C./second (up to 800 ° C.) to 0.67 ° C./second (800 to 600 ° C.), and the cooling rate of the cast iron product in the mold [ 4.5 ° C./second (up to 800 ° C.) to 1.17 ° C./second (800 to 600 ° C.)].
About the front-end | tip part and center part of the cylindrical member of the cooled cast iron product, it measured about material structure and hardness.
Regarding the material structure, the surface of the sample collected from each part of the tip (A) and the central part (B) of the cylindrical member is magnified 100 times with a microscope, and the number of graphite particles of 5 μm or more existing in a predetermined range And the spheroidization ratio of graphite with respect to the total number of graphite particles of 5 μm or more was measured. This graphite spheroidization rate was carried out in accordance with the graphite spheroidization rate judgment test method of JIS G5502 12.6.
In the obtained cast iron product, at the tip (A), the total number of graphite particles of 5 μm or more is 1335 particles / mm ² and the graphite spheroidization rate is 80.4%, and the center (B) Then, the total number of graphite particles of 5 μm or more was 1098 particles / mm ² and the graphite spheroidization ratio was 75.9%.
A micrograph of the sample surface magnified 100 times is shown in FIG. A shown in FIG. 3 is the tip of the cylindrical member, and B is the center.

Furthermore, after immersing the sample collected from each part of the tip part (A) and the central part (B) of the cylindrical member in the nital solution and performing the etching treatment, the sample surface is magnified 100 times with a microscope, The amount of ferrite (%) was investigated. This ferrite content was measured in accordance with the base structure judgment method of JIS G5502 12.6.
FIG. 4 shows a photomicrograph of the microstructure of the sample surface subjected to the etching treatment, enlarged 100 times. A shown in FIG. 4 is the tip of the cylindrical member, and B is the center.
In the micrograph shown in FIG. 4, the spherical black portion is graphite, and the white portion covering the periphery is the ferrite phase. The ferrite amount (%) was measured at five locations with different fields of view, and the average value of the measured values was adopted.
In the obtained cast iron product, the ferrite content was 77.8% at the tip (A), and the ferrite content was 90.6% at the center (B).

Moreover, about the sample extract | collected from each site | part of the front-end | tip part (A) and center part (B) of a cylindrical member, HRB hardness was measured using the commercially available hardness meter. In the obtained cast iron product, the HRB hardness of the front end portion (A) was 90.0, and the HRB hardness of the central portion (B) was 84.5.
As described above, in the obtained cast iron product, the tip portion (A) and the center portion (B) are materials corresponding to FCD450, although a slight difference is observed in the material structure and hardness.

A cast iron product having a master cylinder shape was cast in the same manner as in Example 2. When casting this cast iron, the mold release time from the start of pouring of the molten metal into the mold spout until the mold is opened is changed as shown in Table 1 below. And air cooled. The cast iron product temperature (mold release product temperature) when the mold is opened is also shown in Table 1.
For each of the samples collected from the tip part (A) and the center part (B) of the cast iron product after cooling, the number of graphite grains, the HRB hardness, the graphite spheroidization ratio, and the ferrite content were determined in the same manner as in Example 2. The measured results are shown in Table 2 below.
Further, for each of the cast iron products, the tensile strength, proof stress and elongation were also measured and are shown in Table 3 below.

As is clear from Tables 1, 2 and 3, No. 2, No. 2 At the levels of 3 and No. 4, the mold was at 1060 ° C. (No. 2), 930 ° C. (No. 3) or 765 ° C. (No. 4) which is higher than the A ₁ transformation temperature of the molten metal poured into the mold. When the cast iron product is taken out of the product and air-cooled, the ferrite content is 60% or more and the number of graphite particles having a particle size of 5 μm or more is 900 pieces / mm ² or more at the tip portion (A) and the center portion (B). Moreover, among the graphite particles, a cast iron product having a spheroidization ratio of 70% or more occupied by the spherical graphite particles can be obtained. In particular, No. 2 and No. 2 in which the extraction temperature of cast iron products was 850 ° C. or higher. 3 level, a cast iron product having a ferrite content of 90% or more can be obtained in the central portion (B). In particular, at the No. 2 level in which the temperature for taking out the cast iron product is 1000 ° C. or more, the tip portion Also in (A) and the center part (B), a cast iron product having a ferrite content of 90% or more can be obtained.
On the other hand, at the level of No. 1 and No. 5 where the temperature at which the cast iron product is taken out from the mold is less than 727 ° C., which is the A ₁ transformation temperature of the molten metal, the amount of ferrite at the tip (A) Was cast iron products of less than 60%. In such cast iron products, No. 2, No. Although the HRB hardness increases as compared with the levels of 3 and No. 4, the ferrite content tends to decrease.

Moreover, about each of the tension | tensile_strength, yield strength, and elongation shown in Table 3, it will become as shown in FIGS. 5 to 7, FIG. 5 is a graph showing the relationship between the release product temperature and the tensile strength of the obtained cast product, and FIG. 6 shows the relationship between the release product temperature and the yield strength of the obtained cast product. The graph and FIG. 7 are graphs showing the relationship between the release product temperature and the elongation of the obtained cast product, respectively. 5 to 7, the eutectic temperature and the A ₁ transformation temperature are displayed, and the lower limit values of FCD450 and FCD500 defined by the JIS standard for spheroidal graphite cast iron are displayed.
Table 4 below shows the standard values of FCD450 and FCD500 defined by the JIS standard for the spheroidal graphite cast iron.
As shown in FIG. 5 to FIG. 7, by releasing the mold at a temperature not higher than the eutectic temperature at which both the austenite phase and graphite are crystallized and not lower than the A ₁ transformation temperature at which the austenite phase transforms into a pearlite phase, A corresponding cast product can be obtained.
On the other hand, when releasing the product temperature is the temperature lower than the A ₁ transformation temperature, the resulting cast products, although the amount of ferrite becomes lower than FCD450, a cast product of equivalent FCD500 hardness is high.
In this way, by adjusting the temperature of the release product for taking out the cast product from the mold, it is possible to obtain a cast product corresponding to FCD450 and a cast product corresponding to FCD500.

The phase diagram of iron-carbon alloy is shown. It is a graph which shows the relationship between the elapsed time from the start of pouring of the molten metal in the gate of a metal mold | die, and the temperature of cast iron products. It is the microscope organization photograph before the etching of the sample extract | collected from the casting product obtained by taking out from a metal mold | die and cooling by air when a cast iron product is cooled at 930 degreeC in a metal mold | die. It is a microscope picture after etching the sample of FIG. It is a graph which shows the relationship between mold release product temperature and the tensile strength of the obtained casting product. It is a graph which shows the relationship between mold release product temperature and the yield strength of the obtained casting product. It is a graph which shows the relationship between mold release product temperature and the elongation of the obtained casting product.

Claims (16)

When casting a cast iron product of a desired shape by pouring a molten iron alloy into the cavity in the mold,
The cast iron product obtained by solidifying the molten iron alloy poured into the mold is cooled, and when the temperature of the cast iron product reaches a predetermined temperature higher than room temperature, the mold is opened. After removing the cast iron product,
A cast iron method characterized by gradually cooling a cast iron product taken out of the mold at a cooling rate slower than a cooling rate in the mold.   The cast iron method according to claim 1, wherein the cast iron product taken out from the mold is allowed to cool at room temperature. In the phase diagram of the iron alloy poured into the cavity, the temperature at which the mold is opened and the cast iron product is taken out is below the eutectic temperature at which both the austenite phase and graphite crystallize, and the austenite phase is transformed into a pearlite phase. claim 1 or claim 2 cast iron method according to the a ₁ transformation temperature or higher to be.   The cast iron method according to claim 3, wherein the temperature of the cast iron product from which the mold is opened to take out the cast iron product is 1147 to 727 ° C. The temperature of the mold and mold opening takes out the cast iron products, in the state diagram of the iron alloy poured into the cavity, claim 1 or claim 2, the temperature of A less than ₁ transformation temperature of austenite phase is transformed into pearlite The described cast iron method.   The cast iron method according to claim 5, wherein the temperature of the cast iron product from which the mold is opened and the cast iron product is taken out is less than 727 ° C.   The cast iron method as described in any one of Claims 1-6 which manages the time which opens a metal mold | die and takes out cast iron products with the elapsed time from the pouring of the molten metal to a metal mold | die.   The cast iron method according to any one of claims 1 to 7, wherein an iron-carbon alloy is used as the iron alloy used as the molten metal.   As an iron alloy used as a molten metal, carbon (C) 3.1 to 3.9% by weight, silicon (Si) 2.0 to 3.0% by weight, manganese (Mn) 0.3% by weight or less, phosphorus (P) 0.03% by weight or less, chromium (Cr) 0.10% by weight or less, magnesium (Mg) 0.018 to 0.060% by weight, residual iron and impurities, and CE value (carbon equivalent) 4.0 The cast iron method according to claim 8, wherein 4.7% by weight of an iron alloy is used.   The cast iron method according to any one of claims 1 to 9, wherein when pouring the molten metal into a mold, 0.05 to 0.225 wt% of Fe-Si is poured and inoculated.   The cast iron method according to any one of claims 1 to 10, wherein a mold for gravity cast iron in which a molten metal poured from a gate is filled in a cavity by gravity is used as the mold.   The cast iron method according to any one of claims 1 to 11, wherein a mold having a cooling characteristic capable of controlling a take-out time of a cast iron product in which a molten molten iron alloy is solidified is used as the mold.   The cast iron method according to claim 12, wherein a mold made of steel (S45C) containing 0.45% by weight of carbon (C) is used as the mold. A cast iron product having an HRB hardness of 80 to 100, obtained by pouring a molten iron alloy into a cavity in a mold,
The amount of ferrite measured by a metallographic micrograph of the cast iron product is 70% or more, and the number of graphite particles having a particle size of 5 μm or more is 900 pieces / mm ² or more,
And the cast iron product characterized by the graphite spheroidization ratio which a spherical graphite particle accounts among the said graphite particles being 70% or more.   The cast iron product according to claim 14, wherein the iron alloy is an iron-carbon alloy.   The iron alloy is 3.1 to 3.9% by weight of carbon (C), 2.0 to 3.0% by weight of silicon (Si), 0.3% by weight or less of manganese (Mn), 0.03 of phosphorus (P). % By weight, chromium (Cr) 0.10% by weight or less, magnesium (Mg) 0.018-0.060% by weight, residual iron and impurities, and CE value (carbon equivalent) 4.0-4.7 The cast iron product according to claim 15, wherein the cast iron product is a weight percent iron alloy.