JP2007185696A - Steel casting method and steel casting metallic mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel casting method capable of reducing the variation of hardness or the like in an obtained cast iron product as much as possible when the cast iron product apt to cause a cooling rate difference due to its shape and structure is cast in a cooling stage for a molten casting steel poured into a cavity in a metallic mold. <P>SOLUTION: When the molten casting steel poured into the cavity 16 in metallic molds 10, 12 is solidified and is cast into the cast iron product 18, in the case that the cast iron product 18 having a top end part 18a being an easily cooling part faster in cooling rate than other parts is cast, a gap 22 is formed between the outer circumferential face of the top end part 18a and the inner wall face of the cavity 16 and heat abatement to the metallic molds is blocked for relaxing the cooling rate at the top end part 18a of the cast iron product 18 to be cooled in the metallic molds 10, 12. Thereafter when temperatures of the other parts in the cast iron product 18 reach the predetermined temperature higher than a room temperature, the metallic molds 10, 12 are opened; the cast iron product 18 is taken out, and the whole of the cast iron product 18 is annealed at a cooling rate slower than the cooling rate in the metallic molds 10, 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cast iron method and a cast iron mold, and more specifically, when casting a cast iron product by solidifying a cast iron melt poured into a cavity in the mold, the cast iron product has a cooling rate higher than other parts. The present invention relates to a cast iron method and a cast iron mold for casting a cast iron product having a quick and easy cooling portion.

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 cast iron obtained by pouring the sand mold, in a state diagram of the iron alloy, A ₁ transformation temperature below room temperature vicinity 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, 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 cast iron in a mold made of a highly heat conductive material such as water-cooling structure or copper, in the mold following the A ₁ transformation temperature room A cast iron method is also known which is rapidly cooled to the vicinity and taken out.
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 cast iron into a mold are generally low-strength flake graphite cast iron having eutectic graphite that has been supercooled, or low grade with low ferrite content and low toughness. Of 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.
For this reason, the present inventors considered that the cooling rate was important for casting a cast iron product having a large amount of ferrite and excellent toughness using a mold. As a result, when the cast iron product obtained by solidification of the cast iron melt poured into the mold 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 is opened. After taking out the product, know that this cast iron product can be cast at a cooling rate slower than the cooling rate in the mold to cast a cast iron product with high ferrite content and excellent toughness using the mold. It was.

However, the cast iron product is formed with a portion that is more easily cooled than the other portions due to its shape and structure.
For example, in a pair of molds for casting a caliper body in which a bifurcated portion that is bifurcated is formed, a longitudinal sectional view thereof is shown in FIG. 15 (a) and a transverse sectional view thereof is shown in FIG. 15 (b). Similarly, among the cast iron products 108 obtained by solidifying the molten iron alloy poured into the cavity 106 formed by the pair of molds 100 and 102 and the protruding pins 104, the bifurcated tip portions 108a and 108a are relatively Since the cross section is thinner than other parts, the cooling rate is faster than other parts.
For this reason, when the front end portions 108a and 108a of the cast iron product 108 reach the mold opening temperature, the temperatures of the other portions do not reach the mold opening temperature, and the pair of molds 100 and 102 cannot be opened.
Therefore, when the temperature of the other part of the cast iron product 108 reaches the mold opening temperature, the pair of molds 100 and 102 are opened as shown in FIG. 16A, and as shown in FIG. The cast iron product 108 is projected from the pair of molds 100 and 102 by the projecting pins 104.
In this way, in cast iron products having a difference in cooling rate, the mold is usually opened by the temperature of the portion where the cooling rate is slow, so that variations such as hardness are likely to occur in the cast iron product obtained after cooling is completed. There was found.
Therefore, the object of the present invention is obtained when casting a cast iron product in which a cooling rate difference due to the shape and structure of the cast iron product is likely to occur in the cooling process of the cast iron melt poured into the cavity in the mold. An object of the present invention is to provide a cast iron method and a cast iron mold that can reduce variations in hardness and the like in cast iron products as much as possible.

As a result of studying to solve the above problems, the inventors of the present invention, as a result of the cast iron product cooling in the cavity of the mold, the outer peripheral surface of the easy-cooling portion and the inner wall surface of the cavity whose cooling rate is faster than other portions The inventors have found that a difference in cooling rate with other parts can be reduced as much as possible by forming a gap between the two and preventing heat from being drawn to the mold, and have reached the present invention.
That is, according to the present invention, when a cast iron product is cast by solidifying a cast iron melt poured into a cavity in a mold, a cast iron product in which an easy-cooling portion having a faster cooling rate than the other portion is present in the cast iron product. When casting, in order to reduce the cooling rate of the easy cooling part of the cast iron product to be cooled in the mold, a gap is formed between the outer peripheral surface of the easy cooling part and the inner wall surface of the cavity to the mold. When the temperature of the other part of the cast iron product reaches a predetermined temperature higher than room temperature, the mold is opened, the cast iron product is taken out, and the entire cast iron product is removed. In the cast iron method, the cooling is performed at a cooling rate slower than the cooling rate in the mold.
Further, according to the present invention, when a cast iron melt poured into a cavity in a mold for casting a cast iron product solidifies, the cast iron product casts a cast iron product in which there is an easily cooled portion that is more easily cooled than the other part. In the cast iron mold, the mold part forming at least a part of the cavity inner wall surface of the mold that comes into contact with the outer peripheral surface of the easy-cooling part of the cast iron product cooled in the mold is retracted, and the easy-cooling part The mold part is formed so that the gap formed between the outer peripheral surface of the mold and the inner wall surface of the cavity prevents heat from being drawn to the mold and reduces the cooling rate of the easy-cooling part. When the temperature of the other part of the cast iron product reaches a predetermined temperature higher than room temperature, the entire cast iron product is cooled in the mold. So that it can be slowly cooled at a cooling rate slower than the rate. It is also an iron mold, characterized in that the whole of ironwork is formed retrievable from the mold.

In the present invention, the gap between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity is retreated with at least a part of the inner wall surface of the mold contacting the outer peripheral surface of the easy-cooling portion. Thus, a gap can be easily formed between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity.
Thus, as a mold that can easily form a gap between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity, the inner wall surface of the cavity that contacts the outer peripheral surface of the easy-cooling portion of the cast iron product is used. A split mold formed so that the part to be formed can be moved independently of the other part of the mold, or a pin where the outer peripheral surface of the easy-cooling part of the cast iron product and the tip surface are in contact with the other part of the mold A mold formed so as to be independently movable can be preferably used.
Furthermore, the mold has a cooling characteristic capable of controlling the gap formation time and the cast iron product take-off time between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity where the cast iron melt is solidified. By using a mold, the temperature at which a gap is formed between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity and the temperature at which the cast iron product is taken out can be made constant. Obtainable. As such a mold, a mold made of steel (S45C) containing 0.45% by weight of carbon (C) can be suitably used.
In addition, as a metal mold | die, the metal mold | die for gravity cast iron with which the cast iron molten metal poured from the gate is filled in a cavity by gravity can be used suitably.

Further, by allowing the cast iron product taken out from the mold to cool at room temperature, the cast iron product taken out from the mold can be easily cooled at a lower cooling rate than the cooling rate in the mold.
Furthermore, 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 equal to or lower than the eutectic temperature at which both the austenite phase and graphite crystallize, and the austenite phase is pearlite. phases transformation to the a ₁ transformation temperature or more, specifically, by the 1147-727 ° C., often the amount of ferrite, good cast iron product 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.
Note that the “easy-cooling part” in the present invention is likely to correspond to, for example, a thinner part than other parts in a cast product.

According to the present invention, a gap is formed between the outer peripheral surface of the easy-cooling portion of the cast iron product cooled in the mold before opening the mold and the inner wall surface of the cavity to prevent heat from being drawn into the mold. As a result, the cooling rate of the easy-cooling part of the cast iron product can be relaxed, and the difference in cooling rate with other parts can be made as small as possible. For this reason, it is possible to reduce variations in hardness and the like in the cast iron product as much as possible due to the cooling rate difference based on the shape and structure of the cast iron product.
Furthermore, when the other part of the cast iron product is cooled to a predetermined temperature above room temperature, the entire cast iron product 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 mold. As a result, it is possible to obtain the same effect as when the cast iron product that has been cooled is heat treated.
Accordingly, in the present invention, different types (characteristics) of cast iron products can be obtained by changing the temperature of the cast iron products 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, a cast iron product obtained by solidifying cast iron molten metal (hereinafter sometimes simply referred to as molten metal) poured into a cavity in a mold is cooled, and the shape and structure are changed before the mold is opened. It is important to reduce the cooling rate of the easy cooling part by forming a gap between the outer peripheral surface of the easy cooling of the cast iron product having the cooling rate difference based on and the inner wall surface of the cavity.
By forming such a gap, it is possible to prevent heat from being drawn to the mold, relax the cooling rate of the easy-cooling portion of the cast iron product, and reduce the cooling rate difference from the cooling rate at the other portion of the cast iron product as much as possible.
Here, when cooling without forming a gap between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity, the cast iron product obtained after completion of cooling has variations such as hardness in the inside. It tends to be a thing.
Next, in the present invention, when the temperature of the other part of the cast iron product reaches a predetermined temperature higher than room temperature, the mold is opened, the cast iron product is taken out, and the entire cast iron product is removed from the mold. It is important to cool slowly at a cooling rate slower than the cooling rate.
When cooling the cast iron product taken out of the mold at a cooling rate higher than the cooling rate in the mold, the resulting cast iron product is equivalent to the cast iron product obtained by rapid cooling in the mold. It becomes.

The temperature at which the mold is opened and the cast iron product is taken out (hereinafter sometimes referred to as mold opening temperature) will be described based on the state diagram of the iron-carbon alloy shown in FIG. In the phase diagram shown in FIG. 1, in a molten iron of 3.5 wt%, 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.

In the phase diagram of the iron alloy shown in FIG. 1, the mold opening temperature in the present invention is equal to or lower than the eutectic temperature at which both the austenite phase and graphite crystallize, and is equal to or higher than the A ₁ transformation temperature at which the austenite phase transforms into a pearlite phase. By reducing the cooling rate of the easy-cooling part of the cast iron product and reducing the difference in cooling rate with the other part of the cast iron product as much as possible, the entire cast iron product is gradually cooled, When the cooling of the product is completed, a cast iron product having a large amount of ferrite and a high spheroidizing ratio of graphite and exhibiting excellent toughness can be obtained without heat treatment.
Specifically, the mold opening temperature is preferably 1147 to 727 ° C., and more preferably 1147 to 850 ° C., since the ferrite content of the cast iron product to be obtained can be 70% or more.
If the mold opening temperature exceeds 1147 ° C., the molten metal tends to be incompletely solidified in the mold.
On the other hand, if the mold opening temperature is lower than the A ₁ transformation temperature, specifically 727 ° C., the cast iron product obtained by opening the mold and gradually cooling the entire cast iron product has a high hardness. In addition, although the ferrite content decreases, the tensile strength and proof stress are excellent.

When the gap is formed between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity (hereinafter sometimes referred to as gap formation timing), and when the mold is opened and the cast iron product is taken out In principle, it is best to judge from the temperature of the cast iron product, but it is difficult to directly measure the temperature of the cast iron product at every casting. Therefore, 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 gap was formed based on the elapsed time from the molten metal poured into the mold. It is easy to manage the timing and the timing of removing the cast iron product from the mold.
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 is increased, and cast iron properties tend to be lowered. 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.
In addition, when the CE value (carbon equivalent) is less than 4.0% by weight, carbides are likely to precipitate, pearlite increases, and cast iron properties tend to decrease. 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 Therefore, it is difficult to manage the gap formation time for forming a gap between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity and the time for taking out the cast iron product from the mold.
For this reason, as the mold used in the present invention, the cooling characteristics that can control the gap formation timing and the extraction timing, specifically, the cooling rate of a conventional mold made of a water-cooled structure or a high thermal conductive material such as copper. Also, use a mold with a moderate cooling rate.
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.

The mold used in the present invention is capable of forming a gap between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity while holding the cast iron product solidified by the molten cast iron poured in the cavity. It is necessary to be.
As such a mold, a mold in which a gap is formed by retreating at least a part of the inner wall surface of the cavity of the mold that is in contact with the outer peripheral surface of the easily cooled portion of the cast iron product can be suitably used.
As this mold, it is possible to use a divided mold in which a portion forming the inner wall surface of the cavity that comes into contact with the outer peripheral surface of the easy-cooling portion of the cast iron product is movable independently of the other portion of the mold. it can.
An example of such a split mold is a longitudinal sectional view of a split mold for casting a caliper body in which a bifurcated portion bifurcated is formed, and FIG. ). The split mold shown in FIGS. 2A and 2B is formed by a pair of molds 10 and 12, a protruding pin 14, and a movable mold 20. The movable mold 20 is provided on the mold 10 so as to be independently movable with respect to the other parts forming the pair of molds 10 and 12, and along the parting surfaces of the pair of molds 10 and 12. Moving.
In the split mold shown in FIG. 2A, the cavity 16 is formed by the pair of molds 10, 12, the movable mold 20, and the protruding pins 14. Among the cavities 16, the portion B forming the bifurcated end portions 18 a and 18 a of the cast iron product 18 is the other part of the cast iron product 18 formed by solidification of the molten iron alloy poured into the cavity 16. It is an easily cooled part that is thinner than that and has a high cooling rate. A part of the inner wall surface of the cavity 16 forming the portion B is formed by the movable dies 20 and 20 provided in the mold 10.

Of the cast iron product 18 formed by solidification of the molten iron alloy poured into the cavity 16 formed in the pair of molds 10, 12, the tip 18 a formed by the B portion of the cavity 16, 18a is an easy cooling part whose cooling rate is faster than the other part of the cast iron product 18, as described above. Therefore, before the pair of molds 10 and 12 are opened, as shown in FIG. 3A, the movable mold 20 that forms a part of the inner wall surface of the portion B slides, and the outer periphery of the tip end portion 18a. A gap 22 is formed between the surfaces. By forming such a gap 22, it is possible to prevent heat from being drawn to the molds 10 and 12, and the cooling rate of the tip 18 a can be reduced as compared with the case where the movable die 20 is in contact with the tip 18 a. For this reason, the cooling rate difference of the front-end | tip part 18a and the other part of the cast iron product 18 can be made as small as possible.
The timing for forming the gap 22 is preferably managed by the elapsed time after the molten metal is poured into the cavity.
For example, regarding the temperature change of the tip portions 18a, 18a of the cast iron product 18, after pouring the molten metal into the cavity, in the phase diagram of the iron alloy, the temperature is below the eutectic temperature at which both the austenite phase and graphite are crystallized, and austenite phase advance by measuring the time to reach the a ₁ transformation temperature or more desired temperatures to be transformed into pearlite phase, a molten metal at the time the predetermined time has elapsed since the pouring into the cavity, moving the mobile 20 The gap 22 is formed.
Or the hardness of the front-end | tip parts 18a and 18a and the main-body part of the cast iron product 18 may be measured, and the movement time of the movable mold | type 20 may be adjusted so that the hardness of the front-end | tip parts 18a and 18a may become substantially equal to a main-body part. .
Next, the other part of the cast iron product 18 reaches a predetermined temperature equal to or higher than room temperature, and as shown in FIG. 3B, the pair of molds 10 and 12 are opened, and as shown in FIG. The entire cast iron product 18 projecting from the parting surfaces of the pair of molds 10 and 12 is cooled to substantially the same temperature by the projecting pins 14 provided on the mold 12.
Furthermore, by gradually cooling the cast iron product 18 in the air, it is possible to obtain the cast iron product 18 with as small a variation as possible in hardness.
Although the movable mold 20 may be extracted from the mold 10, the air in the gap 22 can be formed by forming the gap 22 without extracting the movable mold 20 from the mold 10 as shown in FIG. However, since it is difficult to replace the air outside the mold 10, the temperature of the gap 22 can be kept constant, and the cooling rate of the tip 18 a of the cast iron product 18 can be sufficiently relaxed.

A pair of molds shown in FIGS. 4A and 4B can be used in place of the split mold shown in FIGS. 2 and 3. FIG. 4A is a longitudinal sectional view of the pair of molds. FIG. 4B is a cross-sectional view of the pair of molds.
The pair of molds 10 and 12 shown in FIGS. 4 (a) and 4 (b) includes pins 24 and 24 that contact the outer peripheral surfaces of the tip portions 18 a and 18 a of the cast iron product 18 with the tip surfaces. The pins 24 and 24 are provided on the mold 10 so as to be independently movable with respect to the other portions forming the pair of molds 10 and 12, and extend along the parting surfaces of the pair of molds 10 and 12. Move.
Such a pin 24 also slides with respect to the cast iron product 18 cooled in the pair of molds 10 and 12, as shown in FIG. 5, and forms a gap 26 between the outer peripheral surface of the tip end portion 18a. By forming the gap 26, the cooling rate of the tip 18a can be reduced as compared with the case where the pin 24 is in contact with the tip 18a.
When the gap 26 is formed, the pin 24 is slid when a predetermined time elapses after the molten iron alloy is poured into the cavity, as in the case of the split mold shown in FIGS. Thus, the gap 26 is formed.

Further, when the thin portion 18b, which is an easy-cooling portion that is more easily cooled than the other portion, is formed on the contact surface side of the cast iron product 18 that contacts the tip surface of the protruding pin 14 provided in the mold 12, As shown in FIG. 6 (a), a movable die 28 having a protruding pin may be provided. The movable mold 28 is provided so as to be movable in a direction orthogonal to the parting surfaces of the pair of molds 10 and 12.
6A. Of the cast iron product 18 formed by solidification of the molten metal poured into the cavity 16 formed in the pair of molds 10 and 12 shown in FIG. As shown in FIG. 6B, the movable mold 28 slides relative to the thinner portion 18b than the other portion to form a gap 30 between the outer peripheral surface of the distal end portion 18a. By forming the gap 30, the cooling rate of the thin portion 18 b can be relaxed, and the difference in cooling rate with the other portion of the cast iron product 18 can be made as small as possible.
Next, when the other part of the cast iron product 18 reaches a predetermined temperature equal to or higher than room temperature, the pair of molds 10 and 12 are opened as shown in FIG. 6 (c), and as shown in FIG. 6 (d). The cast iron product 18 is projected from the parting surfaces of the pair of molds 10 and 12 by the movable die 28.

Furthermore, when casting the cast iron product 18 in which the cylindrical part is formed, a pair of molds having a core is used. An example of the pair of molds is shown in FIGS. Fig.7 (a) is a longitudinal cross-sectional view of a pair of metal mold | die which comprises a core, FIG.7 (b) is the cross-sectional view.
A pair of molds 10 and 12 shown in FIGS. 7 (a) and 7 (b) has a cylindrical core 34 having a bifurcated portion of the cast iron product 18 so that a cylindrical portion 32 is formed inside the cast iron product 18. It passes between the cavities 16 forming the tip portions 18 a and 18 a of the shape-like portions and is inserted into the cavities 16.
A piston 36 a provided at the tip of the rod 36 is inserted into a cylindrical part 34 a formed on the rear end side of the core 34.
The rear end portion of the pin 40 is fixed to the plate upper body 38 fixed to the rear end portion 36b of the rod 36. The tip surface of the pin 40 constitutes a part of the inner wall surface forming the B portion of the cavity 16 that forms the tip portion 18 a of the cast iron product 18.
As shown in FIG. 7 (b), two pins 40 are provided, and the tip surfaces of the pins 40, 40 are inside the cavities 16 that form the tip portions 18 a, 18 a of the cast iron product 18. It constitutes a part of the wall surface. This part is shown as part B.
Of the cast iron product 18 formed by solidification of the molten iron alloy poured into the cavity 16 formed in the pair of molds 10 and 12 shown in FIGS. As shown in FIG. 8 (a), the piston 36 a inserted into the cylindrical portion 34 a formed on the rear end side of the core 34 is located behind the core 34, as shown in FIG. The pin 40 which moves to the end side and whose rear end portion is fixed to the plate body 38 fixed to the rear end portion 36 b of the rod 36 also moves together with the rod 36. When the pin 40 moves, the core 34 does not move.
By such movement of the pin 40, a gap 42 is formed between the cast iron product 18 and the tip end portion 18a. By forming such a gap 42, the cooling rate of the tip 18a can be relaxed and the difference in cooling rate with the other part of the cast iron product 18 can be made as small as possible.
Next, when the other part of the cast iron product 18 reaches a predetermined temperature equal to or higher than room temperature, as shown in FIG. 8B, after the core 34 and the pin 40 are pulled out from the pair of molds 10 and 12, As shown in FIG. 8C, the pair of molds 10 and 12 are opened and the cast iron product 18 is taken out.

In this way, it is important that the cast product taken out from the mold is gradually cooled at a cooling rate slower than the cooling rate in the mold.
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, with respect to the easy cooling part of the cast iron product cooled in the mold, a clearance is formed between the outer peripheral surface of the easy cooling part and the inner wall surface of the cavity to reduce the cooling rate of the easy cooling part. Later, when the temperature of the other part of the cast iron product reaches a predetermined temperature higher than room temperature, the mold is opened in a short time after pouring, and the mold is opened in a short time after pouring and is in a high temperature state during cooling. The cast iron product in is taken out. 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.
Also, heat transfer from the molten metal and cast iron product to the mold is better than heat transfer from the cast iron product to 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, one or both of the mold into which the molten metal is poured and the mold from which the cast iron product is taken out Forcible cooling may be performed by blowing cold air or the like.

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 at which the mold is opened and the cast iron product is taken out to 1147 to 850 ° C., the ferrite amount measured by a metallographic micrograph of the cast iron product is 70% or more, and the grain size is 5 μm or more. A cast iron product having a graphite particle count of 900 particles / mm ² or more and a graphite spheroidization ratio occupied by spherical graphite particles of 70% or more among graphite particles can be obtained. This cast iron product corresponds to FCD450 and is used for automobile parts and the like.
Here, when the temperature at which the mold is opened and the cast iron product is taken out is 727 ° C. to less than 850 ° C., the ferrite amount measured by a metallographic micrograph of the cast iron product is 60 to 70%, A cast iron product can be obtained in which the number of graphite particles having a particle diameter 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 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 with such a mold is a caliper body having a bifurcated portion.
The mold used in the present embodiment is a split mold shown in FIGS. 2A and 2B, and is formed by a pair of molds 10 and 12, protruding pins 14, and a movable mold 20. The movable mold 20 is provided in the mold 10 and forms the tip of the cavity 16 forming the bifurcated portion of the caliper body. The movable mold 20 is formed on the parting surfaces of the pair of molds 10 and 12. Move along.
(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 was cast four times by pouring molten metal into this mold, the temperature of the cast iron product main body in the mold was measured by a thermocouple inserted from the mold gate. Then, a cooling curve was obtained. The results are shown as a graph in FIG.
The graph shown in FIG. 9 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. 9, 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.).
(4) Movement start time of the movable die 20 The hardness of the tip of the bifurcated portion of the caliper body, which is a cast iron product, and the body of the caliper body is measured, and the tip is moved so that the hardness is substantially equal to that of the body. The moving time of the mold 20 was determined.

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.

The movable mold 20 was moved 40 seconds after the start of pouring of the molten metal into the mold spout, and a gap was formed between the outer peripheral surface of the bifurcated portion of the caliper body, which is a cast iron product, and the inner wall surface of the cavity.
Next, the mold was opened 109 seconds after the start of pouring of the molten metal into the mold spout, 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.)].
The material structure and hardness of the bifurcated portion of the caliper body, which is a cooled cast iron product, and the central portion of the main body were measured.
Regarding the material structure, the surface of the sample collected from each part of the bifurcated tip (A) and the central part (B) of the main body is magnified 100 times with a microscope, and graphite particles of 5 μm or more existing in a predetermined range While counting the number, the graphite spheroidization ratio 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, the total number of graphite particles of 5 μm or more is 1335 / mm ² and the spheroidization ratio of graphite is 80.4% at the tip (A), and at the center (B) of the main body. 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. 10 is the tip of the bifurcated portion, and B is the central portion of the main body.

Furthermore, after the sample collected from each part of the tip part (A) of the bifurcated part and the central part (B) of the main body is immersed in a nital solution and etched, the surface of the sample 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. 11 shows a micrograph of the microstructure of the sample surface subjected to the etching process, magnified 100 times. A shown in FIG. 11 is the tip of the bifurcated portion, and B is the center of the main body.
In the micrograph shown in FIG. 11, the spherical black part is graphite, and the white part 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 portion (A) of the bifurcated portion, and the ferrite content was 90.6% at the central portion (B) of the main body.

Moreover, HRB hardness was measured about the sample extract | collected from each site | part of the front-end | tip part (A) of a bifurcated part and a main-body center part (B) using the commercially available hardness meter. In the obtained cast iron product, the HRB hardness of the tip portion (A) of the bifurcated portion was 90.0, and the HRB hardness of the main body central portion (B) was 84.5.
In this way, in the obtained cast iron product, the tip part (A) of the bifurcated part and the central part (B) of the main body are materials corresponding to FCD450 although some differences in material structure and hardness are recognized. .

A caliper body cast iron product was cast in the same manner as in Example 2. During the casting, the mold release time from the start of pouring of the molten metal into the mold spout until the mold opening was 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. At this time, the moving time for moving the movable mold 20 was set to be the same as that in Example 1.
For each of the samples taken from the tip portion (A) and the central portion (B) of the bifurcated portion of the cast iron product after cooling, the number of graphite grains, HRB hardness, and graphite spheroidization were the same as in Example 2. The results of measuring the rate and the ferrite content 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 level of 3 and No. 4, the mold is 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. The cast iron product is taken out from the steel and air-cooled, so that the ferrite content is 60% or more and the number of graphite particles having a particle diameter of 5 μm or more is 900 at the tip portion (A) and the central portion (B) of the bifurcated portion. / mm ² or more, and among the graphite particles, the graphite spheroidization ratio of spherical graphite grains account it is possible to obtain a cast iron product is 70% or more. In particular, No. 2 and No. 2 in which the extraction temperature of cast iron products was 850 ° C. or higher. 3 level, it is possible to obtain a cast iron product having a ferrite content of 90% or more in the central part (B) of the main body. A cast iron product having a ferrite content of 90% or more can also be obtained at the tip portion (A) and the central portion (B) of the main body.
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 tip of the bifurcated portion (A) Then, it was a cast iron product having a ferrite content 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, when each of the tensile strength, yield strength and elongation shown in Table 3 is arranged according to the release product temperature, it is as shown in FIGS. 12 to 14, FIG. 12 is a graph showing the relationship between the release product temperature and the tensile strength of the obtained cast product, and FIG. 13 shows the relationship between the release product temperature and the yield strength of the obtained cast product. FIG. 14 and FIG. 14 are graphs showing the relationship between the release product temperature and the elongation of the obtained cast product. In FIGS. 12 to 14, eutectic temperature and A ₁ transformation temperature are displayed, and lower limit values of FCD450 and FCD500 defined by the JIS standard of 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 FIGS. 12 to 14, FCD450 is released by releasing 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 sectional drawing explaining an example of the metal mold | die for cast iron which concerns on this invention. It is sectional drawing explaining operation | movement of the metal mold | die for cast iron shown in FIG. It is sectional drawing explaining the other example of the metal mold | die for cast iron which concerns on this invention. It is sectional drawing explaining operation | movement of the metal mold | die for cast iron shown in FIG. It is sectional drawing explaining the operation | movement while demonstrating the other example of the metal mold | die for cast iron which concerns on this invention. It is sectional drawing explaining the other example of the metal mold | die for cast iron which concerns on this invention. It is sectional drawing explaining operation | movement of the metal mold | die for cast iron shown in FIG. It is a graph which shows the relationship between the elapsed time from the injection | pouring start of molten metal to the gate of a metal mold | die, and the temperature of the main-body part of a cast iron product. 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. It is sectional drawing explaining the conventional metal mold | die for cast iron. It is sectional drawing explaining operation | movement of the metal mold | die for cast iron shown in FIG.

Explanation of symbols

10, 12 Mold 14 Protruding pin 16 Cavity 18 Cast iron product 18a Tip 18b Thin portion 20, 28, 30 Moving mold 22, 26, 42 Clearance 24, 40 Pin 32 Cylindrical portion 34a Cylinder portion 34 Core 36a Piston 36 Rod 36b Rear end 38 Plate upper body

Claims (18)

When casting a cast iron product by solidifying the cast iron melt poured into the cavity in the mold, when casting a cast iron product in which there is an easy-cooling part with a faster cooling rate than the other part in the cast iron product,
In order to reduce the cooling rate of the easy cooling part of the cast iron product to be cooled in the mold, a gap is formed between the outer peripheral surface of the easy cooling part and the inner wall surface of the cavity to prevent heat from being drawn into the mold. After
When the temperature of the other part 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 entire cast iron product is removed from the cooling rate in the mold. A cast iron method characterized by slow cooling at a slow cooling rate.   A clearance between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity is formed by retreating at least a part of the inner wall surface of the mold contacting the outer peripheral surface of the easy-cooling portion. The cast iron method according to Item 1.   3. A split mold in which a portion that forms an inner wall surface of a cavity that comes into contact with an outer peripheral surface of an easy-cooling portion of a cast iron product is used as a mold so as to be independently movable with respect to the other portion of the mold. Cast iron method.   The cast iron method according to claim 2, wherein the mold is a mold in which a pin that contacts an outer peripheral surface and a tip surface of an easy-cooling portion of a cast iron product is movable independently of the other part of the mold.   The cast iron method according to any one of claims 1 to 4, wherein the cast iron product taken out from the mold is allowed to cool at room temperature. The temperature to retrieve the cast iron product from the mold, in the state diagram of the iron alloy poured into the cavity, A ₁ transformation of and the austenite phase at a eutectic temperature below the austenite phase and the graphite crystallizes together is transformed into pearlite The cast iron method according to any one of claims 1 to 5, wherein the temperature is equal to or higher than the temperature.   The cast iron method according to claim 6, wherein a temperature at which the mold is opened and a cast iron product is taken out is 1147 to 727 ° C. The temperature of the mold and the mold is opened extracting the cast iron products, in the state diagram of the iron alloy poured into the cavity, of the preceding claims in which the austenite phase is to a temperature of A less than ₁ transformation temperature to transform to pearlite phase The cast iron method according to any one of claims.   The cast iron method according to claim 8, wherein the temperature of the cast iron product from which the mold is opened to take out the cast iron product is less than 727 ° C.   The cast iron method according to any one of claims 1 to 9, wherein the mold is a gravity cast iron mold in which a cast iron melt poured from a gate is filled in a cavity by gravity.   As a mold, a mold having a cooling characteristic capable of controlling a gap formation time and a cast iron product take-off time between the outer peripheral surface of the easy-cooling portion of the cast iron product and the inner wall surface of the cavity where the cast iron molten metal is solidified. The cast iron method according to any one of claims 1 to 10, which is used.   The cast iron method according to claim 11, wherein a mold made of steel (S45C) containing 0.45% by weight of carbon (C) is used as the mold. When the cast iron melt poured into the cavity in the mold for casting the cast iron product solidifies, in the cast iron mold for casting the cast iron product in which there exists an easy-cooling portion that is more easily cooled than the other part in the cast iron product,
The mold part forming at least a part of the cavity inner wall surface of the mold that comes into contact with the outer peripheral surface of the easy-cooling part of the cast iron product cooled in the mold recedes, and the outer peripheral surface of the easy-cooling part and the cavity The gap between the inner wall surface prevents the heat from being drawn to the mold and reduces the cooling rate of the easy-cooling portion. It can be moved independently,
And when the temperature of the other part of the cast iron product reaches a predetermined temperature higher than room temperature, the cast iron product is gradually cooled at a cooling rate slower than the cooling rate in the mold. A cast iron mold characterized in that the entire product can be removed from the mold.   The mold is a split mold in which a mold part that forms an inner wall surface of a cavity that comes into contact with an outer peripheral surface of an easy-cooling part of a cast iron product is provided so as to be independently movable with respect to the other part of the mold. 13. A mold for cast iron according to 13.   The cast iron method according to claim 13, wherein the mold is a mold in which a pin that contacts an outer peripheral surface and a front end surface of an easy-cooling portion of the cast iron product is independently movable with respect to the other part of the mold.   The mold for cast iron according to any one of claims 13 to 15, wherein the mold is a mold for gravity cast iron in which a molten cast iron poured from a gate is filled into the cavity by gravity.   The mold has a cooling characteristic that can control the gap formation time and cast iron product removal time between the outer peripheral surface of the easy cooling part of the cast iron product and the inner wall surface of the cavity where the cast iron melt that has been poured is solidified. The cast iron mold according to any one of claims 13 to 16.   The mold for cast iron according to claim 17, wherein the mold is a mold made of steel (S45C) containing 0.45% by weight of carbon (C).