JP3227051B2 - Method of preventing chilling during casting of cast iron cast products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast iron cast product, that is, a flake graphite type gray cast iron product, a spheroidal graphite cast iron product, an austempered spheroidal graphite cast iron product, an austenitic cast iron product, an iron-based low thermal expansion cast product, and various ductile cast iron tubes. For example, the present invention proposes a method for preventing chilling that occurs during casting of cast iron casting products.

Here, chilling refers to the appearance of a white iron structure (chill layer) having a high hardness. This white iron structure is microscopically a redebrite structure, and is composed of a eutectic of Fe ₃ C and austenite. It is a very inconvenient organization except for specific applications.

[0003] Generally, chilling occurs in the case of mold casting with a high cooling rate or in the case of a thin cast product (for example, a wall thickness of 3 mm or less) even in the case of sand casting. And it is not easy to decompose the chilled, that is, the generated redebrite structure, and if this chilling can be prevented or reduced, the heat treatment of the cast product becomes unnecessary or short, even if the heat treatment is performed. This has advantages such as easy casting and realization of a lightweight product.

[0004]

2. Description of the Related Art Conventionally, a method of adding an inoculant (Ca-Si alloy, Fe-Si alloy, etc.) to molten metal has been used to prevent chilling during casting of cast iron products. In the casting of a die cast product or a thin product, it cannot be a complete chilling prevention means.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method capable of suitably preventing chilling even in the case of casting of a cast iron die cast product or a thin product as described above.

[0006]

The gist of the present invention is as follows. Stir the molten metal under cooling to cause solidification,
A chill at the time of casting of a cast iron cast product, characterized in that a semi-solid metal slurry in which non-dendritic crystals having a solid phase ratio in the range of 0.05 to 0.60 are suspended, and the semi-solid metal slurry is supplied to a mold and cast. This is a method for preventing the formation of a melt, and in the above, it is preferable to add an inoculant to the melt before or together with the melt.

Here, the inoculants include Ca-Si alloy and
Any commonly used alloy such as an Fe-Si alloy or an alloy obtained by adding Sr or Ba to them may be used.

[0008]

The history and operation of the present invention will be described below. As described above, when the cast product is directly cast from the molten metal, the chilling proceeds. In particular, the chilling occurs when casting with a mold or using a sand mold even when casting a thin product.

Therefore, as a result of various experiments and investigations as a means for preventing chilling, it was found that casting a semi-solid metal slurry was extremely effective. It has been found that it is effective to prevent chilling. That is, according to the present invention, the molten metal is stirred while being cooled to obtain a semi-solid metal slurry having a solid phase ratio in the range of 0.05 to 0.60, and casting of the slurry prevents chilling of the cast product.

[0010] In the above, if the solid phase ratio of the semi-solidified metal slurry is less than 0.05, the effect of preventing chilling is small, and if it exceeds 0.60, the viscosity becomes high, casting becomes difficult, and a sound product cannot be obtained. Accordingly, the solid phase ratio of the semi-solid metal slurry at the time of casting is in the range of 0.05 to 0.60.

Further, in the present invention, an inoculant may be used. If the inoculant is added during the production of the semi-solid metal slurry and casting is performed, the effect of further preventing chilling is exhibited.

As described above, by casting a semi-solid metal slurry and further using an inoculant in combination, chilling can be prevented even when casting a die-cast product or a thin-walled cast product, and the product can be commercialized without heat treatment. Thus, even if chilling occurs slightly, the white pig iron structure can be eliminated by a short heat treatment, and the product can be made thinner.

[0013]

【Example】

Example 1 A hypoeutectic gray cast iron (JIS FC250) containing C: 3.10 mass%, Si: 2.03 mass%, and Mn: 0.82 mass% was used as a material, and a melting / casting method called the Durville method was used for semi-solid metal. Applicable to slurry casting, molten metal (temperature: 1380 ° C)
Is supplied directly to a mold (diameter: 100 mmφ) and cast, and as a semi-solid metal slurry, temperature: 1200 ° C --- solid phase ratio: 0.1, temperature: 1160 ° C --- solid phase ratio: 0.4 And temperature:
1150 ° C --- Solid phase ratio: When 0.55 was supplied to a mold and cast, metal structures, hardness and the like of the obtained cast products were investigated.

FIG. 1 is an explanatory view of the melting / casting apparatus used above. In FIG. 1, 1 is a high-frequency melting furnace,
Reference numeral 2 denotes a high-frequency induction heating coil embedded in the high-frequency melting furnace 1, and 3 denotes a runner integrated with the high-frequency melting furnace 1, and a mold 4 is attached to a tip of the runner 3. These have a structure of tilting integrally, and by tilting gently, the semi-solid metal slurry 8 in the high-frequency melting furnace 1 can be tilted.
(Including the case of molten metal) can be supplied into the mold 4 through the runner 3 in a laminar flow state. The dotted line in the figure indicates a state in which the semi-solid metal slurry 8 is supplied into the mold 4 during the tilting.

On the other hand, 5 is a stirrer, 7 is a motor for rotating the stirrer 5 via a drive shaft 6, and these can be moved up and down together by elevating means (not shown). In the case of casting a semi-solid metal slurry by the above apparatus, a cold piece is inserted into the high-frequency melting furnace 1 and the cold piece is melted by the high-frequency induction heating coil 2 to form a molten metal.
The stirrer 5 is lowered and inserted into the molten metal in the high-frequency melting furnace 1. The molten metal is cooled and stirred by rotating the stirrer 5 by the operation of the motor 7 to obtain a semi-solid metal slurry having a predetermined solid fraction. Then, the stirrer 5 is retracted upward. Thereafter, the semi-solid metal slurry 8 was supplied to the mold 4 as described above by tilting the high-frequency melting furnace 1, the runner 3 and the mold 4 and cooled and solidified to obtain a cast product.

In the case of casting from the molten metal, the molten metal in the high-frequency melting furnace 1 was directly supplied to the mold 4 in the same manner as in the case of the casting of the semi-solid metal slurry to obtain a cast product.

The results of the above investigation are described below. First, FIGS. 2 and 4 (a) and 4 (b) show microstructure photographs of a cast product from a molten metal.
FIG. 3 and FIGS. 5 (a) and 5 (b) show photographs of the metal structure of the cast product from the semi-solid metal slurry (solid fraction: 0.4). These were etched with Picral, but FIGS. 2 and 3 were taken so that the chill layer could be particularly emphasized, and (a) in FIGS. 4 and 5 show the interface in contact with the mold. (B) is the central part.

In the cast product from the molten metal shown in FIG. 2, a thick chill layer is formed from the interface (surface) in contact with the mold toward the inside, whereas in contrast, the semi-solid metal slurry shown in FIG. The cast product has a very small chill layer formation thickness, and the chill layer formation area is greatly reduced.

4 (a) and 4 (b) are compared with FIGS. 5 (a) and 5 (b). As shown in FIG. 4 (a) and FIG. There is a large difference in the metal structure between (a) and the center (b),
While the chill layer and dendrite structure can be seen, FIG.
Cast products cast from the semi-solid metal slurries (a) and (b) show almost the same metal structure in the surface layer (a) and the central part (b), and the primary crystal grains are uniformly dispersed .

FIG. 6 shows the hardness distribution from the surface of the cast product toward the center. As is clear from FIG. 6, the cast product from the molten metal has a deeper hardened region from the surface as compared with the cast product from the semi-solid metal slurry, and therefore naturally agrees well with the metallographic findings. Is shown. Also, when compared between cast products from semi-solid metal slurries, the cast products from semi-solid metal slurries having a large solid phase ratio have shallower high hardness regions.

Example 2 A semi-solid metal slurry was cast in the same manner as in Example 1 except that 0.5% of a Ca-Si alloy was added as an inoculant to the molten cast iron. investigated. As a result, the generation of the chill layer could be reduced as in the first embodiment. In addition, the addition of the inoculant prevented the precipitation of cementite which was sometimes slightly observed between the primary crystal grains when no addition was made.

[0022]

According to the present invention, when casting a cast iron cast product, a semi-solid metal slurry having a solid phase ratio in the range of 0.05 to 0.60 is supplied to a mold and cast, thereby forming a chill layer, that is, a chill layer having a high hardness. According to the present invention, the effects of the present invention are great, for example, the heat treatment cost of the cast product is reduced, and the cast product is made thinner, that is, lighter by facilitating the casting of the thin product. It is.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a melting / casting apparatus used in Examples.

FIG. 2 is a photograph of a metal structure of a cast product from a molten metal.

FIG. 3 is a metallographic photograph of a cast product from a semi-solid metal slurry.

FIG. 4 is a photograph of a metal structure of a cast product from a molten metal.
(a) is a photograph of the metal structure of the surface layer. (b) is a photograph of the metal structure at the center.

FIG. 5 is a photograph of a metal structure of a cast product from a semi-solid metal slurry. (a) is a photograph of the metal structure of the surface layer. (b)
Is a metallographic photograph of the center.

FIG. 6 is a graph showing a hardness distribution from the surface of a cast product toward the center.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High frequency melting furnace 2 High frequency induction heating coil 3 Runner 4 Mold mold 5 Stirrer 6 Drive shaft 7 Motor 8 Semi-solid metal slurry

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Seiro Yawata 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside Leotech Co., Ltd. (56) References JP-A-7-204783 (JP, A) JP-A-5-169193 (JP, A) JP-A-7-155904 (JP, A) JP-A-59-42159 (JP, A) JP-A-51-90928 (JP, A) JP-A-63-260667 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 27/20 B22D 1/00 B22D 7/00

Claims (2)

(57) [Claims] 1. A molten metal is stirred under cooling to produce solidification, and a semisolid metal slurry in which non-dendritic crystals having a solid phase ratio in the range of 0.05 to 0.60 are suspended. The semisolid metal slurry is used as a mold. A method for preventing chilling during casting of a cast iron casting product, characterized by supplying and casting. 2. The method according to claim 1, wherein an inoculant is added to the molten metal before or while the molten metal is being stirred.