JPH07276036A - Chilling preventing method in casting of casting iron casting product - Google Patents

Abstract

PURPOSE:To reduce a heat treatment cost, to thin a product and to attain light weight by preventing a chilled layer from being generated by supplying a semi-solidified metallic slurry whose solid phase ratio is specified to a casting mold. CONSTITUTION:A solidified structure is generated by stirring molten metal, and the semi-solidified metallic slurry in which a non-dendrite whose solid phase ratio is in a range 0.05-0.60 is suspended is generated, and casting is performed by supplying the semi-solidified metallic slurry to the casting mold. Also, an effect higher than ever can be obtained by adding an inoculation agent on the molten metal before it is stirred or while stirring. In this way, chilling can be prevented from occurring when the casting of a metallic mold casting product and a thin casting product are performed, and a product can be manufactured without applying heat treatment ment, and a white iron structure can be dissipated in a short time heat treatment even when few chilling occurs, and the product can be thinned.

Description

Detailed Description of the Invention

[0001]

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

Here, chilling means that a white pig iron structure (chill layer) having a high hardness appears, and this white iron structure is a microscopically redeburite structure, which is a eutectic of Fe ₃ C and austenite. It is a very inconvenient organization except for specific applications.

Generally, chilling occurs in the case of die casting with a high cooling rate or in the case of sand casting, which is a thin cast product (for example, a thickness of 3 mm or less). And it is not easy to decompose chilling, that is, the generated redeburite structure, and if this chilling can be prevented or reduced, heat treatment of cast products becomes unnecessary, or even if heat treatment is done in a short time, thinner products It has the advantages that it can be easily cast and the weight of the product can be reduced.

[0004]

2. Description of the Related Art Up to now, a method of adding an inoculant (Ca-Si alloy, Fe-Si alloy, etc.) to a molten metal has been used to prevent chilling during casting of cast iron products. In the casting of mold casting products and thin wall products, it cannot be a perfect chilling prevention means.

[0005]

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

[0006]

The summary 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 casting product, characterized in that the solidification rate is a semi-solidified metal slurry in which non-dendritic crystals in the range of 0.05 to 0.60 are suspended, and the semi-solidified metal slurry is supplied to a mold for casting. In the above, it is preferable to add the inoculant to the molten metal before or at the time of stirring.

Here, as the inoculant, Ca-Si alloy and
Any of the commonly used ones such as Fe-Si alloys and alloys containing Sr and Ba added thereto may be used.

[0008]

The background of the present invention and its operation will be described below. As described above, when the cast product is directly cast from the molten metal, the chilling progresses, and particularly when the casting is performed with a die or a sand mold, the chilling is performed when a thin product is cast.

As a result of various experiments and studies as means for preventing chilling, it was found that casting a semi-solidified metal slurry was extremely effective. Solid-phase particles in the semi-solidified metal slurry were inoculated. We have obtained the finding that it exerts an effect and prevents chilling. That is, according to the present invention, the molten metal is stirred while being cooled to obtain a semi-solidified metal slurry having a solid phase ratio of 0.05 to 0.60, and the cast product is prevented from chilling by casting.

In the above, if the solid fraction 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 and casting becomes difficult and a sound product cannot be produced. Therefore, the solid phase ratio of the semi-solidified metal slurry during casting is set in the range of 0.05 to 0.60.

Further, in the present invention, an inoculant may be used, and if the inoculant is added and cast during the production process of the semi-solidified metal slurry, a further chilling prevention effect is exhibited.

As described above, by casting the semi-solidified metal slurry and further by using the inoculant together, it is possible to prevent chilling even in the casting of die casting products or thin casting products, and to commercialize without heat treatment. Even if some chilling occurs, the white pig iron structure can be eliminated by heat treatment for a short time, 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%, Mn: 0.82 mass% was used as a raw material, and a melting / casting method called a derbil method was used for semi-solidifying metal. Applicable to slurry casting, molten metal (temperature: 1380 ℃)
When directly supplied to the mold (diameter: 100 mmφ) for casting, and as a semi-solidified metal slurry, temperature: 1200 ℃ --- solid phase ratio: 0.1, temperature: 1160 ℃ --- solid phase ratio: 0.4 And temperature:
1150 ℃ --- Solid phase ratio: 0.55 was supplied to the mold and cast, and the metal structure and hardness 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 is a high-frequency induction heating coil embedded in the high-frequency melting furnace 1, and 3 is a runner integrally formed with the high-frequency melting furnace 1, and a mold mold 4 is attached to the tip of the runner 3. These have a structure in which the semisolid metal slurry 8 in the high-frequency melting furnace 1 is tilted as a unit.
(Including the case of molten metal) can be supplied in a laminar flow state into the mold 4 through the runner 3. The dotted line in the figure shows a state in which the semi-solidified 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 rotationally driving the stirrer 5 via the drive shaft 6, and these can be lifted and lowered together by a lifting means (not shown). In the case of casting a semi-solidified metal slurry by the above apparatus, after inserting a cold piece into the high frequency melting furnace 1 and melting the cold piece with 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, and the stirrer 5 is rotated by the operation of the motor 7 while the molten metal is being cooled to stir the molten metal to obtain a semi-solid metal slurry having a predetermined solid phase ratio. After setting to 8, the stirrer 5 is retracted upward. Thereafter, the high-frequency melting furnace 1, the runner 3 and the mold 4 were tilted to supply the semi-solidified metal slurry 8 to the mold 4 as described above, and then cooled and solidified to obtain a cast product.

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

The above survey results will be described below. First, a photograph of the metal structure of the cast product from the molten metal is shown in Figs. 2 and 4 (a), (b).
Fig. 3 and Figs. 5 (a) and 5 (b) are photographs of the metallographic structure of the cast product made from the semi-solidified metal slurry (solid phase ratio: 0.4). These are those etched by picral, but in FIGS. 2 and 3, they are photographed so that the chill layer can be particularly emphasized. (A) in FIGS. 4 and 5 shows the interface in contact with the mold. Including the surface layer part, (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 the semi-solidified metal slurry shown in FIG. 3 is used. The cast product has an extremely thin chill layer formation thickness, and the chill layer formation area is greatly reduced.

Further, comparing FIGS. 4 (a) and 4 (b) with FIGS. 5 (a) and 5 (b), the surface layer portion is found in the cast product from the molten metal of FIGS. 4 (a) and 4 (b). There is a large difference in the metallographic structure between (a) and the central part (b),
While the chill layer and dendrite structure can be seen, FIG.
The cast products cast from the semi-solidified metal slurries of (a) and (b) show almost the same metallographic structure in the surface part (a) and the central part (b), and the primary crystal grains are uniformly dispersed. .

Further, the hardness distribution from the surface of the cast product toward the center is shown in FIG. As is clear from FIG. 6, the cast product made from the molten metal has a deeper high hardness region from the surface as compared with the cast product made from the semi-solidified metal slurry. Is shown. Further, when comparing the cast products made from the semi-solidified metal slurries, the high hardness region is shallower in the cast products made from the semi-solidified metal slurries having a higher solid fraction.

Example 2 Casting from a semi-solidified metal slurry was carried out in the same manner as in Example 1 except that 0.5% of Ca-Si alloy was added as an inoculant to the cast iron melt, and the metal structure of the obtained cast product was obtained. investigated. As a result, it was possible to reduce the formation of the chill layer as in Example 1. In addition, the addition of the inoculant could prevent the precipitation of cementite, which is sometimes slightly observed between the primary grains in the case of no addition.

[0022]

Industrial Applicability According to the present invention, when casting a cast iron casting product, a semi-solidified metal slurry having a solid fraction of 0.05 to 0.60 is supplied to a mold for casting, thereby forming a chilled layer, that is, a chill layer having a high hardness. According to the present invention, it is possible to reduce the heat treatment cost of the cast product, to realize the thinning of the cast product by facilitating the casting of the thin product, that is, to reduce the weight. Is.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a melting / casting apparatus used in an example.

FIG. 2 is a metallographic photograph of a cast product from the melt.

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

FIG. 4 is a metallographic photograph of a cast product from the melt.
(a) is a metallographic photograph of the surface layer. (b) is a metallographic photograph of the central part.

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

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

[Explanation of symbols]

 1 high-frequency melting furnace 2 high-frequency induction heating coil 3 runner 4 die mold 5 stirrer 6 drive shaft 7 motor 8 semi-solid metal slurry

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B22D 7/00 H (72) Inventor Seiro Yawata 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Stock company In rheotech

Claims (2)

[Claims] 1. A semi-solid metal slurry in which a non-dendritic crystal having a solid phase ratio of 0.05 to 0.60 is suspended to obtain a semi-solid metal slurry which is stirred under cooling to cause solidification, and the semi-solid metal slurry is used as a mold. A method for preventing chilling during casting of a cast iron casting product, which comprises supplying and casting. 2. The method for preventing chilling during casting of a cast iron casting product according to claim 1, wherein an inoculant is added to the molten metal before or during the stirring.