JPH0776753A - Thin spheroidal graphite cast iron product and production thereof - Google Patents

Abstract

PURPOSE:To stably produce a thin spheroidal graphite cast iron product by casting molten cast iron into a high temp. lost wax mold after executing Mg treatment and inoculating with ferro-silicon to low silicon molten iron. CONSTITUTION:The Mg as graphite spheroidizing agent is added in the molten iron having comparatively low of 1.4-2.0wt% Si content. Further, after spheroidizing the graphite by inoculating with the ferrosilicon, the spheroidal graphite molten iron is immediately cast into a mold with a lost wax casting method to produce the thin cast product having <=3mm thickness. After solidifying, this cast product is taken out of the mold and charged into a heating furnace at 900 deg.C to decompose cementite in the part chilled caused by the thin thickness into ferrite and graphite. By this method, even in the case of the thin casting, the cementite structure caused by rapid cooling does not exist and the perfect spheroidal graphite cast iron product can be produced at the high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin spheroidal graphite cast iron product and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in order to manufacture a thin-walled spheroidal graphite cast iron product, molten cast iron is subjected to magnesium treatment and inoculated with ferrosilicon or the like for casting. The spheroidal graphite cast iron product having a thin portion has a strong tendency to turn white pig iron, and the effect is not sufficient in the above treatment. As a method of coping with this, a method of decomposing the cementite structure precipitated in the cast state into a ferrite structure having low hardness by heat treatment is performed.

[0003]

However, in order to make the cementite structure a perfect ferrite structure having a low hardness by heat treatment, not only the heat treatment cost is increased, but also the generation of strain by heat treatment is induced in the thin spheroidal graphite cast iron of 3 mm or less. become. Furthermore, since the Si content of the spheroidal graphite cast iron product is as high as about 2.5%, it is extremely difficult to obtain a thin-walled spheroidal graphite cast iron product with high toughness.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to inject a molten metal having high toughness in an as-cast state into a high temperature mold by a lost wax casting method. The obtained thin-walled spheroidal graphite cast iron product and its manufacturing method are provided.

[0005]

The thin spheroidal graphite cast iron product of the present invention is a spheroidal graphite cast iron product obtained by injecting a molten metal having a spheroidal graphite cast iron composition into a high temperature mold by a lost wax casting method, The content of Si is 1.4 to 2.0% by weight. Most of the thin spheroidal graphite cast iron product has a wall thickness of 3 mm or less, and has a base structure in an as-cast state. Has a ferrite structure, and the method for producing a thin spheroidal graphite cast iron product of the present invention is characterized by injecting a molten metal having a spheroidal graphite cast iron composition into a high temperature mold by a lost wax casting method. Is.

Next, the reason for limiting the Si content will be described. If the Si content is less than 1.4% by weight, carbides are likely to precipitate, and the cementite structure is not sufficiently decomposed during the cooling process after pouring into the high temperature mold, so that complete ferrite cannot be formed. This is against the increase in toughness. On the other hand, if the Si content exceeds 2.0% by weight, the low temperature toughness is impaired, which is no different from the conventional spheroidal graphite cast iron product.

[0007]

Embodiment 1 An embodiment of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a shape of a stepped test piece, FIG. 2 is a microstructure photograph (× 100) of a 1.5 mm thick portion of the present invention,
Figure 3 is a microstructure photograph of a 1.5 mm thick part of the conventional product (×
100).

1) Chemical composition From a material composed of iron, inevitable impurities and the components shown in Table 1,
The stepped test piece shown in FIG. 1 was manufactured. The injection temperature at that time was 1430 ° C.

[Table 1] 2) Mold The stepped test piece mold was a lost wax mold, which was heated to 1000 ° C. and baked for 1.0 hour, then immediately taken out of the furnace and poured into the molten metal. As a cooling method after pouring the molten metal into the mold, it was held in the mold for 5 minutes, then held in a furnace heated to 900 ° C. for 5 minutes, cooled to 650 ° C., and taken out of the furnace.

The thickness obtained by the above heat treatment is 1.5 m
FIG. 2 shows a microscopic structure photograph of the test piece of the m part. Further, as a comparative example, a microstructure photograph of a 1.5 mm thick portion of the conventional product is shown in FIG.

[0010]

As is apparent from the above description, in the method for manufacturing a spheroidal graphite cast iron product of the present invention, a molten metal having a spheroidal graphite cast iron composition is poured into a mold fired at 1000 ° C., and after completion of solidification, 9
It is characterized in that it is put into a continuous furnace heated to 00 ° C. to be subjected to chill elimination and heat treatment for ferritization. By injecting the molten liquid of low Si-based spheroidal graphite cast iron composition into the mold heated to a high temperature in this way, the chill decomposition in the cooling process can be decomposed by the heat of the mold itself, so the energy cost is lower than the conventional heat treatment cost. It is very inexpensive and has many excellent effects. Further, since the spheroidal graphite cast iron product is constrained by the mold, the occurrence of strain is significantly reduced as compared with the conventional heat treatment. Further, such a low Si spheroidal graphite cast iron becomes a spheroidal graphite cast iron product excellent in low-temperature toughness, which makes it possible to enter the field of cast steel systems, which is an industrially very significant invention.

[Brief description of drawings]

FIG. 1 Shape of stepped test piece

FIG. 2 is a microscopic metallographic photograph (× 100) of a 1.5 mm thick portion of the present invention.

FIG. 3 is a microscopic metallographic photograph (× 100) of a conventional product having a thickness of 1.5 mm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Watanabe 44 Nagahama-cho, Kanda-cho, Kyoto-gun, Fukuoka Prefecture Hitachi Metals Precision Kanda Factory

Claims (3)

[Claims] 1. A spheroidal graphite cast iron product obtained by pouring a molten metal having a spheroidal graphite cast iron composition into a high temperature mold by a lost wax casting method, wherein the Si content is 1.4 to 2.0 wt%. A thin-walled spheroidal graphite cast iron product characterized by: 2. Most of the spheroidal graphite cast iron product has a wall thickness of 3 mm.
The thin-walled spheroidal graphite cast iron product according to claim 1, wherein the matrix structure is a ferrite structure in the as-cast condition. 3. A method for producing a thin spheroidal graphite cast iron product, which comprises injecting a molten metal having a spheroidal graphite cast iron composition into a high temperature mold by a lost wax casting method.