JPH0235630B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing spheroidal graphite cast iron using as-cast ferrite as a base structure in die casting. In general, in sand casting, the manufacturing method of spheroidal graphite cast iron whose base structure is as-cast ferrite has been established. Because the molten metal turns white or becomes pearlite due to the rapid cooling effect, after the cast product is removed, it is annealed to turn the base structure into ferrite.
There was a need to improve mechanical properties such as tensile strength and elongation. However, annealing generates scale, which may impair the dimensional accuracy of the product, which is an advantage of die casting.Also, since it requires an annealing process, it is economically disadvantageous, and from the perspective of improving productivity. It was also considered a problem. The present invention has been developed in view of these problems, and is an as-cast material in die casting that has high elongation and yield strength, and has mechanical properties that are resistant to impact forces, without going through an annealing process. The object of the present invention is to provide a method for manufacturing spheroidal graphite cast iron having ferrite as a base structure. In other words, the feature of the present invention is that the mold made of copper alloy with high thermal conductivity (0.2 to 0.8 cal/cm ²
By rapidly cooling the mold after pouring the metal to
By accelerating the cooling rate of the product in the mold cavity, the carbon atoms (C) present in the components of the product are turned into spheroidal graphite, increasing the number _of spheroidal graphite nuclei. The amount of carbon atoms is reduced as much as possible. The present invention will be specifically explained below. Manganese (Mn) is a carbide stabilizing element and has the effect of binding carbon atoms and iron (Fe) to stabilize them as cementite (Fe ₃ C), so it must be kept as low as possible. It is desirable that it be 0.6% or less. Furthermore, since sulfur (S) is an element that inhibits the spheroidization of graphite, the content is preferably 0.03% or less. Furthermore, since magnesium (Mg) is an element that promotes spheroidization and at the same time is a strong carbide stabilizing element, the content is preferably about 0.015 to 0.03%. That is, if the magnesium content is less than 0.015%, graphite tends to become spheroidized, and if it is more than 0.03%, it acts as a carbide stabilizing element and pearlite or cementite is formed in the matrix structure. It becomes easier and there is a problem. and calcium (Ca),
The amount of rare earth elements (Re) should also be as small as possible. Furthermore, if the silicon (Si) content is 2.7% or less, graphitization will decrease, so it is desirable that the silicon (Si) content be 2.7% or more. In addition, a purified Fe-Si based inoculant is used as the inoculant to be inoculated immediately before pouring. The mold is made of a copper alloy with high thermal conductivity (0.2 to 0.8 cal/cm ² sec・℃), and as soon as the pouring is complete, cooling water is forced to cool the mold by passing it through the mold. do. In other words, because the mold has high thermal conductivity, the heat of the molten metal poured into the mold cavity transfers to the mold side, and the mold is cooled by cooling water, so The heat of the molten metal moves to the mold side, and the molten metal in the mold cavity is rapidly cooled.
Causes overcooling phenomenon. As a result, the number of graphite particles increases significantly, which reduces the distance between graphite particles, facilitates precipitation of carbon atoms into graphite particles during Ar ₁ transformation, and promotes ferrite formation. Next, examples of the present invention will be described. Example 1 To 100 parts by weight of the base water, 1.2% by weight of a spheroidizing agent consisting of the chemical components shown in Table 1 was added for spheroidizing treatment, and 0.6 weight % of an inoculant with the chemical components shown in Table 2 was added. % inoculation, the melted metal for pouring consisting of the dissolved ingredients listed in Table 3 has a thermal conductivity of 0.6 cal/ ^cm2 .
Figure 2 shows the relationship between Si (%) and ferrite area ratio (%) when a cast product as shown in Figure 1 is obtained by casting into a copper alloy mold at sec/°C.
The relationships among the elongation (%), yield strength (Kg/mm ² ), and impact value (Kg·m/cm ² ) are shown in FIGS. 3, 4, and 5, respectively. Incidentally, FIG. 6 shows a photograph of the structure when the Si content ratio is 3.04% in Table 3.

【table】

【table】

[Table] Example 2 The molten metal for pouring shown in Table 4, which differed from Example 1 in the content of Mn only and had the same content as in Table 3 for other elements, was heated to a thermal conductivity of 0.6 cal/cm. ²・sec・℃
Figure 2 shows the relationship between Si (%) and ferrite area ratio (%) when casting into a copper alloy mold as shown in Figure 1, and the relationship between Si (%) and elongation. (%), proof stress (Kg/mm ² ), and impact value (Kg・
m/cm ² ) are shown in FIGS. 3, 4, and 5, respectively.

[Table] That is, in Figure 2 above, the Mn content is 0.12%,
When the content ratio of Si (%) is 2.7% or more, it indicates that the area ratio of ferrite area is 85% or more. And Si (%) and elongation (%) in this case
Figure 3 shows the relationship between Si (%) and proof stress (Kg/mm ² ), and Figure 4 shows the relationship between Si (%) and impact value (Kg/mm 2 ).
m/cm ² ) is shown in FIG. 5. From these graphs in Figures 3, 4, and 5,
It can be seen that cast iron products have high elongation, high yield strength, and are resistant to impact forces. On the other hand, the Mn content
When it reaches 0.35%, from the graphs in Figures 2 to 5,
The area ratio of the ferrite base is slightly lower, the elongation and impact value are also slightly lower, and the yield strength is too high, resulting in problems such as brittleness and poor workability. As is clear from the above explanation, the cast iron products of the present invention have high elongation, proof strength, and strong impact force without undergoing an annealing process, so there is no scale generation due to annealing and dimensional accuracy is maintained. It can be maintained, is economically advantageous, and has the effect of improving productivity, making it a significant contribution to this type of industry.

[Brief explanation of drawings]

Figure 1 is a sectional view of the cast iron product used in the present invention, Figure 2 is a cross-sectional view of the cast iron product used in the present invention;
The figure is a graph showing the relationship between Si (%) and ferrite area ratio (%), Figure 3 is a graph showing the relationship between Si (%) and elongation (%), and Figure 4 is a graph showing the relationship between Si (%) and proof stress (Kg /
mm ² ), FIG. 5 is a graph showing the relationship between Si (%) and impact value (Kg·m/cm ² ), and FIG. 6 is a photograph of the structure of the cast iron product according to the present invention.

Claims (1)

[Claims] 1 Chemical composition: C: 3.4-4.0%, Si≧2.7%, Mn
A molten metal consisting of ≦0.3%, P≦0.1%, S≦0.02%, Mg≦0.03%, and the balance Fe is cooled with water made of a copper alloy (thermal conductivity: 0.2 to 0.8 cal/ ^cm2・S・℃). A method for manufacturing spheroidal graphite cast iron using as-cast ferrite as a base structure in mold casting, characterized by casting into a mold.