JP2003041338A - High-carbon spheroidal graphite cast iron and refractory cast iron manufactured therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-carbon spheroidal graphite cast iron which can be used for a refractory casting, and has a stable matrix with little variations of mechanical properties such as tensile strength, dilation, and hardness. SOLUTION: The high carbon spheroidal graphite cast iron includes, by weight ratio, 4-4.8% C, 1.7% or less Si, 0.5-1.0% Mn, 0.035-0.1% Mg, and the balance substantially Fe, and has a spheroidal graphite rate of 60% or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high carbon spheroidal graphite cast iron, and more particularly to high carbon spheroidal graphite cast iron melted in an electric furnace, a cupola or the like and a heat-resistant cast iron cast product obtained by using the same.

[0002]

2. Description of the Related Art Conventionally, Ni alloys have been used as cast iron castings.
The chemical composition range containing 2 wt% or more is approximately C: 3.0% or less by weight ratio, Si: 1.0 to 3.0.
%, Mn: 0.5 to 1.0%, Ni: 12 to 22%, C
Spheroidal graphite niresist cast iron having r: 1.0 to 5.0% and Cr: 1.0 to 3.0 is known. This Ni-resist cast iron has hardness, heat resistance, and
A large amount of Ni alloy is used for the purpose of improving corrosion resistance, but it is expensive and the product containing thermal stress has a low C content. Since the amount of graphite that functions as a cushion is small, cracks may occur.

[0003]

In order to solve the above problems, Japanese Unexamined Patent Publication (Kokai) No. 56-136913 discloses compact / vermicula cast iron as high carbon tough cast iron, that is, worm-like graphite cast iron. Japanese Patent Laid-Open No. 57-181357 discloses a mold using such caterpillar-like graphite cast iron. However, it is very difficult to control graphite in the form of a caterpillar, and there is a large variation in that graphite exhibits the desired spherical shape or spheroidization, and it is very difficult to stabilize the matrix structure. is there. Further, since the matrix structure cannot be stabilized, there is a problem that the mechanical properties of such a mold made of cast iron also vary greatly.

Further, when the conventional spheroidal graphite cast iron is used in a place where it is repeatedly exposed to high temperatures, it may be largely deformed in a short period of time and may become unusable. As a measure against this,
Spheroidal graphite cast iron having a chemical composition that suppresses only elongation cannot be applied to large-sized products because the generated thermal stress is large and cracks occur at the initial stage of use.

From the thought that the above-mentioned factor that makes the matrix structure unstable may be due to the addition amount of the spheroidizing agent,
An object of the present invention is to obtain a spheroidal graphite cast iron having a high spheroidization rate by suppressing the deposition of worm-like graphite in order to obtain a graphite cast iron having a stable matrix structure.

[0006]

The invention according to claim 1 is such that the chemical composition by weight ratio is C: 4.0 to 4,8%, S.
i: ≤ 1.7%, Mn: 0.5 to 1.0%, Mg: 0.
It is characterized by high carbon spheroidal graphite cast iron containing 035 to 0.1%, the balance being Fe and inevitably contained impurities, and having a graphite spheroidization rate of 60% or more.

According to a second aspect of the present invention, the chemical composition is C: 4.0 to 4,8%, Si: ≤ 1.7%, M by weight ratio.
n: 0.5 to 1.0%, Mg: 0.035 to 0.1%, the balance consisting of Fe and inevitable impurities, and a graphite spheroidization rate of 60% or more. A heat-resistant cast iron casting obtained by using carbon spheroidal graphite cast iron.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The high carbon spheroidal graphite cast iron according to the present invention has a stable matrix structure composed of dense pearlite leaving ferrite,
It is possible to obtain stable numerical values with little variation in mechanical properties such as elongation and hardness. In order to obtain such a matrix structure, in the high carbon spheroidal graphite cast iron of the present invention, as described above, C: 4.0 to 4,8%, Si:
≦ 1.7%, Mn: 0.5 to 1.0%, Mg: 0.03
It contains 5 to 0.1%.

By thus setting the amount of Mg as the spheroidizing agent within the range of 0.035 to 0.1%, the matrix structure can be stabilized.

Regarding the generated thermal stress and the elongation of the material, which are the main factors of deformation, etc., the following measures are taken: graphite is prepared by setting C in the chemical composition to ≧ 4.0% in order to suppress the generated thermal stress to a low level. Greatly crystallizes to improve thermal conductivity, elongation 2
Si: ≤1.7%, M in chemical composition in order to suppress ~ 5%
n: 0.5 to 1.0% to improve the matrix structure by making it pearlite rich (50% or more), thereby making it possible to use for large heat-resistant products such as ingot casting molds, and its life. Can be greatly improved.

Next, the chemical components and composition of the high carbon spheroidal graphite cast iron of the present invention will be described in detail.

[0012] C is a material necessary for crystallization of graphite and perlite conversion of the matrix, as in ordinary spheroidal graphite cast iron, but if this amount is less than 4.0%, the expansion amount due to graphitization will be insufficient. However, it becomes difficult to secure the internal soundness of the cast product. On the other hand, when it exceeds 4.8%, graphite is excessive, and quiche graphite (primary crystal graphite) is deposited on the upper surface of the product, resulting in product quality. Therefore, the range is 4.0 to 4.8%.

Si is an element that promotes graphitization and has a function of making the matrix uniform, but if its amount exceeds 1.7%, it causes insufficient strength in relation to the amount of C element used. In addition, since there is an adverse effect that the dross amount also increases, ≤1.7% is appropriate.

Mn is an element effective for stabilizing matrix pearlite formation, but if the amount is 0.5 to 1%, an effective action cannot be expected if it is less than 0.5%. Also, if it is used in excess of 1%, it is economically disadvantageous as well as the problem of increased carbides.

Mg is a graphite spheroidizing element, but if its amount is less than 0.035%, it is difficult to stably deposit spheroidal graphite, and even if it has the same composition, it becomes spherical or flaky. However, the shape is not stable and the desired spheroidization rate cannot be obtained. On the other hand, if the amount exceeds 0.1%, the amount of dross generated such as MgS, MgO, and MgC increases, and the segregation of graphite also increases, which is not practical. Therefore, Mg is 0.035 to 0.1
A range of% is suitable.

As described above, the high carbon spheroidal graphite cast iron of the present invention has a chemical composition in a weight ratio of C: 4.0 to 4.8.
%, Si: ≤ 1.7%, Mn: 0.5 to 1.0%, M
g: 0.035 to 0.1%, the balance being substantially F
By setting e, it is possible to obtain a spheroidal graphite cast iron having a spheroidization rate of graphite of 60% or more, a good balance of tensile strength, elongation, and hardness, and in particular, the elongation of a plurality of test pieces cut out from the test material It has a stable numerical value within the range of 2 to 5% and has heat resistance. If the spheroidization rate of graphite is 60% or less, spheroidization is insufficient and flake graphite or caterpillar-like graphite is present in a large amount, and stable elongation and strength cannot be obtained.

The high carbon spheroidal graphite cast iron of the present invention is obtained by adding a Mg-based spheroidizing agent such as Fe-Si-Mg or Fe-Si-M to a molten metal obtained by a general production method using an electric furnace or a cupola.
It can be obtained by adding g-RE (rare earth element) by a pouring method, a plunger method or the like. Then, after the spheroidizing treatment, an inoculant mainly composed of Fe-Si may be inoculated for the purpose of adjusting the graphite shape, the spheroidizing rate, the matrix structure, and particularly the uniform dispersion of graphite. Inoculants may not be used as they tend to be smaller in diameter.

Thus, C: 4.0 to 4, 8 of the present invention
%, Si: ≤ 1.7%, Mn: 0.5 to 1.0%, M
g: 0.035 to 0.1%, and the spheroidization rate of graphite is 6
High carbon spheroidal graphite cast iron with 0% or more is 300-500.
Tensile strength of N / mm ² , elongation of 2-5%, and hardness of 1
50 to 190 HB, a good balance of tensile strength, elongation and hardness, and a stable numerical value with little variation, particularly in the range of 2 to 5% elongation, and therefore accessories such as ingot casting molds and surface plates. It can be used for various purposes such as a furnace mouthpiece for a converter, a tundish cover for continuous casting, a cooling floor and a sliding plate for agglomeration, a heat insulating plate and other heat resistant parts.

[0019]

The present invention will be described in detail below with reference to examples. Examples 1 and 2 The cast iron melts having the chemical composition (% by weight) according to the present invention shown in Table 1 in Examples 1 and 2 were obtained by general melting and spherical graphitization treatment using an electric furnace. Casting JIS G5502, No. C sample material using molten cast iron 1
Sand casting was performed at 300 to 1320 ° C.

After the above casting, JIS Z2201, No. 4 test pieces were cut out from the lower part of the No. C test material taken out from the mold, and the mechanical properties such as tensile strength and elongation were examined. Good results with little variation were obtained. In particular,
By setting the amount of Mg within the range of 0.035 to 0.1%, the elongation was stabilized within the range of only 2.7% (Example 1) and 3.0% (Example 2). Numerical values are shown.

[0021]

[Table 1]

Further, when the metal structure (100 times) of the lower part of the No. C test material of the above-mentioned Examples 1 and 2 was observed by an optical microscope, as shown in FIGS. 1 and 2, FIG. 1 (Example 1) In the pearlite matrix, a large amount of spheroidal graphite was crystallized, and flaky or worm-like graphite was barely seen, and the spheroidization rate was determined to be 90%. Also, FIG.
In (Example 2), the spheroidization of graphite and the pearlite formation of the matrix were further promoted, and the state in which the precipitation of ferrite around the graphite was suppressed was observed, and the spheroidization rate was determined to be 95%.

Comparative Examples 1-2 The cast iron melts having the chemical compositions shown as Comparative Examples 1 and 2 in Table 1 above were subjected to the same general melting and spheroidal graphitizing treatments in an electric furnace in the same manner as in Examples 1 and 2. After this, using this molten cast iron, JIS G5502, No. C test material was sand mold cast at a pouring temperature of 1300 to 1320 ° C., and JIS Z2201, 4
The test piece of No. 4 was cut out and the mechanical properties such as tensile strength and elongation were examined. The results are shown in Table 1. C,
Even if the amounts of Si and Mn are within the range specified in the present invention, Mg
By setting the amount to be outside the range of the present invention, the elongation showed a very large variation of 3.5% (Comparative Example 1) and 0.5% (Example 2).

Further, the metal structures (100 times) under the No. C test materials of Comparative Examples 1 and 2 were observed by an optical microscope, and FIG. 3 (Comparative Example 1) shows that spheroidal graphite crystallized in the pearlite matrix. However, worm-like graphite is also crystallized and a ferrite structure is observed around it. And
The spheroidization rate is about 50%. In addition, FIG. 4 (Comparative example 2)
In the pearlite matrix, a large amount of flake-shaped or caterpillar-like graphite was observed, and only fine spheroidal graphite was observed.

[0025]

As described above, the high carbon spheroidal graphite cast iron according to the present invention has a chemical composition of C: 4.0 by weight.
˜4.8%, Si: ≦ 1.7%, Mn: 0.5 to 1.0
%, Mg: 0.035 to 0.1%, the balance substantially consisting of Fe, and having a graphite spheroidization rate of 60% or more, well balanced tensile strength, elongation and hardness,
In particular, it exhibits a stable numerical value with little variation within an elongation range of 2 to 5%, and is useful as a heat-resistant cast iron casting.

[Brief description of drawings]

FIG. 1 is a micrograph showing the metal structure of spheroidal graphite cast iron obtained in Example 1 of the present invention.

FIG. 2 is a micrograph showing the metal structure of spheroidal graphite cast iron obtained in Example 2 of the present invention.

FIG. 3 is a micrograph showing the metal structure of spheroidal graphite cast iron obtained in Comparative Example 1.

4 is a micrograph showing a metal structure of spheroidal graphite cast iron obtained in Comparative Example 2. FIG.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomonori Hasegawa             3-12 Kanbei-cho, Otsu-ku, Himeji-shi, Hyogo               Nijigi Co., Ltd. Himeji East Factory (72) Inventor Keiji Shirayama             3-12 Kanbei-cho, Otsu-ku, Himeji-shi, Hyogo               Nijigi Co., Ltd. Himeji East Factory

Claims (2)

[Claims] 1. A chemical composition in a weight ratio of C: 4.0 to 4.
8%, Si: ≤ 1.7%, Mn: 0.5 to 1.0%, M
g: 0.035 to 0.1%, with the balance being substantially F
A high-carbon spheroidal graphite cast iron, which is composed of e and impurities inevitably contained, and has a graphite spheroidization rate of 60% or more. 2. The chemical composition by weight ratio is C: 4.0 to 4,
8%, Si: ≤ 1.7%, Mn: 0.5 to 1.0%, M
g: 0.035 to 0.1%, with the balance being substantially F
A heat-resistant cast iron casting comprising a high carbon spheroidal graphite cast iron having a graphite spheroidization rate of 60% or more, which is composed of e and impurities inevitably contained.