JP3061794B1 - Mold for horizontal continuous casting of hypoeutectic cast iron and horizontal continuous casting method - Google Patents

Abstract

【wrap up】 PROBLEM TO BE SOLVED: To prevent slab breakage and breakout,
Excellent continuous quality mold for horizontal continuous casting of hypoeutectic cast iron
And a horizontal continuous casting method. SOLUTION: On the injection side of molten metal, thermal expansion containing nitride is performed.
Tension coefficient is 1 × 10^-6(℃^{- 1}) The following ceramics (A)
CE = C + Si / 3 provided with a member consisting of
Horizontal for continuous casting of hypoeutectic cast iron of 3.9 or less
Using the continuous casting mold and the horizontal continuous casting mold
Horizontal continuous casting method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal continuous casting mold and a horizontal continuous casting method for horizontal continuous casting of hypoeutectic cast iron having a wide solidification temperature range from the start of solidification to the end of solidification.

[0002]

Conventionally, hypoeutectic cast iron has a wide solidification temperature range of 100 ° C. or more from the start of solidification to the end of solidification. Therefore, when the hypoeutectic cast iron is cast by a sand mold or a metal mold, the hypoeutectic cast iron is significantly solidified and contracted, resulting in a poor yield and casting defects remaining inside the product. Further, when a conventional graphite mold used in horizontal continuous casting of cast iron is used during continuous casting of hypoeutectic cast iron, erosion and seizure occur. In addition, when a copper mold used in horizontal continuous casting of steel or alloy steel is used, the cooling rate is too fast, chill crystals are formed, and the cast iron becomes very brittle. Thus, it has been difficult to stably cast hypoeutectic cast iron using a conventional mold.

In order to solve the above-mentioned problems, Japanese Patent Application Laid-Open No. 52-50929 (hereinafter referred to as "prior art 1") discloses a melting temperature of white cast iron, high alloy special cast iron, high alloy copper alloy and the like. And a mold for continuous casting of metal having a large difference between the solidification temperature and the solidification temperature. In Prior Art 1, a refractory having lubricity is used on the molten metal injection side in a continuous casting mold. That is, in the prior art 1, by using a refractory having excellent lubricity with a small amount of wear, the force required for pulling out the solidified ingot is reduced, and the solidified shell of the metal is prevented from breaking. Is what you do.

Further, Japanese Patent Application Laid-Open No. 57-91851 (hereinafter referred to as "prior art 2") discloses a continuous casting method of a low carbon white cast iron material. In Prior Art 2, B
A casting method capable of preventing breakage and breakout of a slab by defining a drawing speed, a drawing stroke, a drawing cycle, and casting conditions using a mold made of a nitride such as N.

[0005]

The above-mentioned prior art has the following problems. That is, in Prior Art 1,
Lubricating refractories are used on the injection side, but lubricating refractories have a large thermal expansion, causing excessive compressive stress on the inner diameter side of the mold, causing delamination or severe damage on the inner diameter surface. Breaks the refractory. As a result, a surface flaw is attached to the product, and porosity is generated in the center. Furthermore, when it deteriorates, it solidifies (bridging) at the injection part.

The prior art 2 discloses that drawing is performed by adjusting the surface temperature of the slab to 800 to 860 ° C. Certainly, when the surface temperature of the slab is adjusted to 860 ° C. or lower and casting is performed, casting stability can be achieved and the surface properties can be improved. However, when the inside of the slab is inspected by ultrasonic flaw detection, porosity at the center of the product is generated, and there is a problem in the quality of the product.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the conventional problems, to prevent slab breakage and breakout,
An object of the present invention is to provide a mold for horizontal continuous casting of hypoeutectic cast iron and a horizontal continuous casting method having excellent quality.

[0008]

Means for Solving the Problems The inventors have conducted intensive studies in order to solve the above-mentioned conventional problems. As a result, on the molten metal injection side, a nitride containing nitride and a thermal expansion coefficient of 1
It has been found that by providing a member made of ceramics having a temperature of × 10 ⁻⁶ (° C. ⁻¹ ) or less, it is possible to prevent the mold from peeling and breaking when the hypoeutectic molten cast iron having a wide solidification temperature range passes through the mold. Further, on the outlet side of the molten metal, another member made of graphite or ceramics containing nitride is provided, and the other member has a gradient corresponding to the heat shrinkage of the slab in its inner diameter. , The gradient provides sufficient contact with the solidified metal, cooling and heat removal become smoother,
It has been found that fracture and breakout of the slab are more reliably prevented.

The present invention has been made based on the above-mentioned findings, and a first aspect of the horizontal continuous casting mold according to the present invention is characterized in that the molten metal injection side contains a nitride and a thermal expansion coefficient. A hypoeutectic cast iron having CE = C + Si / 3 of 3.9 or less, in which a member made of ceramic (A) having a temperature of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided inscribed in the inner wall of the water-cooling jacket. Is a horizontal continuous casting mold for continuous casting.

A second aspect of the horizontal continuous casting mold according to the present invention is characterized in that the molten metal injection side contains nitride and has a coefficient of thermal expansion.
A member made of ceramic (A) of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided, and another member made of graphite or ceramic (B) containing nitride is provided on the outlet side of the molten metal. A member, wherein said another member has a gradient in its inner diameter according to the heat shrinkage of the slab, CE = C + Si
This is a horizontal continuous casting mold for continuously casting hypoeutectic cast iron having a ratio of / 3 or less to 3.9 or less.

[0011] A third aspect of the horizontal continuous casting mold of the present invention relates to a member made of the ceramic (A),
An injection part having a cross-sectional area of 55 to 85% of the product cross-sectional area is provided.

In a first aspect of the method for horizontally and continuously casting hypoeutectic cast iron according to the present invention, the molten metal injection side contains nitride and has a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less. A member made of ceramics (A) is inscribed on the inner wall of the water cooling jacket.
It is provided Te using horizontal continuous casting mold, CE
= C + Si / 3 is a method for horizontally and continuously casting hypoeutectic cast iron having a value of 3.9 or less.

A second aspect of the method for horizontally and continuously casting hypoeutectic cast iron according to the present invention is as follows. The molten metal-injecting side contains nitride and has a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less. A member made of ceramics (A) is provided, and another member made of graphite or ceramics containing nitride (B) is provided on the outlet side of the molten metal; This is a method of horizontally and continuously casting hypoeutectic cast iron having CE = C + Si / 3 of 3.9 or less, using a horizontal continuous casting mold having a gradient according to the heat shrinkage of the slab in the inner diameter.

In a third aspect of the method of the present invention for horizontally and continuously casting hypoeutectic cast iron, the temperature of a molten metal in a holding furnace connected to the horizontal continuous casting mold is set to a value of a liquidus temperature +10.
A hypoeutectic cast iron characterized by being maintained at 0 ° C. or higher, intermittent drawing having a stopping time of 5 to 10 seconds and a stroke length of 20 to 50 mm, and performing cooling at the mold outlet by air cooling. This is a horizontal continuous casting method.

A fourth aspect of the method for horizontally and continuously casting hypoeutectic cast iron according to the present invention is characterized in that the member made of the ceramics (A) of the horizontally continuous casting mold has a cross section of 55 to 85% of the product cross-sectional area. A method for horizontally and continuously casting hypoeutectic cast iron, characterized by providing an injection part having an area.

Another embodiment of the casting mold for horizontal continuous casting according to the present invention comprises a ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less on the molten metal injection side. The member is provided, C: 1.6 to 3.6 wt%, S
i: containing 1.0 to 3.5 wt%, CE = C + Si / 3
Is a horizontal continuous casting mold for continuously casting hypoeutectic cast iron having a range of 2.0 to 3.9.

In another embodiment of the horizontal continuous casting mold of the present invention, a ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on the molten metal injection side. A member is provided, and another member made of graphite or a ceramic (B) containing a nitride is provided on the outlet side of the molten metal, and the other member has a heat of a slab at an inner diameter thereof. C: 1.6 to 3.6 wt%, Si: 1.0 to 3.5 wt% with gradient (0 to 0.6%) according to shrinkage
% Is a horizontal continuous casting mold for continuously casting hypoeutectic cast iron having CE = C + Si / 3 in the range of 2.0 to 3.9.

In another aspect of the horizontal continuous casting mold of the present invention, the thickness of the injection portion in the member made of the ceramic (A) is 1.2 times the thickness of another member made of the ceramic (B). ２．０2.0 times.

Another embodiment of the method for horizontally and continuously casting hypoeutectic cast iron according to the present invention is directed to a ceramic containing nitride and having a thermal expansion coefficient of 1 × 10 ^-6 (° C. ^-1 ) or less on the molten metal injection side. Using a horizontal continuous casting mold provided with a member consisting of (A), C: 1.6 to 3.6 wt%, Si: 1.0
~ 3.5wt%, CE = C + Si / 3 2.0 ~
A horizontal continuous casting method for hypoeutectic cast iron in the range of 3.9.

Another embodiment of the method for horizontally and continuously casting hypoeutectic cast iron according to the present invention is a method of forming a ceramic containing nitride and having a thermal expansion coefficient of 1 × 10 ^-6 (° C. ^-1 ) or less on the molten metal injection side. (A) is provided, and another member made of graphite or nitride-containing ceramics (B) is provided on the outlet side of the molten metal, and the other member has an inner diameter thereof. The gradient (0 to 0.6) corresponding to the heat shrinkage of the slab
%) Using a horizontal continuous casting mold with C:
Horizontally and continuously cast hypoeutectic cast iron containing 1.6 to 3.6 wt%, Si: 1.0 to 3.5 wt% and CE = C + Si / 3 in the range of 2.0 to 3.9. Is the way.

In another aspect of the method for horizontally and continuously casting hypoeutectic cast iron according to the present invention, in the drawing, the surface temperature of the slab at the outlet of the mold may be 860 to 1000 ° C.
Is within the range of

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 2, for example, a horizontal continuous casting mold according to the present invention has a cylindrical water-cooling jacket 3 and a mold which projects in the tundish direction while being in contact with the inner wall of the water-cooling jacket 3. The inner wall of the water-cooled jacket 3 and the front tubular body 1 which constitutes the inner wall of the mold made of ceramic (A) having a predetermined value of thermal expansion coefficient containing nitride and disposed at the entrance side of It comprises a rear tubular body 2 which is connected to the front tubular body 1 and is arranged on the outlet side of the mold and which constitutes a mold inner wall made of graphite or nitride-containing ceramic (B).

The cast iron cast in the horizontal continuous casting method and the horizontal continuous casting mold of the present invention is CE = C + S
It is hypoeutectic cast iron with i / 3 of 3.9 or less. Furthermore, the cast iron to be cast is carbon (C): 1.6 to 3.6 wt.
%, Silicon (Si): 1.0 to 3.5 wt%, and the carbon equivalent (CE) = C + Si / 3 may be hypoeutectic cast iron in the range of 2.0 to 3.9. .

In the horizontal continuous casting mold of the present invention,
On the injection side of molten metal, contains nitride and has a thermal expansion coefficient of 1 × 1
A member made of ceramic (A) of 0 ^-6 (° C. ^-1 ) or less is provided. The reason why a member made of ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on the injection side of the molten metal is as follows.

That is, since hypoeutectic cast iron has a large coefficient of thermal expansion, the casting mold may be divided into an injection side, which is a solidification start portion, and a casting mold body portion which promotes cooling after a solidified shell is formed.
In order to secure the fluidity of the molten metal from the holding furnace and to reduce the reactivity with the cast iron, a ceramic containing a nitride having low thermal conductivity is used for the casting mold.

The ceramic (A) containing the nitride preferably has a smaller coefficient of thermal expansion. On the other hand, the thermal expansion coefficient is 1 × 10
^{If the} temperature exceeds ^-6 (° C ^-1 ), an excessive compressive stress is generated on the inner diameter side due to the thermal expansion of the ceramic, and the mold is peeled or broken. Therefore, the thermal expansion coefficient of the member made of ceramics (A) containing nitride provided on the molten metal injection side is limited to 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less. In addition. The length of the member made of the ceramic (A) containing nitride is 100 to
Preferably it is 300 mm.

As the ceramic (A) containing a nitride, for example, there is boron nitride (BN), and hexagonal boron nitride (h-BN) is preferable. H-BN contained in the ceramic is preferably 50 to 97 wt%. h-
If BN is less than 50 wt%, desired effects such as thermal shock resistance and wettability cannot be obtained. On the other hand, when h-BN exceeds 97 wt%, the abrasion during casting becomes severe, and smooth casting cannot be performed. If necessary, ceramics (A)
Are silicon nitride (Si ₃ N ₄ ), aluminum nitride (Al
N), silicon oxide (SiO ₂ ), aluminum oxide (A
l ₂ O ₃ ), boron carbide (B ₄ C), zirconium oxide (ZrO ₂ ), zirconium boride (ZrB ₂ ), calcium oxide (CaO), and the like.

The mold on the outlet side may be a member made of either ceramic (B) containing nitride or graphite, and this member has a gradient in its inner diameter corresponding to the heat shrinkage of the slab. You may have. When the gradient is 0 to 0.6%, the gradient provides sufficient contact with the solidified metal,
Cooling and heat removal become smooth. Examples of the ceramic (B) containing a nitride include BN and Si ₃ N ₄ .

As one of the casting conditions, the temperature of the molten metal in the holding furnace connected to the mold is set to the liquidus temperature + 100 ° C. or more. The reason is that if the temperature of the molten metal in the holding furnace is lower than the liquidus temperature + 100 ° C., the fluidity at the entrance of the mold cannot be secured, and porosity and bridging occur.

In the present invention, the cooling at the outlet of the mold is performed by air cooling. Generally, secondary cooling is performed at the mold outlet with water cooling to prevent breakout due to reheating.However, with hypoeutectic cast iron, cooling with water reduces the temperature of the molten metal to reduce the fluidity at the mold inlet. I can't secure it. Therefore, air cooling is performed at the mold outlet to prevent breakout due to reheating.

When the casting is performed at a surface temperature of 860 ° C. or lower, casting stability can be improved and the surface properties can be improved.
When the inside is inspected by ultrasonic flaw detection, porosity in the center of the product is generated, and there is a problem in the quality of the product. To avoid this, the surface temperature was raised to 860 ° C.
The porosity was found to diminish. However,
It was found that when the surface temperature was further increased, the solidified shell became thinner, and when the surface temperature exceeded 1000 ° C., breakout occurred. Therefore, the drawing is performed so that the surface temperature of the slab at the outlet of the mold falls within the range of 860 to 1000 ° C.

In the present invention, the stop time is 5 to 10
The drawing is performed by intermittent drawing having a stroke length of 20 to 50 mm for seconds. Stroke length is 20mm
At the rest time of 10 to 15 seconds, the solidified shell becomes coarse, but simultaneously decreases to the temperature of the molten metal inside the mold. As a result, the solid fraction at the inlet of the mold increases, and the fluidity of the molten metal increases. Greatly decreases.

When the flowability of the melt decreases, central porosity is produced, as described above. If the temperature of the molten metal further decreases, bridging occurs at the entrance of the mold, and the solidified shell breaks. In order to avoid this, the stop time is 5 to 10 seconds and the stroke is 20 to 50 m.
Perform intermittent extraction consisting of m. If the stop time is less than 5 seconds, the solidified shell is thinly broken out. On the other hand, if the stroke exceeds 50 mm, the pull-out resistance increases and the possibility of solidification shell fracture increases.

In the present invention, an injection portion having a cross-sectional area of 55 to 85% of a product cross-sectional area is provided in a member made of ceramics (A) of a horizontal continuous casting mold. The reason is that the heat removal from the cooling section is reduced, and the temperature of the molten metal in the injection section is prevented from lowering. In the present invention,
The thickness of the injection portion in the member made of the ceramic (A) is 1.2 to 2.0 times the thickness of another member made of the ceramic (B). The reason is that the heat removal from the cooling section is reduced, and the temperature of the molten metal in the injection section is prevented from lowering.

In the present invention, a member made of ceramic (A) containing nitride and having a coefficient of thermal expansion of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on the molten metal injection side. On the outlet side, another member made of graphite or a ceramic (B) containing a nitride is provided, and the other member described above has an inner diameter with a gradient (0 to 0) corresponding to the heat shrinkage of the slab.
(0.6%). At this time, the above-described effect can be further enhanced.

The present invention will be described in more detail with reference to the following examples.

Example 1 According to the method of the present invention, a horizontal continuous casting of a hypoeutectic cast iron material having a diameter of 50 mm was performed as follows. Chemical component C: 2.5% Si: 2.0% Mn: 0.6% P: 0.01% S: 0.005%, and CE = C + Si / 3 is 3.2. The molten cast iron was poured into a holding furnace at a temperature of 1480 ° C. As shown in FIG. 1, the mold had a thermal expansion coefficient of 5 × 1 including BN.
Length 350 made of ceramic (A) of 0 ^-7 (° C ^-1 )
A non-graded mold having an inner diameter of 50 mm and an outer diameter of 80 mm equipped with a member 1 of mm was used. The drawing was performed by intermittent drawing with a stop time of 9.5 seconds and a stroke length of 35 mm. At this time, the molten metal temperature in the holding furnace was 14
It was 10-1430 degreeC (however, liquidus temperature is 1280 degreeC). As a result, 10 ton hypoeutectic cast iron was cast, and about 80
An excellent product of 0 m quality was obtained.

Example 2 According to the method of the present invention, a horizontal continuous casting of a 100 mmφ hypoeutectic cast iron material was performed as follows. Chemical component C: 2.5% Si: 2.0% Mn: 0.6% P: 0.02% S: 0.010%, and CE = C + Si / 3 is 3.2. The molten cast iron was poured into a holding furnace at a temperature of 1480 ° C. As shown in FIG. 2, the mold 1 is a member 1 made of ceramic (A) having a thermal expansion coefficient of 5 × 10 ⁻⁷ (° C. ⁻¹ ) containing BN on the injection side and having a length of 150 mm, an inner diameter of 90 mm, and an outer diameter of 140 mm.
And an outlet side provided with a 200 mm long member 2 made of graphite having a 0.4% gradient in the inner diameter.
m, a mold having an outer diameter of 140 mm was used. The drawing was performed by intermittent drawing with a stop time of 8.5 seconds and a stroke length of 25 mm. At this time, the temperature of the molten metal in the holding furnace was 141
The temperature was 0 to 1430 ° C (the liquidus temperature was 1280 ° C). As a result, 8t of hypoeutectic cast iron was cast, and about 140m
A product of excellent quality was obtained.

Example 3 According to the method of the present invention, horizontal continuous casting of a hypoeutectic cast iron material having a diameter of 50 mm was performed as follows. Chemical component C: 2.0% Si: 2.0% Mn: 0.6% P: 0.01% S: 0.005%, and CE = C + Si / 3 is 2.7. The molten cast iron was poured into a holding furnace at a temperature of 1500 ° C. As shown in FIG. 3, the mold ^{1 is made} of a ceramic (A) having a thermal expansion coefficient of 5 × 10 ⁻⁷ (° C. ⁻¹ ) containing BN on the injection side and having a length of 200 mm, an inner diameter of 40 mm, and an outer diameter of 100 mm.
A 150 mm long member 2 made of ceramics (B) containing BN having an inner diameter with a gradient of 0.1%
A mold having an inner diameter of 50 mm and an outer diameter of 100 mm was used. Pull-out time is 9.5 seconds, stroke length 3
The intermittent drawing of 5 mm was performed. At this time, the temperature of the molten metal in the holding furnace was 1450 to 1470 ° C. (however, the liquidus temperature was 1330 ° C. As a result, a 12-ton hypoeutectic cast iron was cast, and a product with an excellent quality of about 850 m was obtained. Was done.

[0039]

As described above, according to the method of the present invention, there is provided a mold for horizontal continuous casting of hypoeutectic cast iron and a method of horizontal continuous casting, which prevent breakage and breakout of cast pieces and have excellent quality. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an assembly drawing of a die in the method of the present invention.

FIG. 2 is a diagram showing another assembly view of the dice in the method of the present invention.

FIG. 3 is a diagram showing still another assembly drawing of the dice in the method of the present invention.

[Explanation of symbols]

 1. Front tubular body 2. Rear tubular body 3. Water cooling jacket 31. Flange

Continued on the front page (72) Inventor Toru Niinuma 2-1 Shiraishi-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Japan Foundry Co., Ltd. (72) Inventor Masayuki Tsuchiya 1-4-1, Chuo, Wako-shi, Saitama Pref. (72) Inventor Hiroaki Ueno 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Center (72) Inventor Kentaro Mori 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-63-20140 (JP, A) JP-A-57-91851 (JP, A) JP-A-2-263540 (JP, A) JP-A-8-1644447 (JP, A) JP-A-5-146848 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/04 114 B22D 11/04 311 B22D 11/00 B22D 11/059 120

Claims (7)

(57) [Claims] 1. A member made of a ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on the inner side of a water cooling jacket on a molten metal injection side. A horizontal continuous casting mold for continuously casting hypoeutectic cast iron having CE = C + Si / 3 of 3.9 or less. 2. A member made of a ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on a molten metal injection side, and a molten metal exit side is provided. Ceramics made of graphite or containing nitride (B)
CE = C, wherein the other member has a gradient in its inner diameter corresponding to the heat shrinkage of the slab.
A horizontal continuous casting mold for continuously casting hypoeutectic cast iron having + Si / 3 of 3.9 or less. 3. The horizontal continuous casting according to claim 1, wherein an injection portion having a cross-sectional area of 55 to 85% of a product cross-sectional area is provided in the member made of the ceramic (A). template. 4. A member made of ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on the injection side of the molten metal in contact with the inner wall of the water cooling jacket. CE = C + S using the horizontal continuous casting mold
A method of horizontally and continuously casting hypoeutectic cast iron having i / 3 of 3.9 or less. 5. A member comprising a ceramic (A) containing nitride and having a thermal expansion coefficient of 1 × 10 ⁻⁶ (° C. ⁻¹ ) or less is provided on a molten metal injection side, and a molten metal exit side is provided. Ceramics made of graphite or containing nitride (B)
Using a horizontal continuous casting mold with an inner diameter having a gradient according to the heat shrinkage of the slab, CE = C + Si / 3 of 3.9. The following method for horizontally continuous casting hypoeutectic cast iron. 6. The temperature of a molten metal in a holding furnace connected to the horizontal continuous casting mold is maintained at a liquidus temperature + 100 ° C. or more, a stop time is 5 to 10 seconds, and a stroke length is 20 to 100 ° C. 50mm
The method for horizontally and continuously casting hypoeutectic cast iron according to claim 4 or 5, wherein drawing is performed by intermittent drawing comprising: and cooling at the mold outlet is performed by air cooling. 7. A member made of said ceramics (A) of said horizontal continuous casting mold, wherein a product sectional area of 55 to 8
7. The method for horizontally and continuously casting hypoeutectic cast iron according to claim 4, wherein an injection portion having a cross-sectional area of 5% is provided.