JPH09235609A - Production of cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce an excellent cast iron in which pseudo- spheroidal graphite and fine flake graphite structures are present as a mixture by adding specific amounts of Ti and specific Si alloy to molten cast iron of hyper-eutectic composition, pouring the resultant molten cast iron into a metal mold of specific temp., and molding it. SOLUTION: Ti is added by 0.1-0.3% to a molten cast iron having a hyper- eutectic chemical composition in which the value of (carbon saturation degree Sc)=C/[4.26-0.31Si-0.33P+0.18(Mn-1.76S)] is regulated to >=1. Then, an Si alloy, containing >=10% of Ca, Ce, and Ba, is added to this molten metal by 0.4-1.7%, and, if necessary, a graphite spheroidizing agent is further added by 0.5-1.5%. The resultant molten cost iron is poured at a poring temp. of preferably about 1623 to 1673 deg.K into a metal mold of <=473 deg.K and molded. It is preferable that this metal mold is composed of inexpensive gray cast iron easy of working and having high thermal conductivity. The resultant molding is further subjected to perfect annealing, if necessary. By this method, the cast iron, improved in tensile strength and damping capacity and excellent in castability and machinability, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cast iron material having improved mechanical properties such as vibration absorption and tensile strength in die casting.

[0002]

2. Description of the Related Art Generally, cast iron is manufactured by sand mold casting with a low cooling rate in order to prevent chilling. There are two types of cast iron produced by sand casting and used as industrial materials: flake graphite-shaped gray cast iron and spheroidal graphite-shaped spheroidal graphite cast iron, depending on the shape of the graphite structure. The characteristic of gray cast iron is that it is a piece of graphite with a sharp tip, and when stress acts on it, stress concentrates on this sharp tip,
This is because the tensile strength becomes weak and it becomes brittle and breaks. But,
This flake graphite has high vibration absorption capacity, so-called damping capacity,
It is widely used as an important material for machine tools and precision parts.

On the other hand, spheroidal graphite cast iron is used as a tough member similar to steel because it has a high notch sensitivity and a low stress concentration because it has a spherical graphite shape and thus has a high tensile strength and high toughness. There is. However, this spheroidal graphite cast iron has a small vibration damping capacity like steel, and this is the greatest drawback.

[0004]

By the way, recent industrial members are strongly required to be light, thin, short and small, but it is difficult to cope with these problems by the conventional cast iron sand mold manufacturing technology. Therefore, in recent years, a casting technique using a mold has been researched, but since the cooling rate of the mold is high, the cast iron is chilled, and therefore the mold temperature is 473 ° K.
There is a problem that the following die casting becomes difficult. In particular, in thin-walled cast iron (5 mm or less), rapid solidification by a mold causes a chill structure (carbon does not graphitize and becomes a cementite, which is a hard and brittle metal structure).
Die casting has become difficult. However, if die casting is possible, significant cost reduction and improvement of working environment can be expected.

The present invention has been made in view of the above problems, and has improved physical properties such as tensile strength and damping capacity.
Moreover, it is an object of the present invention to provide a method for producing cast iron, which can be realized by die casting so that cast iron is excellent in casting and cutting workability and can be manufactured at low cost.

[0006]

In order to achieve such an object, in the method for producing cast iron of the present invention, the chemical composition of the cast iron melt is hypereutectic composition [carbon saturation: Sc =% C / (4. 26
-0.31% Si-0.33% P + 0.18 (% Mn-
1.76% S)) indicates a composition of 1 or more]],
0.1 to 0.3% of Ti is added to this, followed by Sr, C
A Si-based alloy containing 10% or more of a metal such as a, Ce or Ba alone or a Si-based alloy containing 10% or more of a mixture of these metals is used alone or in combination to form 0.4 to
1.7% is added, and this is poured into a mold of 473 ° K. or less to be molded to produce cast iron in which pseudo-spheroidal graphite and fine flake graphite structure are mixed.

The term "pseudo-spherical graphite" as used herein means a lump of graphite having octopus-shaped legs at the interface with respect to spherical graphite having a relatively smooth interface (drawing-substituting photographs shown in FIGS. 1 to 8). reference). Further, as the Si-based alloy, a type containing the above metal alone in an amount of 10% or more (for example, Sr-Si)
And a type (for example, Sr-Ca-Si) containing 10% or more of the above-mentioned metals were prepared. The case where the Si-based alloy is used alone means that one type of alloy belonging to any of these types is added. When used in combination, they are combinations of the same type or different types, and two or more alloys are added. Then, if necessary, it is effective to further perform complete annealing after molding with the mold.

To achieve the above object, the method for producing cast iron according to the present invention is characterized in that the chemical composition of the cast iron molten metal is hypereutectic composition [carbon saturation: Sc =% C / (4.26-0.31%). S
i-0.33% P + 0.18 (% Mn-1.76%
S)) shows a composition with a value of 1 or more].
0.1 to 0.3% is added, and then Sr, Ca, Ce,
Si-based alloys containing 10% or more of metals such as Ba alone and Si containing 10% or more of a mixture of these metals
0.4 to 1.7% is added to the system alloy alone or in combination, and 0.5 to 1.5% is further added to the graphite spheroidizing agent, which is poured into a mold of 473 ° K or less. By doing so, the cast iron in which fine spheroidal graphite and fine flake graphite structure are mixed is manufactured. That is, this means is characterized by adding a graphite spheroidizing agent to positively generate spherical graphite. Then, if necessary, it is effective to further perform complete annealing after molding with the mold.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The method for producing cast iron having fine pseudo-spherical graphite and fine flake graphite or the cast iron having fine spherical graphite and fine flake graphite of the present invention is a cast iron of hypereutectic composition having carbon saturation of 1 or more. Immediately before pouring into the molten metal at 1723 ° K ~
At 1773 ° K, 0.1 to 0.3% of Ti is added, and subsequently Si-based alloys containing 10% or more of Sr, Ca, Ce, Ba, etc. are used individually or in combination to obtain 0.4 to 1%. .7
%, And for the purpose of spheroidizing graphite, a graphite spheroidizing agent is added in an amount of 0.5 to 1.5%, and the pouring temperature is 1623.
The temperature is set to about 1673 ° K. Casting is performed using a gray cast iron mold coated with acetylene smoke as a release material.

The reason why the mold is made of gray cast iron is that it is easy to process and has better thermal conductivity than steel, so that the mold life is long and the cost is low. Ti or Si
Silicon oxide in the molten metal is reduced (Si
The lower limit is the temperature of (O ₂ + 2C → Si + 2CO), and the upper limit is to prevent useless heating energy.

Further, the lower limit and the upper limit of the addition amount correspond to changes in the melt components, and the smaller the amount of impurities such as oxide film adhering to the raw material, the less the amount may be. Especially,
The lower limit of the amount of Ti added is when using clean raw materials,
The upper limit is limited because addition of more than this value produces a Ti compound and cures. The addition amount of the graphite spheroidizing agent depends on the content of the spheroidization-inhibiting element such as S in the molten metal. If the amount is small, the addition amount is small, and if the amount is large, the addition amount is large. Since it is economically disadvantageous, the upper limit is set.

[0012]

The present invention will be described in more detail in the following examples. Note that the present invention is not limited to the following examples. The production of cast iron consisting of pseudo-spherical graphite and fine flake graphite is performed by melting a predetermined amount of pig iron using a high frequency electric furnace,
Ferrosilicon, steel materials, etc. were added to this to prepare a hypereutectic composition molten metal. Its chemical composition is 3.85% C, 2.93.
% Si, 0.15% Mn, 0.063% P, 0.025
% S. Fe-Ti (4
5%) alloy is added in an amount of 0.2% as Ti content, followed by Si
(45%)-Ca (12%)-Ba (12%)-Al
Add 1% of (20%) silicon alloy to 100
A (vertical) × 100 (horizontal) × 5 (thickness) mm test body was cast in a mold (made of gray cast iron, preheating temperature 333 ° K).

FIG. 1 (micrograph with a magnification of 100 times) and FIG. 2 (micrograph with a magnification of 500 times) show the as-cast structure composed of this pseudo-spherical graphite and fine flake graphite. In addition, after forming with a die, complete annealing was further performed at 1173 ° K. FIG. 3 (micrograph with 100 × magnification) and FIG. 4 (micrograph with 500 × magnification) show the structure of cast iron composed of pseudo-spherical graphite and fine flake graphite that have been completely annealed. In each figure, a lump that looks relatively black and large is pseudo-spherical graphite.

Further, in the production of cast iron composed of spheroidal graphite and fine flake graphite, in the above case, 1.0% of a graphite spheroidizing agent was added after the addition of the Si-based alloy, and casting was performed in the same manner as described above. . FIG. 5 (micrograph at 100 × magnification) and FIG. 6 (micrograph at 500 × magnification) show the as-cast structure made of this spherical graphite and fine flake graphite. In addition, after forming with a die, complete annealing was further performed at 1173 ° K. FIG. 7 (micrograph with a magnification of 100 times) and FIG. 8 (micrograph with a magnification of 500 times) show the structures of cast iron composed of pseudo-spherical graphite and fine flake graphite that have been completely annealed. In each figure, the lumps that appear relatively black and large are spheroidal graphite. It can be seen that graphite is growing more as it is cast into the ferrite matrix.

Cast iron composed of pseudo-spherical graphite and fine flake graphite,
And, for cast iron composed of spheroidal graphite and fine flake graphite,
9 and 10 show changes in physical properties of the as-cast metal in the mold and complete annealing at 1173 ° K. In these figures, as reference values, sand cast iron (JIS FC200) and spheroidal graphite cast iron (JI) are used.
S FCD450) is also shown. FC2
00 and FCD450 cannot be manufactured by die casting.

As can be seen from FIG. 9, gray cast iron (FC2
As for the annealed sample (00), it is unavoidable that the value is high because it is due to sand mold casting (however, in FIG.
0 is inferior in tensile strength), compared to others,
With the cast iron according to the example, it is possible to obtain a result having a comparable damping ability. In particular, cast iron composed of spheroidal graphite and fine flake graphite
In the one annealed at 173 ° K, a result having a damping ability higher than that of gray cast iron (FC200) as cast was obtained.

Further, as can be seen from FIG. 10, spheroidal graphite cast iron (FCD450) is unavoidably high in value because it is produced by sand mold casting (however, in the damping capacity as shown in FIG. 9). The cast iron according to the example has a tensile strength comparable to that of the others. That is, from the above results, the cast iron according to the example was manufactured as a cast iron having both good tensile strength and good damping capability at the same time in die casting.

[0018]

As described above, according to the method for producing cast iron of the present invention, in mold casting, cast iron in which pseudo-spheroidal graphite and fine flake graphite structure are mixed, or spherical graphite and fine flake graphite is used. Since cast iron having a mixed structure can be produced, physical properties such as tensile strength and damping capacity can be improved. In particular, both tensile strength and damping capacity can be excellently provided at the same time, and epoch-making cast iron in die casting can be provided. Also, since it can be manufactured by die casting, casting is easy, machinability is excellent, manufacturing cost is also low, and much lower cost production is possible by direct injection of blast furnace molten pig iron, etc. Has various effects. In addition, when complete annealing is further performed after molding with a mold, physical properties such as tensile strength and damping capacity can be further improved.

[Brief description of drawings]

FIG. 1 is a drawing-substitute photomicrograph (magnification: 100 times) showing a structure as cast in a mold composed of a ferrite matrix in which pseudo-spherical graphite and fine flake graphite are crystallized.

FIG. 2 is a drawing-substitute photomicrograph (magnification: 500 times) showing a structure as cast in a mold composed of a ferrite matrix in which pseudo-spherical graphite and fine flake graphite are crystallized.

FIG. 3 is a drawing-substituting micrograph (magnification: 100 times) showing a structure that was completely annealed after being cast into a mold composed of a ferrite matrix in which pseudo-spherical graphite and fine flake graphite were crystallized.

FIG. 4 is a drawing-substituting micrograph (magnification: 500 times) showing a structure that was completely annealed after being cast into a mold composed of a ferrite matrix in which pseudo-spherical graphite and fine flake graphite were crystallized.

FIG. 5 is a drawing-substitute photomicrograph (magnification: 100 times) showing a structure as cast in a mold composed of a ferrite matrix in which spheroidal graphite and fine flake graphite are crystallized.

FIG. 6 is a drawing-substitute photomicrograph (magnification: 500 times) showing a structure as cast in a mold composed of a ferrite matrix in which spherical graphite and fine flake graphite are crystallized.

FIG. 7 is a drawing-substitute photomicrograph (magnification: 100 times) showing a structure that was completely annealed after being cast into a mold composed of a ferrite matrix in which spheroidal graphite and fine flake graphite were crystallized.

FIG. 8 is a drawing-substituting micrograph (magnification: 500 times) showing a structure that was completely annealed after being cast into a mold made of a ferrite matrix in which spheroidal graphite and fine flake graphite were crystallized.

FIG. 9 is a graph showing the logarithmic decrement of each test piece according to the example, in which the larger the absolute value of the logarithmic decrement is, the larger the attenuation is.

FIG. 10 is a graph showing changes in tensile strength and hardness of each test piece according to the example.

[Explanation of symbols]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ikuhisa Takahashi 35-2, Iioka-shinden, Morioka-shi, Iwate 35-2 Iwate Prefectural Industrial Technology Center (72) Inventor Yuuo Yonekura 3 Iioka-shinden, Morioka-shi, Iwate Warrior No. 35-2 Iwate Prefectural Industrial Technology Center (72) Inventor Tatsuo Fukasawa 6 Minamiyaburo, Yahaba-cho, Shiwa-gun, Iwate Pref. 151 Ben Ben-Iwate Factory Co., Ltd. (72) Eiji Kajiwara 6 Minami-yaraku, Yahaku-cho, Shiwa-gun, Iwate Land allocation number 151 Ben Co., Ltd. Iwate factory

Claims (4)

[Claims] 1. The chemical composition of cast iron melt is hypereutectic composition [carbon saturation: Sc =% C / (4.26-0.31% Si-
0.33% P + 0.18 (% Mn-1.76% S)) indicates a composition of 1 or more], and Ti to 0.1
.About.0.3% added, followed by Si-based alloy containing 10% or more of metals such as Sr, Ca, Ce and Ba alone and Si-based alloy containing 10% or more of a mixture of these metals. Or 0.4% to 1.7% in a composite form and added by pouring into a mold of 473 ° K or less to form a cast iron in which pseudo-spherical graphite and fine flake graphite structure are mixed. A method for producing cast iron, comprising: 2. The method for producing cast iron according to claim 1, wherein complete annealing is further performed after forming with the mold. 3. The chemical composition of the cast iron melt is hypereutectic composition [carbon saturation: Sc =% C / (4.26-0.31% Si-
0.33% P + 0.18 (% Mn-1.76% S)) indicates a composition of 1 or more], and Ti to 0.1
.About.0.3% added, followed by Si-based alloy containing 10% or more of metals such as Sr, Ca, Ce and Ba alone and Si-based alloy containing 10% or more of a mixture of these metals. 0.4 to 1.7%, or 0.5 to 1.5% of a graphite spheroidizing agent, and 47
A method for producing cast iron, characterized by producing cast iron in which fine spheroidal graphite and fine flake graphite structure are mixed by molding by pouring into a mold of 3 ° K or less. 4. The method for producing cast iron according to claim 3, wherein complete annealing is further performed after forming with the mold.