JPH1060572A - Fine graphite cast iron and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a fine graphite cast iron product excellent in machinability, strength and rigidity by a sand mold casting method by incorporating the molten metal of cast iron with Mn, Ti or the like together with a specified amt. of Bi or Te. SOLUTION: A raw material 1 such as a casting return scrap, casting cutting powder, steel sheet pressing chips or the like is charged to a melting furnace 3 and is melted, and the molten metal 5 of cast iron contg., by weight, 3.4 to 3.7%. C, 2.3 to 2.9%, Si, 0.1 to 0.9% P, 0.6 to 1% Mn, 0.05 to 0.2% S and 0.05 to 0.2% Ti is flowed into a holding furnace 4. Next, while the molten metal 5 is poured into a ladle 6, as the material 7 to be added, to 100 pts.wt. the molten metal 5, at least either 0.01 to 0.05 pts.wt. Bi or 0.001 to 0.01 pts.wt. Te and 0.2 to 1 pts.wt. Mn are added, by which the fine graphite cast iron product contg., by weight, 0.001 to 0.03% Bi or 0.0003 to 0.005% Te, 0.5 to 2% Mn and 0.05 to 0.2% Ti can easily be produced by sand mold casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine graphite cast iron and a casting technique therefor, which has high strength and high rigidity excellent in machinability and is particularly suitable for a sand casting method, and a method for producing the same. About.

[0002]

2. Description of the Related Art Fine graphite cast iron is generally cast by a die casting method utilizing rapid solidification during casting (Japanese Patent Publication No. 55-48).
No. 29) is used. In this method, casting is performed by utilizing rapid solidification when a high-temperature molten metal is poured into a mold.

Also, without using a costly mold casting method,
As a method for casting fine graphite cast iron in a sand mold, it is possible to cast sulfur in a sand mold by lowering sulfur to 0.05% or less, and to cast in a sand mold using a molten metal containing 0.3% or more of titanium. There are known ways to do this.

[0004]

In the above-mentioned mold casting method, a fine graphite cast iron material having good workability can be obtained by performing rapid solidification. Cast defects such as so-called chills, cracks and pinholes are likely to occur.

On the other hand, in the sand casting method, it is difficult to obtain a high-strength cast iron having sufficient workability. In the case of using a molten metal having a sulfur content of 0.05% or less, graphite is refined and the strength is improved by reducing the amount of sulfur, but it is necessary to perform a difficult outflow operation. When a molten metal containing 0.3% or more of titanium is used,
Titanium makes graphite finer and increases the strength, but the workability is significantly impaired by the increase in titanium compound.

Accordingly, an object of the present invention is to provide a fine graphite cast iron having high machinability, high hardness, high strength and high rigidity, and a method for producing the same.

[0007]

In order to achieve the above object, the present invention provides (a) bismuth of 0.001 to 0.03% by weight and tellurium of 0.0003 to 0.005% by weight, At least one of them, and (b) 0.5 to
2% by weight of manganese and (c) 0.05 to 0.2% by weight
And a fine graphite cast iron comprising: Bismuth and tellurium need only contain one of them, but they may contain both.

Further, in the present invention, a melting step of melting a material to be melted to form a molten cast iron;
As additives, (a) at least one of 0.01 to 0.05 parts by weight of bismuth and 0.001 to 0.01 parts by weight of tellurium, and (b) 0.2 to 1 part by weight
There is provided a method for producing fine graphite cast iron, comprising: an adding step of adding a part by weight of manganese to form a molten cast metal; and a casting step of casting the molten cast metal.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention,
By adding (1) an element that causes supercooling in the solidification process by adding to the molten metal, and (2) an element that suppresses white pig iron solidification due to supercooling without coarsening the graphite, By expanding the crystallization range of the fine graphite, it is possible to obtain fine graphite cast iron having high machinability, high hardness, high strength, and high rigidity. In the present invention, sufficient strength can be obtained even if 0.1 to 0.2% of sulfur, which is considered to reduce the strength by preventing graphitization, is obtained, so that it is not necessary to perform a difficult desulfurization operation. Further, this sulfur has an effect of further improving the workability of the fine graphite cast iron. Further, the content of titanium (which enhances strength by making graphite finer) which impairs processability can be reduced to 0.3% by weight or less.

As the supercooling promoting element of the above (1), magnesium is known. However, the effect of magnesium is hindered by the presence of sulfur in the molten metal. Therefore, when magnesium is used, desulfurization must be performed as a pretreatment. Therefore, in the present invention, bismuth and tellurium are employed as elements that exhibit an effect even in the presence of sulfur.

[0011] Further, as the element which inhibits white iron solidification due to the subcooling of (2), there are silicon, aluminum and the like. However, silicon has no effect because it promotes flake graphite solidification.
Aluminum impairs castability by forming an oxide film. Therefore, in the present invention, manganese which does not have such an adverse effect is used.

As the cast iron to which these additives are added,
For example, 3.4-3.7% by weight of carbon and 2.3-2.
9% by weight of silicon, 0.1-0.3% by weight of phosphorus,
Those containing 0.6-1% by weight of manganese, 0.05-0.2% by weight of sulfur, and 0.05-0.2% by weight of titanium.

The casting is desirably performed using a sand mold having good productivity. The melting step preferably includes a step of passing the molten cast iron through the carbon layer. This is because when the molten metal passes through a carbon layer (for example, a layer of carbon lump such as coke), the tendency to chill is reduced.

[0014] Further, as an additive to the molten cast iron, it is preferable to use a bismuth mass for adding bismuth, a tellurium mass for adding tellurium, and a ferromanganese particle for adding manganese. The order of addition of the additive (addition alloy) is as follows: first, an element that promotes supercooling (bismuth and / or tellurium) is added, and then manganese that suppresses white pig iron solidification without coarsening graphite is added. Although this is considered to be good for miniaturization of graphite, an experiment of actually adding graphite at the same time showed that graphite did not coarsen and that these elements could be added simultaneously.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. The configuration of the melting furnace, the composition of the molten cast iron, the amount of the additive, and the like are not limited to the following examples. Further, in the following examples, the sample is made of ferrite, but the present invention is not limited to this, and pearlite may be formed by performing relatively rapid cooling.

FIG. 1 shows steps from melting to addition of an additional alloy. In the present embodiment, a melting furnace 3 in which a carbon layer is formed by spreading a carbon lump 2 on a furnace bottom, a holding furnace 4 for holding a temperature of a molten metal, and a sand mold (not shown) for casting are used. An opening is provided at the lower part of the melting furnace 3 side,
A flow path 9 to the holding furnace 4 is connected to the opening.
In the present embodiment, a ladle 6 was used to cast the molten metal 5 accumulated in the holding furnace 4 into a sand mold.

First, a material 1 to be melted, which is composed of 40% by weight of cast material, 40% by weight of cast metal powder, and 20% by weight of pressed steel sheet, is placed in a melting furnace 3, and a heating coil 10 is energized. Then, the obtained cast iron molten metal 5 was poured into the holding furnace 4 through the flow path 9 and the heating coil 11 was energized to hold the molten metal 5 at 1743K. Next, while pouring the molten metal 5 held in the holding furnace 4 into the ladle 6, a predetermined amount of the additive alloy 7 was charged into the ladle 6. The casting melt 8 thus obtained is poured from the ladle 6 into a sand mold, the solidified casting is taken out of the sand mold, and kept at a temperature of 1173K for 1 hour in a heat treatment furnace to reduce the structure to a substantially complete ferrite ground. After that, the furnace was cooled to room temperature to prepare a cast specimen of fine graphite cast iron having a diameter of 30 mm and a length of 200 mm. However, as shown in Table 1, bismuth and manganese were used as additive alloy 7 in Example 1,
In Example 3, tellurium and manganese were charged, and in Example 3, bismuth, tellurium, and manganese were respectively charged.

In this embodiment, bismuth mass is used as the bismuth-added alloy 7, tellurium is used as the tellurium-added alloy 7, and ferromanganese particles are used as the manganese-added alloy 7 (JIS symbol FMnH1, particle size f: FMn in Table 1). ) Was added to the ladle 6, and a mixture of all kinds of additive alloys 7 to be added was previously mixed. The amount of addition shown in Table 1 indicates that the amount of
The value is based on 0 parts by weight.

As a comparative example, a casting sample was obtained in the same manner as in the present example except that the additive alloy 7 was not added. This comparative example is also shown in Table 1.

[0020]

[Table 1]

Table 2 shows the analytical values of the chemical components of the casting samples obtained in each of the examples and comparative examples. The yield of bismuth and tellurium is generally said to be 10 to 50% by weight.

[0022]

[Table 2]

Table 3 shows the results of measuring the mechanical properties of the casting samples obtained in each of the examples and comparative examples. In this example and the comparative example, since the sound speed is proportional to the Young's modulus of the material if the material is a homogeneous material, the sound speed is used to indicate rigidity (Young's modulus). The ultrasonic method was used to measure the speed of sound.
The test piece was cut into 70 mm, and the time required for an ultrasonic wave having a frequency of 4 MHz to reciprocate in the test piece was measured to calculate the sound velocity.

[0024]

[Table 3]

As can be seen from Table 3, all of the samples of Examples 1 to 3 did not contain the additive alloy 7 in all of hardness, tensile strength and sound speed despite the ferrite ground (Comparative Example). ), And the effect of the additive alloy 7 was remarkable.

[0026]

According to the present invention, a fine graphite cast iron having good machinability, high hardness, high strength and high rigidity can be obtained. In the present invention, by adding an element that causes supercooling in the solidification process and an element that suppresses white iron solidification due to supercooling, carbon, silicon, and even a relatively high material of sulfur, hardness, tensile strength and The rigidity can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method for producing fine graphite cast iron in an example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Material to be melted, 2 ... Carbon lump, 3 ... Melting furnace, 4 ... Holding furnace, 5 ... Molten metal, 6 ... Ladle, 7 ... Additive, 8 ... Molten metal for casting, 9 ... Molten metal flow path, 10 ... heating coil, 11 ... heating coil.

Claims (4)

[Claims] (A) at least one of 0.001 to 0.03% by weight of bismuth and 0.0003 to 0.005% by weight of tellurium; and (b) 0.5% of tellurium.
A fine graphite cast iron comprising manganese in an amount of up to 2% by weight and (c) titanium in an amount of 0.05 to 0.2% by weight. 2. A melting step in which a material to be melted is melted into a cast iron melt, and the following (a) and (b) are added to 100 parts by weight of the cast iron melt.
An additive step of adding an additive of
(A) 0.01 to 0.05 parts by weight of bismuth, and
(B) 0.2 to 1 part by weight of manganese of 0.001 to 0.01 part by weight of tellurium. A casting step of casting the molten metal for casting. Manufacturing method of graphite cast iron. 3. The method for producing fine graphite cast iron according to claim 2, wherein the casting is performed using a sand mold. 4. The method for producing fine graphite cast iron according to claim 2, wherein the melting step includes a step of passing the molten cast iron through a carbon layer.