JPH0146562B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a graphite nodularizing agent for hot metal for producing spheroidal graphite cast iron. Conventionally, in the production of spheroidal graphite cast iron, it has been desired to obtain a ferrite cast iron structure in an as-cast state. Therefore, various methods have been developed, such as 3-10% magnesium and 1.5% magnesium.
Spheroidal graphite cast iron using a graphite nodularizing agent containing ~4.0% calcium, 1.0~3.5% rare earth elements, 40~50% silicon, and ~2.0% aluminum and the balance iron The method of producing it is generally well known and has been quite effective. However, even if this graphite nodularizing agent is used, it is not possible to obtain a ferrite cast iron structure in the as-cast state when producing ultra-thin products using a sand mold or spheroidal graphite cast iron using a mold.
Cementite (Fe ₃ C) will be generated.
Therefore, after casting, it is necessary to perform heat treatment (annealing) to decompose the cementite, which causes various problems such as a significant increase in manufacturing costs and an increase in the size of manufacturing equipment. The present invention has been made against this background, and its gist is that 20 to 70% silicon, 0.01 to 3.0% aluminum, and 0.5 to 4.0% magnesium and 2.0%
less than or equal to calcium and less than 1.0% of rare earth elements;
and the balance iron, and the calcium/magnesium content ratio is 0.3 or less,
And the rare earth element/magnesium content ratio is 0.125~
0.3 is used to produce spheroidal graphite cast iron using a hot metal graphite nodularizing agent, which enables the production of spheroidal graphite cast iron using sand molds or molds. It became possible to obtain a ferritized cast iron structure as is. What is important about the graphite nodularizing agent for hot metal in the present invention is that 20 to 70% silicon (Si)
and 0.01~3.0% aluminum (Al) and 0.5~3.0% aluminum (Al)
4.0% magnesium (Mg), 2.0% or less calcium (Ca), less than 1.0% rare earth element (RE) (e.g. Mitsushi Metal whose main component is cerium), and the balance iron (Fe). In addition to containing these elements, the content ratio of calcium/magnesium (Ca/Mg) is 0.3 or less, and rare earth elements/magnesium (RE/Mg) content ratio is 0.3 or less.
The amount of calcium (Ca), magnesium (Mg), and rare earth elements (RE) is limited so that the content ratio of Mg) is 0.125 to 0.3, and the graphite spheroidizing agent has a specific content ratio. It is. Among these elements, if the ratio of magnesium is increased, the reaction becomes more intense, promoting the generation of magnesium oxide (MgO), reducing the yield of magnesium remaining in cast iron, and causing magnesium oxide itself to become intercalated in cast iron. As a result, the generation of chill (cementite) is promoted, resulting in a decline in product quality. On the other hand, if the proportion of magnesium is reduced, the effective spheroidization reaction will no longer occur. Therefore, in the present invention, it is important that magnesium is contained in a range of 0.5 to 4.0%, particularly preferably
It should be contained in a range of 1.5 to 3.0%. In addition, calcium (Ca) acts as a magnesium reaction inhibitor and also has an inoculating effect, so it is necessary to add it to some extent, but if it is added in excess, it will suppress the magnesium reaction too much and the spheroidization reaction will not occur. There is a risk that it will become uniform. Therefore, in the present invention, it must be contained at a ratio of 2.0% or less. Furthermore, rare earth elements (RE) have the effect of neutralizing impurities in molten metal, such as sulfur, so it is necessary to add a certain amount, but if added in excess, it promotes the formation of cementite (chill). Therefore, it is undesirable. Therefore, in the present invention, it is necessary to contain it at a ratio of less than 1.0%. Incidentally, the rare earth element contained according to the present invention may be a lanthanum group (lanthanide) existing in a metallic state, and its main components are cerium (Ce) and lanthanum (La). Further, this rare earth element (RE) may be added in the form of a compound without any problem. Among these elements, the amounts of calcium, magnesium, and rare earth elements are adjusted so that the calcium/magnesium content ratio is 0.3 or less and the rare earth element/magnesium content ratio is 0.125 to 0.3, It is necessary to set a specific content ratio. In other words, the graphite spheroidizing agent for hot metal according to the present invention has a major feature in that the ratio of calcium and rare earth elements to magnesium is significantly lowered by a certain percentage compared to those used conventionally. It has the following. For example, conventionally, magnesium is 3%, calcium is 1.6% and rare earth elements are 1.5%.
In the present invention, for example, 2.6% magnesium and 0.5% calcium were used.
and rare earth elements with a ratio of 0.5%, and as a result, in the production of spheroidal graphite cast iron using molds, it has become possible to convert ferrite into as-cast iron, which was previously considered impossible. It has become possible to obtain a cast iron structure, and there is no need for heat treatment to generate cementite as in the past, resulting in a significant reduction in casting costs. Furthermore, if the graphite spheroidizing agent of the present invention is used, even in the production of ultra-thin spheroidal graphite cast iron by sand molding,
The generation of cementite can be suppressed, and a ferrite cast iron structure can be obtained in the as-cast state. In this way, in the production of ultra-thin products using sand molds or spheroidal graphite cast iron using molds, it has become possible to obtain a ferritic cast iron structure that does not generate cementite in the as-cast state, which reduces the shrinkage of the product. This makes it possible to prevent the formation of cavities and, in turn, to reduce the number of feeders, resulting in a significant improvement in product yield. This made it possible to achieve miniaturization. In addition, the present invention eliminates the need for annealing in a heat treatment furnace, which conventionally consumed a large amount of energy to decompose cementite, thereby saving gas, electricity, or heavy oil consumption. This is truly revolutionary, as it not only eliminates the risk of distortion at high temperatures due to heat treatment. In addition, in the graphite nodularizing agent for hot metal of the present invention, 20
It is also possible to replace part or all of the silicon contained at a ratio of ~70% with at least one element selected from the group consisting of nickel, copper, barium, and manganese. In this case, nickel and copper have the effect of improving the strength of cast iron, and barium has the effect of accelerating ferrite formation. Also, manganese, like nickel and copper, contributes to improving the strength of cast iron. EXAMPLES The present invention will be explained in more detail by way of examples below, but the present invention is not limited in any way by the description of these examples. Example 1 Hot metal (molten metal) having the composition shown below and a graphite nodularizing agent were reacted in a ladle at 1520°C. Then, the spheroidized molten metal was poured into a predetermined metal mold to obtain a spheroidal graphite cast iron product which had been made into ferrite as it was cast. Composition of hot metal Composition of graphite nodularizing agent C: 3.81% Mg: 2.5% Si: 1.53% Ca: 0.6% Mn: 0.40% RE: 0.4% (Mitsushi Metal) P: 0.035% Si: 46.4% S: 0.015% Al: 1.8% Fe: Balance Fe: Balance Example 2 Hot metal (molten metal) having the composition shown below and a graphite nodularizing agent are reacted in a ladle at 1500°C. Then, the spheroidized molten metal was poured into a metal mold to obtain a spheroidal graphite cast iron product which had been made into ferrite as it was cast. Composition of hot metal Composition of graphite nodularizing agent C: 3.74% Mg: 3.6% Si: 1.68% Ca: 0.8% Mn: 0.29% RE: 0.8% (Mitsushi Metal) P: 0.024% Si: 46.5% S: 0.018% Al: 1.6% Fe: Balance Fe: Balance Example 3 Hot metal (molten metal) having the composition shown below and a graphite nodularizing agent are reacted in a ladle at 1510°C. Then, the spheroidized molten metal was poured into a metal mold to obtain a spheroidal graphite cast iron product which had been made into ferrite as it was cast. Composition of hot metal Composition of graphite nodularizing agent C: 3.70% Mg: 3.0% Si: 1.38% Ca: 0.6% Mn: 0.25% RE: 0.5% (Mitshu Metal) P: 0.064% Si: 45.8% S: 0.016% Al: 1.7% Fe: Balance Fe: Balance Comparative Examples 1 to 3 Hot metal (molten metal) having the same composition as Examples 1 to 3
and the graphite spheroidizing agent shown below are reacted in a ladle at 1520°C, 1500°C and 1510°C, respectively. The spheroidized molten metal was then poured into a metal mold to obtain spheroidal graphite cast iron products.

[Table] The chemical components, mechanical properties, and product pass rates of the spheroidal graphite cast irons obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were investigated and shown in the table below. Further, a microscopic photograph of the spheroidal graphite cast iron obtained in Example 1 is shown in FIG. 1, and a microscopic photograph of the spheroidal graphite cast iron obtained in Comparative Example 1 is shown in FIG. 2.

[Table] As is clear from Fig. 1, no cementite is observed in the spheroidal graphite cast iron produced using the hot metal graphite nodularizing agent of the present invention, and the ferrite cast iron structure is clearly shown. . On the other hand, in spheroidal graphite cast iron manufactured using a conventional graphite nodularizing agent, a large amount of cementite is generated, as shown in FIG. In addition, as shown in the table, the spheroidal graphite cast iron produced by the graphite nodularizing agent of the present invention has much higher tensile strength and elongation than the conventional example, and can be used as a product as is. Therefore, there is a significant difference in the acceptance rate of the products.

[Brief explanation of drawings]

Figure 1 is a micrograph (150x magnification) showing the metal structure of spheroidal graphite cast iron produced using the hot metal graphite nodularizing agent of the present invention, and Figure 2 is a micrograph (150x magnification) showing the metal structure of spheroidal graphite cast iron produced using the conventional graphite nodularizing agent. This is a micrograph (150x magnification) showing the metal structure of spheroidal graphite cast iron.

Claims (1)

[Claims] 1 20-70% silicon, 0.01-3.0% aluminum, 0.5-4.0% magnesium, 2.0% or less calcium, and less than 1.0% rare earth elements,
and the balance iron, and the calcium/magnesium content ratio is 0.3 or less,
And the rare earth element/magnesium content ratio is 0.125~
A graphite spheroidizing agent for hot metal, characterized in that it is 0.3.