JPS6157106B2 - - Google Patents

Description

[Detailed Description of the Invention] In the production of ductile cast iron, Mg, which reacts extremely violently and is easily combustible, is alloyed and spheroidized in a ladle to increase the yield of Mg, or in a sealed high-pressure container. There are many known methods for increasing the yield and saving Mg by adding Mg, and there is too much time to list them. Various methods have been studied. This in-mold spheroidization method consists of a casting method equipped with a specially prepared reaction chamber and straining function, as shown in Japanese Patent Publication No. 46-16260 (see Figure 1), in which granular powder is formed. There is a known method for manufacturing ductile castings by placing a crushed spheroidizing agent into contact with the spheroidizing agent in a mold by injecting a base water of ductile cast iron whose composition has been adjusted. In this prior art, as shown in Japanese Patent Publication No. 57-21004, the phenomenon of flowing away due to the flow of molten Mg alloy with light specific gravity occurs, so the volume of the reaction chamber is made sufficiently large, and the flowing out that occurs occurs. Because it was necessary to use a sufficiently large scouring method to remove particles and oxides, the casting method had a disadvantage in that the yield was lower than that of ductile casting, which is made by pouring Mg-treated molten metal in a ladle. . However, this method of spheroidizing in a mold has many advantages over the method of casting Mg-treated molten metal in a ladle. This means that there is no need to take into account the so-called "fedeng" phenomenon, in which Mg disappears over time, and that it is possible to create castings with a large number of graphite grains and no carbides, and it is possible to make cast irons with a large number of graphite grains without carbides. The point was that the yield was high. However, as mentioned above, this first developed prior art technology uses fine particles of about 3 m/m or less as the Mg alloy, so it has the disadvantage of being easily floated and washed away. When using a sand mold line containing 2 to 6% moisture, which is commonly used to use fine particles and is called a green sand mold making line, the time required from installing the fine particulate Mg alloy to pouring the mold is There were also some restrictions. This is because these sand molds are used repeatedly, so they have a certain amount of heat, and there is water vapor inside the molded green sand mold, which may oxidize the active Mg particles with a large surface area ratio that have been inserted in advance. Therefore, it was not recommended to leave it for a day or night. In other words, by using fine particulate Mg alloys, there are slosh defects caused by suspended particles, defects partially caused by segregation of Mg and Si, and apparent volume reduction due to particulates. There were problems such as a decrease in the casting method yield due to the increase in the reaction chamber and the complexity of the dust removal mechanism, the possibility of surface oxidation in the green sand mold, and problems with alloy crushing and handling during storage. Furthermore, as shown in Japanese Patent Publication No. 46-16260, it is stated that a spheroidizing agent made of Mg alloy is crushed and then solidified, or it is extruded and compressed and used as an integrated molded product, but it is extremely active.
After turning Mg alloy into powder, it is processed into resin, water glass,
According to the research of the inventors, even if it is hardened by various methods such as starch glue, organic binder, inorganic binder, etc., it does not dissolve at all due to surface oxidation, and this is because even if it is crushed in an inert gas atmosphere. The surface oxidizes during the hardening process, making it completely impractical. Note that wax, which is hardened with solder, may appear to melt, but this is a so-called phenomenon called "barakel" and does not mean that it gradually melts from the surface. For this reason, after turning the spheroidized Mg alloy into powder,
No method of solidifying it in any way has been put to practical use. In order to correct the drawbacks of the manufacturing method of in-mold ductile cast iron using such a particulate Mg alloy, a spheroidizing treatment using an integrated modifier as shown in Japanese Patent Publication No. 57-21004 has been proposed ( (See Figure 2) This had the following imperfections. It is inevitable that the upper part of the cast spheroidizing agent fitted into the recess with which the molten metal to be treated comes into contact has a thin oxide film because it is cold hardened in the mold. This means that even when cast using a metal mold, graphite mold, water-cooled copper mold, or any other type of mold, the surface always has an oxide film.
This was well known in the casting of Mg-Ca-RE. In addition, when the molten metal to be treated flows over the surface of the cast and cold-hardened spheroidizing agent that is placed in the recess, the molten metal reacts with the Mg contained in the mold. The aim was to obtain spheroidized graphite cast iron within the reactor, but it was discovered that the reaction was momentarily delayed due to the surface oxide film. Furthermore, it has been found that a certain amount of time is required before the cast, cold-hardened spheroidized block is preheated by the injected molten metal and a full-scale reaction begins. The above two points were decisive flaws when implementing this in-mold spheroidization method. In other words, due to improved efficiency in recent automatic pouring lines and ladle pouring, the pouring time has traditionally been 13 to 20 minutes.
Time periods of about seconds have been shortened to about 4 to 10 seconds. This means that the first molten metal that passes through the injected metal does not react sufficiently with Mg, and as a result, in the mold, graphite may be spheroidized or not fully spheroidized. It has not been put into practical use in Japan because it is unreliable as there are places where it is not inspected, and it requires inspection for each frame. The present invention provides a system that can guarantee a completely uniform Mg reaction even in the very early stage of injected molten metal. To describe the details according to the present invention (see Fig. 3), the upper part of the graphite spheroidized Mg alloy block that is fitted into the recess directly below the sprue in the sand mold and cast is not a smooth casting surface, but always has an uneven surface. It consists of installing a cast block with a certain room-temperature fracture surface, and is also designed to increase reactivity by intentionally increasing the Mg concentration inside the cast block from the outer periphery. be. This segregation of Mg into the interior does not result in a sudden increase in the Mg concentration, but rather in such a way that it gradually becomes higher than in the outer periphery. The reason why this must be done is as follows. The Mg concentration in the central core was increased by 6% in the Mg alloy for graphite spheroidization used in normal molds.
It is said that Mg level is suitable. However, for the reasons mentioned above, the reactivity is 6%, and in a block with a surface oxidation layer facing the cold and hard mold, the reactivity is too low to make the instantaneous flowing initial molten metal into spheres. be. According to the inventors' research, more than 8% of Mg is
It is necessary for the initial molten metal. However, the overall Mg concentration of the cast block was reduced to 8%.
Based on the above, if the reaction in the mold starts after the initial molten metal has passed, then
If the strength is too strong, the reaction vapor may blow out of the mold or boil inside the mold, which is not good, so we consciously made Mg highly unevenly distributed in the center.
This point is said to provide sufficient guarantee for the Mg reaction in the initial molten metal without increasing the temperature.
The technical idea is fundamentally different from the method shown in 21004, which uses an integral modifier in which the molten metal contact surface is cold-hardened and has no homogeneous Mg segregation. Furthermore, in the case of the present invention, the surface in contact with the molten metal is always crushed at room temperature to expose a surface with no oxide film, and by creating an uneven surface by crushing, the rapid response to the initial reaction can be improved. The aim is to increase the reaction area. These Mg alloy blocks, in which Mg is segregated in the center, used in the present invention can be easily produced by heating the mold with a high-frequency heat source or by using a mold whose outer periphery is sufficiently preheated. can be put in. In this way, increasing the central concentration of Mg. The molten metal contact surface is a room-temperature fracture surface. The molten metal contact surface is made uneven to increase the reaction area. Due to the above reasons, even in the case of high-speed, short-time casting where the injection speed is extremely high, there is no uncertainty in the Mg content of the initial molten metal because the Mg reaction in the initial molten metal is guaranteed. Therefore, it is no longer necessary to overflow and waste the initial molten metal, so-called pouring, refluxing in the mold, etc., which can lead to deterioration of the casting method yield, and improve the casting method yield. In addition, it is possible to reliably produce a casting without variation in the degree of spheroidization in the preliminary casting region and the final casting region. This method can also be used to completely spheroidize molten metal that has undergone RE treatment or Mg treatment in a ladle, so it has an extremely wide range of industrial applications. be. Next, examples will be shown. Example: Using a sand mold as shown in Figure 4, the size and width of the reaction chamber,
46mm length, 46mm depth, 1 is 30mm, 2 and 3 are 20m/
A reaction chamber of m was made, and C.3.7%, Si.2.4%, Mn.0.3%, P.0.035 were melted in a 300Kg high-frequency furnace.
% and S.0.015% were each treated to form spheroids in the mold using the following method, and the state of foreign matter entrapment and spheroidization in each product part was investigated. The capacity of the cast ductile source water in the sand mold is 15 kg. 1 Mg alloy powder consisting of Mg.6.5%, Ca.0.8%, RE.1.5%, Si.46% less than 2m/m at 0.8%120
Put 4 g of the molten metal into the reaction chamber, and add 15 kg of the above-mentioned molten metal to it.
Cast in seconds. 2 Mg alloy consisting of Mg.6.7%, Ca.0.8%, RE.1.4%, Si.45%, width 4.5cm x 4.5cm, height 17mm
The above-mentioned molten metal (15 kg) was cast in the same 4 seconds by setting the cast material in the upper and lower quenching hard molds. 3 If analyzed after rapid cooling, Mg.6.5%, Ca.0.7%,
Width: Mg alloy consisting of RE.1.4% and Si.46%.
4.5cm x 4.5cm, height. When casting into a 17 mm graphite mold, the components in the core are solidified while being heated by a high-frequency heating device wrapped around the outside of the graphite mold.
Mg.8.9%, Ca.0.9%, RE.1.4%, Si.45%, outer peripheral components are Mg.5.6%, Ca.0.6%, RE.1.4%,
A block made by breaking the upper part at room temperature after solidification consisting of 46% Si was set, and 15 kg of the aforementioned molten metal was poured in the same 4 seconds. The results are as shown in Table 1, in which the spheroidization rate and the state of entrainment of undissolved matter and oxides were investigated using a microscope for the parts No. 1 to No. 11 shown in FIG. 【table】

[Brief explanation of the drawing]

FIGS. 1 and 2 are longitudinal sectional views of a sprue system showing the installation status of graphite spheroidized Mg alloy in a green sand mold used in the prior art. FIG. 3 is a longitudinal sectional view of the sprue system showing the installation status of the graphite nodularized Mg alloy in the green sand mold used in the present invention. Figure 4 shows the first method for comparison with the method of the present invention.
FIG. 2 is a central cross-sectional elevational view of a green sand mold device tested using the same sprue system as the prior art shown in FIGS.

Claims (1)

[Scope of Claims] 1. In the solid graphite spheroidizing agent used in the process of in-mold graphite spheroidizing treatment during the production of ductile cast iron, casting solid graphite spheroidizing agent that comes into contact with molten metal placed in a sand mold. The upper surface of the agent should not be the casting surface, but should be the room-temperature fracture surface after casting. The upper surface of the cast solid graphite spheroidizing agent that comes into contact with the molten metal placed in the sand mold is formed into a deeply uneven surface. To segregate the Mg concentration of the cast solid graphite spheroidizing agent that comes into contact with the molten metal placed in the sand mold so that the Mg concentration is low at the outer periphery and high at the central core. A solid graphite spheroidizing agent with a high segregation of Mg is placed in the sand mold at a predetermined position in the center core where the reaction surface has deep irregularities due to the room-temperature fracture surface exposed and the reaction surface is exposed as described in ~ above, and the composition is adjusted. A method of making ductile cast iron in a mold by injecting the ductile base water.