JPH0580523B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a metal material having a refined crystal structure, and is particularly directed to metals and alloys with relatively high melting points such as iron and nickel-based alloys. The present invention relates to a method for producing a finely crystalline metal material using a self-fusing stirring rod without contaminating foreign matter. [Conventional technology] In addition to powder metallurgy, casting methods such as mold rotary scraper solidification and rheocasting have been known as methods for manufacturing metal materials with finer grains without adding chemical elements. ing. The former mold rotary scraper solidification method uses a mild steel stirring rod to stir the molten aluminum alloy during solidification, while the latter rheocast method uses a ceramic material such as alumina that does not chemically react with the molten metal after melting the alloy material. A stirring rod is used to stir during solidification. In all of these types of methods, the molten metal is stirred with a stirring rod, but in this case, there are the following problems. That is, the above-mentioned stirring rod is made of a material that is excellent in heat resistance and high-temperature strength, but especially when targeting a high melting point metal alloy,
Part of the stirring rod may melt during stirring, or may be scraped or damaged during stirring during solidification, and may be mixed into the molten metal. In order to solve these problems, the present inventors experimentally stirred various molten metals using stirring rods made of various materials. However, in the case of iron or nickel-based alloys that melt at higher temperatures, not only will the strength at high temperatures be insufficient, but the graphite in the stirring rod and the molten metal will chemically react and form carbides. I made it and confirmed that it mixed into the molten metal. It was also found that even if a stirring rod made of other ceramics or the like is used, when the solid phase increases due to solidification, it is scraped off and mixed into the molten metal. [Problems to be Solved by the Invention] An object of the present invention is to completely eliminate contamination of molten metal material due to breakage of the stirring rod during rotational agitation solidification in the production of the above-mentioned fine crystalline metal material targeting the high melting point material. The present invention aims to provide a method for manufacturing a metal material having a homogeneous fine microstructure and having a desired chemical composition. [Means and effects for solving the problems] In order to achieve the above object, the method for producing a finely crystalline metal material of the present invention includes inserting a stirring rod into the molten metal, and inserting the stirring rod into the molten metal during the cooling process of the molten metal. The method is characterized in that a self-fusing stirring rod made of a material having the same composition as the molten metal is used to stir the molten metal when rotating to refine the crystal grains. In this way, if a self-fusing stirring rod made of a material with the same composition as the molten metal is used, even if part of the stirring rod melts, is scraped off, or is damaged by contact with the solid phase during solidification, the molten metal There is no contamination of the material, and a metal material with a homogeneous fine microstructure having a desired chemical composition can be produced. In addition, the stirring rod that is rotating at high speed is more likely to be heated by the molten alloy and partially melted than the crucible that contains the molten metal, and the fragments of the stirred rod that have melted are likely to be broken into many fine pieces. When stirred, the particles become uniformly dispersed in the molten metal and become suspended, but since their temperature is close to the solidification temperature and lower than that of the bulk liquid, they become nucleation sites and multiple fine particles are generated simultaneously. Because of the large number of crystals, the growth of each crystal is suppressed, resulting in fine crystals. That is, the fine particles of the agitated stirring rod effectively act on the generation of a homogeneous fine microstructure, making it possible to obtain a metal material with an even more homogeneous fine microstructure. The above-mentioned self-fusing stirring rod is generally made of a material with exactly the same composition as the molten metal. In cases where it is not necessary to maintain the temperature, the composition may be the same as that of a molten metal that does not contain such reinforcing materials. [Example] Below, a manufacturing apparatus for a finely crystalline metal material used to carry out the method of the present invention and the results of experiments conducted using the apparatus will be described. FIG. 1 shows a sectional view of the above manufacturing apparatus. In the apparatus shown in the figure, a chamber main body 1 having an opening/closing door on the front constitutes a vacuum container, and the inside thereof is divided into upper and lower parts by molybdenum shutters 2 expanded by an air cylinder 3. A tungsten heating furnace 5 is disposed inside, and a water-cooled outer cylinder 7 and a stirring rod 9 hanging from above inside the cooling outer cylinder 7 are arranged in an upper cooling chamber 6, and this stirring rod 9 is driven by a torque motor. It is attached to a rotating shaft 10 that is rotationally driven. As described above, the stirring rod 9 is made of a metal or alloy material having the same chemical composition as the molten metal, that is, a self-fusing stirring rod is used. In addition, in the figure, 15 is a reflector, 16 is a viewing window, and 17
indicates the temperature measurement port. In this device, the inside of the chamber body 1 is connected to a vacuum source (not shown), and after evacuation, the test material is heated and melted in an alumina crucible 12 in a furnace, and after the melting, the shutter 2 on the furnace is opened. Then, the alumina crucible 12 is raised into the water-cooled outer cylinder 7 by a crucible lifting mechanism that allows the support rod 11 passing through the lower surface of the chamber body 1 to be raised and lowered, and the self-soluble stirring rod is inserted into the molten metal in the crucible 12. 9 is inserted, and the semi-solidified test material is stirred by the rotation of the stirring rod 9 during the rapid cooling process in the cooling chamber 5. In this case, first, the stirring rod 9 was inserted into the crucible 12 and started rotating immediately, and during the cooling process of the molten metal in the crucible 12, the stirring rod 9 was rotated at a low speed until the material reached almost the solidification start temperature. At times, the rotational speed of the stirring rod is increased to perform high-speed rotational stirring to crush and refine the formed crystals. Therefore, the above-mentioned high-speed rotation is continued until the latter half of solidification or, at the longest, just before the end of solidification, and the stirring rod is pulled out from the sample material before solidification. Since the stirring rod 9 is made of a metal or alloy having the same composition as the test material, it may be partly melted or partly scraped off by contact with the molten metal during the above-mentioned stirring. , this does not change the chemical composition of the test material. Furthermore, the fine particles of the agitated stirring rod effectively act on the generation of a homogeneous and fine microstructure. Next, an experimental example using the above device will be explained. To operate, first, about 1 kg of flaky graphite cast iron strips having the chemical composition shown in Table 1 are heated to
The alumina crucible 12 is placed in an alumina crucible 12 with a diameter of 55 mm on the lower surface, an outer diameter of 83 mm, and a depth of 130 mm, and is loaded into the lower tungsten heating furnace 5 in the chamber body 1 of the apparatus shown in FIG. 1×
After evacuation to 10 ^-5 torr or less, the sample was resistance heated and vacuum melted.

[Table] For this melting, in order to uniformly heat the alumina crucible 12 in the tungsten heating furnace 5, it was placed in an outer graphite crucible 13. Temperature measurement was performed by connecting a recording device to a Pt94%Rh6%-Pt70%Rh30% thermocouple 14 with a diameter of 0.5 mm whose tip was disposed on the bottom of the alumina crucible. When heating the sample, melting of the sample was confirmed using the recording device, and the molten metal was held at 100°C for 30 minutes just above the liquidus temperature (1188°C) of flaky graphite cast iron to homogenize it. At this point, the shutter 2 directly above the heating furnace 5 is opened, and the crucible lifting mechanism raises the crucible 12 containing the molten metal, and a stirring rod 9 made of flaky graphite cast iron having the same composition as that of the molten metal is placed in the water-cooled outer cylinder 7. Insert the stirring rod 9
The ascent of the crucible was stopped when the lower end of the crucible reached a position 10 mm above the inner bottom surface of the crucible 12. Next, while cooling the sample, stir the stirring bar 9.
The stirring rod 9 was rotated at a relatively low speed of 1000 rpm or less (approximately 900 rpm), and the rotation speed of the stirring bar 9 was gradually increased and finally maintained at a constant speed of several stages between 2000 and 4200 rpm. At this time, in order to prevent as much as possible the semi-solidified material from scattering out of the crucible 12 due to the sudden increase in speed of rotational agitation, the rate of increase in the number of rotations was kept constant. Thereafter, rotational stirring was continued at the above-mentioned constant speed for an appropriate time depending on the sample, and the sample was lowered by the crucible lifting mechanism at a point from the late stage of solidification to just before the completion of solidification (1116°C), thereby lowering the sample. Stirring rod 9
This prevented welding between the material and the sample. For comparison, a standard sample was prepared by removing the stirring rod and letting the molten metal naturally solidify in the water-cooled outer cylinder 7. The photograph in Figure 2 (magnification: 100x) shows the microstructure of flake graphite cast iron FC20 solidified by rotational stirring with the final rotational speed of the stirring bar being 3000 rpm.
In this case, 260 seconds after completion of insertion of the stirring bar, the sample was immediately lowered by the crucible lifting mechanism to prevent welding of the sample and the stirring bar. Observing the sample shown in Figure 2 when the stirring bar is at 3000 rpm, the width of one flake graphite is approximately
The matrix itself has a microstructure consisting of very fine crystal grains of approximately 30 μm or less. Furthermore, as can be seen from this photograph, no foreign matter was observed entering the sample from the stirrer, indicating that the microstructure was clean. Furthermore, X-ray microanalyzers and chemical analyzes have also revealed that flake graphite cast iron
It was confirmed that the FC20 sample was extremely clean. Therefore, it was confirmed that a very fine and clean microstructure could be obtained by the above-mentioned rotational stirring. The photograph in Figure 3 (magnification: 100x) shows the normally solidified microstructure (comparative example) of a standard sample of flake graphite cast iron FC20 obtained by sand casting the above sample. In this case, a microstructure consisting of large graphite flakes with a width of about 300 μm or more and a coarse matrix is observed. According to the structure observation of such experimental results, the third
Compared to the sand casting material shown in the figure, the rotary agitation solidified material shown in FIG. 2 has flaky graphite and matrix that are significantly more homogeneous and finer. In addition, there was no foreign matter mixed into the sample due to breakage of the stirring rod, which is often seen during rotational stirring solidification of high melting point materials, and it was possible to obtain a metal material with an extremely clean microstructure. [Effects of the Invention] According to the manufacturing method of the present invention detailed above, a stirring rod is inserted into the molten metal, and the stirring rod is rotated during the cooling process of the molten metal to refine the crystal grains automatically. By the extremely simple method of stirring with a soluble stirring rod, it is possible to obtain a metal material with the desired homogeneous fine microstructure without contamination by foreign matter.
In addition, the fine particles of the agitator rod that have been melted and damaged effectively act on the generation of a homogeneous and fine microstructure, making it possible to obtain a metal material with an even more homogeneous and fine microstructure.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of the configuration of a manufacturing apparatus used to carry out the method of the present invention, FIG. 2 is a photograph substituted for a drawing showing the micrometallic structure of flaky graphite cast iron obtained by the method of the present invention, and FIG. The figure is a photograph substituted for a drawing showing the micrometallic structure of similar flaky graphite cast iron when molten metal is cast into a sand mold. 9... Stirring stick.

Claims (1)

[Claims] 1. When inserting a stirring rod into the molten metal and rotating the stirring rod during the cooling process of the molten metal to refine crystal grains, use a stirring rod made of a material with the same composition as the molten metal to stir the molten metal. A method for producing a finely divided crystalline metal material using a self-fusing stirring rod.