JP3824693B2 - Method for forming spheroidal graphite cast iron - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a molding method such as die forming, rolling, forging, and extrusion that uses good fluidity without causing deterioration of the spheroidization rate of spheroidal graphite in spheroidal graphite cast iron.
[0002]
[Prior art]
As a method for obtaining spheroidal graphite cast iron, a method is generally employed in which a cast iron molten metal whose components are in a dissolved state is subjected to a graphite spheroidization treatment and cast. According to this method, the melting temperature or casting temperature is very high (usually about 1400 ° C.), and the heat load on the mold is large, so that the life of the mold is significantly reduced. In addition, a nest may be generated due to shrinkage during solidification, and it is necessary to cast at as low a temperature as possible. However, there is a problem that the spheroidizing action of the graphite disappears with time, and there is no time for reducing the temperature.
On the other hand, there is a method in which spheroidal graphite cast iron is heated to a solid phase temperature range, for example, 1000 ° C., and molded by forging, rolling, or the like. According to this method, since it is solid phase molding, it is necessary to increase the molding load, and there is a problem that graphite that should be spherical is deformed by the plastic flow of the solid phase. The deformation of graphite leads to a decrease in the original tough properties of spheroidal graphite cast iron.
[0003]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for forming spheroidal graphite cast iron that can reduce the thermal load on the mold and does not deform the graphite. .
[0004]
[Means for Solving the Problems]
The present invention has been completed by discovering that there is a temperature range in which the spheroidal graphite cast iron has excellent fluidity when heated and melted and the spheroidizing rate of the spheroidal graphite does not deteriorate. That is, the means of the present invention includes a process in which a material made of spheroidal graphite cast iron is heated and melted within a temperature range of 1150 ° C. to 1300 ° C., and a period in which the spheroidal graphite remains in the melted spheroidal graphite cast iron. And a molding process.
The molding process uses a normal die casting using a die, indentation pressure casting, suction casting, die forging, rolling with a roll that has a uniform longitudinal cross-sectional shape, or extrusion through a die, Etc.
[0005]
In the above means, the reason why the temperature range is limited as described above is that if it is less than 1150 ° C., since there are many undissolved solid phases, fluidity cannot be ensured, it is difficult to form into the desired shape, and the temperature is low This is because the possibility of cracking increases. When the temperature exceeds 1300 ° C., the effect of spheroidizing graphite disappears, that is, the higher the temperature, the more spheroidized graphite dissolves into the structure and becomes non-spherical, and the spheroidizing rate decreases. This is because a structure containing spherical graphite cannot be obtained.
The state in which the raw spheroidal graphite cast iron is heated in the range of 1150 ° C. to 1300 ° C. is a semi-molten state exhibiting fluidity, and the spheroidal graphite is present as it is. The results of the basic experiment are as follows: Spheroidal graphite cast iron containing C3.5 wt% and Si3.2 wt% and having a graphite spheroidization ratio of 86.8% is used as a raw material, and the raw material is placed in a crucible and heated to 1200 ° C. Then, after being kept at this temperature for 5 minutes, it was allowed to cool in the atmosphere and solidified, and the graphite spheroidization ratio was examined. The result was 87.4% (Experimental result 1). The same material as above was heated to 1240 ° C. and held for 5 minutes, and then cooled and solidified in the same manner. When the graphite spheroidization ratio was examined, it was 82.6% (Experimental result 2). FIG. 5 (a) is a raw material, (b) is an experimental result 1 and (c) is a microstructural photograph of each cast iron of the experimental result 2, and (b) and (c) are compared with the spherical graphite of (a). It can be seen that the spherical graphite has hardly changed. In subsequent experiments, it has been confirmed that the spheroidization rate of graphite hardly changes even if the graphite is solidified after being held at a predetermined temperature within the above range for 20 minutes. Therefore, if the molding is completed within the period in which the spherical shape of the spheroidal graphite is maintained in this way, it becomes possible to obtain a molded product of high quality spheroidal graphite cast iron corresponding to the original material. The time of 20 minutes is a period that can be substantially satisfied as the time required for molding.
[0006]
In addition, even at 1300 ° C, which is the maximum value in the above temperature range, 100 ° C lower than the casting temperature of normal spheroidal graphite cast iron, which is 100 ° C, the heat load on the die and the die is reduced accordingly, It is easy to secure the strength of molds and dies. Therefore, suction casting and indentation pressure casting are possible. Also, the mold life is extended. The lowest temperature range of 1150 ° C is higher than the conventional forging and rolling of spheroidal graphite cast iron, ie, forging and rolling by heating in the solid phase temperature range (1000 ° C). Graphite is a solid phase, but most of the other is a liquid phase, and spherical graphite does not deform even when a forming process corresponding to die forging or roll rolling is performed. Therefore, it becomes possible to obtain a molded product of spheroidal graphite cast iron having a quality corresponding to the original material. Further, when the material is pressed during the molding process, the structure becomes dense but has fluidity, so There is no deformation and the quality is improved.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the first embodiment, molding is performed by pressurization, and as shown in a schematic diagram in FIG. 1, the spheroidal graphite cast iron as a raw material is heated to a predetermined temperature within a range of 1150 ° C. to 1300 ° C. to be melted. The melt 1 is accommodated in the container 2, and the ram 3 is advanced downward to be pushed into the mold space of the mold 4 to be solidified and taken out as a molded product. In the figure, reference numeral 5 denotes a heating means comprising a high frequency heating coil or a resistance heating element, which is used as required. The time within the above temperature range from the melting of the material to the start of solidification at the time of molding is preferably 20 minutes or less. Further, in the apparatus used in this embodiment, in addition to the above usage method, an unmelted material can be accommodated in the container 2 and melted by the heating means 5 from the beginning. Good.
The obtained molded product is spheroidal graphite cast iron substantially the same as the raw material, and since it is pressure-molded, the structure is denser.
[0008]
The second embodiment is suction casting, and as shown in a schematic diagram in FIG. 2, a melt obtained by heating the raw spheroidal graphite cast iron to a predetermined temperature within the range of 1150 ° C. to 1300 ° C. 6 is sucked into the mold space of the mold 7 and solidified to be taken out as a molded product. In the figure, 8 is a holding furnace, 9 is a heating means comprising a high-frequency heating coil or a resistance heating element, 10 is a suction nozzle, and 11 is a suction pipe. The time within the above temperature range from the melting of the material to the start of solidification at the time of molding is preferably 20 minutes or less.
The obtained molded product is spheroidal graphite cast iron substantially the same as the raw material, and since it is suction molding, it is degassed during suction, and the quality is improved.
[0009]
The third embodiment is extrusion molding, and as shown in a schematic diagram in FIG. 3, a melted product obtained by heating the raw spheroidal graphite cast iron to a predetermined temperature within a range of 1150 ° C. to 1300 ° C. A predetermined amount of 12 is accommodated in the container 13 and pushed out through the die 15 by advancing the ram 14 to obtain a molded product 16 having a predetermined cross-sectional shape. In this case, immediately after exiting the die 15, the vicinity of the surface is solidified, but the central part is still in a molten state and is easily deformed, so it is preferable to guide it to a linear state using a molded product guide. Further, the container 13 is provided with heating means as shown in FIG. The time within the above temperature range from the melting of the material to the start of solidification at the time of molding is preferably 20 minutes or less. Further, the apparatus used in this embodiment may also be configured so that unmelted material is stored in the container 13 from the beginning and melted when the heating means is provided.
The obtained molded product is spheroidal graphite cast iron substantially the same as the raw material.
[0010]
The fourth embodiment is a molding corresponding to a rolling process using a roller. As shown in a schematic diagram in FIG. 4, the raw spheroidal graphite cast iron is brought to a predetermined temperature in the range of 1150 ° C. to 1300 ° C. The melt 17 melted by heating is supplied so that a substantially constant amount is always accumulated on the roller portion between the pair of rotating rollers 18 and 19 provided with a cooling means, and is removed from between the rollers 18 and 19. It is obtained as a continuous molded product 20 having a predetermined cross-sectional shape whose surface is solidified. The time within the above temperature range from the melting of the material to the start of solidification at the time of molding is preferably 20 minutes or less.
The obtained molded product is spheroidal graphite cast iron substantially the same as the raw material. The molded products 16 and 20 of the third and fourth embodiments have uniform cross-sectional shapes, for example, cross-sectional shapes 21 and 22 shown in FIGS. 4B and 4C. In connection with the third embodiment, when an apparatus using a mandrel is used, it is possible to form a spheroidal graphite cast iron pipe, particularly a pipe having a modified cross section.
[0011]
【Example】
In the first embodiment, as the material of spheroidal graphite cast iron, a material containing 3.5 wt% C, 3.2 wt% Si, and having a graphite spheroidization rate of 86.8% is used. The heated one was melt 1 and a cup-shaped molded product having an outer diameter of 50 mm, an inner diameter of 44 mm, and a height of 75 mm. A micrograph of the microstructure at the intermediate height position of the peripheral wall of the molded product is shown in FIG. The graphite spheroidization ratio of the molded product was 87.4% as an average value in several places. From this result, it can be determined that the graphite spheroidization rate is substantially the same between the material and the molded product. In general, it is recognized that defects in strength do not occur when the graphite spheroidization rate of spheroidal graphite cast iron is 70% or more. Therefore, it can be said that this molded article is a sufficiently high quality spheroidal graphite cast iron product.
[0012]
【The invention's effect】
According to the first aspect of the present invention, it is possible to obtain a molded product of spheroidal graphite cast iron having a quality corresponding to the original material, and reheat the spheroidal graphite cast iron of the material within a predetermined temperature range to form. It is possible to melt a necessary amount of raw material to cope with the production of a small lot of spheroidal graphite cast iron molded product. By stocking the raw material, it is possible to produce quickly according to a small amount of orders. In addition, since the melting temperature range is lower than the casting temperature of conventional spheroidal graphite cast iron, the occurrence of nests is reduced, and the thermal load on the mold and die used in molding is reduced, so that the service life is extended. Play.
Since invention of Claim 2 is pressure molding, there exists an effect which can obtain the high quality spheroidal graphite cast iron molded product of a complicated shape.
Since invention of Claim 3 is casting by suction, there exists an effect which degassing is performed and a quality spheroidal graphite cast iron molded article is obtained.
Since invention of Claim 4 is extrusion molding, there exists an effect which can respond to a spheroidal graphite cast iron molded product which changes only by change of dice | dies.
Since the invention according to claim 5 is rolling forming with a roller, the structure becomes dense, and an effect of obtaining a high quality spheroidal graphite cast iron molded product is obtained.
[Brief description of the drawings]
FIG. 1 is a longitudinal front view schematically showing a first embodiment of the present invention together with a pressure casting apparatus to be used.
FIG. 2 is a longitudinal sectional front view schematically showing a second embodiment of the present invention together with a suction casting apparatus to be used.
FIG. 3 is a longitudinal front view schematically showing a third embodiment of the present invention together with an extrusion molding apparatus to be used.
FIG. 4 (a) is a longitudinal front view schematically showing a fourth embodiment of the present invention together with a rolling apparatus to be used, and (b) and (c) are third and fourth embodiments. It is sectional drawing which shows the example of the molded article obtained with this form.
FIGS. 5A and 5B are micrographs of spheroidal graphite cast iron as a raw material, and FIGS. 5B and 5C are micrographs of spheroidal graphite cast iron obtained by heating and melting the raw material and solidifying by holding for a predetermined time. ) Is a micrograph of the spheroidal graphite cast iron of the example.
[Explanation of symbols]
1 Melted material 2 Container 3 Plunger 4 Mold 5 Heating device 6 Melted material 7 Mold 8 Holding furnace 9 Heating device 10 Suction nozzle 11 Suction tube 12 Melted material 13 Container 14 Plunger 15 Die 16 Molded product 17 Molten material 18 Roller 19 Roller 20 Molded product

Claims (5)

A melting process in which a material made of spheroidal graphite cast iron is heated and melted within a temperature range of 1150 ° C. to 1300 ° C., and a molding process in which the melted spheroidal graphite cast iron is molded during the period in which the spheroidal graphite remains. A method for forming spheroidal graphite cast iron, comprising: 2. The forming method of spheroidal graphite cast iron according to claim 1, wherein the forming step is mold forming in which the molten spheroidal graphite cast iron is pressed into a mold and pressed. 2. The forming method of spheroidal graphite cast iron according to claim 1, wherein the forming step is mold forming in which the molten spheroidal graphite cast iron is sucked into a mold. 2. The forming method of spheroidal graphite cast iron according to claim 1, wherein the forming step is extrusion forming in which the molten spheroidal graphite cast iron is extruded through a die. 2. The forming method of spheroidal graphite cast iron according to claim 1, wherein the forming step is rolling forming by rolling the molten spheroidal graphite cast iron through a pair of rollers. .

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