JP2010149129A - Holder for die-casting die, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a holder for a die-casting die in which the reduction of strength does not occur even if thickness increases, so as to stably secure the strength of the substance. <P>SOLUTION: When a casting product as a holder for a die casting die with a shape having a part with a thickness of ≥50 mm is produced, the molten metal of spheroidal graphite cast iron having a composition containing, by weight, 3.0 to 4.0% C, 2.0 to 2.7% Si, ≤0.6% Mn, ≤0.03% P, ≤0.03% S, 0.02 to 0.06% Mg, 1.8 to 3.5% Cu, 0.01 to 0.05% Sn and 0.003 to 0.01% Bi, and the balance Fe with inevitable impurities is poured into the die of a sand die directly disposed with a cooling metal having a volume of ≥30% of the casting volume. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a die casting mold holder having a portion having a thickness of 50 mm or more and a method for manufacturing the same.

  Conventionally, die-cast mold holders have been manufactured from cast steel (JIS SCMn2A, etc.). However, cast steel products have a higher melting temperature of 200 to 300 ° C. compared to spheroidal graphite cast iron products, and wear of refractories is large. There is a lot of energy to raise the temperature, and the cost is high because extra resources are used. Another problem is that delivery time is required.

  For this reason, in recent years, attempts have been made to use spheroidal graphite cast iron (see, for example, Patent Documents 1 to 4). However, in ordinary sand castings, since the cooling is slow, the spheroidization of the graphite collapses and the graphite grows coarsely. Therefore, the solid casting does not have strength and the elongation decreases. In addition, graphite having a broken shape called “chunky graphite” is formed in the final solidified portion in the vicinity of the thickness center portion, which significantly impairs the strength. For this reason, many efforts have been made to increase cooling. For example, iron particles are used instead of sand, and the heat conductivity of the mold is increased to accelerate the cooling. If the thickness is increased, the strength is reduced and chunky graphite is produced, and the problem has not been solved.

  On the other hand, attempts have been made to solve the problem by adding alloy elements to spheroidal graphite cast iron from the viewpoint of increasing the strength (see, for example, Patent Document 5), and Ni, Cr, Mo, etc. are added, and a certain degree of effect is recognized. Sometimes it is not stable. In addition, the manufacturing cost is increased, which is not practical.

Japanese Patent Laying-Open No. 2005-256088 (paragraph [0014] etc.) JP 2001-321917 A (paragraphs [0004] to [0007]) JP 2001-240934 A (paragraphs [0002] to [0005]) Japanese Patent Laid-Open No. 06-108199 JP-A-10-99960

  The present invention has been made to solve the above problems, and does not cause a decrease in strength even when the wall thickness increases, and can be used for die casting molds that can stably secure the strength of the substance. It is an object to provide a holder and a manufacturing method thereof.

  The die-casting mold holder according to the present invention is a die-casting mold holder having a portion having a thickness of 50 mm or more as described in claim 1, wherein C: 3.0 to 4 in weight%. 0.0%, Si: 2.0 to 2.7%, Mn: 0.6% or less, P: 0.03% or less, S: 0.03% or less, Mg: 0.02 to 0.06%, It contains Cu: 1.8-3.5%, Sn: 0.01-0.05%, Bi: 0.003% -0.01%, and is characterized by being composed of the balance Fe and inevitable impurities. Is.

Regarding Cu, Sn, and Bi added as alloy components of the above die casting mold holder, each additive element has unique characteristics and there is also an interaction of each element. Therefore, an alloy design considering these is important. .
The inventors first focused on the influence of Cu. Cu is a pearlite-promoting element and is known to improve the graphite shape and strengthen the dough. Therefore, the following experiment was conducted to confirm this matter.
Using a low-frequency induction furnace with a capacity of 2,000 kg, using steel scrap and return material to make a molten metal equivalent to FCD450, and adding Cu to 1.3% to 2.8%, and then adding commercially available Fe-Si-Mg-Ca-REM alloy added sandwich spheroidizing process by sandwich method, inoculated at the time of transferring hot water ladle, cast into JIS G5502 Y type B (25t x 215l) of CO ₂ mold It is. The result is shown in FIG. From this, it has been found that the balance between tensile strength and elongation is improved when the amount of Cu added is in the range of 1.8 to 3.5%, more preferably in the range of 2.4% to 3.3%.

Next, with respect to Sn, if less than 0.01%, there is no synergistic effect with Cu or the effect of improving the graphite shape, and the upper limit is set to 0.05% because the embrittlement action is strong above this and mechanical This is because the properties are greatly deteriorated.
When Bi is added to the cast iron material, it not only consumes the spheroidizing agent, but also segregates at the austenite grain boundaries to form liquid-phase grooves, along which graphite easily grows. Since crystallization is inhibited and spheroidization is also inhibited, it is generally not a preferable element in a ductile cast iron material. However, in the ductile cast iron containing Cu of 1.8% to 3.5% and Sn of 0.01% to 0.05%, the present inventors inhibited graphite crystallization. It has been found that the graphite can be uniformly and finely dispersed even in the interior where the cooling rate is slow. When Bi is added in an excessive amount, the amount of graphite decreases and the tendency to cause embrittlement of cast iron appears more remarkably than the uniform fine dispersion effect. Therefore, Bi is set in the range of 0.003% to 0.01%. Therefore, in the present invention aiming at a casting in which there is no difference between the surface layer portion and the inside, it is necessary to determine the Bi content as a component. From the above, if the Bi content is about 0.003 to 0.005% in the thickness range of 50 to 300 mm, and the Bi content is about 0.007 to 0.01% at 300 mm or more, the surface layer portion And almost the same strength and elongation can be secured.

When Mn, which is another component, exceeds 0.6%, it segregates strongly at the eutectic cell boundary, and forms cementite, significantly lowers the ductility, and lowers the machinability, thereby providing an upper limit.
When P exceeds 0.03%, the elongation decreases due to the influence of steadite, and the upper limit is obtained in order to prevent quench cracking when the surface is quenched.
S is an Mg consuming spheroidizing inhibiting element, and is set to 0.03% or less. C, Si and Mg are in the range of general spheroidal graphite cast iron. That is, C was 3.0 to 4.0%, Si was 2.0 to 2.7%, and Mg was 0.02 to 0.06%.

  According to the method for manufacturing a die casting mold holder according to the present invention, when manufacturing a casting product which is a die casting mold holder having a shape having a thickness of 50 mm or more, the casting volume of In a sand mold where 30% or more of direct cooling metal is arranged, C: 3.0 to 4.0%, Si: 2.0 to 2.7%, Mn: 0.6% or less, P: 0.03% or less, S: 0.03% or less, Mg: 0.02-0.06%, Cu: 1.8-3.5%, Sn: 0.01-0.05%, Bi : It contains 0.003% to 0.01%, and is characterized in that it is manufactured by injecting molten spheroidal graphite cast iron consisting of the remainder Fe and inevitable impurities.

  The direct cooling method is well known for cast steel, etc., in order to speed up the cooling in thick castings, but the amount of time to use this is unclear and the volume of the mold is limited. The present inventors have found an optimum value from the viewpoint of heat removal. That is, the heat of the molten metal injected into the mold is directly cooled and removed with gold. A cast iron material (JIS FC250, etc.) used as a commonly used chiller has a much better thermal conductivity than sand particles constituting the mold, and therefore accelerates cooling quickly. However, since the temperature rises instead of removing the casting heat, the cooling metal itself has a cooling capacity unlimitedly because the temperature difference with the casting decreases as the casting cools and the heat flow also decreases. Absent. If the freezing point of the casting is about 1470 ° C., the heat capacity for the chiller installed at room temperature to rise to this temperature is about 120 kcal / kg when the chiller is made of cast iron. On the other hand, since the casting is phase-converted from a liquid to a solid at the freezing point, the amount of heat is known as a physical property value of latent heat of solidification, and in the case of spheroidal graphite cast iron, it is about 50 kcal / kg. It becomes about 2.4. That is, if the volume of the cooling metal is 1 / 2.4 relative to the volume of the casting, this indicates that the amount of heat at the freezing point of the casting is balanced with the sensible heat of the cooling metal. The material of the molten metal poured into the mold (the size of the graphite and the form of the graphite) is determined until it solidifies, and the subsequent cooling has little effect, so the minimum amount of cooling metal required Is almost commensurate with this idea. Actually, there are the shape of the casting and the heat capacity of the sand surrounding the chill metal. Therefore, the minimum chill metal volume is preferably 30% or more of the casting volume.

  The alloy components of Cu, Sn, and Bi, and Mn, P, C, Si, and Mg are as described above.

  According to the die casting mold holder of the present invention, Bi is added as an alloy component, and the minimum amount of Bi is determined according to the thickness of the casting, and Cu and Sn affecting the strength are scientifically grounded. As a result, the strength and elongation did not decrease even when the wall thickness increased, and the strength and elongation of the substance could be secured stably.

  According to the method for manufacturing a die-casting mold holder of the present invention, a cooling metal is installed directly in order to accelerate cooling compared to a normal sand casting, and a cooling metal of 30% or more of the casting volume is used as this amount. By adding Bi as an alloy component and determining the minimum value of this Bi amount according to the cast wall thickness, and calculating Cu and Sn affecting the strength based on scientific grounds, the wall thickness increases. However, strength and elongation did not decrease, and the strength and elongation of the substance could be stably secured.

  The embodiment of the present invention will be described with reference to the schematic diagram of the casting method of FIG. In FIG. 2, 1 is a cast (die casting mold holder), 2 is a cast iron cooling metal, 3 is a mold filled with furan sand, 4 is a gate, and d is the thickness of the cast 1. Incidentally, the height of the casting 1 is set to about 500 mm and the width is set to 800 mm. Using this mold, the components were adjusted in a 5-ton high-frequency induction furnace, the molten metal was treated with Mg at the time of pouring, and then poured into the mold 3 in FIG. 2 using the molten metal inoculated in the ladle. A test piece (JIS G5502) was collected. Thereafter, JIS No. 4 test piece (JIS Z2201) was sampled from the vicinity of the center where casting strength was most clearly reduced, and a tensile test was performed. In this way, experiments for confirming the rationale so far were conducted by changing the mold conditions and the molten metal components, and the optimum values were extracted.

In order to confirm the effect of the chilling metal, first, casting molds were manufactured by changing the conditions of the chilling metal according to the chemical composition and casting temperature shown in Table 1 below (chemical component analysis result (% by weight)). After the casting 1 was cooled, a JIS No. 4 tensile test piece was cut out from the vicinity of the center of the casting 1 and a tensile test was performed. The result is shown in FIG. It can be seen from FIG. 3 that the strength can be maintained at a predetermined 600 MPa level if the chill metal / casting volume ratio (cool metal ratio) is 0.3 or more. However, this elongation value was 0 to 3%, and all were below the standard value.

  As the cast wall thickness increased and the time until solidification increased, the graphite became coarse, and it was found that this phenomenon could not be solved by cooling metal alone, so the effect of alloying elements was tested. In the experiment of Table 1 above, it was confirmed that the strength reduction could be prevented as shown in FIG. 3 by setting the chilling metal ratio to 0.3 or more. The effect of the components was tested by changing the Bi content as in weight%)). As shown in FIG. 4, the test results show that all specimens passed with a tensile strength of 600 MPa or more (not shown in the figure), but with a thickness of 50 to 300 mm, the Bi content was 0.003 to 0. It was confirmed that when the Bi content was 0.007 to 0.01% at 0.005% and 300 mm or more, the decrease in elongation could be prevented and the substantial strength and elongation were exhibited in a well-balanced manner.

  Based on the above points, the effect of each component was tested. The results are shown in the following Table 3 (chemical component analysis results (% by weight)). The presence of Cu and Sn is also important for increasing the strength, and a well-balanced blend of Bi, Cu, and Sn is important.

It is a graph which shows the tension test result in this invention. It is a casting plan schematic diagram in the present invention. It is the figure which compared the chill metal / casting ratio and tensile strength in this invention. It is the figure which compared cast wall thickness and elongation in this invention.

Explanation of symbols

1 Casting (Die-casting die holder)
2 Cooling metal 3 Mold d Cast wall thickness

Claims (2)

  A die-casting die holder having a shape having a thickness of 50 mm or more, and by weight, C: 3.0 to 4.0%, Si: 2.0 to 2.7%, Mn: 0.6 % Or less, P: 0.03% or less, S: 0.03% or less, Mg: 0.02 to 0.06%, Cu: 1.8 to 3.5%, Sn: 0.01 to 0.05 %, Bi: 0.003% to 0.01%, the balance being Fe and unavoidable impurities, a die-cast mold holder.   When manufacturing a cast product which is a die casting mold holder having a shape having a thickness of 50 mm or more, in a sand mold in which a direct cooling metal of 30% or more of the casting volume is disposed, C: 3 0.0 to 4.0%, Si: 2.0 to 2.7%, Mn: 0.6% or less, P: 0.03% or less, S: 0.03% or less, Mg: 0.02 to 0 0.06%, Cu: 1.8 to 3.5%, Sn: 0.01 to 0.05%, Bi: 0.003% to 0.01%, and the balance consisting of Fe and unavoidable impurities A method for producing a die-cast mold holder, characterized by injecting molten graphite cast iron.

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