JP2007270339A - Metal mold for die casting and its peripheral member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal mold for die casting of a long lifetime and its peripheral member by improving the oxidation resistance of a W-based alloy having excellent heat resistance. <P>SOLUTION: The sintered alloy having a composition consisting of 75 to 98 mass% W, 1 to 15 mass% Ni, Ce, and Fe in total, 0 to 30 mass% the Fe and the Co among these in total with Ni, 1 to 20 mass% Cr, and the balance inevitable impurities, in which 10 mass% of the W is substituted with one or two or more kinds of transition metals belonging to periodic law table group IVa, Va, and VIa excluding W and Cr, and the W particles are ≥5 μm, is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a die-casting die used for manufacturing various parts such as an Al alloy, a Mg alloy, and a Zn alloy and its peripheral members.

  Many of various parts such as Al alloy, Mg alloy, and Zn alloy used in automobiles are manufactured by a die casting method. The material of the mold and its peripheral members used in such a die casting method is required to have excellent mechanical properties and oxidation resistance at high temperatures. Conventionally, as a material for this kind of application, Steel and cemented carbide have been proposed.

  Since die casting of Al alloy or the like is usually performed at high temperature and in the atmosphere, materials for mold peripheral members such as molds, die plates and guide pins are required to have heat resistance and oxidation resistance. Although heat-resistant steel has excellent mechanical properties at room temperature, the hardness is remarkably reduced at high temperatures, and ordinary cemented carbides contain binder phase metals such as Co and Ni, so the hardness tends to decrease at high temperatures and the oxidation resistance is poor. . In addition, the so-called binderless cemented carbide contains almost no binder phase metal, so its hardness is hardly lowered at high temperatures, but it is still inferior in oxidation resistance. Ceramics have a drawback that they have excellent oxidation resistance but poor toughness. Other alloys having excellent mechanical properties at high temperatures include W-based alloys such as W—Ni—Fe (for example, see Patent Document 1) and W—Ni—Fe—Mo (for example, see Patent Document 2). Although there are mentioned, all have a problem in oxidation resistance.

JP-A-5-311206 JP-A-6-192804

  The present invention has been made to solve the above problems. That is, the oxidation resistance of a W-based alloy having excellent heat resistance is improved, and a long-life material suitable for a die-casting die such as an Al alloy and its peripheral members is provided.

  The reason why the die casting die material of the present invention is made of a W-based alloy is that W is excellent in mechanical properties at high temperatures. Ni is added to improve the sinterability. If the amount added is less than 1% by mass, the effect of improving the sinterability decreases, and if it exceeds 15% by mass, the rate of decrease in hardness at high temperatures increases. . A part of Ni may be substituted with Fe and Co. However, if the amount added exceeds 30% by mass of the total amount with Ni, the oxidation resistance decreases. Cr is added to improve the oxidation resistance. If the addition amount is less than 1% by mass, the effect of improving the oxidation resistance is insufficient, and if it exceeds 20% by mass, the sinterability is lowered, which is not preferable. . Further, a part of W may be substituted with a transition metal belonging to Groups IVa, Va and VIa of the periodic table excluding W and Cr. However, if the substitution amount exceeds 10% by mass, the sinterability decreases. , The bending strength is reduced.

  It is not preferable that the average grain size of W constituting the alloy structure is 5 μm or less because thermal cracks are likely to occur.

  The sintered alloy according to the present invention has a small reduction rate in hardness at high temperatures and is superior in oxidation resistance as compared to cemented carbide and ordinary W-based alloys. When used for peripheral members, their life can be extended, and the coefficient of thermal expansion is smaller than that of cemented carbide and heat-resistant steel, so the dimensional change of the mold due to heating and cooling is small, and the mold design is easy. It has a characteristic that it has a high industrial utility value.

  For example, in the case of an aluminum foil die-casting mold for ordinary automobiles, the portion where the molten metal first comes into contact with the molten metal is as high as about 700 ° C. This part is kept warm in order to keep the hot water flow, and is always kept at a high temperature. Conventionally, SKD61 is used after being nitrided and protected by a coating mold or the like, but since a molten metal at 700 ° C. passes, it melts at about 2000 to 5000 shots and has a lifetime. Since this mold is a large device with a working part dimension of several meters, it takes time to replace the melted part, and the production efficiency is extremely low at this level of life. Almost no longer needed, and tens of thousands of shots can be used with only simple daily maintenance, greatly improving productivity.

The material for the die-casting mold of the present invention can be manufactured by a usual powder metallurgy method. That is, W, Ni, Fe, Co, and Cr powders are blended in a predetermined composition, dried by wet mixing with a ball mill or attritor, and then molded into a desired shape at a press pressure of about 1 to 5 t / cm ² . Next, the compact is vacuum sintered at 1350-1500 ° C. for 30-120 minutes and then processed into a final shape.

Table 1 shows the composition of the alloy of the present invention and the comparative alloy. Invention alloy No. Nos. 1 to 4 were obtained by keeping the amounts of Ni and Fe constant and changing the amount of Cr. Nos. 5 to 11 are obtained by changing the total amount of Ni, Fe and Co and the amount of Cr. No. Nos. 12 to 14 show the amounts of Ni, Fe and Cr in No. 12 to No. 12, respectively. It is the same as Alloy 2 and a part of W is replaced with Ti, Ta and Mo. No. of comparative alloy Nos. 15 to 20 are W-based alloys containing no Cr; 21 to 24 are general cemented carbides for wear resistant tools. Here, all W-based alloys were prepared using W powder having an average particle size of about 6 μm, under conditions of wet ball mill time: 24 hr, press pressure: 1 t / cm ² , vacuum sintering: 1460 ° C.-60 minutes.

Table 2 shows the measurement results of the bending strength, hardness, high temperature hardness, oxidation resistance (oxidation increase), and thermal expansion coefficient of the alloys of the present invention and comparative alloys shown in Table 1. In the oxidation increase test, the entire surface of a 4 × 8 × 25 mm ³ test piece was mirror finished, heated in the atmosphere at 800 ° C. for 30 minutes, and the increase in oxidation per unit area was calculated from the change in weight. The high temperature hardness (HV1) was measured in an Ar atmosphere. The thermal expansion coefficient was measured from room temperature to 600 ° C. at a heating rate of 1.5 ° C./min using an electrical resistance thermal expansion simultaneous measurement device (KD-ER, Naruse Scientific Instruments Co., Ltd.).

  No. From 1 to 4 and 15, the oxidation increase decreased (oxidation resistance improved) as the Cr addition amount increased. No. When the total amount of Ni, Fe and Co increases as in 15 to 19, the oxidation resistance and high temperature hardness deteriorate. By increasing the Cr amount as the total amount of Ni, Fe and Co increases as in 5 to 11, deterioration of oxidation resistance can be suppressed. In addition, the bending strength is low compared to general cemented carbide, but the alloy of the present invention is very excellent in terms of oxidation resistance, so when used in a die-casting die and its peripheral members, Long life can be achieved. Furthermore, since the alloy of the present invention generally has a small coefficient of thermal expansion, there is an advantage that the dimensional change after die casting and after cooling is small, and the mold design is easy.

Claims (2)

  W is 75 to 98 mass%, the total amount of Ni, Co and Fe is 1 to 15 mass%, of which Fe and Co are 0 to 30 mass% of the total amount of Ni, Cr is 1 to 20 mass% and unavoidable A die-casting die and a peripheral member thereof, wherein the die-casting die has a composition composed of impurities and is composed of a sintered alloy having W particles having an average of 5 μm or more on an optical micrograph.   The sintered alloy according to claim 1, wherein 10 mass% or less of W is substituted with one or more transition metals belonging to Groups IVa, Va and VIa of the periodic table excluding W and Cr. The die-cast mold and its peripheral members.