JP2011246797A - Electrode for electric heating upsetting machine and peripheral member thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for an electric heating upsetting machine having long service life, and the peripheral member thereof.SOLUTION: The electrode is composed of a sintered alloy having a composition comprising 75 to 98 mass% W, and NiCo and Fe by 1 to 15 mass% in total, in which the total of the Fe and Co is 0 to 30% of the total content with Ni, and the content of Cr is 1 to 20 mass% with inevitable impurities, and in which the average of the major axis diameters of the W particles is ≥5 μm. Further, in the above sintered alloy, ≤10 mass% of the W is substituted with one or more kinds of transition metals belonging to the group 4A, 5A and 6A in the Periodic Table except for W and Cr. In this way, its oxidation resistance and high temperature mechanical properties are improved.

Description

  The present invention relates to an electrode for an electric heating / shrinking machine and its peripheral members used for manufacturing various parts such as special alloy steel and Ti alloy.

  Many engine valves made of special alloy steel used for automobiles and the like are manufactured by electric heating forging. The electrode and its peripheral member materials used for such electric heating / shrinking are required to have excellent electrical conductivity, high-temperature mechanical properties and oxidation resistance. For example, Cu alloys, heat-resistant steels and cemented carbides have been proposed.

  Electrical heating and shrinking of special alloy steel is usually performed in the atmosphere at high temperature, so the materials of peripheral members such as table electrodes and sliding electrodes have electrical conductivity, heat resistance and oxidation resistance, and thermal shock resistance. High temperature mechanical properties are required. Although Cu alloy has high electrical conductivity and is easy to heat and cool, oxidation at a high temperature is remarkable. Heat resistant steels are significantly oxidized and deformed at high temperatures. Since ordinary cemented carbide contains a binder phase metal such as Co or Ni, the hardness is likely to decrease at high temperatures, and the oxidation resistance is poor, and it is cracked by thermal shock. In addition, so-called binderless cemented carbide contains almost no binder phase metal, so the hardness is hardly lowered at high temperatures, but it is still inferior in thermal shock resistance. Other alloys excellent in oxidation resistance and high-temperature mechanical properties include W-Ni-Fe-based (for example, see Patent Document 1), W-Ni-Fe-Mo-based (for example, see Patent Document 2), and the like. Examples include base alloys, but all have problems in oxidation resistance and high-temperature mechanical properties.

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

  The present invention has been made to solve the above problems. In other words, the W-base alloy that excels in heat resistance and high-temperature mechanical properties further improves the oxidation resistance and high-temperature mechanical properties, and aims to provide a long-life material suitable for an electrode for electric heating / shrinking machines and its peripheral members. To do.

  The reason why the material of the electrode for electric heating / shrinking machine of the present invention is a W-based alloy is that W is excellent in mechanical properties at a high temperature. 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 total amount of Ni exceeds 30% by mass of the total amount with Ni, the oxidation resistance decreases. Cr is added to improve oxidation resistance and high-temperature mechanical properties. When the amount added is less than 1% by mass, the effect of improving oxidation resistance is insufficient, and when it exceeds 20% by mass, sinterability is increased. Since it falls, it 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.

  In addition, it is not preferable that the average particle size by the major axis diameter of W constituting the alloy structure is less than 5 μm 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 as a member, they can have a long life and have high industrial utility value.

  For example, in the case of electric heating / shrinking of an automobile engine valve, the temperature of the workpiece is raised to 1000 ° C. or higher and pressed against the base electrode. At this time, in the case of heat-resistant steel or the like, the oxidation progresses and deforms after 100 shots and is exchanged. This deformation of the base electrode affects the final shape of the engine valve, leading to the occurrence of defective products and lowering the productivity. However, when the alloy of the present invention is used, oxidation and deformation are greatly suppressed, and 200 to 300 shots. Can be used for a long time, greatly improving productivity.

  The material for the electric heating / shrinking machine electrode and its peripheral members according to the present invention can be manufactured by an ordinary 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 pressed into a desired shape under a press pressure of 100 to 500 MPa. 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. The grain size of WC is obtained by the Fullman equation in the alloy structure. Here, all W-based alloys were prepared using W powder having an average particle size of 4 μm as measured by a Fischer sub-sieving sizer under conditions of a wet ball mill time of 24 hours, a pressing pressure of 100 MPa, and vacuum sintering of 1460 ° C.-60 minutes. The particle size depending on the major axis diameter of the W particles after sintering was in the range of 10 to 100 μm, although depending on the composition.

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.

  No. From 1 to 4 and 15, the oxidation increase decreased as the Cr addition amount increased, that is, oxidation resistance was improved, and room temperature and high temperature hardness were improved. 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 a general cemented carbide, but the alloy of the present invention is very excellent in terms of oxidation resistance, so when used for an electrode for electric heating and shrinking machine and its peripheral members, Their life can be extended.

Claims (2)

  W is 75 to 98% by mass, the total amount of Ni, Co and Fe is 1 to 15% by mass, of which the total of Fe and Co is 0 to 30% by mass of Cr and 1 to 20% by mass of Cr And a composition composed of inevitable impurities, and at least partly composed of a sintered alloy having an average major axis diameter of W particles of 5 μm or more on an optical micrograph Electrode for machine and its peripheral members.   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. An electrode for electric heating / shrinking machine and its peripheral members, characterized in that at least a part thereof is constituted.