JP5777591B2 - Electro-heating and shrinking machine electrode - Google Patents

Description

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

  Many engine valves made of special alloy steel used for automobiles and the like are manufactured by electric heating forging. Electrode materials used for such electric heating and shrinkage are required to have excellent electrical conductivity, high-temperature mechanical properties and oxidation resistance. Conventionally, as a material for this type of application, Cu Alloys, heat-resistant steels, cemented carbides and the like have been proposed.

  Electrical heating and shrinkage of special alloy steel is usually performed at high temperatures in the atmosphere, so electrode materials such as table electrodes and sliding electrodes have high temperatures as well as electrical conductivity, heat resistance and oxidation resistance, and thermal shock resistance. 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.

  The present invention has been made to solve the above problems. That is, the present invention aims to further improve the oxidation resistance and high-temperature mechanical properties of a W-base alloy having excellent heat resistance and high-temperature mechanical properties, and to provide a long-life material suitable for an electrode for an electric heating / shrinking machine. .

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. 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 circumferential Kiritsuhyo group 4 or 5, but the amount of substitution sintering property is lowered and more than 10 wt%, the deflecting strength reduction To do.

  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 decrease in hardness at a high temperature and is superior in oxidation resistance as compared with a cemented carbide or a normal W-based alloy. Their lifespan can be extended and their industrial utility value is high.

  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.

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

The raw material of the electrode for electric heating / shrinking machine of the present invention can be produced by a usual powder metallurgy method. That is, W, Ni, Fe 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 , the reference alloy, and the comparative alloy. The alloys of the present invention and reference alloys Nos. 1 to 4 have a constant amount of Ni and Fe and the amount of Cr is changed, and reference alloys Nos. 5 to 11 are the total amount of Ni, Fe and Co and the amount of Cr. Is a change. The alloys of the present invention and reference alloys Nos. 12 to 14 have the same amounts of Ni, Fe and Cr as the No. 2 alloy, and a part of W is substituted with Ti, Ta or Mo. Comparative alloys Nos. 15 to 20 are W-based alloys not containing Cr, and Nos. 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, and oxidation resistance (oxidation increase) of the alloys of the present invention , reference alloys, 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.

  From Nos. 1 to 4 and 15, as the amount of added Cr increases, the oxidation increase decreases, that is, the oxidation resistance is improved, and the room temperature and high temperature hardness are improved. Moreover, when the total amount of Ni, Fe and Co increases as in Nos. 15 to 19, the oxidation resistance and high-temperature hardness deteriorate, but the total amount of Ni, Fe and Co as in Nos. 5 to 11 decreases. By increasing the Cr amount with the increase, it is possible to suppress the deterioration of oxidation resistance. In addition, the bending strength is low compared to general cemented carbides, but the alloys of the present invention are very superior in terms of oxidation resistance. Can be achieved.

Claims (2)

W is 91 to 95 mass%, a total amount of Ni and Fe is 3 mass%, 0-25 mass% of the total amount of the amount of its inner Fe is Ni, Cr 2 to 5 wt%, and unavoidable impurities The average of the major axis diameter of the W particles is 5 μm or more on the optical micrograph and the entire surface of the 4 × 8 × 25 mm ³ test piece is mirror-finished and then 800 ° C. for 30 minutes in the atmosphere. At least a part is composed of a sintered alloy that is heated and has an oxidation increase calculated from a weight change of 22 g / m ² or less and a high temperature hardness at 900 ° C. of 170 HV1 or more. An electrode for an electric heating / shrinking machine for manufacturing an automobile engine valve, which is pressed by raising the temperature of a workpiece to 1000 ° C. or higher. 10% by mass or less of W is replaced with one or more transition metals belonging to Group 4 or Group 5 of the periodic table, and the entire surface of a 4 × 8 × 25 mm ³ test piece is mirror-finished, then the atmosphere Heating at 800 ° C. for 30 minutes in the medium, the oxidation increase calculated from the change in weight per unit area is 22 g / m ² or less, and the high temperature hardness at 900 ° C. is 170 HV1 or more. An electrode for an electric heating / shrinking machine for manufacturing an automobile engine valve, which is pressed by raising the temperature of a workpiece to 1000 ° C. or higher, characterized in that the sintered alloy is at least partially configured.