JPH0319293B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a heat-resistant molybdenum material with excellent high-temperature properties. Molybdenum wires, rods, and other materials manufactured by powder metallurgy are used as tube materials to form the anchors, supports, grids, etc. of electron tubes, but conventional molybdenum materials generally do not have a sufficient recrystallization temperature. It was easy to cause embrittlement due to high temperature heating. This invention was developed as a result of various research efforts to provide a molybdenum material with a higher recrystallization temperature than conventional molybdenum materials.The invention was developed by adding a small amount of calcium to molybdenum, which has an excellent embrittlement prevention effect. It was discovered that it could be obtained and was completed, and its feature is that 0.02 to 0.2% by weight of calcium (Ca) is added to molybdenum. In this case, a more preferable addition amount of calcium is 0.03 to 0.06% (weight %, same hereinafter). This invention will be explained in detail below. To illustrate the method for producing a molybdenum material according to the present invention, as a starting material, for example, molybdenum lower oxide powder (MoOx) obtained by decomposing ammonium paramolybdate can be used. This raw material powder is generally called brown powder, and calcium (Ca) can be added thereto by, for example, adding and kneading an aqueous solution of calcium nitrate (Ca(NO ₃ ) ₂ ). In this case, the amount of calcium added is preferably about 0.05 to 0.3% in terms of calcium oxide CaO. Adding more than 0.3% at this time is not preferable because the amount of calcium Ca remaining after sintering becomes too large, resulting in a decrease in workability and a tendency to cause clutches during plastic working. Further, if the amount added at this time is less than 0.05%, the desired embrittlement prevention effect cannot be sufficiently obtained. Note that trace amounts of elements other than calcium may be present, such as impurities that are unavoidably mixed. The molybdenum oxide powder to which the calcium nitrate solution has been added is dried and then reduced by heating in a hydrogen stream in a conventional manner. This results in a calcium-containing molybdenum metal powder. The specific surface area (Blaine method) of the obtained metal powder is preferably 1500 cm ² /g or more. The obtained metal powder is charged in a predetermined amount into a mold, and is pressure-molded into a molded body having a predetermined shape and size using a pressure device such as a hydraulic press. The size of the molded object varies depending on the dimensions of the final product, but it is approximately 1 kg for wire products.
Appropriate weight is approximately 2 to 5 kg for board products. The molding pressure is usually about 1 to 2 t/cm ² . The obtained molded body is presintered in a hydrogen stream under conditions of, for example, 1100° C. for about 30 minutes. After that, main sintering is performed according to the usual method, but the temperature of this main sintering is 1700℃.
℃ or higher, and the holding time is usually about 1 to 3 hours. Once a sintered body (called an ingot) is obtained in this way, it is subjected to processing such as swaging and wire drawing to obtain the desired products such as wires and rods. If the product is a plate, the ingot is flattened with a hammer and then rolled into the desired plate product. Molybdenum materials obtained in this manner generally have a higher recrystallization temperature and higher strength (for example, tensile strength) after being heated to a high temperature than conventional materials. [Example] A wire rod (wire diameter: 0.6 mm) made of molybdenum to which a trace amount of calcium was added was manufactured by the above manufacturing method. The properties of the obtained 0.6 mmφ wire were compared with conventional products of the same diameter, and the results were as follows.

【table】

[Table] When the microstructure was observed, the conventional product recrystallized at about 1200°C, whereas the product of the present invention had a recrystallization temperature of about 1300°C. Furthermore, when heated to high temperatures, the crystal structure of the conventional product tends to become stone wall-like, whereas the product of the present invention maintains an intertwined elongated fiber-like structure. When the chemical components of the molybdenum material (0.6φ) of the above example were analyzed, it was found that it contained 0.0497% calcium and 0.004% silicon, which is an impurity. As is clear from the above description, the molybdenum material according to the present invention has a higher recrystallization temperature than conventional molybdenum materials, and is superior in that it is less susceptible to embrittlement even when heated to high temperatures.

Claims (1)

[Claims] 1. A heat-resistant molybdenum material containing 0.02 to 0.2% by weight of calcium (Ca), with the remainder being substantially molybdenum.