Effect of annealing process on hot formability of molybdenum lanthanum alloy thick plate
Due to its high melting point, excellent high temperature strength, good conductivity and thermal conductivity, high wear resistance, good processability and low cost, molybdenum has become an ideal high temperature structural material under harsh conditions. However, molybdenum used at high temperature shows severe brittleness when it returns to room temperature.
In order to improve the room temperature toughness of molybdenum and prolong the service life of molybdenum parts, in recent years, most researchers add rare earth oxides or second phase particles to molybdenum matrix to enhance the strength of molybdenum alloy and reduce room temperature brittleness. Molybdenum lanthanum alloy is widely used in this material research. Due to the high melting point of tungsten and molybdenum (higher than 2500 ℃), it can not be produced by traditional smelting process. The mature preparation process at home and abroad is powder metallurgy method. Most containers used to reduce tungsten and molybdenum powder are made of high temperature alloy. With the wide application of refractory metal and its alloy material, the purity requirements are more and more strict. Therefore, the powder can be filled in this way.
The container was gradually replaced by molybdenum and its alloy. Due to the brittleness of molybdenum at room temperature, it is impossible to press molybdenum products with wall thickness greater than 2.0 mm at room temperature. In order to study the characteristics of high temperature forming of molybdenum and its alloys, the high temperature mechanical properties of the alloys were studied, so as to prepare qualified products and ensure the stable performance of the products. Through the special processing method of the product, through the research of heat treatment process and hot drawing process of molybdenum lanthanum alloy, the reasonable processing technology is determined.
Most of the deep-processing of molybdenum and its alloy sheet is to press or press the sheet with thickness less than 0.5mm at room temperature. Due to the poor plasticity of molybdenum at room temperature and the low plastic brittle transition temperature, the sheet with thickness greater than 1.0mm cannot be formed by conventional stamping. In order to ensure that molybdenum and its alloy thick plates can be processed by stamping process, hot working must be carried out at appropriate high temperature. In the experiment, mo-0.8% La alloy was used to prepare 3.5 mm thick plate. The test data suitable for high temperature hot forming were obtained by testing its high temperature properties.
The MoLa alloy sheet with a thickness of 3.5mm can exert its maximum mechanical properties and ensure its stability in the subsequent hot forming process by controlling the processing technology and reasonable annealing system. Through the annealing test and high temperature mechanical properties research of rolling Mo La alloy sheet with thickness of 3.5mm, it is obtained that the mo-0.8% La alloy plate will recrystallize after annealing at 1300 ℃ for 2 h, and the grains are equiaxed. After annealing at 1300 ℃, the high temperature tensile test shows that the tensile strength at 700 ℃ is low, the elongation is high and the mechanical properties are good.
