Study on delamination peeling in molybdenum plate rolling
Molybdenum is a brittle metal, and layered peeling is one of the main forms of brittleness. Delaminated peeling is not only very common in molybdenum plate rolling production process, but also in various links of plate stretching, shearing, circular punching and other reprocessing processes. Because the peeling layer is an irreparable defect, once it appears, it can not be eliminated, so it causes a lot of scrap of molybdenum plate and its products, which seriously affects the performance and yield of molybdenum plate. There are two main factors that affect sheet layer peeling, one is impurity element, the other is processing process.
Impurity elements can be divided into gap impurity and metal impurity. The gap impurity is almost not dissolved in molybdenum, so it can only be distributed on the molybdenum grain boundary in the form of oxides or compounds. Even if the content is very small, the grain boundary will become very fragile, especially the coarsening of the grain will cause greater harm. The strength of the molybdenum plate decreases after recrystallization annealing. The reason is that the grain boundary area is reduced due to the mutual annexation and growth of grains, which makes the impurities on the grain boundary more concentrated, resulting in brittle transgranular fracture during tensile process, leading to delamination and peeling. Metal impurities fall into two categories. One is low melting point, small hardness, easy to deform, because this kind of impurities can be deformed with the deformation of molybdenum plate, so less harm. The other is high melting point, high hardness, difficult to deformation, this kind of impurities in the whole rolling is difficult to deformation, and difficult to diffuse, and even always in the original shape of the nailed on the molybdenum grain interface, which seriously affects the deformation and flow of surrounding grains, resulting in the production of layered skin in the rolling.
The processing process includes the billet process and the rolling process, the billet process in addition to control the density of the slab can not be low, but also should control the geometric shape of the slab neat, in order to reduce the rolling process deformation of the uneven phenomenon; In hot rolling, the excellent plasticity of billet at high temperature should be fully utilized, and the large amount of deformation should be used to make the deformation deep inside, to ensure the uniform deformation and structure, and to reduce the inhomogeneity of the original stratification; In the warm rolling to control the amount of processing, repeated rolling track times; The uneven intermediate annealing is also easy to cause peeling in the subsequent processing.
