Cold rolling of wide width molybdenum plate
Molybdenum plate with width from 400mm to 510mm is carried out on 550mm cold rolling mill, while molybdenum plate with width from 700 mm to 800mm is carried out on 1200mm four high reversing cold rolling mill.
Due to the large size of molybdenum slab and the corresponding size of finished product, reversing rolling must be adopted in cold rolling. According to the experience, the head peeling and delamination of molybdenum plate are easy to appear in cold rolling reversing rolling. In order to ensure the smooth cold rolling process of wide width molybdenum sheet, it is necessary to reduce or overcome the phenomenon of head peeling and delamination as far as possible. Therefore, the small-scale process test is arranged first, and the small-scale test is carried out on the 550mm four high reversing cold rolling mill. Through the cold rolling test of various deformation modes and different processing rates, we found that only the surface quality of molybdenum plate rolled by some process systems is better, and there is no obvious defect form, while the edge of molybdenum plate rolled by most process systems has crack edge or peeling and delamination at the head and tail.
Through analysis, it is found that the internal structure of molybdenum sheet is different due to different processing rate. When the processing rate is small, the short coarse and uneven "fiber structure" will be produced along the rolling direction; when the processing rate is large, the slender and uniform "fiber structure" will be produced along the rolling direction, which will make the molybdenum plate produce "anisotropy" in the subsequent deformation, which will have adverse effect on the continuous deformation, especially the reversing rolling. In order to overcome this disadvantage factor, after moderate deformation, reversing rolling is carried out. On the basis of existing equipment, rolling high quality wide molybdenum plate is the key content of our research. According to the results of small-scale test, three kinds of cold rolling process for large size wide molybdenum plate were designed. The first kind: longitudinal rolling; the second kind: one-time reversing rolling; the third kind: secondary reversing rolling.
Through the test, we found that the first process has the highest yield, the least defects, no delamination and slag dropping, but the existing equipment can only produce cold-rolled molybdenum sheet with width less than 630mm. When the second process is used, there are some defects such as head slag dropping, edge cracking and surface peeling, but the phenomenon of head and tail peeling in small deformation rolling and large deformation rolling is obviously reduced. When the third process is used, only the side cracks appear and the surface quality is good. If the defects can be removed in time, the defects will not appear in the subsequent processing, and the yield of finished products will be the highest.
