Fundamental Research On Key Technology Of TA1 Titanium Titanium Hot Rolling

Compared with other titanium alloys, commercially pure titanium has excellent workability, especially when its oxygen content is low. The production of commercially pure Ti coils in a steel rolling mill has become a dominant process due to high production efficiency and low cost. By adjusting the equipment setup and process parameters of the different stages of rolling, including heating, roughing, fine rolling and coiling according to the characteristics of commercially pure titanium, the steel rolling line has been adapted to smoothly produce commercially pure titanium coils. However, some problems still exist, such as width reduction or increase near endings in rough rolling, curved head in fine rolling, thickness inaccuracy and surface defects. Therefore, this work aimed to solve those problems and guide the industrial production, with the study of the hot deformation behavior of TA1 alloy, head and tail width control at the roughing stage, strip head bending at the final rolling stage and surface defect formation mechanism. The main research results are as follows:(1) The true stress-strain curves were obtained for TA1 alloy with different chemical compositions. With the true stress-strain curves, constitutive equations and processing maps based on a DMM (dynamic material model) were developed. In addition, a deformation resistance formula based on the J-C model was built using non-linear regression analysis. The variables are deformation temperature, strain rates, total strain, and chemical compositions. The results provided necessary data for building the simulation model in the future, also could be used in determining rolling temperatures and optimizing other rolling parameters.(2) A finite element model for the rough rolling was built to study the evolution of head and tail width in rough rolling, short stroke control equation and influence of short stroke on the head and tail width. The differences in rough rolling short stroke control equations between titanium and steel rolling were compared. These investigations have been successfully applied in controlling the rolling head and tail width of titanium coil.(3) A finite element model for the finish rolling was built to systematically study the influences of oxide scale, friction coefficient, rolling temperature and roller diameter differences on head bending in final rolling and asymmetrical wear of rollers. Remarkable differences were found in the flow behavior of titanium and steel, which leads to the opposite behavior of asymmetrical wearing of the upper and lower working rollers. A series of technical measures were successfully established to control the thickness of oxides on the titanium billet and surface roughness.(4) The main cause of the surface defects in the hot rolling process was due to the implant of falloffs or stripped particles into the titanium surfaces after the relative sliding between the titanium strips and contacting parts (including the roller). Thanks to this finding, a series of technical changes in the equipment and process were carried out to make the number of surface defects drop by an order of magnitude accompanied by remarkably improved surface quality improvement.(5) Based on the continuous tandem hot rolling production line for steel, a complete production technology with large-scale, low-cost, high-efficiency, high-quality was successfully developed for manufacturing hot rolled commercially pure titanium coils, and industrialization of this rolling process has been achieved.