Pyroplastic Deformation Behavior And First Hot-Rolling Process Of Large Single Heavy Pure Molybdenum Slab

As high added value product, molybdenum plate is in low proportion of molybdenum product structure. For the domestic molybdenum plate, the weight of single heavy is below 20 kg. In order to optimize molybdenum product structure and meet domestic and international market demand for larger, wider, and longer molybdenum plate, the large single heavy molybdenum slab rolling technology is explored in this paper. Using Gleeble-1500 simulate machine, the thermal simulation test is performed on molybdenum slab which single heavy is 100 kg. The influence of different deformation parameters on the deformation resistance and microstructure is studied by establishing constitutive equation and using material analysis equipment so as to develop reasonable rolling technology. The cogging technology is especialy studied by four-roll reversing mill with 1500t. The mechanical properties at room and high temperature were performed on hot-rolled plates. Fracture morphology and texture were analysed with SEM and XRD. The main conclutions were followed as:1. The flow stress of pure molybdenum slab is decreased with the increasing of deformation temperaure in the higt temperature compressive experiment, but increased with the increasing of deformation rate. The different in flow stress at different temperature was decreased gradually with the increasing of strain rate. Peak stress goes on the direction to smaller strain with the increasing of deformation temperature. When strain rate ? = 0.01 s-1～1s^-1, molybdenum slab in the machining process appeared the phenomenon of dynamic response and recrystallization but appeared the phenomenon of dynamic response when strain rate ? = 1 s-1～5s-1.2. The constitutive equation among temperature, strain rate and flow stress isε= 6. 19182×10⁸[s inh( 0.0038σ)]^7.7175exp[-282478.9/(RT)]. The average thermal activation energy Q=282.4789 KJ/mol. Predicted value deduced from constitutive equation is consistent with the experimental value. The maximum relative error is 12.53%, and average relative error is only 3.68%. The constitutive equation can provides the theoretical basis for hot forming process of pure molybdenum slab.3. Cross rolling can weakenï½›110｝ texture caused by unidirectional cross in hot- rolled plate. Also can helps reducing anisotropy of molybdenum plate. Meanwhile, along with the increase of rolling deformation, it is helpful for formating and strengthening the texture of {100} and {111} . When deformation amount is more than 90%, the strongest texture is {100} .4. The primary rolling experiment followed by reasonable rolling technical range in thermal simulate test indicated that the optimum cogging temperature, average deformation degree and rolling speed is 1450℃～1500℃, 20～22% and 48～53 m/min respectively. In this process parameters range can obtain ideal rolled sheet.5. The maximum resistance strength of pure molybdenum plate with total deformation of 94% is 586.2 MPa and elongation is only 0.54% at room temperature. At high temperature, 1000℃～1200℃, the related value are 336.02～175.5 MPa and the elongation are 26.7%～67%. This is almost consistent with standard samples that have same deformation. Fracture morphology indicated that brittle fracture occurs at room temperature but ductile fracture at high temperature. Also, the delamination indication was found in plate interior, and the thickness of experimental samples is thicker than standard sample.