Issue 37

U. Muhin et alii, Frattura ed Integrità Strutturale, 37 (2016) 312-317; DOI: 10.3221/IGF-ESIS.37.41 315 Thus, the cooling section should be included, since the last finishing stand. By increasing the thickness of the final sections of the rolled strip inclusion cooling should be transferred to the latter gap to the first, to minimize the heterogeneity of the austenite grain on the strip thickness and suppress the recrystallization process during long pauses. Figure 1: Comparison of the structural state of rolled strips using between standing cooling. Development of hot strip rolling regimes According to studies by rolling strips 3x1250 mm of steel 08U constant finishing temperature tf = 840°C, the temperature after roughing stands tr = 1000°C, thred speed Vth = 9 m/s and acceleration a = 0.026 m/s2 decrease in the average grain size of austenite along a strip in finishing train was 2.3 microns. Change the size of the austenite grain along the strip leads to uneven metal microstructure after winding into a roll. According to the Hall-Petch equation decrease in grain size increases the yield strength and ultimate strength along the length of finished hot-rolled strips. In order to stabilize the microstructure of the metal strip along the rolling schedule is calculated using betweenstand cooling with variable flow of cooling water. Stabilization of the microstructure of the metal can reach the end of rolling temperature increase of 7°C during rolling acceleration without finishing group and with a rolling speed Ve = 11.2 m/s. The drop in temperature at the inlet to peal finishing in the rolling process is compensated by the change of the total water flow in the cooling system betweenstand band from 840 m 3 /h to 0. Water flow in the system QMKO changes synchronously to each gap. Comparison of existing and design modes hot rolling is shown in Fig. 2. Rolling without acceleration in the finishing train almost completely stabilize the cooling conditions of the band on the run-mill roller table. Temperature increase by the end of the rolling length of the bar and the stabilization conditions of accelerated cooling can solve the problem of a uniform microstructure of metal for a significant proportion of the bands mix mill 2000. Application between stand cooling of size bands and temperature regimes rolling limited to a maximum filling rate band, which for the mill 2000 is 12.5 m/s. This level is the maximum speed of a gas due to the necessity of accident-free transportation of the front end of the strip to a discharge roller conveyor mill due to the aerodynamic effect. Stabilization of microstructure metal along bands which use rolling betweenstand cooling impossible can be achieved with high values of acceleration of finishing group. The task of rolling mode destination, depending on the thickness of the strip and the required temperature level to the end of the rolling mill 2000 mix resolved on the basis of the developed mathematical model of the thermal state of the metal.