Issue 37

U. Muhin et alii, Frattura ed Integrità Strutturale, 37 (2016) 312-317; DOI: 10.3221/IGF-ESIS.37.41 313 Another way to stabilize the microstructure is the temperature increase by the end of the rolling length of the strip, which compensates for the temperature drop at the entrance to a peal finishing train. Temperature increase can be achieved by the end of rolling two ways that do not require additional capital expenditures: 1) using a rolling with between stands cooling mode for variable-speed distribution of cooling water; 2) rolling with an increased acceleration of finishing group. Between stands cooling mode with variable flow rates is to reduce the supply of water along the rolled strip. This mode eliminates the rolling acceleration, thereby virtually eliminating the negative effects arising from its use. Mode with high acceleration to stabilize the microstructure of the metal and reduce the computing time in the production of rolled strips, which increases the rolling speed cannot be applied because of the technical features of the mill. Application of the cooling capacity is limited only by the installation of accelerated cooling strip on the run-out roller conveyor and power parameters of the rolling process in the strips production. T ECHNIQUE TO STUDY THE THERMAL AND STRUCTURAL STATES OF THE METAL tudy of the thermal and structural states of the metal was carried out using mathematical modeling for the conditions of continuous broadband hot rolling mill 2000 “NLMK”, Russia. The mill includes 5 methodical furnaces, roughing group of stands, intermediate roller table with installing thermal screening lag, 7 stands finishing group, run-out roller table with installation of fast cooling strip and coiler area. The finishing group is equipped with a system of cooling the strip which can significantly increase its throughput. The maximum flow rate of cooling water in the cooling system is 1200 m3/h. Calculation of the temperature strip mill line was carried out using the developed mathematical model of the thermal state of the metal from the issuance of a peal of roughing stands to strip winding into a roll. A mathematical model based on the solution of one-dimensional transient heat conduction Eq. (1) finite difference method.          2 2 ( ) ( ) ( ) V T T T c T T q x (1) where: ρ is the density of the metal, kg/m 3 ; c - specific heat capacity of the metal J/(kg.K); λ - thermal conductivity of the metal, W/(m.K); T - temperature of the metal, K; τ – time, s; x - coordinate of the strip thickness, m; q v - power density heat sources, W/m 3 . Mathematical model takes into account the effect of the screening device of roll, cooling strip in finishing group, heat generation due to plastic deformation of the metal, and polymorphic γ → α transformation of super-cooled austenite on the thermal state of the metal [3,4]. The model also accounts for the effect of the phase state and chemical composition of the steel on the physical properties of the metal. A mathematical model of the thermal state of the metal was adapted to the conditions of the mill 2000. Share lanes with an error calculating the metal temperature over 20°C was less than 2 %. The calculation of the microstructure of the metal in the rolling mill finishing train carried by mathematical models recrystallized austenite low carbon steel grades set out in [4-8]. The calculation of the microstructure in finishing train was limited to the determination of the recrystallized volume fraction and the average grain size of austenite along the strip . H OT STRIP ROLLING WITH USING THE BETWEEN STANDS COOLING Influence of the cooling for formation of cooling metal microstructure nvestigation of the effect of cooling in finishing group on the structural state of the metal made in modeling for the strip 3x1250 mm of steel grade 08U of the mill in 2000 for four modes is shown in Tab. 3. The chemical composition of the steel is shown in Tab. 1. The deformation mode in finishing group is shown in Tab. 2. S I