The Research Of Flatness Of Hot-rolled Strip On Run-out Table

After the steel strip is hot rolled, it is subjected to cooling on run-out table formicrostructure and mechanical properties. Reducing coiling temperature and increasingcooling rate have been effective cooling strategy to refine microstructure and properties.Uneven cooling of the strip under high cooling rate will cause uneven phasetransformation, and both of them pose the root of residual stress which still couldn’t beprecisely control. Therefore, it is a significant project to study about the residual stress onrun-out table theoretically.In Q345-B’s case, coupling model of temperature, phase transformation and stress isestablished to study on the residual stress of cooling process. Numerical model is used toresidual stress’s calculation and analyses of varied cooling conditions’ influence on theresidual stress. Offline calculation realized by means of C++program combined with thenumerical model.Temperature expression of each cross section node is induced base on the finitedifference method. With the heat source of phase transformation, temperature evolution isobtained base on the boundary conditions according to device parameters. Influence ofcooling strategy, initial temperature and edge masking on the temperature distribution isobtained from simulation data.Thermodynamics is used to ascertain the equilibrium temperature of phasetransformation. Dilatometry is used to obtain the start temperature and volume fraction ofphase transformation combine with optical microscope. Based on Kwon’s model,incubation period and transformation fraction of Q345-B during cooling are regressedfrom experiment data. Influence of cooling strategy, initial temperature and edge maskingon volume fraction distribution is analyzed with numerical simulation.Increments of thermal strain and transformation elastic strain are calculated based onthe simulation data of temperature and volume fraction. Plastic train and transformationinduced plasticity are considered as influence factors on the residual stress on run-outtable. Evolution of residual stress is obtained, and from which the influence of cooling strategy, initial temperature and edge masking on residual stress is consequently analyzed.