Numerical Investigation Of Plan View Pattern Optimization And Yield Improvement During Wide And Heavy Plate Hot Rolling

Steel plate yield is one of the key economical and technical indexes during heavy plate hot rolling, which is directly determined by plate plan view pattern and plate sizes accuracy. Competition between steel plate enterprises becomes fiercer and fiercer due to the decreasing domestic and international plate markets, energy shortage and iron ore shortage. Reducing production cost is an practical method to strengthen competitive ability of domestic enterprises, and optimizing plate plan view pattern during hot rolling can substantially reduce the production cost by improving plate yield, saving energy and reducing emission. Establishment of effective plate plan view pattern control models would be the key to take advantage of domestic advanced plate mills, improving the plate plan view pattern rectangularity during hot rolling.Finite Element (FE) simulations and industrial trials on heavy plate hot rolling were carried out to establish the plate plan view pattern control models and try the the models out. The main content and the conclusions of this dissertation are as follows:1. Basing on a5000mm heavy plate mill, a Finite Element Method (FEM) based simulation system DEFORM-3D was employed to establish a three dimensional (3D) thermo-mechanical rigid plastic FE model of conventional heavy plate hot rolling. Using production data, a single pass rolling process, a longitudinal rolling process and a broadside-longitudinal rolling process were simulated by this3D FE model. The simulation results of the single pass rolling showed that width spread at plate side edge region and the end effects led to the formation of concave shapes at the plate side edge lines. The width spread became a difference in the elongation of rolling direction, which contributed to the formation of convex shapes at the plate end lines. The convexity shape at plate head line and that at plate tail lines resulted from different ways. The plate uneven shapes upon the completion of the longitudinal rolling process were the accumulated results of inhomogeneous deformations occurring in every single rolling pass. And the final plate plan view pattern of broadside-longitudinal rolling process was the superposition of the plate plan view pattern developed in the broadside rolling phase and that developed in the longitudinal rolling phase. Crop losses due to both the concave side line shapes and the convex end line shapes increased during the longitudinal rolling phase till the plate thickness was reduced to a certain value. But the convexity length kept increasing in the whole longitudinal rolling phase. The reliability of this3D FE model was verified by comparing the simulation results with the measured data, and this3D FE model can be used to investigate plate plan view pattern control during hot rolling.2. Basing on the above3D FE model of conventional heavy plate hot rolling, the heavy plate mill parameters and the vertical mill parameters were used to establish a3D thermo-mechanical rigid plastic FE model of vertical-horizontal rolling.320vertical-horizontal rolling processes under different rolling parameters were simulated by this FE model. Metal flow regularity during vertical-horizontal rolling was clarified by analysis of the simulation results. The influences of the rolling parameters on dog bone shape and the plate plan view pattern during the vertical-horizontal rolling were analyzed. Taking a sample of the simulation results, the relations between the rolling parameters and the plate plan view pattern were determined with the aid of a back propagation (BP) artificial neural network (ANN). Then a plate edging model with short stroke control was established. Prediction results of the plate edging model were used in the simulation of actual plate rolling. The simulation results showed that the predicted plate width was in good agreement with the measured one and the plate plan view pattern was improved by the plate edging. So the plate edging model can be used in practice.3. Heavy plate conventional rolling processes with different broadside rolling ratios were simulated by the above3D FE model of conventional heavy plate hot rolling. Plate plan view pattern prediction models were formulated by nonlinear regression analysis of the simulation results. The model predicted plan view patterns were in good agreement with the finite element simulation results and the measured ones. Basing on the plate plan view pattern prediction model, slab optimization and rolling schedule optimization methods were proposed to improve plate plan view patterns and a plate broadside compensation rolling model was established for further improvement. The theoretical broadside compensation rolling model was simplified for on-line use. The simplified model prediction results were used in the simulation of heavy plate actual rolling and the simulation results showed that the simplified broadside compensation rolling model was effective to reduced plate end crops. The simplified broadside compensation rolling model can be used in practice.4. On the basis of the plate plan view pattern prediction models, the plate edging model and the plate broadside compensation rolling model, methods to improve plate plan view pattern during hot rolling were proposed. In order to decrease plate convexity-shape crop at plate side edges or at plate end edges, slab optimization and rolling schedule optimization were suggested to improve the plate plan view pattern on the basis of the plate plan view pattern prediction model. Then according to the predicted plate plan view pattern and the plate rolling strategy, plate edging or broadside compensation rolling can be chosen for further improvement of the plate plan view pattern. Simulation results showed that plate edging during the longitudinal rolling phase or broadside compensation rolling during broadside rolling phase can decrease plate end convex shapes and improve plate side edge shapes some what. The optimal combination of broadside compensation rolling and plate edging can roll the convexity-head concavity-edge plate plan view pattern into rectangle. The optimal combination of plate edging at both broadside rolling phase and longitudinal rolling phase can roll the convexity-edge concavity-end plate plan view pattern into rectangle.