Methodology for draft schedule design of plate rolling process with peening effect considered

We propose an approach for designing a draft schedule applicable to thick plate rolling. In the proposed approach, the peening effect, i.e. thick material is rolled with a small reduction ratio, is considered fully in computing roll force and torque. To determine an initial draft schedule, we calculate material thickness at each pass and total number of passes by taking the smallest of the critical reduction ratios (reduction ratio by maximum reduction increment, reduction ratio assigned in designing a plate mill, reduction ratios by allowable roll force and roll torque). To make a final draft schedule, we then propose two ways (thickness ratio correction (TRC) method and reduction ratio correction (RRC) method) that redistribute reduction ratios predetermined in the initial draft schedule. The proposed approach has been applied to POSCO No. 2 Plate Mill. Results reveal that the reduction ratios are determined by allowable roll torque if the material being rolled is relatively thick, but reduction ratios are decided by roll force as the material thickness being rolled decreases. It has been found that the thickness ratio correction method is useful when a heavy reduction ratio is necessary in the later part of the rough rolling sequence, and obtaining a uniform microstructure over material thickness during rolling is important. Meanwhile, the reduction ratio correction method is effective if surface defect generation on the material during rolling is a concern.