Strategy of discrete edge masking in the laminar cooling process of hot rolling strip

Abstract:

The laminar cooling process can cause flatness defects of high strength hot rolled strip. Proper edge masking strategy is benefit to improve its flatness after cooling. For 12 mm thickness hot rolled X70 pipeline steel strip with the coiling temperatures of 500 ℃, a coupled thermo-mechanical-phase transition model of Finite Element Model (FEM) was established for the strip in laminar cooling process. The temperature field, phase transformation and internal stress distribution along the width of hot rolled strip were calculated in the duration of the conventional laminar cooling and the cooling process with discrete edge masking strategies. The results show that there is plastic deformation at the strip edge of 25 mm width during the conventional laminar cooling. Strip flatness tends to edge waves in the early stage and shifts to center waves in the end stage of the later half water cooling process. However, by cooling with the strategy of discrete edge masking, the temperature difference decreased significantly between edge and middle of strip in width direction, leading to evenly distributed bainite transformation and residual stress along the strip width. The masking strategies effectively eliminate the plastic deformation and improve of the flatness of the cooled strip.