Investigation on the genesis of the shape deformation of plates in New Plate mill, Rourkela Steel Plant

Abstract

New Plate Mill (NPM), a state of the art facility has been commissioned at Rourkela Steel Plant (RSP). Facilities like roll bending, roll shifting and plan view rolling are integral part of the mill. High pressure de-scaling, accelerated cooling control (ACC) with high capacity hot plate leveller (HPL) & cold plate leveller (CPL) are other process facilities of the NPM. A special feature of the NPM (New Plate Mill) is its high roll separating force of 90MN. This enables high shape factor rolling that leads to the rolling of metallurgically sound thicker steel plate. Therefore it is possible to apply modern thermo-mechanically processing routes for the development of tailor made properties like high strength, toughness, close dimensional tolerance and excellent surface finish in plate.Trials were carried out for the achieving target mechanical properties with leaner chemistry by thermo-mechanical control processing (TMCP). After rolling, plates are passed through the Accelerated Cooling Control (ACC) unit for achieving desired mechanical properties. After ACC, waviness is visible in the plates and hence HPL is used for flattened the plate profile. Plates get flattened after hot plate leveling but after several minutes some waviness again occurs in the plates on the cooling bed. Initially several factors were considered for possible reason and thermal images of the plates were taken for understanding thermal variations in the plates. Finally, improper descaling and temperature inhomogeneity was found major factors affecting plates shape.