INTEGRATED MODEL FOR MICROSTRUCTURAL EVOLUTION AND PROPERTIES OF STEEL PLATES MANUFACTURED IN PRODUCTION LINE

The mathematical model for the prediction of microstructural evolution and mechanical properties shown in the previous report is integrated with the process models those calculate the strain and temperature distribution through thickness at multiple points in the plate during the rolling and the cooling steps for the adoption to a commercial production line. The experiments that cover the wide range of the chemical compositions and the manufacturing conditions of steel plates were conducted and the obtained results such as microstructures and mechanical properties of the plates were compared with the calculated results of the present integrated model. The main points of the present report are summarized as follows: (1) For the observation of austenite (gamma) grain size during the interpass time of the rolling, the Thermal-Sampler that could cut off and quench a small specimen within 100 sec after the previous rolling pass was equipped in the commercial rolling line. The gamma-grain size calculated by using the present model almost agreed with the observed ones. (2) In the case of the air-cooled plates after the rolling whose microstructures were mainly ferrite (alpha) and pearlite, the calculated microstructures such as alpha-grain size, the volume fraction and the microhardness of each phase showed good agreement with the observed ones. As a result, the calculated mechanical properties agreed well with the observed ones. (3) In the case of the acceleratedly cooled plates after the rolling whose tensile strength was above 600 MPa and major microstructure was bainite, the accuracy of the calculated results of microstructures and mechanical properties were inferior a little to the cases of the air-cooled plates. Even in the plates whose tensile strength was above 600 MPa, the calculated results were confirmed to be practically adoptable for the plates whose major microstructure consists of ferrite.