Evaluation of internal and subsurface quality of continuously cast billets and slabs by ultrasonic techniques

The paper highlights the developments made in ultrasonic techniques at R&D and SS Division of Tata Steel Ltd in detecting, measuring and analysing the continuously cast billets/slabs with respect to its internal as well as subsurface quality. Different continuously cast billets and slabs could be ranked according to their cleanliness levels even with the conventional ultrasonic flaw detector. The effectiveness of ladle furnace treatment and vacuum degassing (RH degassing) in improving cleanliness level in slabs of extra deep drawing grade and that of electromagnetic stirring in low and high carbon billets, could be successfully assessed using these techniques. In order to convert the down graded first and last slabs of a sequence of auto grade interstial free into the prime grade slabs, the scarfing depth and cutting length were optimised based on the ultrasonic results. Some results using a computer controlled ultrasonic multiscan imaging system, on continuously cast steel billets, have also been presented.