Ultrasonic Immersion C-Scan Imaging Technique : A Novel Tool to Evaluate and Optimize EMS Parameters for Continuously Cast Steel Billet Quality

Abstract

With increasing demand for clean steels, the quality, in terms of internal defects and macro structural features (cnetral porosity, equiaxed zone, etc.), of billets has become of utmost importance. By optimizing the Electro Magnetic Stirrer (EMS) parameters viz., EMS current and frequency the severity of defects, area of columnar zone as well as central porosity, in continuously cast billet can be effectively minimized. The result would be an inc-rease in equiaxed zone area and improved internal sound-ness. In the present work attempts have been made to determine the best combination of EMS current as well as frequency to ensure good internal soundness of billets. The EMS current and frequency were changed to different value in the range of 240A to 300A and 3Hz to 4Hz resp-ectively. Corresponding billet samples were collected for macro structural evaluation. The samples were scanned using an automatic computerized multi-scan immersion ultrasonic immersion ultrasonic C-scanner to get images of samples. C-scan images obtained through system have been used for as a tool for evaluating and obtaining optimum electromagnetic stirrer (EMS) parameters i.e. current and frequency. Macro structural features revealed by ultrasonic C-Scan were analysed for determining the best combination of EMS parameters. The most significant improvement was found at 280 ampere EMS current and freq-uency 3.5HZ. Beyond this there was only a marginal impro-vement in the billet quality as well as equiaxed zone. Based on the experimental observations, it is recommended to operated EMS at 280A current and EMS frequency should not increase beyond 4Hz in the plant.