Evaluation of Internal Slab Quality by an Advanced Ultrasonic Testing System

Thyssenkrupp Steel Europe AG at Duisburg, Germany performs comprehensive efforts to improve slab quality. According to the current state of the art, the internal quality of slabs could only be determined by extensive destructive and time-consuming slab sampling. ln collaboration with the Fraunhofer Institute for NondestructiveTesting IZFP, Saarbrücken, a new tomographic ultrasonic system was developed and set in service for evaluating the internal slab quality in situ in the process chain. The new ultrasonic slab testing system is able to inspect the complete slab by providing cross-section images, which allow quantifying the internal homogeneity. To perform an inspection a mobile unit is placed on the slab surface at the slab yards. The system automatically scans the slab over its whole length, acquires ultrasonic data, performs reconstruction and presents images. For an intuitive evaluation directly after measurement, cracks and segregation porosity can be visualized in situ without destroying the examined slab or taking samples. For comparison of testing results and quality management, a new classification standard for scoring the slab quality was developed. With the new device, real time testing of internal slab quality can be performed, which enables adjusting the casting machine and slab handling parameters quickly after production.