Development of an Ultrasonic Technique to Optimize the Scarfing Depth and Length of First and Last CC Slabs of a Sequence of IF Grade at Tata Steel

Presence of non-metallic inclusions & macro-flaws (cracks, pin holes/blow holes, segregation etc.), in a large number, in first and last continuously cast (CC) slabs of a sequence of casting, makes the CC slabs inferior in quality. Due to this problem these slabs were being downgraded and a huge loss in net realization was observed due to the difference in the prices of downgraded and prime grade CC slabs of IF grade. A need was, therefore, felt to determine the optimum scarfing depth and optimum length of these slabs to upgrade them into prime quality. The paper highlights the effectiveness of ultrasonic techniques in detecting, measuring and analyzing macroflaws in these slabs. 6 MHz twin crystal (T/R) along with 2 MHz single crystal probes were used to study the number of high gain internally reflected signals (flaw echoes) to assess overall flaws / inhomogeneities. The study revealed that the optimum scarfing depth was 7 mm from both top as well as bottom in case of both first and last IF grade slabs of the sequence casting. This helped in converting the inferior slabs into the prime grade. The optimum useful slab length in first and last slabs of IF grade, that can be converted to prime grade, in 11 meters long slabs, will be 8 meters and 9 meters respectively.