During the continuous casting of advanced high-strength steel slabs, both surface and internal discontinuities are prone to occur. These discontinuities can include cracks, voids, coarse nonmetallic inclusions, and heavy local chemical and microstructural segregation. Many nondestructive testing techniques have been developed to assess the presence of these discontinuities, which correspond to specific “fingerprint” responses in sound wave interactions. The factors responsible for these discontinuities are often related to the mechanical, thermal, or transformation stresses that take place during the solidification of the slabs. The high thermal stresses result from the difference in volume expansion or contraction behavior caused by frequent temperature fluctuations during solidification. In order to study the effect of these temperature fluctuations, a two-dimensional finite element method simulation model was established. In addition, to validate the model results, an ultrasonic testing (UT) system was used to detect and localize the discontinuities caused by thermal or transformation stresses. The results from the UT scanning were assessed with an image processing analysis to identify the size and location of the discontinuities in the slabs. These results were enhanced with a systematic advanced microstructural characterization technique.
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