Investigation on the Susceptibility to Surface Crack Formation in Continuous Casting by a New In Situ Bending Test

The surface quality in continuous casting of the semi-finished product is one of the most important criteria for the successful processing into a finished product. Any defects that may occur should be completely avoided and therefore parameters have to be defined by external experiments. However, this presupposes that the examination is as close to the process as possible. A new approach is to determine the crack sensitivity using the in situ material characterization by bending (IMC-B) test. The advantage of this test method is that the entire process, from the solidification to the bending of the sample in a 3-point bending test, offers conditions close to the continuous casting process. The occurring microstructure, the oxidation processes during controlled cooling, and the bending parameters are similar. Therefore, the obtained results regarding the necessary strain for crack formation can be transferred directly for quality prediction in continuous casting. Within the scope of this publication, the crack susceptibility for a low-carbon and medium-carbon steel in a temperature range of 650 °C to 1100 °C is analyzed in detail for different parameters such as maximum strain or strain rate. Furthermore, the influence of the tramp elements Cu and Sn is investigated for expected future concentrations. The most critical temperature range for all investigated steels is from 850 °C to 1000 °C and it is aggravated by the presence of Cu and Sn. The strain required for cracking is then reduced to less than 1 pct.