Prevention of transversal corner cracking in continuous casting of micro-alloyed steels

摘要

Transversal corner cracking during the continuous casting of micro-alloyed steels is well known to be a consequence of the presence of film-like ferrite along the austenite grain boundaries. Surface structure control cooling (SSCC) has been found to be a promising technique in order to prevent transverse corner cracking. It consists of cooling below the Ar3 temperature and a subsequent heating over the Ac3 temperature followed by mild cooling. Cracking is prevented by promoting a double phase transformation which results in a ferrite microstructure that is different from the film-like ferrite along the grain boundaries, and a much more uniform microstructure without any chain-like precipitation at the grain boundaries. This technique has been studied and applied to the continuous casting conditions. Experiments based on the SSCC method with a micro-alloyed steel containing Nb, V and Ti have been carried out in order to evaluate the different parameters that are involved in the process. However, the double phase transformation phenomenon could not be achieved in these experiments. The SSCC based samples show a finer microstructure than the mild cooling samples. In addition, it could be that cooling until 510 °C and holding time at high temperature of 2 minutes are the most optimal parameters to obtain a microstructure with two dif-ferent austenites, differenced by their carbon content. No other differences were found between the SSCC based and the mild cooling (normal cooling concept in continuous casting) samples.