9th ECCC European Continuous Casting Conference – ECCC 2017

One of the challenges when casting new high-alloyed steel grades, is to cope with segregation, leading to central segregation. The central segregation is influenced by the cast structure (which in turn depends on the alloy content of the steel melt, on superheat, on secondary cooling) and the machine state. There are several possibilities to perform an assessment of the macrosegregation (central segregation). Sulphur-prints or other etchants are considered visual methods used to assess the macrostructure of an as-cast slab, without any information regarding chemical analysis. On the other hand, a scanning of the chemical composition by using a microprobe (SEM-EPMA) is highly accurate but time-intensive and costly. By contrast, the Optical Emission Spectrometry with Pulse Discrimination Analysis Mapping (OES-PDA) test is accurate, fast and cheap. When the results of the OES measurement along the thickness of the slab are related to shell thickness calculations based on 3D modelling of the primary and secondary casting conditions, the effect of different cooling patterns or variations in casting speed can be used to assess the effect of these casting parameters on the segregation. Moreover, the PDA results can be qualitatively compared to the elements that locally segregate, leading to the formation of unwanted precipitates which in itself, can be related to internal cracking susceptibility. These elements have been detected qualitatively with PDA and through SEM-EDS analysis of the samples, locally some precipitates have been found. In this publication, a complete assessment of the segregation and inclusions formation with the combination of the above mentioned methods will be presented focussing on two different type of steels, namely the advanced high strength steels (AHSS),and microalloyed grades.