Continuous development of complex new steel grades to meet the ever-increasing demand of high
performance causes recurrent issues in steel continuous casting such as surface quality defects
(eg cracks, depressions, deep oscillation marks) and productivity challenges (eg faster casting,
near-net shape casting). Continuous casting of steel is a highly successful metallurgical process.
Much of this success can be attributed to the performance of the casting powder that is added to the
top of the mould, creates a liquid slag pool as it is heated, and forms a slag film between the watercooled
copper mould and steel shell during its passage down the mould.
Mould powder selection is a compromise between the conflicting requirements of heat transfer and
lubrication. In an EU RFCS (Research Fund for Coal and Steel)-funded project, various techniques
are developed to offer the opportunity to adapt the slag film to meet the conflicting needs in different
parts of the mould such that mild cooling can be generated in the meniscus, mid-broad face or corner
areas whilst maintaining lubrication and offering higher cooling rates in other areas of mould. This
has significant potential to address the industrial issues in product quality and productivity of
continuous casting.
This paper reports, as part of the EU RFCS project, the determination of crystallinity and porosity in
slag films for casting challenging and innovative steel grades using new methods. In comparison
with the methods such as X-ray powder diffraction (XRD) analysis and optical microscopy / scanning
electron microscopy (OM/SEM) analysis that are currently adopted by the industries, EBSD (electron
backscatter diffraction) has been employed to determine the crystallinity of the slag films taken from
industry casters. X-ray computed tomography (XCT) plus 3D image reconstruction has been used
to determine the slag film % porosity with pore volume, pore size distribution, and pore location,
which can be linked with the performance of the slag films during casting different steel grades.