Detection of non-metallic inclusions on an entire cross-section of the continuous casting bloom of a heavy rail steel

Abstract

In this current study, a 380 mm wide × 280 mm thick continuous casting heavy rail steel bloom was sampled from an industry plant under a stable casting condition. The morphology, size, number and spatial distribution of oxide inclusions on the entire bloom cross-section were detected by the scanning electron microscope. Characteristics of the number density, area fraction, size and spatial distribution of inclusions in the bloom were analysed and summarised, which can provide an important basis for the optimisation of the distribution of inclusions. The average number density of inclusions on the entire bloom cross section was 5.012 #/mm² and the average diameter was 4.75 μm. The 1–3 μm inclusions were mainly gathered on the surface and subsurface of the bloom, resulting in a high number density and a small average size of inclusions at the edge of the bloom. Inclusions with a diameter of 3–10 μm mainly showed a dispersed distribution on the cross-section, and the number density of 3–15 μm inclusions was the lowest at the centre. While the inclusions larger than 15 μm relatively obviously distributed at the centre. The number density of large-sized inclusions over 15 μm was relatively low, mainly concentrated within the range of 1/4 bloom thickness to the centre of the bloom, resulting in an increased average size at 1/4 bloom thickness. Due to factors such as the geometry of the vertical bending continuous caster, mould electromagnetic stirring, turbulence characteristics and SEN clogging, the distribution of inclusions on the bloom showed non-uniformity, mainly manifested on the left and right sides along the bloom width, as well as at the 1/4 bloom thickness from the loose side and fixed side.