Analysis of large-sized inclusions in rail steel by combining CT imaging and electrolytic method

Large-sized inclusions in rails compromise service performance and safety, necessitating precise characterisation. Conventional methods combining ultrasonic testing with metallographic or electrolytic extraction showed limitations in localisation, efficiency and morphology preservation. A novel method integrating three-dimensional X-ray computed tomography (CT) with three-dimensional electrolytic etching technique was proposed. This approach enabled non-destructive localisation, in-situ exposure, and multi-dimensional analysis. In U75 V heavy rail steel, CT first revealed the three-dimensional morphology and spatial distribution. Electrolytic corrosion then selectively dissolved the metal matrix for full inclusion exposure. Subsequent scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and ternary phase analysis were performed. Results confirmed successful extraction and characterisation. The inclusion composition exhibited characteristics of both continuous casting mould flux and ladle slag encapsulating refractory, identifying it as a composite entrapment product. This integrated method provides a reliable pathway for precise analysis, source tracing, and process optimisation of large inclusions in rail steel.