U71Mn重轨钢中夹杂物表征

Non-metallic inclusions are the main cause of internal damage and fatigue failure of heavy rail steel.Heavy rail steel adopts aluminum-free deoxidation process and strictly controls spinel brittle inclusions.In this study,a furnace of heavy rail steel produced by a conventional process in a domestic steel mill was used to study the non-metallic inclusions in the steel from the tundish,continuous casting billet and finished rail.Based on the combination of automatic electron microscope scanning and energy spectrum,the morphology,average composition,number density and area fraction of inclusions in the three stages were analyzed.It was found that the composition of Al2O3 inclusions changed greatly,and the proportion increased from 64.81%in the tundish to 78.86%in the rail.SiO2 decreased from 16.80%to 2.57%.MnO decreased from 4.65%to 1.76%.CaO decreased from 9.46%to 4.64%.MgO increased from 4.28%to 12.17%.The typical morphology of inclusions in the rail is a composite inclusion of MnS wrapped with oxides.The number density of inclusions gradually decreases from the tundish to the rail,and the area fraction and average size of inclusions in the slab increase due to the precipitation of inclusions and some MnS wrapped oxides.