Characterization of inclusions in axle steel by ingot casting

The composition, size distribution and number density of inclusions in the rolled billet of bottom-teemed axle steel have been investigated through the inclusion automatic analysis system (INCAFeature, Oxford Instruments). Additionally, the thermodynamics calculation of sulfide precipitation during the solidification and rolling processes has been carried out. Seven types of inclusions are found in rolled billets, which are almost originated from the refined molten steel. However, re-oxidation, sulfide precipitation and mold powder entrainment modify the composition of inclusions during the pouring, solidification and rolling processes. Precipitation of CaS is initiated during the solidification process of molten steel. The precipitation of MnS can only be found during the hot rolling process. Inclusions in the interior of the rolled billet are more and larger than those in the subsurface of rolled billet. The inclusion index increases from the rear to the head of the rolled billet (from the bottom to the top of the ingot). Furthermore, the inclusion index increases as the superheat increases. On the basis of the results, it is recommended that molten steel should be poured at a low superheat under the protection of argon shroud. Furthermore, attention may be paid to the way of adding the mold powder.