Analysis of Large Inclusions in Crankshaft Steel by Ingot Casting

By means of the anhydrous solution electrolysis, large inclusions in crankshaft steel samples are non-destructively extracted. Through optical microscopy and scanning electron microscopy, the three-dimensional morphology, composition, size distribution and quantity density of the large inclusions in the refining, teeming and steel ingot were revealed. The size of the inclusions obtained is 50–200 μm. The results showed that the main components of inclusions in ladle furnace (LF) sample, the heated billet and the rolled products were Al2O3 and SiO2. After LF and Ruhrstahl Hereaeus (RH) refining, the main components were Al2O3, SiO2, CaO, and a small amount of MgO. It is found that the secondary oxidation during the pouring process is the main source for large inclusions. The shapes are mostly irregular blocks. There are more inclusions at the top of rolled products, and more inclusions in head and less inclusions in tails. During the pouring process, the molten steel in the ingot mold circulates, and the molten steel near the wall of the ingot mold flows downward and entangled in the protective slag, then captured by the solidified shell near the wall of the ingot mold, which is also the reason why large inclusions are distributed on the surface layer.