The Effect Of TiO₂ Nanoparticle Adding On Inclusions And Microstructure In Steel

In this thesis,electric iron was used as the raw materials,and the TiO₂nanoparticles,TiO₂ nanoparticles/Mg alloy and TiO₂ nanoparticles/Ce alloy were added to molten steel,respectively.The aim was to investigate the adding effect on inclusion and microstructure characteristics.The main conclusions are shown as follows:1)The TiO₂ nanoparticles were directly added into the molten steel,and after holding in the melting state for 10 minutes,the crucible was taken out.After solidification,the sample was quenched in water.On the one hand,a large number of micron-size titanium-bearing complex inclusions were found,which indicated the agglomeration and reactivity of TiO₂ in the molten steel.The explanation was based on the stability of TiO₂ in the molten steel,its wettability with the molten steel and the higher surface free energy of nanoparticles.On the other hand,after etching,it was found that these titanium oxides can induce intragranular ferrites.The line scanning results and the calculation of diffusion coefficient hint that the manganese depletion zone may be the possible mechanism;2)For TiO₂ nanoparticles and magnesium alloys,they were introduced into molten steel by simultaneously adding and successively adding.The results showed that the latter has a higher yield,led to the forming of a large number of micro-size Ti-Mg complex oxides,and significantly increased the oxide density.The obvious intragranular ferrites were observed after etching,and the manganese depletion zone was the possible mechanism;3)The molten steel was treated by TiO₂ nanoparticles and cerium successively.The results showed that a large number of micron-size titanium-cerium composite oxides were formed.The oxide density was increased,and its size was refined.Based on the mechanism of manganese depletion zone and the theory of lattice mismatch,the phenomena of intragranular ferrite induced by Ti-Ce composite oxides were explained.