Population density function （PDF）, which can eliminate the arbitrariness caused by the choice of the num- ber and the size of bins compared to the well-used histograms, was introduced to analyze the amount of inclusions. The population evolution of oxide inclusions in forms of PDF in Ti-stabilized ultra-low carbon steels after deoxidation during industrial RH refining and continuous casting processes was analyzed using an automated SEM-EDS system. It was found that after deoxidation till the early stage of casting, the alumina inclusions exhibited a lognormal PDF distribution, and three factors including the existence of a large amount of alumina clusters, the generation of alumi- na from the reduction of Al-Ti-O inclusions and the reoxidation of molten steel were estimated as the reasons. The shape parameter σ was high after deoxidation and then decreased after Ti treatment, indicating that in a short period after deoxidation, the size of alumina inclusions was widely distributed. After Ti treatment, the distribution of inclu- sion size was more concentrated. The scale parameter m decreased with time during the whole refining process, indi- cating that the proportion of large inclusions decreased during refining. Contrarily, the Al-Ti-O inclusions presented a fractal PDF distribution except at the end of casting with fractal dimension D of 4.3, and the constant of propor- tionality C decreased with time during RH refining and increased during casting process. The reoxidation of steel by slag entrapped from ladle was considered as the reason for the lognormal PDF behavior of Al-Ti-O inclusions at the end of casting.
Wen YANGYing ZHANGLi-feng ZHANGHao-jian DUANLi WANG
A comparative study on the corrosion resistance of NiFe_2O_4 ceramic inert anode for aluminum electrolysis prepared in the different sintering atmosphere was carried out in Na_3AlF_6-Al_2O_3 melt.The results show that the corrosion rates of NiFe_2O_4 ceramic inert anodes prepared in the vacuum and the atmosphere with oxygen content of 1×10^(-2) are 6.08 cm/a and 2.59 cm/a,respectively.A densification layer is formed at the surface of anode due to some reactions which produce aluminates.For the anode prepared in the atmosphere with oxygen content of 1×10^(-2),the thickness of the densification layer(about 50 μm) is thicker than that(about 20 μm) formed at the surface of anode prepared in the vacuum.The content of NiO and Fe(Ⅱ) in Ni(Ⅱ)x Fe(Ⅱ)1-x Fe(Ⅲ)_2O_4 increases with the decrease of the oxygen content of sintering atmosphere,which reduces the corrosion resistance of the material.
