Population Evolution of Oxide Inclusions in Ti-stabilized Ultra-low Carbon Steels after Deoxidation

• Published in: Journal of iron and steel research, international international, 2015-12, Vol.22 (12), p.1069-1077
• Main Authors: YANG, Wen, ZHANG, Ying, ZHANG, Li-feng, DUAN, Hao-jian, WANG, Li
• Format: Article
• Language: English
• Subjects: Applied and Technical Physics; Engineering; Machines; Manufacturing; Materials Engineering; Materials Science; Metallic Materials; Metallurgy and Metal Working; non-metallic inclusion; Physical Chemistry; population density function; Processes; reoxidation; titanium treatment; ultra-low carbon steel; 对数正态分布; 氧化物夹杂; 种群; 脱氧; 超低碳不锈钢; 进化; 铸造过程
• ISSN: 1006-706X; 2210-3988
• DOI: 10.1016/S1006-706X(15)30114-X

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.