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INTRODUCTION

TI-STABILIZED austenitic stainless steel is widely used in various applications which require both high strength and excellent corrosion resistance in an aggressive environment. However, the presence of non-metallic inclusions can seriously affect the production process as well as the quality of the final steel product,[1,2] for example, clogging of the submerged entry nozzle, degradation of mechanical properties, surface defects, initiation of corrosion-fatigue cracks, and hydrogen embrittlement. For such reasons, it is desirable to keep the inclusion concentration as low as possible.

XUE YIN, Ph.D. Candidate, is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing, 100083, China, and also Visiting Researcher with the Department of Materials Science and Engineering, University of Toronto, 184, College Street, Toronto, ON, M5S 3E4, Canada. YANHUI SUN, Associate Professor, and XUEFENG BAI, Master’s Candidate, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing, 100083, China. YINDONG YANG, Senior Research Associate, MANSOOR BARATI, Associate Professor and Gerald R. Heffernan Chair in Materials Processing, and ALEX MCLEAN, Professor Emeritus, are with the Department of Materials Science and Engineering, University of Toronto. Manuscript submitted June 24, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B

Although aluminum is one of the strongest deoxidizers,[3,4] the deoxidation product alumina can be harmful to the final product. In addition, inclusions containing MgO can be generated from several sources including ferroalloys with a certain amount of Mg,[5] ladle and tundish refractories such as MgO-graphite or MgO-CaO-graphite bricks,[1] and ladle slag containing MgO.[6–8] Titanium is a beneficial element in austenitic stainless steel, as it suppresses grain boundary chromium carbide precipitation and reduces susceptibility to intergranular corrosion through the formation of very stable titanium carbide.[9] The formation of Al-Mg-Ti oxide particles as cores for TiN precipitation has been investigated by several investigators.[10,11] In these studies, spinel particles enhanced the formation of TiN in molten steel due to the very low disregistry between them, and this generated an equiaxed fine-grain structure by the heterogeneous nucleation of delta ferrite on the TiN particles. However, the presence of excessive titanium induces the precipitation of coarse TiN particles exceeding 0.5 lm.[12] TiN inclusions have a cubic or rectangular-prism morphology with a high melting point [3203 K (2930 C)] and high hardness[13] and are not easily deformed during rolling. In addition, coarse TiN inclusions can act as fracture initiation sites,[14–16] thus adversely affecting the fatigue life and toughness of the steel.[17–20] Moreover, in titanium-stabilized steels, the clogging of the submerged entry nozzle (SEN) can increas