Effects of Ti and Al addition on the Formation and Evolution of Inclusions in Fe-17Cr-9Ni Austenite Stainless Steel

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INTRODUCTION

AUSTENITIC stainless steels as common and economical structural materials are widely used in several engineering industries, such as the chemical, petrochemical, and nuclear industries. Their good mechanical properties and excellent corrosion resistance under various aggressive environments enable them to perform well in harsh environments.[1,2] However, the presence of nonmetallic inclusions with high melting point and hardness in steel are harmful to the fatigue resistance, toughness, and ductility of the final steel products.[3,4] Moreover, in casting, the clogging of the submerged entry nozzle caused by nonmetallic inclusions could deteriorate castability and reduce productivity.[5–8] Thus, it is necessary to reduce the impact of inclusions on the mechanical and corrosion resistance properties of steel products by studying the formation and evolution mechanisms of inclusions in molten steel.

CHAO PAN, XIAOJUN HU, and KUOCHIH CHOU are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, 100083, China. Contact e-mail: [email protected] PING LIN is with the Ruipu Technology Group Co., Ltd., Qingtian, 323903, China. Manuscript submitted January 17, 2020.

METALLURGICAL AND MATERIALS TRANSACTIONS B

Titanium is an essential alloying element for improving the intergranular corrosion resistance of austenitic stainless steel to make it suitable for high-temperature services.[9,10] Since titanium has strong affinity for oxygen in molten steel and is costly, aluminum is generally used as a deoxidizer before titanium is added to the austenitic stainless steel. After the addition of aluminum and titanium, nonmetallic inclusions containing Al and Ti will inevitably be produced in the molten steel. Many researchers have reported the formation of Al2O3, TiOx, TiN, and Al-Ti-O inclusions to be the prime cause of the clogging of the submerged entry nozzle and defects in steel surface.[11–14] Therefore, it is necessary to study the formation and evolution mechanisms of nonmetallic inclusions after the addition of aluminum and titanium. Van Ende et al. studied the change in inclusion composition after adding aluminum and titanium and found that maintaining an aluminum content of not less than 0.02 wt pct before the added titanium content reaches 0.05 wt pct can effectively prevent the oxidation of titanium.[15] Matsuura et al. investigated the transient stages of inclusions after aluminum and titanium addition and found that the reduction of TiOx by Al leads to the inclusions morphology changing from spherical to polygonal shape, which would increase the probability of nozzle clogging.[16] Wang et al. studied the evolution behavior of inclusions in molten steel under various titanium-to-aluminum ratios. They found that changes in

the inclusion composition led to the changes in morphology when the melt composition changed from Al2O3 stable region to Ti3O5 stable region in the molten steel.[17] In previous studies, the research system for the formation and evol

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