In Situ Observation of the Precipitation, Aggregation, and Dissolution Behaviors of TiN Inclusion on the Surface of Liqu
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QIANREN TIAN and XINGHU YUAN are with the School of Materials and Metallurgy, University of Science and Technology Liaoning, Anshan, 114051 Liaoning, P.R. China. GUOCHENG WANG, QI WANG, and JING LI are with the School of Materials and Metallurgy, University of Science and Technology Liaoning and also with the Key Laboratory of Chemical Metallurgy Engineering Liaoning Province, University of Science and Technology Liaoning, Anshan, 114051 Liaoning, P.R. China. Contact e-mail: [email protected] DELI SHANG is with the State Key Laboratory of Metal Material for Marine Equipment and Application, Anshan, 114051 Liaoning, P.R. China. HONG LEI is with the Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang, 110004 P.R. China. Manuscript submitted March 9, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
INTRODUCTION
THE GCr15 bearing steel is one of the most widely used high-carbon chromium steels. It has strict requirements for the content, microstructure, and purity of steel because of its special usage and service environment. The non-metallic inclusions are the undesired second-phase particles in the GCr15 bearing steel ingot. The content and distribution of inclusions have a great influence on the service life of the bearing steel; the higher the amount of inclusions, the shorter the life. With the continuous improvement of the smelting technology, the control of oxide inclusions in the smelting process has been significantly improved. However, it is still difficult to control some inclusions, such as TiN and MnS, which precipitate during solidification.[1,2] The TiN inclusion is one of the most dangerously rigid inclusions in the GCr15 bearing steel. Fatigue cracks are easily caused during the usage and rolling process in bearing steel because of the hardness
and poor deformability of the TiN inclusions.[3] A large-sized TiN is greatly harmful to the quality of steel, whereas fine TiN can significantly improve the microstructure and properties of the heat-affected zone (HAZ) of the welded steel. Therefore, it is considered to be a kind of inclusion that can play the role of an oxide metallurgy inclusion.[4–7] Kanazawa et al.[8] observed that fine TiN particles could significantly increase the strength of the HAZ of a weld steel. Tomita et al.[9] used the method of adding TiN-MnS composite precipitates to improve the strength of the HAZ in ultralow-carbon steel. TiN can induce the precipitation of acicular ferrite (AF) and nail the grain boundary to prevent the coarse grain.[10,11] TiN can induce MnS inclusion precipitation during solidification, which is a good heterogeneous nucleation site of AF due to its poor manganese area around it.[12] However, in low-carbon steel, TiN will dissolve at a temperature higher than 1623 K (1350 C) and lose its effect as the oxide metallurgy inclusion,[13,14] because the effective size of an oxide metallurgy inclusion is considered to be 0.2 to 3 lm.[15] Therefore, keeping the size of the TiN inclusion within 0.2 to 3 lm is
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