In order to clarify and control the silver defect on surface of cold-rolled sheet of the Ti-stabilized ultra-pure ferrite stainless steel, the distribution of TiN inclusions on the cross section of hot-rolled plate was studied using automated scanning electron microscopy/energy-dispersive X-ray spectroscopy inclusion analysis (ASPEX 1020 system). It was found that the number density decreases sharply from the surface to the center of the hot-rolled plate, whereas the average size increases. Then, the distribution of TiN inclusions on the cross section of continuously cast slab was investigated. Similarly, numerous small-sized TiN inclusions were generated at the subsurface of the slab. The average size rapidly increased and the number density dramatically decreased from the subsurface to 1/4 thickness, while from 1/4 thickness to 1/2 thickness, the increase in average size and the decrease in number density were slight. Thermodynamics results showed that TiN inclusion was formed below the liquidus temperature, which indicated that TiN inclusions could not be formed during secondary refining. Considering the microsegregation of solute elements and the equilibrium of TiN formation during solidification, TiN precipitated in the mushy zone when the solid fraction was close to 0.2. The growth of TiN was analyzed based on the diffusion-controlled growth model. With the increase in cooling rate, the time for TiN growth decreased and the size of TiN inclusions was diminished, which revealed the size distribution of TiN inclusions in the cast slab qualitatively.
TiN inclusion Ti-stabilized ultra-pure ferrite stainless steel Distribution in slab Thermodynamics Diffusion-controlled growth model
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The authors are grateful for support from the Fundamental Research Funds for the Central Universities (Grant Nos. FRF-TP-15-001C2, FRF-TP-15-067A1 and FRF-TP-17-039A1), Beijing Key Laboratory of Green Recycling and Extraction of Metals (GREM) and the High Quality steel Consortium (HQSC) at the School of Metallurgical and Ecological Engineering at University of Science and Technology Beijing (USTB), China.
J.F. Almagro, X. Llovet, M.A. Heredia, C. Luna, R. Sánchez, Microchim. Acta 161 (2008) 323–327.CrossRefGoogle Scholar
L.Y. Sun, J.S. Li, L.F. Zhang, S.F. Yang, Y.F. Chen, J. Iron Steel Res. Int. 18 (2011) No. 11, 7–11.Google Scholar
C.W. Sinclair, J.D. Mithieux, J.H. Schmitt, Y. Bréchet, Metall. Mater. Trans. A 36 (2005) 3205–3215.CrossRefGoogle Scholar