Observational Study of Clogging Specimens from the Tundish Well Showing Origin and Growth of a Clog in an Al-Killed Ti-Alloyed Steel Cast
Post-mortem tundish skull samples of Ti-alloyed, Al-killed IF steel have been studied regarding the formation of clogging. By using modern characterization equipment and applied methods, we performed a detailed characterization of microstructures found in the tundish well. Aside from the primary metallographic examination, newly developed methods of particle size distribution analysis based on population density functions (PDF) and newly developed electron microscope EDS template mapping have been applied, allowing differentiation of complex particles according to phases and interphase contact relationships. Furthermore, detailed EDS analyses of individual inclusions with complex substructure regarding minor and trace elements within the alumina networks have been performed. These composite data on carefully selected clog microstructures allowed us to observe the presence of layering microstructures throughout the clog: “Coarse” layers (abundant microbubbles and internally complex alumina aggregates) and “Fine” layers (no microbubbles and complex alumina aggregates). Two populations of particles: Population I (2 to 5 µm) and a Population II (5 to 20 µm) build up the layers, both having lognormal PDF, in contrast to power-law PDF of secondary metallurgy inclusions. Coarse layers are further distinguished by selective concentrations of spinel with lognormal PDF as well as the occurrence of complex alumina particles with metal sub-inclusions often with elevated Cr, V, and Si content. Based on these observations, we derive a model for the origin and accumulation of the inclusions making up the clog, which suggests that the NMI of the two dominant populations do not come from the bulk steel, although secondary metallurgy-derived inclusions can be traced in the clog. Overall, microstructures show that the clog behaves as a coherent solid, and is able to displace and fracture.
The authors thank Tata Steel for the permission to publish. Many colleagues contributed to the work and observations presented here. We want to thank C van Hoek for help with EDS analyses, F van der Does and E Dogan for material preparation and W Tiekink, J Small, and SR van der Laan for helpful discussions. This work is a part of the graduation thesis of one of the authors (B. K.) performed at Rzeszow University, Poland, in 2017 (Supervisor: W. Bochnowski).
- 1.G. C. Duderstadt, R. K. Iyengar, J. M. Matesa: J. Met., 1968, 20:89-94Google Scholar
- 3.K. Rackers and B.G. Thomas: in 78th Steelmaking Conf. Proc., 1995, vol. 78, pp. 723–34.Google Scholar
- 10.O. Araromi, B.G. Thomas, E. Conzemius: Mat. Sci. Tech. Conf., AIST, 2009, pp. 1–10Google Scholar
- 11.S. Wu, Y. Wang, L. Zhang, and J. Zhang: AISTech 2009, Proceedings of the Iron & Steel Technology Conference, pp. 543–58Google Scholar
- 13.H. Barati, M. Wu, A. Kharicha, and A. Ludwig: Powder Technol., 2018, pp. 29181–98Google Scholar
- 17.T Matsui, T Ikemoto, K Sawano, I Sawada: Taikabutsu Overseas, 1997, 18 3-9Google Scholar
- 20.F Tehovnik, J Burja, B Arh, M Knap: Metalurgija (2015) 54:371-374Google Scholar
- 23.E. Zinngrebe, J. Small, S.R. van der Laan, and A. Westendorp: Unpubl. Res. Submitted to Met. Mat. Ser. B, 2018 (under review)Google Scholar
- 24.B Karnasiewicz: Unpubl. Masters Thesis, Univ of Rzeszow, 2017.Google Scholar
- 29.L. Zhang, W. Pluschkell, and B.G. Thomas: 85th Steelmaking Conf., 2002, vol. 85, pp. 463–76Google Scholar
- 30.O. Adaba, P. Kaushik, R. O’Malley, S. Lekakh, L. Von Richards, E. Mantel, and E. Ellis: Iron Steel Technology, 2017, pp. 38–49Google Scholar
- 34.R. Dekkers: PhD Thesis, Kath Univ. Leuven, 2002.Google Scholar