Steelmaking ›› 2019, Vol. 35 ›› Issue (6): 60-66.

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Evolution of Inclusions in Pipeline Steel Producted by the Route of BOF-LF-RH-Ca Treatment-CC

  

  • Accepted:1900-01-01 Online:2019-12-05

Abstract: The evolution of inclusions in the pipeline steel producted by the route of “BOF→LF→RH→Ca treatment→CC” was investigated. It was found that the polyhedral Al2O3 changed to spherical MgO-Al2O3-CaO-CaS complex inclusions after LF refining. There was no obvious change on the composition of inclusions, on the contrary, both the number density and the size of inclusions decreased during the RH refining process. After Ca treatment, the contents of CaO and CaS in inclusions increased, induced the increase of CaO/Al2O3, and the moving out from the low melting point zone of inclusions. During the continuous casting, the contents of Als and T.Ca in steel decreased due to the reoxidation, leading to the decrease of CaO and CaS in inclusions and the increase of the number density and maximum size of inclusions. Thus, protective casting should be strengthened to ensure the effect of calcium treatment. Due to the equilibrium movement between steel and inclusions during the cooling process, inclusions changed from liquid CaO-Al2O3 in tundish to high-melting-point inclusions in slab, which were mainly of Al2O3-CaS and MgO-Al2O3 types.

Key words: pipeline steel, Ca-treatment, inclusion transformation, reoxidation