Inclusions evolution during the LF refining process of 439 ultra-pure ferritic stainless steel

摘要

The morphology, composition, size, and number of inclusions in 439 ultra-pure ferritic stainless steel samples were analyzed using an automatic scanning electron microscope combined with an energy-dispersive X-ray spectrometer. In addition, the appropriate contents of titanium, aluminum, and calcium were analyzed through the coupling of thermodynamics calculation and experimental results. CaO-Al2O3-MgO inclusions existed in the 439 steel before Ti additions in the ladle furnace (LF) refining process. After Ti addition in the LF refining process, the inclusions were transformed into CaO-Al2O3-MgO-TiO, inclusions. The evolution of these inclusions was consistent with thermodynamic calculation, which indicated that when the Al, Ca, and Ti contents were within a reasonable range, Ca treatment could significantly modify the aluminate and spinel to form CaO-Al2O3-MgO liquid inclusions. In addition, the compositions of inclusions after the addition of titanium were mostly located in the Al2O3-TiO, stable phase. The collision of the CaO-Al2O3-MgO liquid inclusions and Al2O3-TiO, inclusions resulted in the modification of the CaO-Al2O3-MgO-TiO, inclusions. The compositions of most inclusions were located in the liquid zone. The control range of the aluminum, calcium, and titanium contents was obtained: logAl% >= 1.481logTi% - 0.7166, Ca% 34.926(Al%)(3) - 3.3056(Al%)(2) + 0.1112(Al %) - 0.0003.