Abstract

MAPHUTHA, M.P.; STEENKAMP, J.D.  and  PISTORIUS, P.C.. Investigation into the dephosphorization of ferromanganese alloys for the production of advanced high-strength steel. J. S. Afr. Inst. Min. Metall. [online]. 2021, vol.121, n.9, pp.487-496. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/1510/2021.

Advanced high-strength steels (AHSS) are sophisticated materials being developed by the steel industry to mitigate challenges related to the performance of motor vehicles. To meet the requirements of AHSS, the ferromanganese alloys (FeMn) utilized in the production of the steel are required to contain acceptable levels of unwanted impurities, i.e. P, S, N, H, and C. The focus of the current study was to investigate dephosphorization of ferromanganese to produce a low-P alloy that could be effectively utilized in the production of AHSS. The study involved conducting laboratory-scale testwork to study the efficiency of CaO-based slag systems to dephosphorize FeMn alloys. The addition of Na₂O, CaF₂, and BaO to MnO-CaO-SiO₂ slag was considered. The test work was carried out in a 25 kW induction furnace at temperatures of 1350°C, 1400°C, and 1450°C. The P partition coefficient (L_p) remained small at <1, which is an indication that dephosphorization had not been achieved. The baseline slag, comprising 40%CaO-40%SiO₂-20%MnO, reported higher L_pvalues. Addition of Na₂O and CaF₂ did not show any further benefit. Substituting half of the CaO by BaO, resulted in similar L_pvalues to those of the baseline slag under conditions of 1350°C and 1450°C at 30 minutes. In summary, based on the L_pvalues obtained, the conditions investigated with the CaO-based slags appeared to have been unfavourable for dephosphorization of FeMn alloys, as most of this impurity element remained in the alloy.

Keywords : ferromanganese; dephosphorization; advanced high-strength steel.

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