The diploma work presents the optimisation process for the production of PK3 stain-less steel in an electric arc furnace. The aim was to improve the yield of chromium and iron. Special attention was paid to the influence of the chemical composition of the scrap and melt and to the method of slag refining.
The research was carried out at the SIJ Metal Ravne steelworks. We analysed the production of three heats of PK3 steel. For each heat, we took 5 melt samples: after melting, decarburisation, reduction, tapping and at the final composition, and three slag samples: after melting, before reduction and after reduction. The chemical com-position of the slag was determined by X‑ray fluorescence spectrometry, and additio-nal analyses were performed by optical emission spectrometry with inductively cou-pled plasma. Based on the results of the first two heats, we optimised the composition of the charge, the amount of silicon in it, the amount of reducing agents and the basi-city of the slag.
The results of chemical analyses showed that the initial heats exhibited significant oxidation of chromium and iron, which was reflected in the increased content of chro-mium and iron oxides in the slag. The result was insufficient recovery of alloying ele-ments. After optimisation, the iron oxide content in the final slag decreased to 4.80 wt. %, and the chromium oxide content to 27.75 wt. %. Chromium recovery increased to 77 %, which is 12 % better than in the initial heats.
We found that the increased silicon content in the charge, the addition of ferrosilicon and aluminium, and the appropriate basicity of the slag effectively reduced chromium oxidation and improved the reduction of oxides from the slag. We assessed the first step of process optimisation as successful, but we also found that there is scope for further improvement of chromium recovery. Two paths can be used: either additional optimisation of reduction conditions in the electric arc furnace or further processing with secondary metallurgy processes.
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