3rd International Iron and Steel Symposium (UDCS’17) 3 – 5 April 2017, Karabük University Effects of Slag Optimization on Steel Cleanliness in Secondary Metallurgy Process Emre ALAN Steelmaking and Casting Tech. R&D Department Ereğli Iron and Steel Works, Co. (Erdemir) 03.04.2017

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Outline Introduction Experimental Results Conclusion

Slag in Steelmaking Steelmaking slags are by-products of smelting and refining proesses of liquid steel in high temperatures and they consist of a mixture of various oxides. The role of slag in steelmaking process; acts as a thermal barrier to prevent heat transfer from liquid steel to surrounding, protects liquid steel from re-oxidation, Absorbs non-metallic inclusions and provides steel cleanliness, etc. Ladle slag in steelmaking process.

Non Metallic Inclusions (NMIs) Non metallic inclusions (NMIs) are chemical compounds that are formed in steel making process such as oxides, sulfides, nitrides, etc. The term of “clean steel” should mean a steel free of non-metallic inclusions. There are generally two sources of inclusions in steel; Exogenous Usually larger in size, are results of reoxidation, slag entrainment and refractory erosion. Indigenous Generally smaller in size, are results of chemical reactions; deoxidation, etc. Depending on their size, distribution and morphology NMIs may cause adverse effects on; Mechanical properties like strength and fatigue, Machinability Nozzle clogging in continuous casting process Surface polishing and finishing Welding properties Magnetic properties

Steelmaking Process Route Tapping Alloying addition Flux addition BOF Process LF Process Continuous Casting Homogenization Heating Alloying addition Inclusion removal

Tapping Addition Practice Experimental In this study, the effects of different tapping addition practices were compared in order to produce a cleaner steel. TABLE I Comparıson of Tappıng Addıtıons Tapping Additions [kg] Tapping Addition Practice Regular Trial Ferro Manganese [H.C] 1550 Ferro Silicomanganese 1500 1700 Calcium Fluorite 100 - Calcium Aluminate 550 Lime 1350 1100 Aluminium [Ingot] 350 80

(a) regular and (b) trial heats. Results Computational Thermodynamic Studies Ternary phase diagrams of ladle furnace slags plotted by using FactSage Computational Thermodynamic Software; (a) regular and (b) trial heats.

Results Secondary Metallutgy Process Conditions LF Process TABLE III Comparıson of feot and mno Contents ın Ladle Slags Accordıng to Tappıng Addıtıon Practıces Sample Component [%] FeOt MnO BOF Slag 20,4 3,8 Regular 1,5 0,8 Trial 0,6 0,1 CaSi wire Alloying Addition Steel sample LF Process [S] content in secondary metallurgy process. Addition practices in secondary metallurgy process.

Results Spark-DAT/OES Investigations CaS inclusions in liquid steel according to S content before CaSi wire injection. ARL Spark-DAT/OES analyzing instrument and methodology. Comparison of total non-metallic inclusions after secondary metallurgy process.

(a) regular and (b) trial heats. Results Optical Microscopy Investigations Optical microscopy images with 100X magnification of samples taken from end of secondary steelmaking process; (a) regular and (b) trial heats.

Conclusion In this study, the effects of different tapping additions to ladle slag conditions and steel cleanliness were investigated. In trial heats, increasing of Al2O3 content of slag in tapping process provided an increment in fluidity of initial ladle slag by dissolving over-saturated CaO content. Slag deoxidation was applied by adding Al onto slag to obtain lower FeOt content in initial ladle slag. Therefore, the desulphurization efficiency of slag is increased by obtaining a proper slag formation, increasing slag basicity and reducing FeOt content in trial heats. It was observed that the total number of detected non-metallic inclusions were reduced after secondary metallurgy process by reducing the amount of addition materials in secondary metallurgy process by increasing the addition amounts during tapping.

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