Panchenko O. Development, research and introduction of production of high quality and competitive ball-bearing steel

The thesis is devoted to the synthesis and analysis of theoretical and experimental research and in-dustrial implementation of production of ball-bearing steels ShH15SG-V, ShH15-V in electric furnaces of PJSC "Dneprospetsstal". Data analysis of the ball-bearing steel quality in recent years (2003-2006) has shown its decline mostly by presence of globular and oxide inclusions due to increased calcium content. The sources of calcium and its content variations at all stages of steel production have been analysed. It was found that one of the major calcium sources is commercial ferrosilicon FeSi65 (DSTU 4127-2002) with has non-regulated varying calcium content (0.3-0.6% Ca). The key provision of new technology of steel production is the diversification of ferroalloys use, es-sentially exclusion of ferromanganese FeMn78 (DSTU 3547-97) and application of MnSi17 (DSTU 3548-97) and ferrosilicon to adjust the silicon content. Thermodynamic analysis of the reactions of semi-product metal deoxidation with Mn, Si, Al and Ca coming from ferrosilicon and reduced from slags by silicon and aluminium has been carried out. The phase equilibria were analyzed in the Fe-1%C-O-Al-Ca-Mg system according to G.G. Mihailov. The mi-crostructure and composition of heterogeneous globular and stroke-like oxide inclusions in billets and rollings of ShH15SG-V steel were investigated using energy-dispersive spectrometer with an electron mi-croscope JSM 6360 LA and microanalysis REMMA 101A. Application of imported low-Ca ferrosilicon has demonstrated reduction of globular inclusions in 21 experimental heats, but simultaneously it led to increase of oxide inclusions, so the total metal quality was not reduced. The effect of CaF2 additions on the stability and acting capacity of refining slag was ana-lysed for processing steel in the furnace-ladle combination and the increase of FeO activity in the slag has been confirmed. Computer thermodynamic modelling of the equilibrium compositions of all possible phases in the gas phase (for which the partial pressure of not less than 10-25 atm) has been carried out. It was found that in the temperature range 1300-1800°C leading compounds of the argon-rich gas phase are CaF2, OAlF2 and AlF, with their partial pressures at 1800°C (atm) 1.06^10-2; 5.61^10-3; and 2.14^10-3 re-spectively. The technology of smelting and refining of ball-bearing steels ShH15SG-V and ShH15-V has been developed and implemented by PJSC "Dneprospetsstal" using silicomanganese alloy MnSi17. The yield of billets and rolled steel from the first commissioning of control according to GOST 801-78 and ASTM E-45 (Method A) has increased from 63-70% (conventional technology) up to 92-98% in developed new technology. Specific consumption of ferroalloys was decreased by 15% per each ton of steel. The eco-nomic effect of new technology commercialization is 1,661 mln hryvna. The novelty of the technology has been protected by Ukrainian patent № 98284 "Method of bearing steel smelting" (with priority from 25.04.2012)