Acta Metallurgica Slovaca - Conference, Vol. 4, 2014, p Acta Metall. Slovaca Conf. 138

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1 Acta Metall. Slovaca Conf. 138 DEPHOSPHORIZATION OF FERROMANGANESE Mirosław Karbowniczek 1)*, Andrzej Michaliszyn 1), Zygmunt Wcisło 1), Wojciech Ślęzak 1) 1) AGH University of Science and Technology, Krakow, Poland Received: Accepted: * Corresponding author: mkarbow@agh.edu.pl, Tel.: , Department of Ferrous Metallurgy, Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, Krakow, Poland Abstract Phosphorus in steelmaking processes is a harmful admixture and at every stage of the production of steel must be removed from the melt. One of the sources are ferroalloys, which are used to introduce alloying element for steel. The paper presents method of dephosphorization of high and medium carbon ferromanganese using mixture based on CaO-CaF, containing in its composition CaSi and CaC. The experimental heats were conducted in an induction furnace with the capacity of 0 kg, in temperature about 1450 C. While the dephosphorizing mixture was being added, a stream of argon was being injected into the metal bath. Dephosphorization efficiency raged from 1 to 4%. This work has been shown the relationship between dephosphorization, and the amount of inert gas and initial concentration of phosphorus in ferromanganese. Keywords: iron alloys, steelmaking, ferromanganese 1 Introduction The removal of phosphorus out of the iron solutions in steelmaking processes is very important. Phosphorus causes large solution strengthening of ferrite, reduces the ductility and fracture toughness. It significantly increases the hardenability of steel. It has a negative effect on the impact strength and temper brittleness because phosphorus quickly migrates to the grain boundaries and interphase boundaries. There is a tendency to eliminate phosphorus already in the preparation of charge materials for steelmaking. Ferroalloys are such materials. In the production of ferromanganese main problem is the quality of raw materials, which determine the economics of the dephosphorization process, and thus the final product quality and purpose in the steelmaking processes. The best dephosphorizing properties cause slags to be formed on the base of oxides and halides of barium or calcium. The phosphate capacity of the slags containing barium compounds is higher, so the dephosphorization becomes more effective. As barium compounds are more expensive, whereas those of calcium are more available, the slags based on CaO-CaF are now mainly considered [1]. Especially the production of FeMnHC in blast furnaces contributes to high phosphorus content [-5]. In consequence the further treatment of the prime material to the grades with medium and low carbon contents meets the same task, namely the reduction of phosphorus to contents below 500 ppm. High affinity of manganese to oxygen as well as a low evaporation pressure does not prefer dephosphorization treatment under the oxidizing conditions. An alternative possibility is

2 Acta Metall. Slovaca Conf. 139 the dephosphorization by reducing treatment. Some publications [6-11] report about treatments with CaC, CaSi, CaSi or the other application. It was found that dependent on the carbon content using CaC at temperature about 1500 C can satisfactorily dephosphorize liquid FeMn. The reported efficiencies are in the range of 40-80%. It is also reported, that alternatively the CaSi or especially the CaSi with almost the same results can be used. The dephosphorization efficiency was obtained in these cases at >70%. The relationship between the phosphide capacity and the activity of CaO in the flux exhibited good linearity, indicating that the phosphorus was removed from the SiMn melt by the reducing refining mechanism [1]. The reducing refining mechanism occurs through the transfer of Ca from the CaSi introduced into the melt and the reaction between CaO in the flux and Si in the melt under strongly reducing conditions (equations 1 and ) [13]: ( CaO) + [ Si] = ( SiO ) [ Ca] + [ Ca ] + [ P] = ( Ca ) 3 P 3 Under reducing conditions phosphorus is removed by calcium carbide according to the reaction: (1.) (.) 3 1 [ P] + ( CaC ) = ( Ca P ) 3[ C] 3 + (3.) The efficiency of dephosphorization process may be given by the distribution coefficient for phosphorus between slag and the metal phase L P = (%P O 5 )/[%P], and dephosphorization degree, which is equal to the ratio of the phosphorus concentration removed from the metal to the initial phosphorus concentration η P = [% P]/[%P ini ]. Dephosphorization of a metal bath at oxidative conditions follows the reaction below: [1, 14] [ P] + [ O] + ( O ) = ( PO ) 4 (4.) The equilibrium constant of this reaction is given by a 3 ( PO4 ) K = 5 / 3/ a[ P] a[ O] a ( O ) (5.) This article analyses experimental possibilities and conditions for dephosphorization of ferromanganese. The study was focused on the selection of the optimal slag composition and the way the slag should be added. Methodology of research The experimental heats were conducted in an induction furnace with the capacity of 0 kg. The electrical parameters of the furnace were as follows: Current intensity: 0 1,5 ka Max. power: 30 kw Frequency 8 khz The power of the furnace was adjusted in the following way: 5 kw (melting the charge), 15 kw (time when the dephosphorization of the metal bath was conducted), 0 kw (the remaining time

3 Acta Metall. Slovaca Conf. 140 of the heat). The furnace was equipped with a pressed refractory lining made of high-aluminum refractory mass, which has the following chemical composition: 84% Al O 3 and 14% MgO. Fig. 1 shows construction of the induction furnace used for dephosphorization of FeMn trials. Fig. 1 Induction furnace for dephosphorization trials of FeMn During the heat the temperature of the metal bath was controlled by taking thermocouple temperature measurements as well as by taking metal and slag samples in order to analyse their chemical composition. In the course of research 3 heats of FeMnHC (high carbon ferromanganese) and 3 heats of FeMnMC (medium carbon ferromanganese) were conducted and various dephosphorization mixtures were used. The chemical composition of the manganese alloys and mixtures and that of components used to produce the mixtures can be seen in Table 1 and. Table 1 The chemical composition of manganese alloys Element Chemical composition [%] FeMnHC FeMnMC Mn 76,50 78,98 C 6,85 1,15 Si 0,97 0,41 P 0,096 0,09 S 0,007 0,009 N 0,039 0,049 Table Technology of experimental heats Test Material CaC CaSi CaF CaO Ar flow rate [Nl/min] Duration [min] 1. FeMnHC FeMnHC FeMnHC FeMnMC FeMnMC FeMnMC

4 Acta Metall. Slovaca Conf. 141 Mixtures packaged in paper bags dispensed in 4 portions every 3 minutes. While the dephosphorizing mixture was being added, a stream of argon was being injected into the metal bath. The stream had a precisely set intensity of flow. The intensity of the injected gas was kept at the level of 10 Nl/min for 0 or 5 min. (depends on technological variant). During the process temperature of metal bath was kept at about 1450 C. After melting of charge in the heats and 4 desiliconization was carried out by the scale addition in an amount of 50 g/heat and then after 3 minutes formed slag was removed. During the heats samples of metal was taken after melting and reaches the metal bath temperature about 1450 C, before addition of third batch of mixture and before tapping. With the final metal sample also slag sample was taken and temperature of metal bath was measured. 3 Results Table 3 shows result of dephosphorization of ferromanganese. It presents kind of material used in mixture, the initial and final content of phosphorus, process efficiency and kinetics, also gas consumption. The added dephophorising mixtures were composed of CaO, CaF and CaSi or CaC. The slag formed contained, apart from the used mixture components, products of the metals oxidation, i.e., FeO, MnO, SiO, P O 5 and the products of dissolution of the lining, MgO and Al O 3. The relations that were found on the basis of the conducted analysis are shown in Fig. through 5. Table 3 Results of dephosphorization of FeMn Heat Material P ini [%] P fin [%] % P/%P ini - P/ t [%]/min L P - Ar blown volume [Nl] 1. CaC 0,1 0,079 0,1 0, , CaSi 0,11 0,083 0,45 0, , CaSi 0,13 0,075 0,43 0, , CaC 0,094 0,068 0,77 0, , CaSi 0,095 0,066 0,305 0, , CaSi 0,13 0,1 0,31 0, ,87 19 Fig. shows the change in phosphorus concentration in the heats. The points on the curves represents moment of melting and reaches the metal bath temperature about 1450 C, moment before addition of third batch of mixture and moment before tapping. Fig. Change in phosphorus concentration during the heats

5 Acta Metall. Slovaca Conf. 14 Fig. 3 shows effect of argon consumption on the dephosphorization degree. The amount of injected gas mixture per heat ranged from Nl depending on the process. Efficiency increases with increasing of argon consumption. Dephosphorization efficiency raged from 1 to 4%. Fig. 3 Effect of gas consumption on the dephosphorization degree Fig. 4 shows effect of initial concentration of phosphorus on the dephosphorization kinetics. Rate of dephosphorization increases with higher initial concentration of phosphorus. Fig. 4 Effect of initial concentration of phosphorus on the dephosphorization kinetics Fig. 5 Effect of gas consumption on the distribution coefficient for phosphorus

6 Acta Metall. Slovaca Conf. 143 Fig. 5 shows effect of argon consumption on the distribution coefficient for phosphorus. Distribution coefficient for phosphorus between slag and the metal phase increases with increasing of argon consumption, which is dependent on time. 4 Summary This work has undertook dephosphorization of ferromanganese. Research were performed using high and medium carbon ferromanganese, using two types of dephosphorization mixtures. Research were carried out in an induction furnace, the melt temperature was about 1450 ºC. The mixture was introduced in portions, the metal bath was stirred using argon. Dephosphorization efficiency raged from 1 to 4%. Greater efficiency was observed at higher initial concentration of phosphorous and at higher total gas flow, therefore with the longer term of heat. A higher degree of dephosphorization obtained using CaSi, but a small amount of trials and difficulty in obtaining equal conditions of the process, at this stage does not allow to state clearly which compound is preferred. Research should be extended to a larger number of trials and the wider comparison of mixtures. It is advisable to also examine the effect of the addition CaSi or CaC and comparison with the base CaO-CaF system. References [1] M. Karbowniczek, E. Kawecka-Cebula, J. Reichel: Metallurgical and Materials Transactions B, Vol. 43, 01, No. 3, p , DOI: /s x [] M. Karbowniczek, J. Gładysz, W. Ślęzak: Journal of Achivements in Materials and Manufacturing Engineering, Vol. 55, 01, No., p [3] L.A. Smirnov, V.I. Zhuchkov, E.I. Arzamastsev, A.A. Babenko: An overview of current manganese and chromium ferroalloy production in Russia, In: 10th International Ferroalloys Congress, Cape Town, 004, p [4] G.N. Mulko, A.A. Bondar, V.A. Zaitsev, E.A. Nitskii, E.G. Cherkasov: Metallurgist, Vol. 44, 000, No., p , DOI: /BF [5] A. L. Groshkova, L. A. Polulyakh, A. Ya. Travyanov, V. Ya. Dashevskii, Yu. S. Yusfin: Steel in Translation, Vol. 37, 007, No. 11, p , DOI: /S [6] K. Kitamura, M. Funazaki, Y. Iwanami, T. Takenouchi: Transactions of the Iron and Steel Institute of Japan, Vol. 4, 1984, No. 8, p [7] G.G. Roy, P.N. Chaudhary, R.K. Minj, R.P. Goel: Metallurgical and Materials Transactions B, Vol. 3, 001, No. 3, p , DOI: /s [8] P.N. Chaudhary, R.K. Minj, R.P. Goel: Development of a process for dephosphorisation of high carbin ferromanganese, In: 11th International Ferroalloys Congress, New Delhi, 007, p [9] X. Liu, O. Wijk, R. Salin, J.O. Edstrom: Steel Research, Vol. 66, 1995, No. 3, p [10] Y. Nakamura, K. Harashima, M. Itoh: Tetsu-to-Hagane, Vol. 63, 1977, No. 14, p [11] Y. Watabene, K. Kitamura, I.P. Rachev, F. Tsukihashi, N. Sano: Metallurgical and Materials Transactions B, Vol. 4, 1993, No., p , DOI: /BF [1] H. Saridikmen, C.S. Kucukkaragoz, R.H. Eric: Phosphide and sulphide capacities of ferromanganese smelting slags, In.: Proc. 8th Int. Conf. on Molten Slag, Fluxes and Salts, Santiago, Chile, 009, p

7 Acta Metall. Slovaca Conf. 144 [13] J. H. Shin, J. H. Park: Metallurgical and Material Transactions B, Vol. 43, 01, No. 6, p , DOI: /s [14] C. P. Manning, R. J. Fruehan: Metallurgical and Materials Transactions B, Vol. 44, 013, No. 1, p , DOI: /s Acknowledgements Authors are grateful for the support of experimental works by project AGH