ISIJ Interntionl, Vol. 43 (003), No. 10, pp. 1487 1494 Deoxidtion Equilibrium of Mngnese nd Silicon in Liquid Iron Nickel Alloys V. Y. DASHEVSKII, A. M. KATSNELSON, N. N. MAKAROVA, K. V. GRIGOROVITCH nd V. I. KASHIN Bikov Institute of Metllurgy nd Mteril Science, Russin Acdemy of Sciences, Leninskii prosp., 49, Moscow-119991, Russi. (Received on Februry 6, 00; ccepted in finl form on My 5, 003) The thermodynmic nlysis of oxygen solutions in Fe Ni melts contining mngnese nd silicon hs been crried out. The deoxidtion power of mngnese essentilly increses with the nickel content in melt. The solubility curves pss through minimum, which shifts to lower mngnese contents, s nickel content in melt increses. For lloys contining more thn 50 60% nickel, the miniml oxygen concentrtions re obtined t mngnese content equl to 1 1.5%, the further increse of mngnese concentrtion results in n increse of oxygen content. Silicon deoxidtion power lso increses with the increse of nickel content in melt, but not so shrply s in the cse of mngnese. In the rnge of silicon contents considered, no minimum ws observed in oxygen solubility curves. Thermodynmics of oxygen, mngnese nd silicon solutions in the Fe 40%Ni melts hs been studied experimentlly in temperture rnge of 1 83 1 93 K. With temperture drop, deoxidtion power of both mngnese nd silicon increses. In the Fe 40%Ni melts in both cses it is higher thn in iron but lower thn in nickel. Dependence of oxygen concentrtion on mngnese nd silicon contents is expressed by empiricl equtions. Upon combined deoxidtion with mngnese nd silicon, it is possible to obtin lower oxygen concentrtions in metl, in comprison with seprte deoxidtion due to decresed ctivities of mngnese oxide nd silic. KEY WORDS: deoxidtion equilibrium; mngnese; silicon; iron nickel melts; thermodynmic nlysis; experimentl study. 1. Introduction The Fe Ni lloys re widely used in modern engineering nd re, in prticulr, the bsis of lrge group of specil lloys. It is known tht oxygen is hrmful impurity in these lloys. Deoxidizing elements used upon lloy production llow one to obtin the finl metl with low oxygen content nd smll mount of nonmetllic inclusions. Mngnese nd silicon re most often used s deoxidizing elements. Avilble thermodynmic dt on the oxygen solutions in liquid iron 1,) nd nickel 1,3) re useful to estimte the oxygen solubility in the Fe Ni melts 4) s well s effect of mngnese nd silicon on the oxygen solubility. This study presents nlyticl nd experimentl investigtions on the thermodynmics of oxygen solutions in the Fe Ni melts contining mngnese nd silicon.. Thermodynmic Considertion Rection of deoxidizing elements R with oxygen in the Fe Ni melt: R m O n (l, s) m[r] n[o]...(1) m n ([% R] fr O] fo KR ) ([% )...(1) X RmOγ n RmOn where X i is mole frction, f i nd g i is the ctivity coefficient of element i in mss percent bse nd mole frction bse, respectively, cn be written s the sum of rections: n R mon( l, s) mr(l, s) O ( g)...() R(l, s) [R] 1% (Fe Ni)...(3) DG (3) RT ln(g R(Fe Ni) M Fe Ni /M R 100) 1...(4) O ( g ) [ O] 1%(Fe Ni) DG (4) RT ln(g O(Fe Ni) M Fe Ni /M O 100) where g i denotes the ctivity coefficient of element i in infinite dilution, nd M i denotes the moleculr mss of element i. From Gibbs energy of rection (1): DG (1) DG () mdg (4) ndg (4)...(5) it is possible to clculte the equilibrium constnt of rection (1): ln K R DG (1) /RT...(6) The concentrtion of oxygen, which is in equilibrium with R, t given R content cn be clculted by the eqution: 1487 003 ISIJ
ISIJ Interntionl, Vol. 43 (003), No. 10 Tble 1. Equilibrium constnts for rection (1), ctivity coefficients nd interction prmeters for in the Fe Ni melts t 1 873 K. log[%o] Fe Ni (1/n){log K R log X Rm O n log g Rm O n m log[%r] (Fe Ni) [me R R(Fe Ni) ne R O(Fe Ni) ][%R] (Fe Ni) [ne O O(Fe Ni) me O R(Fe Ni) ][%O] (Fe Ni) }...(7) where e j i denotes the interction prmeters when the component concentrtions re expressed s mss percents. The vlue [%O] (Fe Ni) in the right-hnd prt of Eq. (7) cn be expressed through the rtio (K R /[%R] m ) 1/n, ssuming tht X Rm O n 1, g Rm O n 1, f R 1, nd f O 1 in Eq. (1). This substitution does not result in pprecible error becuse of smll vlue [%O] (Fe Ni). This Eq. (7) tkes the form: log[%o] Fe Ni (1/n){log K R log X Rm O n g Rm O n m log[%r] (Fe Ni) [me R R(Fe Ni) ne R O(Fe Ni) ][%R] (Fe Ni) [ne O O(Fe Ni) me O R(Fe Ni) ](K R /[%R]m ) 1/n }...(7) The Gibbs energies, J/mol, for rection () re quoted from the published dt 5) : DG () (MnO) 401 63 84.3T ; DG () (SiO ) 906 44 175.85T For iron the reference literture ) gives the vlues of the equilibrium constnts of rection (1) for the deoxidtion of this melt with mngnese nd silicon: log K Mn(Fe) 14 880/T 6.67 ; log K Si(Fe) 30 110/T 11.40 For nickel the equilibrium constnt of rection (1) is given for the melts deoxidized with silicon s follows: log K Si(Ni) 15 680/T 1.83 6) In other cses the vlues of the equilibrium constnt of rection (1) for Fe Ni melts re clculted ccording to the scheme described bove (Eqs. () (6)). The moleculr mss for the Fe Ni melts ws clculted by the formul: M Fe Ni M Fe X Fe M Ni X Ni...(8) Bsed on subregulr model, the ctivity coefficients in dilute solution rnge g R(Fe Ni) nd g O(Fe Ni) re represented by the following eqution 7) : ln g i(fe Ni) X Fe ln g i(fe) X Ni ln g i(ni) X Fe X Ni [X Ni (ln g i(ni) ln g i(fe) e Fe i(ni) ) X Fe (ln g i(fe) ln g i(ni) e Ni i(fe) )]...(9) where e i denotes the interction prmeters in mole frction bse. The ctivity coefficients for iron nd nickel re given in Tble 1. Interction prmeters used in clcultions were the following: e Ni Mn(Fe) 0.007) ; e Ni Si(Fe) 0.0016) ; e Ni O(Ni) 0.05.8) ws ssumed to be zero similr to e Fe Si(Ni) Si(Ni) 0 6) ; e Ni O(Fe) 0.0068) ; e Fe The e Mn(Ni) Fe prmeter becuse of bsence of experimentl dt. The results of clcultions re listed in Tble 1. Dependence of clculted vlues of the equilibrium constnt for rection (1) on the content of deoxidizing gent nd nickel in the Fe Ni melt deoxidized with mngnese nd silicon t 1 873 K is represented in Tble 1 nd Fig. 1. The equilibrium constnts re given for the rection of deoxidizer with one tom of oxygen dissolved in melt, this llows one to more conveniently compre the bove reltionships. As is seen from the given dt, the equilibrium constnt of rection (1) in both cses decreses with n increse in the nickel content in melt, which indictes n increse in the deoxidtion power of both silicon nd mngnese. With mngnese, the degree of this increse is much lrger thn tht with silicon. 003 ISIJ 1488
ISIJ Interntionl, Vol. 43 (003), No. 10 Fig.. Dependence of MnO mole frction in oxide phse on Mn nd Ni contents in melt t 1 873 K. Fig. 1. Dependence of the equilibrium constnt of rection (1) on Ni content for deoxidtion of Fe Ni melts t 1 873 K. The interction prmeters for different melts (Tble 1) re estimted from the following ssumption: e i(fe Ni) j e i(fe) j X Fe e i(ni) j X Ni...(10) In cse of the deoxidtion of iron-bsed melt with silicon nd the residul silicon content in melt bove 0.00%, n oxide phse contins only SiO, 1) nd SiO X SiO 1. In the nickel-bsed melt, the silicon content in the presence of only SiO is quite low, since nickel is chrcterized by the less ffinity to oxygen in comprison with iron. When iron nickel melts re deoxidized with mngnese, the oxide phse, in ddition to MnO, lso contins FeO nd NiO. Therefore, it is necessry to consider the following rections 10) : Mn (l) FeO (l) MnO (s) Fe (l)...(11) DG (11) 91 614 J/mol, K (11) 357.81 t 1 873 K; Mn (l) NiO (s) MnO (s) Ni (l)...(1) DG (1) 168 751 J/mol, K (1) 50 68.9 t 1 873 K In the FeO MnO system, the continuous series of solutions is observed both in the liquid nd solid sttes 11) ; however, there re no published dt on the NiO MnO phse digrm. Therefore, bsed on the FeO MnO phse digrm, s the first pproximtion, we ssume tht the oxide phse formed upon deoxidtion of iron nickel melts with mngnese is the perfect solution (g MnO 1, g FeO 1, g NiO 1). The mngnese solutions in the iron nickel melts re chrcterized by slight positive devitions from the idelity (Tble 1) nd the dependence of the mngnese ctivity coefficient on its concentrtion in liquid iron t 1 843 K cn be described 1) by the expression lg g Mn lg g Mn (1 X Mn ) ; therefore, it cn be ssumed tht, t the low mngnese contents (X Mn 0.03), g Fe 1, g Ni 1, g Mn g Mn for the iron nickel melt. In this cse, the following equtions my be written: X X K 11 γ X MnO ( ) Mn(Fe Ni) FeO Fe X Mn X MnO K Mn(Fe Ni) XMn ( 1) γ...(13) X NiO X Fe X MnO X FeO X NiO 1 A mole frction of MnO in the oxide phse cn be clculted by these three equtions. The dependence of MnO mole frction in the oxide phse on the contents of mngnese nd nickel in melt 10) is shown in Fig.. In ironbsed melt, the MnO mole frction in the oxide phse reches to 0.3 0.5 t the low mngnese content ( 0.%). With incresing nickel nd mngnese contents in melt, the mole frction of MnO in oxide phse increses lso. For pure nickel, it pproches unity, i.e. prcticlly the oxide phse consists of mngnese oxide. The dependence of equilibrium oxygen concentrtion estimted by Eq. (7) on the contents of mngnese nd silicon in the Fe Ni melts t 1 873 K is given in Fig. 3. From the given dt one cn see tht the mngnese deoxidtion power considerbly increses with the increse of nickel content in melt (Fig. 3()). The oxygen solubility curves pss through the minimum, which shifts to the lower mngnese content with increse of nickel content in melt. For lloys contining more thn 50% of nickel, the minimum oxygen concentrtions re observed t the mngnese content equl to 1 1.5%.The deoxidtion power of silicon lso increses with the increse of nickel content in melt (Fig. 3(b)). In considered rnge of silicon content no minimum ws observed s seen from the oxygen solubility curves. 3. Experimentl Deoxidtion of Fe Ni melts with mngnese nd silicon (seprtely or together) hs been studied experimentlly by using Fe 40%Ni lloy in wide rnge of tempertures nd concentrtions of deoxidizing gent. The experiments hve been crried out in n induction furnce fed by n 10 kv A HF genertor. Crbonyl iron (99.99%), electrolytic nickel (99.99%), electrolytic mngnese (99.99%) nd crystlline silicon (99.999%) were used s chrge. The metl ws melted in the Ar H tmosphere t tempertures of 1 83 1489 003 ISIJ
ISIJ Interntionl, Vol. 43 (003), No. 10 Fig. 3. Dependence of oxygen content in the Fe Ni melts on the content of Mn (), Si (b), nd Ni t 1 873 K. 1 93 K in n lumin crucible in the cse of mngnese or mngnese silicon deoxidtion nd in qurtz crucible in the cse of silicon deoxidtion. Deoxidizing gents (Mn, Si) were introduced into the melt without breking the furnce ir-tightness; then this melt ws held t given temperture until equilibrium in Ar tmosphere. The temperture ws mesured by Pt 6%Ph/Pt 30%Ph thermocouple. Equilibrium being chieved, smple ws tken from the melt nd nlyzed for nickel, mngnese nd silicon. The oxygen concentrtion ws determined by inert gs fusioninfrred bsorptiometry. 4. Results nd Discussion 4.1. Deoxidtion with Mngnese The experimentl results re shown in Fig. 4() s compred to the clculted lines. As is seen from the experimentl dt points, the mngnese deoxidtion power considerbly increses with the temperture drop. Oxygen solubility curves pss through minimum, which shifts to the lower mngnese contents when temperture drops. Experimentl vlues of the equilibrium oxygen concentrtion for the Fe 40%Ni lloy t 1 873 K re lie below the clculted lines. The distinctions between experimentl nd clculted dt my be ttributed to the fct tht oxide phse contined smll mounts of Al O 3 long with MnO, FeO, nd NiO, owing to rections of oxide phse with lumin crucible used in these experiments. Dependence of oxygen concentrtion nd vlue of log K Mn (K Mn [%Mn][%O]) on the mngnese content nd temperture cn be described by the following empiricl equtions: 1 83 K ; 0.1.50% Mn log[%o].49 0.18[%Mn] 0.68 log[%mn]...(14) Fig. 4. Dependence of oxygen content in Fe 40% melts on the contents of Mn () nd Si (b). log K Mn.5 0.68 log[%mn]...(15) 1 873 K ; 0.05 1.47% Mn log[%o].6 0.14[%Mn] 0.76 log[%mn]...(16) log K Mn.13 0.35 log[%mn]...(17) 1 93 K ; 0.07 1.99% Mn log[%o] 1.18 0.6[%Mn] 0.18 log[%mn]...(18) log K Mn 1.59 0.48 log[%mn]...(19) 4.. Deoxidtion with Silicon The experimentl results re given in Fig. 4(b) s compred to the estimted dt. As is seen from the given dt, the silicon deoxidtion power considerbly increses with the temperture drop. Dependence of oxygen concentrtion nd vlue of log K Si (K Si [%Si][%O]) on the silicon content in melt nd the temperture within the rnge of silicon concentrtions considered cn be described by the following empiricl equtions: 1 83 K ; 0.08 4.30% Si log[%o].67 0.50 log[%si]...(0) log K Si 5.3 0.037 log[%si]...(1) 1 873 K ; 0.08 4.30% Si log[%o].53 0.51 log[%si]...() log K Si 5.03 0.06 log[%si]...(3) 003 ISIJ 1490
ISIJ Interntionl, Vol. 43 (003), No. 10 1 93 K ; 0.08 1.90% Si log[%o].35 0.5 log[%si]...(4) log K Si 4.65 0.075 log[%si]...(5) The experiments hve been crried out to study the deoxidtion of the Fe 40%Ni with silicon t its low contents (0.009 0.08%) t 1 873 K. Dt obtined re plotted in Fig. 4(b). The experimentl finding tht reltionship between oxygen nd silicon contents is not liner t [Si] 0.05% suggests the presence of iron nickel silictes (Fe, Ni)O SiO s rection products t such silicon concentrtions. 1) Extrpoltion of the reltions log K Si [%Si] obtined for the Fe 40%Ni lloy to zero silicon content llowed one to determine the equilibrium constnt K Si for the tempertures considered: (SiO ) [Si] [O]...(6) K Si...(6) nd to obtin eqution for the temperture dependence of the equilibrium constnt: log KSi 3 607....(7) T 7 610 The K Si equilibrium constnt determined by Eq. (7) t 1 873 K is in good greement with the dt bove estimted (Fig. 1). 4.3. Complex Deoxidtion with Mngnese nd Silicon Complex deoxidtion with mngnese nd silicon gives lower concentrtions of oxygen in metl due to decrese in the ctivities of silic nd mngnese oxides. The deoxidtion of the Fe 40%Ni lloy with silicon hs been studied experimentlly t the mngnese content in melt equl to 0.05 0.06, 0.10 0.1, 0.0 0., nd 0.48 0.51% t 1 873 K. The results obtined re given in Fig. 5. As is seen from these dt, the mngnese silicon complex deoxidtion enbles one to obtin the lower oxygen concentrtions thn silicon deoxidtion nd the considerbly less contents thn mngnese deoxidtion. Dependence of oxygen concentrtions in melt on the silicon content for ech mngnese concentrtions rnge cn be described by the following empiricl equtions: 0.05 0.06% Mn nd 0.0 0.19% Si log[%o].77 1.05[%Si] 0.61 log[%si]...(8) 0.10 0.1% Mn nd 0.01 0.% Si log[%o].77 0.94[%Si] 0.57 log[%si]...(9) 0.0 0.% Mn nd 0.0 0.50% Si log[%o].75 0.51[%Si] 0.5 log[%si]...(30) 0.48 0.51% Mn nd 0.05 1.41% Si log[%o].67 0.04[%Si] 0.43 log[%si]...(31) The region of silic-sturted silictes ( SiO 1) is bound by curve 1 (Fig. 5), which corresponds to Eq. (). These results gree with those of combined deoxidtion of ironbsed melts with mngnese nd silicon. 13) Solving Eqs. [Si] [ O] (SiO ) Fig. 5. Dependence of oxygen content in the Fe 40%Ni melt on the contents of Mn nd Si t 1 873 K. (8) to (31) nd () together, one cn determine the content of silicon ([Si]*) corresponding to the deoxidtion products sturted with silic t 1 873 K for the given mngnese content in the Fe 40%Ni melt: [Mn], % 0.05 0.06 0.10 0.1 0.0 0. 0.48 0.51 [Si]*, % 0.15 0.0 0.43.63 The results obtined cn be described by the following eqution: log[%si]* 0.96.78[%Mn]...(3) Solving this eqution for [Mn] 0, we obtin [%Si]* 0.11%, which grees with the bove given results of deoxidtion of the Fe 40%Ni melt only with silicon. When deoxidized with couple of mngnese nd silicon, they re in the equilibrium with the deoxidtion products: (SiO ) [Mn] (MnO) [Si]...(33) K (33)...(34) The ctivities of mngnese oxide nd silic in the deoxidtion products cn be clculted by the following formuls 14) : MnO [%O] MnSi /[%O] Mn t the sme [%Mn]...(35) SiO [%O] MnSi /[%O] Si t the sme [%Si]...(36) These ctivities estimted by Eqs. (35) nd (36), re given in Tble. This clcultion performed for 0.0% Mn nd 0.01 0.43% Si in melt. Oxygen concentrtions for the melts deoxidized with mngnese ([O] Mn ) were estimted by Eq. (16), for the melts deoxidized with silicon ([O] Si ) by Eq. (), nd for the melts deoxidized with mngnese nd silicon ([O] MnSi ) by Eq. (30). Dependencies of MnO nd SiO ctivities in the MnO SiO melt on their mole frctions reported by Abrhm et l. 15) re given in Fig. 6. If it is ssumed tht MnO nd SiO were only present in the oxide phse during our experiments on mngnese nd silicon deoxidtion, then, by plotting the estimted vlues of the SiO ctivity (Tble ) on the line obtined in previous work, 15) it is possible to determine the MnO nd SiO mole frctions in the oxide phse (Tble 3). The obtined dependence of the MnO ctivity on MnO [Si] SiO Mn 1491 003 ISIJ
ISIJ Interntionl, Vol. 43 (003), No. 10 Tble. Clculted ctivities of silic nd mngnese oxide for the combined deoxidtion of the Fe 40%Ni lloy with mngnese nd silicon t 1 873 K. Tble 3. Clculted vlues of SiO nd MnO mole frctions in oxide phse. The vlues of K (33) given in Tble were clculted by the following eqution: K (33) MnO SiO [%Si] [% Mn]...(37) Fig. 6. Activities of MnO nd SiO in the MnO SiO melt. the mole frction (Tble 3) is shown in Fig. 6 by dotted curve. As is seen from Fig. 6, the dependence obtined in the present study grees stisfctorily with the reported one. 15) Smll discrepncy seems to be cused by smll mounts of Al O 3 dissolved from Al O 3 crucibles t the experiment. Clculting K (33) nd ssuming tht ctivity coefficients of mngnese oxide nd silic clculted t [Mn] 0.% re vilble t different mngnese nd silicon contents in melt, it is possible to evlute the silicon content by Eq. (37) nd the oxygen concentrtion in the melts deoxidized with silicon nd couple of silicon nd mngnese by Eqs. () nd (36), respectively. Clcultion hs been performed for mngnese concentrtions of 0.1, 0.3, 0.4 nd 0.5%. Dependence of the oxygen concentrtion on contents of silicon nd mngnese in melt t 1 873 K cn be written in the form of the following empiricl equtions: t [Mn] 0.1% log[%o].75.33[%si] 0.5 log[%si]...(38) t [Mn] 0.3% log[%o].75 0.3[%Si] 0.5 log[%si]...(39) t [Mn] 0.4% log[%o].75 0.13[%Si] 0.5 log[%si]...(40) 003 ISIJ 149
ISIJ Interntionl, Vol. 43 (003), No. 10 t [Mn] 0.5% log[%o].75 0.08[%Si] 0.5 log[%si]...(41) The obtined dependencies re in good greement with similr results clculted on the bsis of experimentl dt (Eqs. (9) nd (31)). Figure 7 shows the dependence of oxygen concentrtion on the contents of silicon nd mngnese in melt t 1 873 K. The joint solution of Eqs. (30), (38) (41) nd () llowed one to evlute the content of silicon ([Si]*) when deoxidtion products re sturted with silic: [Mn], % 0.1 0. 0.3 0.4 0.5 [Si]*, % 0.105 0.430 0.945 1.680.65 The obtined dt cn be empiriclly written s: log[%si]* 1.167 3.398[%Mn]...(4) If [Mn] 0, then [Si] 0.07%, which grees with tht clculted by Eq. (3). It is lso possible to clculte the corresponding mngnese contents for given silicon contents by Eq. (37) when silic sturted oxide phse ( SiO 1) is formed. In this cse, Eq. (37) cn be revised to Eq. (43) [%Mn] MnO ([%Si]/0.555) 1/...(43) where MnO represents the ctivity of mngnese monoxide in the silic-sturted oxide phse t 1 873 K, which equls to 0.30 (Tble ). The reltions of residul mngnese nd silicon contents for the boundry of immiscibility region in the MnO SiO system t 1 873 K re represented below nd in Fig. 8: [Si], % 0.05 0.1 0. 0.5 1.0.0 3.0 5.0 [Mn], % 0.069 0.098 0.138 0.18 0.309 0.436 0.535 0.690 [%Mn]/[%Si] 1.380 0.976 0.690 0.436 0.309 0.18 0.178 0.138 It is seen from the dt shown tht the high [%Mn]/[%Si] rtios re necessry when silicon residul contents re rther low, nmely, not bove 0.05%, i.e. when the loss of deoxidizers is high. At low losses (low degree of oxidtion in melt), it is not necessry to hve the high [%Mn]/[%Si] rtio. The oxide phse contining lrge mount of mngnese oxide is inexpedient becuse of the high melting point of mngnese oxide ( 058 K); t MnO 80% the solid phse is formed in the MnO SiO system. 14) Super high [%Mn]/[%Si] rtio cn be clculted by Eq. (37), bove these rtios the deoxidtion product contins solid mngnese oxide. As shown bove, in the cse of MnO 0.99, SiO 0.079, nd K (3) 3.10 (Tble ), Eq. (37) is revised s follows: [%Mn].00([%Si]) 1/...(44) The results clculted by this eqution t 1873 K re shown below: Fig. 7. Fig. 8. Oxygen content in the Fe 40%Ni melt deoxidized with Mn nd Si t 1 873 K. Boundry of immiscibility region in the MnO SiO system between solid SiO nd liquid silictes t 1 873 K. [Si], % 0.01 0.0 0.05 0.1 0. 0.5 1.0.0 3.0 5.0 [Mn], % 0.00 0.83 0.447 0.63 0.894 1.414.000.88 3.464 4.47 [%Mn]/[%Si] 0.00 14.14 8.944 6.34 4.47.88.000 1.414 1.155 0.894 Fig. 9. Regions of solid nd liquid products of deoxidtion with Mn nd Si in the Fe 40%Ni melt t 1 873 K. On condition tht the liquid products of deoxidtion should be obtined s result of deoxidtion of the Fe 40% Ni melt nd summrizing the dt given bove, the region of solid nd liquid products of deoxidtion with mngnese nd silicon t 1 873 K cn be determined from the dependence given in Fig. 9. Curve 1 seprtes mngnese sili- 1493 003 ISIJ
ISIJ Interntionl, Vol. 43 (003), No. 10 ctes sturted with silic from the silic solid solutions. Curve is boundry between liquid mngnese silictes nd the solid solutions bsed on mngnese oxide in the MnO SiO system. The region between these curves corresponds to liquid mngnese silictes in equilibrium with mngnese nd silicon in metl. In the left-hnd portion of this plot (Fig. 9) the zone (up to 0.05% Si) of liquid silictes (iron silictes minly) is shown, s the equilibrium oxide phse bove the Fe 40%Ni melt contins 99% FeO nd 1% NiO. 4) In ddition, two stright lines in prllel to X-xis re drwn in the region of liquid silictes, which divide this region into three portions. These lines re drwn from the viewpoint of deoxidtion kinetics. When the complex deoxidizer ws used, for exmple, silico-mngnese, processes of dissolution nd oxidtion proceed simultneously. Thus, it is most probble to ssume tht deoxidtion rte is controlled by the dissolution nd diffusion of deoxidizing gent in melt. Therefore, mngnese nd silicon rect in mounts directly proportionl to their contents in the deoxidizer. So, it is s optimum to ssume [%Mn]/[%Si] 1.4 8. Bsed on the resons indicted, despite of the mount of mngnese lloys dded s deoxidizing gent, the solid rection products cn be in the form of solid inclusions due to low diffusion rtes. Shded zone (Fig. 9) represents liquid silictes formed fter deoxidtion with mngnese nd silicon. Within the region A deoxidtion products should be in the liquid stte under equilibrium conditions. However, if to consider the deoxidtion process from viewpoint of kinetics or choice of deoxidizer composition through the rtio [%Mn]/[%Si], then, the liquid solid products will be obtined fter deoxidtion using lloys with [%Mn]/[%Si] rtio 1.4. To form liquid mngnese silictes, mngnese should be consumed in mounts thn those of silicon by fctor 1.4. Therefore, silicon is first oxidized, being precipitted in the form of solid inclusions nd, when [%Mn]/[%Si] rtio increses, liquid silictes re formed. Formtion of solid mngnese oxide in the region B is possible due to the resons similr to those indicted in the cse of A region. With temperture drop, the rnge of the optimum mngnese to silicon rtios in the deoxidizer nrrows. 5. Conclusions The thermodynmic nlysis of oxygen, mngnese nd silicon dissolved in Fe Ni melts hs been crried out. The deoxidtion power of mngnese essentilly increses with n increse in the nickel content in melt. The solubility curves pss through the minimum, which shifts to the lower mngnese contents with n increse in the nickel concentrtion in melt. For lloys contining more thn 50 60% nickel, the minimum oxygen concentrtions re reched t the mngnese content in melt equl to 1 1.5% The further increse in the mngnese content cuses the increse of oxygen concentrtion. The silicon deoxidtion power lso increses with n increse in the nickel content in melt, but not so shrply, s in the cse of mngnese. In the considered rnge of silicon contents, no minimum ws observed in the oxygen solubility curves. Thermodynmics of oxygen solutions in the Fe 40%Ni melts contining mngnese nd silicon hs been studied experimentlly within temperture rnge of 1 83 1 93 K. With temperture drop, the deoxidtion power of both mngnese nd silicon increses. In the Fe 40%Ni melts, the deoxidtion power of mngnese nd tht of silicon re higher thn in iron but lower thn in nickel. Dependence of oxygen concentrtion on mngnese nd silicon contents is described by empiricl equtions. When complexly deoxidized with mngnese nd silicon, it is possible to obtin the lower oxygen concentrtions in metl, in comprison with the individul deoxidtion, due to the decrese in the ctivities of mngnese oxide nd silic in the oxide phse. 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