Modification of Nonmetallic Inclusions in Steel with Yttrium

D0I:10.13374/j.issn1001-053x.1989.06.022 北京科技大学学报 第11卷第6期 Vol.11 No.6 1983年11月 Journal of University of Science and Technology Beijing Nov.1989 The“Point”and“Volume”Fusion Behaviour of Prefused Type Powder Fluxes' Jin Shantong(金山，问)，Zou Mingjin（邹明金)* ABSTRACT:The relationship among particle size,properties of heat transfer and melting rate of fluxes as well as the main factors which have effect on the prefused fluxes have been studied.Under the conditions of same components and particle size,the melting temperature of prefused fluxes is lower than that of mixed fluxes.With the decreasing of particle size,the difference of melting te- mperature between the two type of fluxes decreases also.The larger the parti- cle size,the greater the melting rate of prefused type fluxes. KEY WORDS:fusion behaviour,flux,prefused type The proeprties of cast fluxes in the mold is usually determined by their che- mical compositions,the components of raw materials and the physical properties of the fluxes produced by different ways which include the processes of mixing, prefritting and prefusing. A series of researches has been done for simple mixed type powder fluxe- st2-01,and sufficient know ledges and experience are available.The relationship betwcen the properties of mold fluxes,such as viscosity,interfacial tension,abi- lity of absorbing inclusions,activity of the compositions and the temperature are sufficiently clear,but the influence of the properties of the raw materials on the melting characteristics difference between the prefused and the simply mixed pow der fluxes must be understood clearly.Therefore,this paper mainly focused on studying the difference of the "point"and "volume"fusion characterislics be- tween them,with the aims of finding the effect of some primary faclors,such as the major composition of fluxes,kinds of additives and particle size,on the be- haviour of prefused fluxes,and studying the relations of the particle size with the heat transfer as well as the fusion rate. Manuscript Reccived March 1,1989 ·Dcpt.of Metallurgy 516

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1 Experimental In order to compare the fusing behaviour of two kinds of fluxes,chemically pure reagents were used to compound fluxes which were carbon-free.The ingre- dients of fiuxes and the particle size are shown in Table I. Table 1 The ingredient of fluxes and the particle size Composition Composition,% Particle size type SiO2 CaO Al2O3 CaF Na2 CO3 Fe2Os mesh mixed <10055-75,75- 50 40 10 100,100-150, prefused 150-200,<200 mixed <10055-75,75- Il 44 35.5610 10 100,100-150, prefused 150-200,<200 III mixed 4444 35.5610 10 <100 IV mixed 52.78 42.2210 5 <100 At the same lime,an investigation of the fusion behaviour of prefused powder fluxes used in industrial production has been shown as follow:composition(%)- Si02,3982;Ca0,37.47;Mg0,318;Fe20g,331;A1,0g,9.31;Na20,2.23: K20,0.57;size range of fluxes(mm):0.71~1.4;1.4~3.0;3.0~5.0;5~7; 7~11.8. The drip-melt method was adopted to measure the "point"melting behaviour of flux in the experiment.Because the heat capacity of samples were much less than that of furnace,it was supposed that the samples were so small (63mmx 3mm)that they had the same temperature of the furnace and the temperature homogenization of the samples could be reached in a twinkling,ie.,the effect of interior heat transfer of sample on its melting behavior could be neglected. The precedure of experiments was as follows: (1)Heating the furnace up to 1000C; (2)Charging the sampling into the furnace; (3)Keeping the heating rate in the range of 5.5-6.8C/min; (4)Observing the change of sample height with the increase of furnace tempe- rature; (5)Recording the starting melting temperature toto finish melting tempe- rature (1.)and the rate (dHi/dti)during melting (shown in Figl.) 517

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He Temperature,℃ Eig,1 Change of sample height of mold flux with furnace 妞 temperature Fig,2 Schematic of the apparatus used for measuring the "volu- In fact,the melting of fluxes is me"melting behavlour of flux completed in three-dimensional space 1.flux; 2.corubin tube; 3.coil 4.Al2O3 crucibler in practical utilization,that is,a tempe- 5.Al203 packing;6.graphite base; rature gradient exists in the vertical 7.corubin tuber 8.supporty 9.Pt/Rh themocouples direction of flux layer. 10,corubin crucible, The graphite base heated by induction was used for finding the "volume" melting characterislics of flux.The mold flux whose weight was 140g was set in the furnace and whose temperature had been rised to 1550C and kept stable. Absorbed heat in horizontal direction,the molten flux flowed out from the cen- tral hole of the graphite base.The weight of flowout liquid flux were measured at regular intervals,the observation of the tendency to forming glass phase and the homogenization of samples after it was melted as well. 2 Experimental Results The difference of the melting characteristics between prefused fluxes and simply mixed fluxes with variation of their principal flux systems,additives and particle size has been studied. 2.1 Melting Curves of Principal Composition of Flux Systems Bascd on the SiO,-CaO-Al2Oa flux system,the prefused type powder flux and simply mixed type powder flux were compounded separately according to the ingredients of fluxcs of type I in Table l.The experimental results of the me- Iting characteristics measured with drip-mcthod in the case of same particle size are shown in Fig.3. 518

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1.0 1.0 0.8 0.8 0. 0.6 0.4 0.4 0.2 0.2 0 .1140 12201300 1220 1260 1300 1340 t,℃ t,℃ Fig.3 The melting characteristics of Fig,4 The effect of CaF2 additive prefused type (A)and simply on the melting characteristics mixed type (B)fluxes based of prefused (A)and simply on SiO-CaO-Al2O3 flux system mixed (B)fluxes (CaF2 =10%) Experimental results for the prefused powder flux (A),the starting melting temperature was about 1245C,and finishing melting temperature was 1285C,so the range of melting temperature was 40C.For the simply mixed powder flux (B),these three values were about 1300C,1340C and 40C respectively.That is,both of them had same fusion rate.This conclusion indicated that the melting behaviour of them could be kept as the same unless the temperature of hot metal with using simply mixed flux was 60C higher than that with using prefused flux.And it was predicted that the difference of melting behaviour between them should vary with the change of chemical compositions and particle size of fluxes. The prefused fluxes had a strong tendency to form glass phase themselves after re-melted.This glass phase was homogeneous (photograph 1.A).But the tendency to form homogeneous glass phase for the melted simply mixed fluxes were related to the compositions and componenls of raw materials.Excepted few cases,the tendency to form glass for most of the simply mixed fluxes were not completed because the small solid particles were often surrounded by a layer of two-phase mixture (photograph I.B). 2.2 Effect of Additives The melting curves of fluxes in which CaF2 was added as additive to the above basic composition of flux system were shown in Fig.4.for prefused and simply mixed fluxes. The results showed that,for both kinds of fluxes,the melting temperature of prefused flux was lower than that of simply mixed flux,but the difference between them slightly decreased. 519

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A B Photo,1 The tendency to form glass phasc and homogenization of melted fluxes(A,prefused flux;B,simply mixed flux) 2.3 Effect of the Particle Size of Raw Materials The strong effect of particle size on the melting behaviour of simply mixed fluxes have been proved by some researcherst10-111.In these experiments,the particle sizes of raw materials were classified into four grades (75-100 mesh,100- 150 mesh,150-200 mesh,and<200 mesh)to compound the prefused flux and sim- ply mixed flux.The melting curves of fluxes under the condition of the heating rate in the range of 5.5-6.8C/min has been recorded and shown in Fig.5. .5-100mesh 100-150mesh 1.00 0.75 0.5 0.25 150-200mcsh <200 mesh 1.0 0.75 0.5 0.25 12601300 13801260 1340 1430 t,℃ Fg.5 The effect of particle size on the melting behaviour of simply mixed (.and prefused (o)flux It was concluded that the melting temperature of prefused powdcr flux was always lower than that of simply mixed flux for all grades of particle size,but 520

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