D0I:10.13374/i.issm1001-053x.1989.06.025 北京科技大学学报 第11卷第6期 Vol.11 No.6 1989年11月 Journal of University of Science and Technology Beijing Nov.1989 Modification of Nonmetallic Inclusions in Steel with Yttrium' TapactoK JI.I."Cai Kaike(蔡开科)，Liu Xinhua(刘新华)， Qu Ying(曲英)· ABSTRACT:The modification affects of yttrium on formation of nonmetallic inclusions in steel has been studied by use of metallographic method.The effect of added quantity of modificater on type and size of inclusions was also studied in this work. KEY WORDS:yttrium,modification,nonmetallic inclusions A complex modification effect of yttrium on Fe-C melt has been discussed in several references[1-3).It changes the interface tension of crystal-melt boun- dary and can form the high melting combinations in the melt.Moreover,some particles in melt are able to adsorb isomorphous crystallizing grain to its surface. In this work,a different amount of yttrium has been added in the melt,and the type and size of nonmetallic inclusions were studied in order to find the optimum quantity of modificator in the melt. 1 Research Method The metal is melted in a Tamman furnace with an alumina crucible and fini- . shed with the modificator.The charge was calculated on purpose to obtain a ingot of 600g.Then the specimens were cut out by scheme as shown in Fig.1.The upper, middle and lower pieces of the half ingot were carried on the metallographic study. The specimen for chemical analysis was taken on the centreline of another half. The chemical compositions are as follows (wt%): C-0,30;Si-1.50;Mn-1.80;P-0.010;S-0.020;A1-0.083;0-0.0096. In the molten steel with above composition the different amount yttrium was Manuscript Received May 11,1989 ..Marioupol Metallurgical Institute in USSR,This work was carried out in USTB EIJING ...Dept.of Metallurgy 539
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added.Ingot was cooled in the furnace and then it was cut to the specimens. 0,0250C 10.0100 0.0218 0.0093 20 0.0187 0.0086 0.0156 0.0078 0.0125 0.0070 0.009 0.D053 0.006 0.0055 0,003 0.0048 (a) (b) 90.0040 0.010.03 0.07 0.11 0.15 0.19 fY),% Fig.1.Scheme for specimens Fig.2.The relation of [O]and [S] a.Position of chemical analysis of with [Y]In steel specimens b.Position of metallographic specimens The metallic melt was deoxidized with silicon,manganese and aluminium and kept 1600C within a time~10 min before adding yttrium.After modification with yttrium about 5 min the furnace was switched off and the ingot was cooled slowly in the furnace.The added yttrium was coated with aluminium foil,because it is easy oxidized upon the melt.Quantity of added modificator into the melt was different for cach heat.As shown in Table 1,the yttrium was added in the range of0.091~0.553%- Table 1 Amount of modificator for each heat No. Quantity of added Percentage of added heat modificator,g modificator to the melal 1 0 0 2 0.5 0.091 0 1.5 0.277 3.0 0.553 Metallogrphic study of nonmetallic inclusions were carried out with a optical micruscope NEOPHOT-2,and chemical composition of inclusions has been analyzed with a scanning clectron microscope. 2 Results and Discussion 2.1 Composition of Steel The chemical compositions of steels for cach heat are given in Table 2. 510
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Table 2 Contents cf some elements in steel No. Added Content of elements in steel,wt Yttrium heat % P S Al 0 Y 1 0 0.010 0.020 0.038 0.0096 0 2 0.091 0.010 0.021 0.170 0.0082 0.014 9 0.277 0.010 0.015 0.220 0.0078 0.053 4 0.553 0.010 0.010 0.390 0.0044 0.190 The experiments show that the yield of yttrium is dependent on its initial concentration.Yield of yttrium is increased with the added amouot of modifi- cator as follows:15.4%6-for heat No.2;19.1%-for No.3 and 34.4%-for No.4.The relationship between contents of S and O in steel and residual concen- tration of Y was shown in Fig.2. The results of the research shows,a small amount of yttrium in steel has not observable influence on the variation of sulfur in steel.This is in agreement with result of reference [4. 2.2 Thermodynamic Calculation of Decxidation with Vttrium Reaction betwcen yttrium and oxygen may be【s】 mCY]+ncO]=YmO(s) Further more in our condition it may be 2CY)+3[0]=Y2O3(s) K=aa=(fC%Y])(fo%)) In case of minimum in the relationship of [and [%Y],then d〔%O) d〔%Y) =0 893>0 From first expressicn we can get 2.303c%Y)-(e+ne From second expression we shall have 2.303〔%0>〔-加0-ne8 The interaction coefficents are taken from reference [4,5) e8=-0.20;e￥=0.006：e=-16.3;e9=-01.58 Inserting them in the expressions and the results can be cbtained by solution 541
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of the equations 2.303-C%Y=-C2×0.006+3×(-16.3)门，〔%Y)=0.018 2 2.303c%0>-C2×(-90.58)-3×(-0,20);〔%01<0.0072 3 As a result of calculation the oxygen content in steel can be decreased at most to a level~0.0072%by deoxidation with yttrium in the condition of equilibrium. More content of yttrium even promates to pick up some oxygen in the steel. However the other elements -deoxidizers in the steel and their interaction can decrease the oxygen content in more extent.This is indicated in the chemical analysis of experimented steel. 2.3 Composition of Nonmetallic Inclusions The metallographic pictures of nonmetallic inclusions in experimented heats are shown in Fig.3.The nonmetallic inclusions in comparative steel,which was not modified with yttrium,is mainly consisted of Al2Os and (Mn,Fe)S.The biggest inclusion is not beyond 400um.The finished steel with yttrium contains nonme- tallic inclusions with complex composition;besides,the inclusions morphology is b 50林m 2写4知 25科m Fig.3 Nonmetallic inclusions in steel a.without Y,b.~0.014%Y, c.0.053%Y,d.-0.190%Y 2002222 a8200223 Fig.4 Distribution of Y(b)and S(c)Inside Incluslons (a)In steel with Y (0.190%Y) 542
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also varied.The inclusions are changed into globular form.Nonmetallic inclusions type (Al2O3.Y2Os).S and Y2O2S.(Fe,Mn)S appeared.Scanning electron mi- croscopic analysis of inclusions indicates that content of yttrium in complex inclusions is varied from 6~8%to 60~70%due to increase of added amount of modificator.Fig.4 shows that distribution of Y and S inside the studied nonme- tallic inclusions.Moreover the concentration of elements appears uniformly inside inclusions.Size of containing yttrium inclusions is not more 300um. 3 Conclusions Metallic melt with yttrium causes modification of nonmetallic inclusions in the melt.Inclusions in the conparative steel are oxides and sulfides,but inclusions in the steel,which was finished with yttrium,are complex oxisulphides.Not only the inclusions morphology is varied,but the inclusions size is also changed.It is established that a little amount of yttrium (Y]/CS]<3)has insignificant effect of modification.This is coincided with results of well-known researches. Yttrium can act as a deoxidizer and a desulfurizer simultaneously.Products of reaction of oxygen and sulphur in the melt with added yttrium are the origin of complex nonmetallic inclusions. The further developed research is necessary because of limited experiment data in a short days. Acknowlegement:The authers are grateful to the colleagues of Steelmaking Division USTBEIJING for their friendly help in the course of the study. REFERENCES 1 Averin VV.Proc.Metallurgicheskie Methody Povyschenia Ka- fchestva Stali,Izd.Nauka,1979;33 2 Maltsev M V.Modifitsirovania Structury Metallov i Splavov Jad.Meta- 11 ur gia,1964;213 3 Tiagunov G V,Ystnhuk.Trudy M Konferentsii po Slitku Izd.Metallu- rgia,1978,98 4 Du Ting,Wang Longmei.J.Less Common Metals,1985;110:179 5 Du Ting,Wang Longmei.Proc.of Inter.Conf.On RE Developm:ent and Applications,Beijing,PRC,Sept.10~14 1985;Vo1.II,1238 543
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