The desulphurization  and   the  control of sulphides by treatment of CaO-MgO-RE-CaF2  synthetic powder in liquid alloy is used with success in ladle for many alloy prod-ucts. The  results  indicated  that the synthetic powder ladle  treatment  is  possible  to  reduce  sulphur from

0.035% to 0.009%S by  employing  agents amounting l4kg/t liquid metal.

   The results  also  show that treated CaO-MgO-RE-CaF2 powder positively affect the globular type I morphology, small-smooth  size  and  distribution  of the remaining inclusions in  the 12Cr20Ni38Mo5 alloy, The powder CaO- MgO-RE with increasing MgO shows better efficiency than powder with increasing CaO. Some calculated values have been compared with those reported in literature

Duy, P To

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EI''I' ECf OF CaO-J11gO-RE-CaF2 S\'N'i'IIET[C POWDER ON[)ESULPiiURiZATION OF I2('r20Ni38Mio5 ALLOY76 I)u}, Ca * National Aletallrurgical I.aborotwr - .lcun.checllucr 831 007ABSTRACTThe desulphurization and the control of sulphides by treatment of CaO-MgO-RE-CaF2synthetic powder in liquid alloy is used with success in ladle for many alloy products. Theresults indicated that the synthetic powder ladle treatment is possible to reduce sulphur from0.035% to 0.009%S by employing agents amounting l4kg/t liquid metal.The results also show that treated CaO-MgO-RE-CaF2 powder positively affect theglobular type I morphology, small-smooth size and distribution of the remaining inclusions inthe 12Cr20Ni38Mo5 alloy, The powder CaO-MgO-Rl; with increasing MgO shows betterefficiency than powder with increasing CaO. Some calculated values have been compared withthose reported in literature.KEYWORDS: synthetic powder, alloy, desulphin izationINTRODUCTIONThe problem of ladle refining of steel and alloy is overcome by a very promisingmethod of treating liquid alloy t 1"1?1 by CaO-MgO-RE-CaF2 synthetic powder. The effectivedeoxidation, desulphurization and elimination of non-metallic inclusions in steels and alloysare very important to improve product quality 1' A-221 of late, considerable efforts are beingmade to improve steel and alloy quality through inclusion shape and composition control 123"301 The works on improving cleanliness of steel and alloy by removal of oxide and sulphidecluster and/or through modification of inclusions morphology have been reported in literature131-481The present work has been done as a co - operative research project of Vietnam KC-05t 471. This work describes the effect of synthetic powders containing CaO - MgO-RE (withincreased CaO or MgO percentage . When Ca() is in exec,,s, it is called CaO-RE powder andwhen MgO is in exess, it is called MgO - RE powder on desulphurization , formation anddistribution of sulphide inclusions and improving cleanliness of I2Cr2ONi38Mo5 alloy.* Ur. Alanagrr o/'Departrnent of Afetullic Alatr'ria/v, on lcwve fromIH.sYitutr of llutcrriuls S'cirrrce .'I'N('N,ti'l, Nghio clo- t o Brun- llunoi , Vietnam35FXI'F IZII111,'N''1'AI. \Ih:T1101)I:xpcrintents wcic carried out in the lab scale in inaenesite open bath induction fu naceof capacity 5OLg and electric power 130k1'1' The I 2C'r20Ni38Mo5 alloy of the compositiongiven in table I was charged into the furnace bath.Ni n 1oMSi ^In P S Ali Mn I' AI ('u CrC .li18 . 001820 3 0 5 A 00I.12 1 28 1 . 3 5 OA d O U Ol5 0 .0 7 2.28 5 0 . 010 0 035 . 3 2 SO 0 . 00 4 The I2C2ONi38Mo5 alloy was melted in Rn nice to all melting and temperature of themelted bath vaned flour 1600"C to I650°C then melt was lust deoxidized by FeMn (2 kg/t),FeSi (2.5 kg/t), and aluminum wire (0.3 legit). The molten bath was stabilised for about 10minutes and the temperature adjusted to 1660 - 1680'C In the meantime the heated ladle wasprepared heated rare earth metals - RE (2 kg /t mischmetal shows table 2), the syntheticpowder (>6 kg/t) (shows table 3) and fluorspar (2 kg/t).Table 2. Composition nrischmetal for adding with synthetic powder (wt/'O)^hLa Ce Nd Pr Fe Mg Al Si c t er50 40 1.7 4.4 2,7 0 4_ 0 03 - -Fable 1. Analysis of 12Cr2ONi38Mo5 alloy (wt°,o)Table 3. Composition rate of CaO-MgO-RI:-Al;C)t synthetic powderNo 1 2 3 4 5 6 7 8 9 10 11 12 13CaO 6.0 6.5 7.0 7.5 8.0 8.5 9.0 6.0 6.0 6.0 6.0 6.0 6.0M >0 1.0 1.0 1.0 1.0 1.0 1.0 1,0 1.5 2.0 2.5 3.0 3.5 4.0Ladle addition of the synthetic powder was done in two instalments. At first 2/3rd ofthe total amount was added to melt. After pouring 1/2 the amount of ladle into the mould, theremaining 1/3rd fraction of powder was added. The melt was stirred by a graphite plunger.Samples of both the slag and the alloy were taken before and after addition of powder forcomparision. Complete chemical analysis was done. Scanning electron microprobe analysis byJEOL - 35CF, LINK 860/II (EDX) was done on selected samples for the determination ofinclusions.RESULTS AND DISCUSSIONSThe results of chemical analysis of alloys and slags are shown in table 4 and 5.'fable 4 . Chemical analysis of alloy samples ( wt",^)C Si Mn 1' S Cr Ni Mo Cu Al Ce '1 i0.120.201.262.101.522.000.030.0350,0090.03018.1021.3037.2040,804.726.001.782.020. 020 .030.0180.0200.0090.012DesulphurizationThe aim of the treatment of liquid alloy by synthetic powder was mainly fordesulphurization, or control of the sulphur content and shape control of sulphide inclusions.Effect on desulphurization of liquid alloy is expressed in literature of Richardson 1401according to which desulphurization can best be achieved by using RE (Ce,La ...) and alkalineearth metals (Ca,Mg...).Typical reactions are given below l5 551:RI /S/ -p /RES/ (I )/RE/ CK, > /RI;C1/; AGr = -74023 i 37 51 ]' (2)RI. were unable to read with carbon at tenrperatnie 18711K by equation (2).Table 5 ('henrical analysis ol'slap samples anti sulphur in alloy (wt%sample No CaO NIg0 Si02 A1,0, CaF2 FeO, S1 31.82 3 40 15 00 17 69 0.09 2.00 0.0352 33.60 3.12 15 51 45.79 0.08 1.90 0.0273 34.05 3.21 15.05 45.78 0.05 1.86 0.0184 35.18 3.00 15 03 44.84 0.05 1.90 0.0165 35.89 .3. 10 11.90 45 17 004 1 80 0.0156 36.45 3 29 14.98 43 32 0 04 1.92 0.0147 36.82 3,41 15 12 42.75 0.10 1.80 0.0138 30.90 3.74 14, 57 49.09 0.10 1.60 0.0259 31.00 3.91 1413 49.15 0.09 1.72 0.01810 31.50 4.01 13.95 48.77 0.07 1.70 0.01311 31.00 4.51 13.91 48.73 0.05 1.80 0.01112 31.90 6.65 15.15 45.44 0.02 1.74 0.01013 31.85 10.41 16 65 39 47 0 02 1 .60 0,009(CaO) + /S/ -> (CaS) +/0/ (5)(CaO) + /S/ + CA,-> (CaS) + K'0) (6)(N1g0) + /S/ -> (N1gS) + /0/ (7)(MgO) 4- /Sl V C8,-> (NIBS) + ;COI (8)and (0-2) .t. /S/ -> (S-) t- /O/ (9)The slag basicity for desulphurizatiun can be described as follows [ 15]:B = (Ca0 r 1.4 MgO (10)5102The analysed and calculated slag basicity effecting desulphurization is shown in figure. 1.The successive reactions ate2/RES/ -r- 2/0/ -> /RI;2O2S/ I- /S//RE202S/ + /0/ -> /RE2Oi / + /S/0 040 0350 0300250 020015a0010005♦ Smir^tn f,,, r,2aOREMp0-REuawdermr, dern0 1 1 r I24 245 2 255 26 265 27 275 20slag. basicity 13Figure 1. 'I In' tclalio:isltill ll1'r1^t 'ctl sla);-basicity doling use ofsyntbctic powders andsulpbul content in I2020Ni38N1o5 alloyFigure I shows desulphutii;ttion level of I2('r20Ni38N1o5 alloy due to addition ofpowder . The influence ofCaO-RIB 11t1\\ der via slag-basicity is clearly visible the slag-basicityof 2 to 2 7 reduced the sulphur cuntcnl of alloy rapidly, but when it was higher than 2.7 the37IdesuIphurizzation of alloy was subdued and may not be \.uied (figure In ). The maximumresidual sulphur content in alloy was 0.0131.oS. The figure 11) shows that M80-RE powderreduced sulphur content of the alloy to 0,009"% (Milli 11111111) thus its desulphurization abilitywas better than CaO-RE powder.The desulphurization of MgO-RI: powder has occurredunabated throughout the experiments compared to Cali-RE powder. Owing to the use of REas shown by reactions from (1) to (4) therefore the reaction (8) can be attained intense. Theresidual sulphur content in alloy was the lowest. Thus comparable order of desulphurizationlevel between MgO-RE powder and CaO-RE powder was obtained. The results has shownthat desulphurization efficiency of MgO-RE powder is higher than that of CaO-RE powder.The same efficacy of desulphurization was obtained at much lower amount of MgO-RE thanthat of CaO-RE.The reduction of sulphur by MgO-Rli is from 0.035 to 0.009%S.In spite of the fact that rare earth metals do not r cact with carbon, but onestransformed into deoxidation zone desulphurization reactions (6) and ( 8)1"1 occur,The desulphurization efficiency as expressed ahove is explicit. It is customary now tocorrelate the percentage drop in sulphur with weight of the reagent. Now the elTect ondesulphurization efficiency the modification of inclusion in alloy will be discussed,Inclusions and cleanliness of alloyNormally, inclusions in the alloy produced by stnaaiglut aluminium addition are A12O3 -clusters and manganese sulphides which is shown in figure 2.A ->Al2O34665 VV X500 13 >A12O3SiO2Figure 2 . Typical inclusions in cast alloy made by straight Al-additionBefore treatment with synthetic powder, the samples taken from the furnace, contained mainlylarge randomly distributed angular type III inclusions. After treatment, both CaO-RE and MgO-RE synthetic powders had changed A12O3 clusters and manganese inclusions into low meltingcalcium and magnesium aluminates and small-smooth R1:-Mn complex inclusions (figure 3).The RE reacts with the dissolved sulphur following reaction (1) and by reductants CaO and MgOtogether agitating carbon plunger following reaction (3) and precipitates RE••oxysulphide(figure 5 ). The primary inclusions act as nucleus for the precipitation of RE-oxysulphide with theresult that the RE2O2S phase is contiried to the outer sun lace and commonly very small smoothglobular. The secondary inclusions precipitated during; the solidification process from dissolvedCa, Mg with remaining RI: the alloy The covering prim, v 12fi-oxysulphide is shown in figure 4,38.1rA >RE202S4667 W X500 13-CaSFigure 3 . Typical inclusions by using 8.5CaO- RE powder ( sample No.6)ft 0A >RE202S4668 W X500 i3->MgSFigure 4. Typical inclusions by using 3.5MgO-RE powder (sample No12)For comparison , sulphides appearing in alloy by treating with CaO-RE and MSO-RE powderare shown in figure 5. They are in accordance with desulphurization principle.A >RE202Sf3->(RE,Mn)SFigure 5. Typical oxide-sulphide inclusions by using 7.5CaO-RE powder( sample No. 4 )The sulphides in alloy of figure 5 treated with the 7.5CaO-RE based powder were of duplextype containing CaS and RES. In fact diflcrencc of the influence of synthetic powder on bothinclusion compositions and morphologies were comparable. It can be seen from figures 4and figure 5 that the numberof inclusions was mole with 85CaO-RE powder than with3.5MgO-RI? powder.Figure 6 also shows composition of inclusion in alloy, with treatment 4.MgO-REpowder and may be explained for inclusion structure N^itli reference to figure 4.39CaOSi02r---r--r--^r--r^ * r^A1203 C a 0 A12031.MgO-RE .a Mt;O-itEFigure 6. Transformation of A110.1 - cluster ill ,111o), by 1.Mg0-RE:synthctic powder ( sample No 13 )The RE addition in such an alloy did not appreciably reduce the total inclusion level. Rareearth metal treatment usually results in several oxides (I.a•O , Ce203 ), oxysulphides( La2O2S, Cc201S ) and sulphides ( LaS, CcS ). 'T'heir inclusions are relatively heavier andtherefore probably remain in the bottom of the the melt and may contain relatively higheramount of inclusions in the alloy. Therefore use of synthctic powder containing combinationCaO-RE" and MgO-RE for desulphurization and inclusion rnoipholugy me benificial.CONCLUSIONSResults of experiments concluded to study the effect of treatment synthetic powdersCaO-MgO-RE-AI203 on desulphurization and inclusions in 12Cr20Ni38Mo5 alloy using 50 kginduction furnace are presented below:1. The rare earth metals reduced sulphur content in the I2Cr20Ni38Mo5 alloy owingto the reductants CaO and MgO together of graphitic car bun.2. The desulphurization could be achieved by M!;()-RE powder better than CaO-REpowder and the niaximun sulphur distribution coefficient I, of 75.11 in slag is attained, whilstthe lowest sulphur content of 0.009%S obtained by n1t;0-RE: powderThe effective on desulphurization was obtained at much lower amount of Mg0-REthan that of ('a0-RIi,4. The ladle treatment by CaO-RE and NIgO-RI: Lowder modified angular type 11 ofaluminium cluster into globular type I of small-smooth o\)-sulphides morphology in the alloy.In this regard also the Mg0-R1; powder shows better results Than ('a0-RI7 powder.5. The synthetic powder ladle treatment iniprmc I cleanliness of alloy explicity.6. Although enough development has been obser \ cd in this It & 1) work with MM1g0-RE powder, there is further scope of development tier which continued research work isenvisaged.ACKNOWLEDGEMENTSThis work was supported by the National Scientific and technological program fund ofVietnam under contract number KC-05-23N4. Thu mi rui is indebted to President,Academician Nguyen Van iiieu Leader of NST program I hanks are to Prof. P. RamachandraRao Director of National Metallurgical I.aboralur y and 1)1 P K lhiswas Sv. Scientist andCAP division oh National Metallurgical I.abouatury Janisbcdpur, India fur eneourage nient andhelping manuscript.406(REFERENCESI. W. 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Kerstin GarbrachtRedaktions- andIndustr le-Prosse-ServiceND-3ar Dr. Ca,thank you for having sent us your manuscript:Co, To Duy:A study on the desuiphurization and sulphide inclusions in 12Cr2ONI38Mo5alloy by CaO-MgO-RE-CaF2 synthetic powderLike all manuscripts received, your paper will first be submitted to the Editorial Boardfor comment.We will advise you subsequently without delay whether your paper can be publishedin "steel research".Y666 sincerely,E-dltorial Office " steol research".(Ichendorlkhofo 44 it 1063221545 IA 0 Deursche Aenk A03Pr,57 And Ilerrhurg roc 105 .11215 46 74 PII 27070042Germsuy 11 D IX 10 53 221 5 45 74 KDnlo • Nr. 7P43303

Effect of Cao-Mgo-Re-Caf2 Synthetic Powder on Desulphurization of 12Cr20Ni38Mo5 Alloy

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Effect of Cao-Mgo-Re-Caf2 Synthetic Powder on Desulphurization of 12Cr20Ni38Mo5 Alloy

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