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Large Inclusions in Continuously Cast Carbon Steel Billets* IVU~

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Large Inclusions in Continuously Cast Carbon Steel Billets* IVU~ Large Inclusions in Continuously Cast Carbon Steel Billets* By Hisashi MORl,** Nobuyoshi TANAKA,*** and Masazumi HIRAl '** Synopsis shown in Table I by SIX strand continuous casting JlIacroscopic huge inclusions qf about IJ.05 mm or II/ore ill diameter. machine of ordina ry bending type. A tes t pl a nt Jound in the cross sections qf continuously cast 80 10 250 mm square or vertical stra nd was employed to prepa re recta ngula r 260 x 370 mm reclangular billets qf common carbon steels have been in ­ n"stigated. T he number oj sucit inclusions decreased resjJeclil'e(v with T a ble I. Bill el size increasing sol. aluminum /Jeranlage iI/ Ihe billel, wilit decreasing to lal Bille t oJ91gen, with increasing (arbon /Jerccn lage. willz decreas ing MnJS i, with 80t.j:J 100t.j:J 11 340 145 t.j:J 16040 2 10 x 350 260 x 370 size ( mm) increasing billet si::.e. and b,v a/J/Jlimtion oj subllwged no.:zie and /JOlvder ca., til/g. The IfI~~e il/elllS ioll s ,ure JOllnd 10 collsisl, in additioll to Casti ng deoxidatioll /}fOdllcIS. of air oxidation /}foducts qf Ihe molten steel and speed 4 .03.02.3 1.7 1 . .'i 0.75 0 .55 (mJmin) SCllms entra/J/Jed into the mold. The Jormation oj large inclusions wa.1 disCllssed .from ,\lIch as/Jecls as the cleanliness of liquid steel ill Ihe CC 6 strand o rd in a ry bending I stra nd, ve rtical lundish. tlze air oxidation oj /Jouring stream, th e entra/Jlnent oj scums machi ne into tlze mOllld and tlze coagulation, and jioating-u/J of inclusions during solidification process . 350 I. Introduction The solidification of continuo usly cast carbon steel bi ll ets is cha racteri zed by the fact tha t the cra ter is narrow and deep and the directi on of solidi fi cation is nearly tra nsversal, because o f the sma ll er section of ~40- cast billet as well as fas ter casting speed than those of (mm ) in got. 210 X 350 80 1- 14 5 1 160 1 260 X 370 For tha t reason, the size a nd d istribution o f' non­ meta lli c inclusions in billets a re quite different from SampleD D q those of ingot. Especially, la rge inclusions a re found I VU~ CId)J usually oftener tha n in ingots. H owever, few reports a re fo und about la rge in­ Sample I, 11, II' : observati on of large in clusion on polis hed cl usions in billets. This paper- is concerned with the section results of experim ent on large inclusions in carbon Sample 111 : step down test of p inhole a nd e ntra pped sc um steel bi ll ets prepa red by the 6-strand bi ll et continuous Sampl e I , II : sulfur p r int ~ macrostructure casting machine of' Yawa ta W orks of Nippon Stecl Samp le II ', if: analysis for A l a nd N B : analysis for total 0 Corpora ti on. C: analys is fo r Quant-\'ac and point counting of inclusion II. Experimental Fig. I. Sampling position Pla in carbon steels conta ll1l11 g 0. 10 to 0.85 0 0(:, 0.20 to 0. 37 0 oSi , 0.40 to 0.85 0 oMn, less than 0.030 % S, 0 a nd less than 0.030 0 P were used to prepare the test samples. H ere, let us classify the steels by C % or o Nln o, into the low-carbon steel with 0.10 to 0.25 % C, the m edium-carbon steel with 0.28 to 0. 50%C, and the hig h-carbon steel with 0. 58 to 0.85 % C, or the low­ ma nganese steel with less tha n 0.60 0 0Mn (MnJSi :::;; 2.5) a nd the high-manganese steel with more tha n 0.60% Mn (MnJSi > 2.5 ). Billets with more tha n 0 0.0 10 o so l. a luminum a re referred to as AI-ki lled, 0 a nd those wi th less tha n 0.0 I 0 0 (mos tl y bcl ow 0.00 5(~ 0 ) sol. a luminum as Si-kill ed . (x 8111 ) Steels were m elted in a 75 t B.O .F., transferred Photo. I. An example of very large in cl usion On a polished to the 75 t ladle, a nd cast into billets of severa l sizes cross section of a bi ll et * O rigi na ll y pll bli shed in TelslI -ln-IIflgan!, 56 ( 19 70). IR :2 "1. in Japancse. I ~ n g li s h vcrsion r('c(' ivccl June 3, 197 1. ** 'l'edl11i cn l Resenrch Institll te. N ippo ll Sll'e l Cllf'p .. Yawaln l ron \\'1II'ks. Y:Jw:J ta-k li . K itnk), lI s 111 1 !lO:,. *** Steelma kin g Di v ision. Nippon Steel Corp .. Yawa ta Ironworks. Yawala-ku. K itakyushll eo:). ( 424 J Report Transactions ISIJ, Vol. 11, 1971 ( 425 ) bl ooms of vari ous sizes, such as 260 X 370 mm. a bsorptiometry, and sol. a luminum was ana lyzed b y Bill ets of 80 to 11 3 mm cp were cast mostl y by the magnetic mercury cath odi c electrolys is a lu minon open nozzle and oil casting process, while most of the absorptiometry. bi lI ets 0 (" 160 mm ,*, and recta ngu lar large section were cast by the ubmerged nozzle a nd powder casting III. Large Inclusions process. An inlet type submerged nozzle was used An exa mple of large inclusions visible by naked eye for prevent ing th e entrance of a ir. on the poli shed section of bill et is shown in Photo. I. Sample billets of 350 to 400 mm leng th were cut Since the small est diameter of inclusions detecta bl e as shown in Fig. I. The to tal oxygen contents of by the eye is a bout 0.05 mm, visible inclusions have bi ll ets were measured by vacuum fu sion infra red been divided into three groups: small er than 0.2 mm, T otal 0 % 00 0 > 0.010 o 0.005 - 0.009 6 0 " < 0.004 -.J ., ~ o 0 bl) <II I- " -'" -iii0 '0 ...:: o 0 u o ~. .,I- " .D E :> Z 0 _ 0 0 o cRe o 0 £J. <II 10 · .: o" 160 mm ' Rect angul ar <II :> u 8 " v ~ ~E 6 ~ (.) 0 0 '; 0 0 ~o 0 ;:: 0 " 0 '0 1- --­ v ~ Fig . 2. .D ;; E Effect of sol. A I"" o n the :> ~ 2 " :> o 0 la rge inclusio ns 111 160 " o 6 "3o « m m g, a nd rccta ng ula r f- 15 20 25 10 15 20 f- 10 blooms cast with sub1l1 c rg-cd Sol. AI in bill et (I O 3%) " nozzle a nd powder ~ AI < 0.005% l ~~ 3 I- U o '0'" Sol. AI 0.006 - 0.0 10% "'0 L6 Sol.AI > 0.011 % -0 E '::- ~ ~ E E o u I- <II "'0 60 .DV 0" E .;;; 2 I\ c::::. 3 ,.2 ~- <II Z u '"bl) I- .;;;0" " ..:: :> o u l- " E V E .D E N :> o 8 " 6 o . ". Z 1\ 0 ~_-+-_-L_ 12 .~ 0 <II .;;;0" 0" .;;; 10 :> 10 :> 160 mm ! U Rec t angul ar U " " ., ~ 8 ~ _ 8 ~ N ~('.IE E '" u ~ U 8 6 o g6 '0 I- ~ :::: ., ...... .,... - .D ~ .D ; 4 - E ~ :> " 0 0 ~ " w " 0 o " ~ « g; :0 0 "3o 2 f- f-" 0 Fig. 3. 10 12 14 Effect o f to ta l 0 o n the T otal 0 in bl oo m (x 10 3 %) nu mbe r of la rge inclusions Report ( 426 J Transactions ISIJ, Vol. 11, 1971 0.2 to 0.5 mm, and larger than 0.5 mm in diameter. of total 0 % of bille ts. As shown in Fig. 3, the number of large inclusions i . Effect of Various Factors on L arge inclusions in 160 mm cp and rectangular blooms increases pro­ 1. Effect of Alutninurn, Oxygen, Carbon , and Mn/Si Ratio portionally with increase of total 0 % . As shown in Fig. 2, the number of large inclusions When total 0 % is equal, the number of large in­ in 160 mm 90 and rectangular blooms decreases hyper­ clusions decreases with increase of sol. Al %. bolically with increase of sol. Al % . The effect of' As shown in Fig. 4, the number of large inclusions so l. Al % is especiall y marked in large inclusions of' in open nozzle Si-killed 80 to 11 3 mm 90 billet decreases over 0.2 mm diameter. In case so l. Al % is equal, hypel'bolically with increase of C % in billets. the numbel' of' large inclusions increases with increase F igure 5 shows the effect of C% in steel on the average number of inclusions in Si-killed billets, which No. I and No.6 strand a re classified by C %, Mn%, and billet size. The 40 number of large inclusions is larger in the low-carbon steels than in the high-carbon steels, except the low­ N 30 E manganese steels o f 80 mm cp . u 0 20 As shown in Fig. 6, the number of large inclusions 0 .. ' .:::: lJl open nozzle Si-killed low-carbon 80 to 11 3 mm 90 10 VI billets increases with increase of MnjSi.
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