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UDC 621.746.27.047 : 669.14-194.3

Continuous of High Alloy *

By Fumio HOSHl** and Yoshimasa AOYAMA***

Synopsis (3) The number of machines excluding tes t plants The /JalJer is a technical note for the continuous castillg of higlt alloy are totall y twelve strands; nine for slab, two for b ille t steels, esllecially of tlte stainless . Charactpristics of steels, facilities, or bloom, and one for slab a nd billet. Of these operatiolls, defects alld their remedies, propertips ~f tlle /Jroducts, yield twelve stra nds, ten are exclusively onl y for stainless and cost of tlte products com/Jared with ingot making process are rlescribed steel and the remaining two are both for stainless and respectively based on mallY research and invesiigatioll papers. Tlte outline plain steel. The sectional dimension of the of j alHUlese casters is surveyed through answers to tlte questionnaire sellt strands and the capacity of these facilities installed are to domestic makers. smaller than those for the plain carbon steel. The I. Introduction capacity of the plants, exclusive o nl y for stainless steels, is estimated at 130000 t/month. It is evident that the continuous casting of high (4) As for machine type, the vertical tvpe ac­ alloy steels is also grounded on the same technical counts for eight a nd bending one for four, but the basis as that of plain carbon steels. About twenty m achines constructed recently a re a ll of bending type. years have passed since conLinu ous casting of steel had been industrialized. W e might say that continuous casting of steels began with high alloy steels, and it III. Characteristics of Steel would also be true to say that it has been developed through effol-Ls a nd achievements of many pioneers]) J. Characteristics of Molten Steel with some different backgrounds. W e can consider many importa nt characteristics A few years ago, we reported a technical note on o f steels in rela tion wi th continuous casting; such as the continuous casting of high alloy steels. 2 ) In the chemical co mpositions, Q, tL the extent of deoxida­ presen t pa per, adding recent resul ts, we describe tion a nd of oxidizing, casting temperature, liquid us briefly but as completely as possible the outline of a nd soli dus temperature, the degree of super-heat, j a panese casters, characteristics of steel, faci li ties a nd viscosity, fluidity, surface tension, specific heat o f the operations, defects observed on strand and final pro­ molten steel, and so on. These fac tors influence each ducts, their remedies, properties of products, yield a nd other in complicated manner, so we cannot isolate its influence on cost, based specificall y on continuous each influence clearly. However, some concrete casting of stainless steel. examples are given below. It is well known that Cr is a n element to decrease II. Outline of Japanese Casters the activity of oxygen greatl y. For example, activity W e hope that japan would be one of the most coefficient of oxygen fo in SUS 430 is nearly equal to 4 advanced countries in the fie ld of continuous casting 1/8 of that in plain carbon steel. ) Normall y, stainless of high alloy steels in terms of the number of plants, steels contain a substantial amount of Mn and Si a nd the amount of products and the technique on opera­ sometimes we use Al a nd Ti as a d eoxidizer, so the tion. Now, in j apan the ratio of continuously cast melt does not necessari ly contain eight times of stainless steels to the total stainless steels has risen to oxygen compared with tha I of plain carbon steel under over 60% ,3) a nd the continuous casting process has the same carbon a nd temperature conditions. Thus, become a main casting method in the steelmaking of the residual prima ry a nd secondary deoxidation pro­ stainless steel. An outline of the continuous casting ducts through rapid solid ification in the continuous of high a ll oy steels in j apan is shown in Table 1 ( p. p. casting tend to affect the quality of cast products more 430 - 3), based on the a nswers to ques tionnaires sent markedly than in the case of ingot making or of plain to domes tic mills. The main features may be sum­ carbon steels. The chemical composition of steel and m ari zed as follows. the method of deoxidation affect the shape and the (1) The continuous casting is operated in almost a mount of nonmetallic inclusions. Examples are a ll the main stainless steel makers in j apan . shown in Figs . 15 ) and 26 ) (see p.432). All elements, (2) Almos t all the cast steels a re stainless steels. such as Cr, Mn, Si, AI a nd Ti, are oxidized mort' Also almost all the steel grades corres ponding to easily than Fe, so that preventing the ox id a tion o f " SUS" of j a pan Industrial Sta ndards have been molten steel during casting is of most importance. covered. The fluidity of molten steels also appears to be one

* Pa rtl y published in T elsu-/o-Hagane, 60 ( 1974), 82 1, in J a panese. Presented a t the 40th and 4 1st Nishi yama M emori al Technical Lectures, ISIJ, September, 1976, in Tokyo and October, 1976, in Kitakyushu. M anuscri pt received J uly 4, 1977. ** Steelmaking and Hot R olling Department, Shunan ''''orks, Nisshin Steel Co., Ltd., Shin-Nanyo, Yamaguchi 746. *** Nisshin Steel Co., Ltd., M arunouchi, Chiyoda-ku, Tokyo 100.

Technical Features ( 429 ) ( 430 ) Tran sactions ISH, Vol. 18, 197 8

Table I. Continuous casting of high alloy steels in Japan

Nippon Steel Corp. Pacific Nippon Yakin

Hikari I Murora n· Hachinohe Kawasaki ' EF-AOD Process EF-AOD LD-RH·OB EF-AOD.VD ELO-VAC 1------------------------ ------ EF x 2 Steelmaking EF x 2 LD x2 AOD x l EF x 3 I Furnace & numbe r process & unit I VD x l AOD x l RH x l (ASEA-SKF) VOD x l

Capacity; F'ce/ Ladle (t) 50, fIl /- fIl/50 30/ 30 fIl / 65, 30 '40

Start·up date Dec. 19f1l Oct. 1968 J uly 1965 Feb. 1964 Ma r. 1965 Dec. 1970

Number of machine

2 (Billet) or Number of strand 1 (Slab) I (Billet) 1 (Slab) 1 (Slab) I (Slab) 1 (Slab)

Machine type Ver tica l Vertica l Height or R/ Le ngth (m) 11. 4/ 23. 4 16.0/ 27. 0 1--v-ll-e~-5~'-~C-I~-~-+--~-:-~~-'/-:a-2 1--II--~-:-ro-t ~_:0_a. _15__ I---~-:-.~-~-i:-:-15--1 Designe'l" Concast Concast Hitachi DEMAG Concast Concast Outline of --______1------'------1 continu ous Manufacturer Sumitomo S. M. t' Hi tachi DEMAG Sumitomo S. M. casting unit I Straight Straight------s;r" ~I- St rai ~ 1 Straight Stra ight Mold type - Block or tube Width adjustable 125 115 x 1l5 Thickness I 130, 140 210 x 210 150,220 150 130 x 130 145 145 Dimension of ,------I cast product 1 Width 1 700~1,350 210 x 250 730-1.300 ~~~ 1 : ~~ ~ :~~ 950~1,300 1 (mm) :------1------1------1

1--s-e-c-o-n d-a-r-y-.-L-e-~-1 :-lt-' I:-t-~,-ll-) -1-4-,-5_00_:_. -: '-0-o-0-1-2-, -80-0-~-:-' 0_0_0_, ~oo~:' 400 II M a~~.: 800 I 4, OOO~:' 500 I 4'000~:' 500

cooli ng zone Me thod - - - \-V ater s pray Water s pray \V ater spray

Cutting method I Powder cutling Powder cu tting Powder cu tting Powder cutting Powder cutting I Powder cutting (Propane) ___!. ~~~)P~ _ ( P r opa~ 1. _ (Propane) I (- ) (- ) Specification withdrawa l speed . 5 1--0 2~0 . O. 2~2. 0 0 ,__ _ O. 2~ 1.4 (m/ mln) O~I ~5. --- -'---1-- - I Standard cas ting spee d (m/ min) 0.8 ~ 1.1 o. 5~0. 9 ~W I~t ~: 8:::J ~ Capacity of --- Slab continuous Capacity (t I (hr/ stra nd)) 25~30 1 1_0 ~_30__ ! ___ 4_ 5 _~_72_ _ _ B_i l_I e_t_I _2~_15____ _ casting I Planed or sta nda rd ca pa ~ 0-;- 1---10 4, 500 1 15,000 I 7,500 33,000 (t month) ,

_--, I---M- a-x-. -ac-t-u-a l capac ity 1--- -, 9~ (t 'month) 12 ~ , 900 15, fIlO 3,725 21,000 ------1 ------1 Ratio of continuous casting stee l (°0) 70 20 40 I Stainl~s steel I Stainless steel 95 I f s-te-e-I Staini'li>s steel I----S-ta- i-n-Ie-s-s- s-t-ee- I- IO-O--- Ratio of high alloy steel (fa) Sta inl ess stee l Stainless steel Stai nl 2~s I 10_0__ 1 100 __

SUS 20 1, 202 ,SUS ~02, 304 IS US 304 SUS ~~~: ~~~ SUS 301, 302 30 I, 302 305, 308 410, 430 308, 309 304, 304 L Authori ze d standard g rade 304, 305 316 310, 316 309, 316L (SUS, AISl, etc.) 316, 32 1 410, 430 m' 32 1 32 1, 347 410, 430 410, 420 430 -

YUS 120 1 Nothing NAS 45M (I6Cr, 9Mn, 2Ni) (24Cr, 5Ni, 1.5Mo) 1- I YUS 27 A NAS 126 (I7C,', 6N i. 2Cu) (l8Cr, 12N i, 3.5Si) Casting grade of h igh a ll oy steels

Other standard grade

Te chnical Features Transactions ISIJ, Vol. 18, 1978 ( 431 )

(This table is a summa ry of a nswers to questionna ires se nt for stainless steel makers in J apan)

Sumitomo Nippon Industry Kawasaki Steel Corp. Kobe Steel M.1. t' Nisshin Steel I Daido ~ t ee l IMitsUbiShi H .Lt2 ------C-h-ib- a- ' Shibukawa '-- ]-w-a-Y-a-'-3- - 1 Hiroshima' Wa kayama Sagamihara Kinuura Shunan I--I~N-is-h-i -nO-m-i y-a-'-21 3

I EF, E1.O-VAC EF (EF) EF EF AOD EF AOD EF- LD,VAC LD-RH I EF- LRF EF x 2 EF x I EFx4 LD x 2 EF x 2 I EFx2 1 EF x l LD x 2 VS8 : t PIlot p lant Pilot plant AOD x l AODx l VOD x I RH x 1 I (ASEA-SKF) ILadle Degas~ I ______8() ' 8() 70 75 104 / 104 0.5 0.5 50 60 -I 40 40 15 15 I - Oct. 1959-1- Jan. 1969 I-Feb. 1969-I~a r. 19;- 1 Feb. 1971 June 1971 -1-;e~ 1 Mar. 1973 I (Removed) ,sept. 1965 -----:------______June 1965______- 1 I 1 ------1 ,,,.,, I ( ) (Slab) ~. ~,., I (Slab) (Slab) 4-Mold (Slab) 1___ (_ B_IO_O_In_) (Bi ll et)

Vertical Vertical Vertica l Curved Curved Fixed mold Curved Vertical Vertical 10R/30.14 (I 0 I?) 1 Vertica l-bending II. 5' 24. I 11.426.1 10. 5R/ 33. 5 51. 39 Moving tunk 10.3523.81 Semi-continuous etc. 17.0 '32.2 1 Olsson -- Con cast DST I Con cast --A-m-s-te-d-----DST Concast U. E. Hitachi S. E. Kobe Steel Olsson 1_ 1 Sumitomo S. M. Mitsubishi 11. 1. 1 SUI11itoI11~ s. M· I Hi tachi S. E. t 4 1-s-u-m-i-to-m- -o s-.-M- . 1'-- U-. -E-·---- Hitachi S. E. I I. I. H. I. t s Kobe Steel ~1it subishi 11. ----- Straight Stnl ight I Straight Curved Curved Graphite Cu rved Straigh t Straight Width adjustable Width adjustablelWidth adjustable Width adjustable Width adjustable Block Block ------,----.---- 130 130 165 130, ISS 200, 260 200 II0 x 110 120 136 156 100 165 ' 165 165? --- -- 185 x l85 80 x 80 l\Jax. 1I0 x 110 220" --;-:Z65~ 1-955~ SOO~ I, 240 1 61O~ 610~ 150 x 2:10 950~ 1, 280 1 950~ I I, 270 ~ I 650~1, 300 150x l 50 420 I. 300 I. 040 1,300 1,585 I, 260~1, 700 1,070 1, 300 230 x 320 ------'---- 4, 000~7, 000 4, 100~9, 200 5, 550~ 4 lOO~ 1 4, 000~9, 800 4, 500~!O, 000 1__ 6, 150 ~O ______3_, 0_0_0~_5,_0_00______

7.3 6.43 9. I 120 1 12.9 7.5 0.8 . Cooling plate 1 /1 ,"Vater spray ,"Vater spray \rater spray 1 ,"Vater spr ay 1 (Upper part) \ Vater spray \Vater spray \Vater spray I vV ater spray - I ------. -1- Powder culling - ,-- -:- Powder culling Powder culling 1 Powder cutting Powder c uttll1g Powder cutting ( Propanc-) lowder cutting (-) (Propane) (Propane) (Propane) (l'ropanc) Hot top _ ( Pr op~e )_ - -,-

0~2.0 :via". 1.3 rvlax, 2.0 O. 2~2 . 0 ------;

0.5~1.0 O. 7~1.0 O. 6~1 . 4 O. 7~ 1. 3 O. 5~2. 5

35~70 35~80 35~JOO 35~90 80~ 1 20

12, 000 9,000 10,000 I 40,000 3,500 3,000 -1------13,250 I 13,000 I 22,300 ---;~ I 5,500 2,600

Stainle~s-;ee l Sta inless sleel 99:- StainICss sleel I' Stainless steel Stainless s t~ 1 Stainless steel '1 St3inless-;;'-el 100 j Others 99 100__ . 80 W ~ § 1 'Test cast T est cast Stainless stee l 'Stainless stee l 981 Stainless steel Stainless steel Stainless steel Stainless steel 1 Stainless steel 100 Othe rs 21 100 _I. _ 100 ~ 100 100 '1-- SUS 20 1, 301 SUS 301, 304 SUS 30 1. 304 302 . 304 SUS 410 SUS 304, 316 SUS 002, 302 SUS 304, 304 I. SUS 303, 304 304L. 310S 30'1I., 309S 304L. 316 410, 430 304. 316 310, 316 309, 310 3161.. 317 316 1. , 308 316, 3161. 31OS, 316 3171.. 32 1 3081.. 309 3161., 321 316, 321 321 316 1. , 321 403, 405 I ~g~ L 410 AISI 410, 430 409, 430 410 . 420 J I 410, 430 420 J 2, 430 420]1 , 420J2 434A 434 430. 440 B ,WNR 4511. 4841 440C ------1 N SS200 - - I - - - (l5Cr, IlMn,2Cu) 1 - I DSH IOU - I NSS 304 M2 (O.4C, 13Cr) 1 < High ·speed (l7Cr, 8Ni, 2C u) I 1 DSN 050 N 3095 (0.3C, 17.5Cr , steels> (24Cr, 14 Ni) 12 .5 Ni) I USB 009 1.]( I (22C r , I INi) 1 DNS 03FA USB 3091.1' (O.OOC, 17.5Cr, (2ICr, 12Ni) I 9.3Ni. 0.2755) 1 N 347S DSR IK7 l(lgCr. 10Ni) (0.7C, 13 .5Cr) N 347SA (2 ICr, 13Ni) NSS 410MI (0 .02C, 12Cr ) USB 410 (0.05C, 14Cr) NSS 420J2 (0.3C, 14Cr) NSS 430M3 (l7Cr , Ti) USB 430 (0.03C, l7Cr) NSS 430 M5 (0.3C, 16er) ..

Technical Features ( 432 ) Transactions ISH, Vol. 1 8 , 1978

Table I. Continued.

------~ N ippon Steel Corp. Paci fic :'vI cta ls N ippon Yakin 1------Hikari Murora n *1 Ilachinohe Kawasaki

T ee ming Sliding nozz le Slidi ng nozz le Sliding nozz le Sliding nozzle Sli ding nozzle Ladl e to tundish Pr ~ i~~~ ~~;ll~; g ll1 II11:~~::I ~o n I m~::;~~i~ n Gas sea l Gas seal or open Immersion nozzle or gas seal

Capacity (t) I 1. 2 ). 2 4. 5 1.0 6.0 Tundish Protection from Sy nthetic Syn thetic slag Gas sea l atmosph er e Gas sea l Gas seal or ga s sea l Gas seal

r Subme rged - Tundish to I Protec tion from Submer ged S Ubm e r g~ 1 Submer ged Submerged nozzle nozz le nozzle nozzle nozzle Ca~t i ng powder mold a tmosphere Casting powder Casti ng powde r Casting powde r Ieas ting powder --- Other Surface conditioning of cast Grinder Planer No-cond ition ing Grinding I Grinding I G ri nding chara cteris ti cs product j (KBS. T SG) --- Ha v i n g . r espect H aving r espect to uniform to uniform cooling (Cascade control of I c Doling Ap ply ing I spraying water . etc.) electr omag· netic stirrer to liquid cen ter of Special no tes )illet.

I

- After grinding 11 2 11 2 11 1 113 Comparison Yi eld No t com pa r ed I with Final product 118 118 III b eca use 11 3 ingot making I I) r oducts Li r e product Afte r ~ inding 91 83 87 'hipped as 92 (Index )" Cost I ) illet a nd s lab. Final product 91 83 87 93 ------Cold-ro ll ed sheet Main fina l product I II ca vy pla te Wire. Tube Hot-roll ed shee-It Billet, Slab Cold·r oll ed sheet -- tl Sumitomo M. 1. : Sumitomo Metal Industries, Ltd. t2 Mitsubishi H. 1. : Mitsubishi Heavy Industries, Ltd. n Sumitomo S. M. : Sumitomo Shipbuildi ng & Mac hinary, Ltd. t4 Hitachi S. E. Hi tachi Shipbuilding & Eng ineering Co., Ltd. t5 1. H. 1. Ishikawaj ima- l-Iarima Heavy In dustries Co., Ltd.

ran ge with nozzle clogging steel grade SUS 305 WR, 18 - 9CH casting temperature 1460 - 1500·C I o casting speed II00mm / min "'o .---e__ ___ 0.010 DO --, " 0 " .~ 0.008 - "'.S 3 "-- ' o with submerged nozzles both fo r ladle to tun-;; -- __ ~. and tundish to mold --X • With submerged nozzle only fo r tundish to mold X without submerged nozzle

0.3 0.4 0.5 0.6 0.7 0.8 0.9 Si (%) a MnO - CrzO) & Mn - silicate T ilOs containing AI & Ti Fig. 2. InOuence of Si on line-shape defects·)

0.010 0.015 0.020 0.025 Ti (%) 7 9 than that of ingot casting and or pressure pouring. - ) Fig. I. Influence of both At a nd Ti deoxid a tion on shape The solidification constant, k, although difficult to of non-metallic inclusions and on nozzle clogging of compare unless measured under the comparable condi­ tundish5 ) tions, is usuall y smaller in high alloy steels than in plain carbon or in low alloy steels. 10 -12 ) It is demon­ of the fundamental properties [or casting with the strated that solidus temperature, whi ch has important powder and for the casting of Al- or Ti-containing significance in the solidification phenomena, is a ffected steels. by cooling rate,13) but it has not been es tablished whether or not this applies to high alloy steels. 2. Characteristics of Solidification It is a well-known phenomenon that the hot work­ One of the features o[ continuous casting is a ability is improved by making eq uiaxia l cast structure high cooling rate. Its solidification speed is higher and that the the a-ferrite in cast structure in aus-

Technical Features Transactions ISIJ, Vol. 18, 1978 ( 433 )

(The same)

Sumitomo M. 1. tl N ippon Metal Industry Nisshin Steel I Kawasaki Steel Corp. Daido Steel Kobe Steel Mitsubishi H.I.t2 -- -- - \Vaka yama I Sagamihara- I--Ki ll uura Shunan Chiba *1 I NishinOmiya :- Shibukawa Iwaya * 3 Hiroshima *3

. . I Sliding nozzle Sliding nozz le Shdmg nozzle Sl iding nozzle Slidi ng nozzle Sliding nozzle Sliding nozz le - - r~otar y nozzle I Rotary nozzle --- I I - Immers ion Imme rsion Ga::; sea l Gas seal I mllle r Si~ 1 - I nozzle nozzle nozzle IGas sea l or open - -I - 3.0 4.0 60 6.0 8.0 I 1.5 ------_~ s sea l _ Synthetic s lag Synthetic s lag I Gas seal Synthetic slag Synthetic slag - I - - --- Submerged Submerged Submerged I Submerged I Submerged Ar- purge in Submerged I nozzle nozzle nozzle nozzle nozzle mold nozzle - g - I Casting po\\der Casting powder Casting powder Cast1l1g powder Castmg powder Ab03 COd tll1 111 CastIng powder I mo lcl ------Grinding- Grinding Grinding Grinding G· r Grinding I Grinding I (KES, T SG ) (KBS, NIG, GM) (NTG) I (KBS, TSG) r lllclllg (KBS, TSG) (KIlS)

H a\'ing r espect Nothing Nothing Cascade control N othing Applying to uniform of sp raying electromag­ coolin g water netic st ir r er

INi etectroly tic 1 I coating mold I Thickness ad­ I justable sup­ por ting r oller segment Tundi sh - exchanging continuous­ continuous casting(8 heat)

110 113 11 3 114 100 1I1 116 114 112

85 94 87 95 99 91 89 95 94

Cold-rolled sheetl Hot- and cold-rolled sheet Cold-rolled sheet Hot-rolled sheet Cold-roll ed sheet Small- and middle-bar ---'------*1 Serving both as pla in carbon steel and hig h alloy steel *2 P ressure casting (not continuous casting) *3 P ilot plant *4 lndex 100 equal to ingot making's case and numbers of each index between other wor ks cannot be compared. Not answered

tenitic stainless steel m akes ho t worka bility poor,14 -1B) in a cast sla b with vertical cracks. The example is Columnar str uctures, which are usuall y observed in shown in Fig. 4 in comparison wi th that of norma l the cast slab, a re a p t to grow m ore easily for Cr- N i sla b .31) I t has been thought to be attributable to grades such as SU S 304 than for Cr grades such as uneven cooling of the strand.31) SU S 430.19,20) The same tendencies are observed in The condi tion of solidification can be estima ted by ingot casting a nd press ure pouring as well as in con­ observing microstructure for high alloy steel, toO. B,31,32) tinuous casting. 7,9,21,22) The m ethods to m ake cast The d endritic structures of cast SU S 430 steel a re not structure equiaxial a nd fine includ e addition of in­ detected by etching,33) but it is supposed that the oculator, mecha nical vibration, supersonic vibra tion, structures solidify in d endritic shape similarly as those m echanical stirring, m agne ti c induction stirring, structures of SUS 304 a nd SUS 3 16, in which we can adjustmen t or chemical compos ition, low casting tem­ directly observe dendri tes.B) The secondary spacing pera ture a nd so on.14 ,1 6,21,23 - 25) Of these m ethods, of d endrite arm becomes wider a nd the micro segrega­ the m agnetic induction stirring a nd the low tempera­ tion of solute elem ents becomes m ore remarka ble as ture casting have been ap plied to the continuous the dendri te is kept longer time at the co-existence zone casting of high alloy steel according to litera ture. One both of liquid and solid.32 ,34) The seconda ry spacing example of the influences of the casting structure on of a ustenitic stainless steel is affe cted by amounts of final products is the ridging property of SUS 430 sheet Ni and Cr,10,1l ) and the differences of the a rm spacing m ade through continuous casting26- 2B ) (Fig. 329) . a mong steel grad es can be clarified through observa­ The a-ferrite observed in continuous-cast SUS 304 tions of the continuous cast structure, though the sla bs is larger in am ount but sm aller in shape com­ influence of those solute elem ents is not q uantitatively pa red with that of ingot structure. T herefore, it known.B) Through observing the continuous cast disappears more easily by heating the cast sla b . I t is structure, it has been reported tha t the ferrite dis­ su pposed tha t the a-ferrite readily dissolves in to m a trix tributes in d endrite arm in SU S 304, a nd that the because of its sm all thickness. 21 ,3 0) The a-ferrite ob­ concen tration of Ni, Cr, Si, Mn, P a nd S are un­ served in the cast structure distributes complicatedly uniform in the interdendrites of SUS 310 S.35 ) Clarifi-

Technical Features ( 434 ) Transaction s ISIJ, Vol. 18, 1978

~ SUS430 E 80 -L oo 155 X 1055slab 0, casting spee d j 0.7m/min '~,---- U; 60 0 00

. 0 .~ 40 ~~ 0 '"'5 g- 00 ------. o 20 "'- \J g A · o~ ~ o 20 40- .. "" o 20 40 60 80 6 t super heat at tundish ee) Rat io of equiaxial structure ( % ) (a ) ( b)

(a) Rela tion between casti ng temperature and cast structure (b) R elation between ra tio o f equiaxia l structure a nd ridging (c) S urfa ce observation a nd ro ugh ness o f tes t p ieces (0.7 mm cold- rolli ng sheet with 20% el ongation ) corresponding to their macrostruct ure of cast sla b

2 (c) F ig. 3. E ffect of cast structure on fin a l products 9)

100 20 • • ductility

.. _~o- :80 "- ~ 15 ~ a) Ferrite distr ibution in normal specimen ~ ~60 ~. '" \ ,'" '---' ~'.~~.l ~ 1.W~ 20 . .. C1025 (0.23C 0 52Mn 0.22S.) ·~\I 'i .. longitudinal crack o fj, Type304 (0.07G 9. 17N. 18. 16Cr ) I!. ~ b) Ferrite distribution in longitudmal crack specimen . ~ F ig . 4. Ferrite distributions on sl ice sample of SUS 304 cast -600 -4 sla b3L1 temperature ~ T OF Fig. 5. Compa ri son between 0.23% C steel a nd T ype 304 sta inless steel on strength and reduction o f a rea cation of these phenom ena wi ll bring a bout the pro­ based on melting poin t')· ) gresses in the continuous casting of a ustenitic single phase steels. As aforementioned, though the m icro­ segregation exists in the structure of continous cast SU S 304 is a steel grad e which is easy to cast in view stainless steels,22,36 - 40 ) the macro segregation is sub­ of its cracking properties in comparison with other stan tiall y free except for hig h ca rbon sta inless stcels grades o f sta inless steel a nd even with pla in carbon a nd the resul t compares favorably with ingot struc­ steel. There a re a lot of da ta at compa ra tively low tu re. 16,21 ,41- 44) tempera ture u p to hot roll ing tempera ture, but there are not so much data in hig h tempera ture ra nge as 3. Characteristics of Solidified Steels m elting tempera ture to I 300°C except the d a ta of In con tinuous casting tha t involves quickly cooling RA (reduction o f a rea) measured in the field of a nd m oving of strand under solidification, d efects such .45) Figure 5 shows percent change in the as ruptures of stra nd shell, interna l a nd surface cracks, ducti li ty and the streng th of SU S 304 a nd 0.23% C d epress ions, a nd so on a re easily caused by the stresses steel up to the melting poin t. 46 ) As can be seen f!"O m which a re produced by tra nsformations, a ferrosta ti c the fi gure, the properties of SU S 304 a re superior to pressu re, uneven coolings, a nd rollers used to support, 0.23% C steel a t near the mel ting point. On the o ther draw a nd straighten the sla b . Factors rela ted include ha nd, the a ustenitic-single-phase steels such as SU S specifi c heat thermal expa nsion, thermal conductivity, 3 10, SU S 3 16 a nd SU S 32 1 are se nsitive to the surface behaviors of tra nsforma ti o ns a nd precipita ti o n phases, cracks a nd to the sta r cracks by C u-penetration in spite a nd mecha nical properties. Each gra de of steel, of the sam e a ustenitic g rade as SUS 304. Above a ll such as a ustenitic, ferriti c a nd m artensitic sta in less SUS 3 10 is d iffi cult to cast. 35,Q 7 - 49) I t is genera ll y steel has different properties. F urther, even in the known tha t the ducti lity of SUS 430 becomes evid ently same groups of grade the cha racteristics in continuous low at the temperature ra nge of und er I 300°C in casting m ay not be identical. Some a ctua l exa mples which the two-phase structures a re a ppeari ng. Figure are shown below. 6 shows the tensile properties of continuous cast SUS

Technical Features Transactions ISIJ, Vol. 18, 1978 ( 435 )

o 0 SUS304 C- direction to co lumnar 28 Note. 1. numbers show JIS (SUS) grades 6 SUS304 L - dlrectlon to columnar 2. almost all of the plotted grades are commercially produced xe,\(~fl, 26 • SUS 430 C- dlrectlon to column ar • ~ :~:c~r:~~S~~I::ltlve ()c)c .~~((*"~ ... SUS430 L-dl recbon to columnar •• not crack senSitive but ~OIC~~~~*"~ troublesome after casting ,,0°.0 • plots are om itted when differences of ~ ~ values between C and L are small Olo~"'f\\.e 18 Au sten it e ~ ,!-'0 (~~e ~ o __ ::-- 16 A+M r,,'0%<;;e ~ ~ 14 .- 'i~ 'i==== 'i Z ~ 12

100 ~ ~ 80 Fernte g 60 W 22 24 26 28 30 32 34 36 38 Chromium EQuivalent= %Cr+ % Mo+ 1.5 X %SI+0.5X%Nb 40 Fig. 7. Estimation of each stainless steel grades on Shaemer 100 Diagram after experiences of continuous casting''''''"'

~ 80