ISIJ International, Vol. 31 (1 991 ), No. 7, pp. 661-668

Revie wStrip Casting Techniques for Steel

Kiyoshi SHIBUYAand Michiharu OZAWAlron and Steel Research Laboratories, Technical Research Division, Kawasaki Steel Corporation.Chiba-ken, 260 Japan,

(Received on November22. 1990, accepted in final form on March22. l991)

Kawasaki-cho, Chiba,

The concept of casting molten steel directly into strip can be ttaced to the work of Sir Henry Bessemer,Aversion of Bessemer's concept can be seen in state-of-the-art continuous casting techniques for largesection slabs, and an extension of CCslab casting knownas thin slab casting is also nearing commercialuse. On the other hand, the development of a practical strip caster with thickness ranging from severalhundred microns to about IOmmis still in the research stage. This paper describes the main trends in thedevelopmentof strip casti ng techniques in terms of both processes and material characteristics. Thetwin-rollcaster is the main trend in Japan, while the single-roll caster forms the mainstream in the United States.

Theanswersto a questionnaire indicated that surface quality is the mostserious impedimentto the realizationof a practical process, followed by strip shape. To date, the merits of process integration have usually beendiscussed in terms of the relative energy requirements of the respective processes, i.e. in terms of energysaving. However, the additional energy reductions which can be achieved by the strip caster in place ofthe conventional slab CCare marginal. Instead, reductions in finishing cost are considered to bean appropriateindicator of economic benefit where the strip CCis concerned. Thus, the goal of the race in developing acommercial strip caster is to establish techniques to assure good surface quality.

KEYWORDS:continuous casting; solidification; rapid solidification; castings; stainless steel; Iow carbonsteel, economy;energy.

l. Introduction

The idea of casting molten steel in strip form datesfrom the work of Sir Henry Bessemerl,2) and has longbeen the dream of steel engineers, but none of thetechniques developed to date has been completelysuccessful in reducing Bessemer's concept to practice.

Until thirty years ago, virtually all steel was producedby the ingot casting-slabbing mill route. A variant ofBessemer's concept is the current state-of-the-art

continuous casting machine for large section slab. Aslogical extension of the heavy slab CC, the thin-slab

caster is in the early stages of commercial application asa short-cut in the production of sheet-bar.3)

About 1960, anewconcept in metallurgy wasadvancedwhenPol Duwetzpublished the results of research on agunmethodof producing a single phasesystem of Ag~;uand an amorphoussystem of Au~Si.4,5) A thin strip

casting technique for amorphousalloys called the rapidcooling methodwas invented by R. B. Pond in 19696)

andproved effective in producing long, continuously castthin strips.

In a short time, steel engineers combined the rapidcooling method with the traditional idea of steel strip

casting. The resulting concept becamethe focus of strip

casting work in the steel industries and gavenewlatitude

to research activities. Anumberof groups have studiedthis subject, including the Committee on Rapid So-

661

lidification of lron and Steels of the lron and Steel

Institute of Japan,7) the Department of Energy projectin USA,8) and the projects in Europe.9)

This report discusses trends in techniques for the strip

casting of steel at thicknesses of several hundredmicronsto 10mmin terms of processes and product characteris-tics, with particular reference to the results of aquestionnaire sponsored by the Conference on RapidSolidification of the lron and Steel Institute of Japan.

2. Aimsof Strip Casting

For over 100 years, steelmakers have beendeveloping

ways of shortening the production process, mainly byintegrating functions and eliminating certain steps.

Continuous casting, for example, integrates the casting

and slabbing steps while eliminating ingot making androughing, thus realizing enormoussavings in energy. Inspite of the progress madeto date, the direct casting ofmolten steel into strip of thicknesses from several

hundred microns to lOmmhas remained in the early

stages of research and development, particularly for twomainproducts, mild steel and stainless. Amajor negative

opinion on strip casting emphasizes the importance offinishing processes such as cold rolling in realizing

desirable structural, profile, and surface characteristics.

However, strip-cast material requires little reduction,

making it impossible to correct problems originating in

C 1991 ISIJ

t

Table

ISIJ International, Vol. 31 (1991), No. 7

1. Objects ofthe direct strip casting in the steel industry.

Objects Products

l Process shortening

2 Production of hard-to-roll materials

3 Creation of newmaterials

Reducing the cost for commoncarbon steel

Expansion of business

e Advanceinto the fine-steel

e Substitute for silicon-steel

Plain carbon steel, Stainless steel, elc'.

High-alloy, Intermetallic compound

AmorphousmetalHigh-silicon steel, elc.

Strip CC

Thin slab CC

CC-HDR

CC-HCR

CCWarmslab

CC-Cold slab

100 200 300 400Energy consumption (xlo'kcal/t)

Fig. 1. Energy requirement of each technotogy.

the casting process and obtain the desired characteristics

by downstreamrolling. Fromthis viewpoint, these critics

claim, the strip casting process by its very nature entails

a serious disadvantage. Another negative opinion stresses

basic solidification theory, according to which thesolidification front is composedof non-uniform co-lumnar dendrite. Consequently, strips would not havehigh quality.

Nevertheless, steel engineers have beenchallenging torealize a practical strip casting process. Thegeneral aimsof development are described in Table 1. These three

aims are process integration, which is the traditional

aim of strip casting, the manufacture of hard-to-roll

materials, and the production of newmaterials such asamorphousalloys.

Asmentioned above, strip casting produces an as-cast

material with thin thickness, and thus makesit difficult

to control material characteristics and shapeuniformity.

The requirements for a commercial strip caster aretherefore morestringent than the case with conventionallarge section slab casters.

To date, the benefit of process integration has usually

been calculated on the basis of energy consumption,which means mainly the fuel consumption of the

reheating furnace and the electric requirements of therolling mills (Fig. 1).10) The reduced cost of the finish-

ing processes required to obtain the desired materialcharacteristics has generally not been considered. Dif-

ficulties arise because the benefit calculation for strip

casting is based mainly on reductions in finishing costs,

andnot on reduced energy consumption. In strip casting,

finishing is a major part of the total production cost,

and the effect of fiuctuations in these costs, which arecaused by process variables, is not negligible.

In the case of cost ratio of high-grade stainless steel

as shownin Fig. 2, the cost of manufacturing the strip

of 0.3mmthickness, which includes conventional CC,hot rolling and cold rolling, is 850/0 of the total. While

C 1991 ISIJ

Thin Strip

CC(t=0.3mm)

Strip CC(t=3 mm)

Conven-tional CC(t=260 mm)

cc Dressingll

\\

CC+cold Dresslng /\+\\\

1\\\\\2lll3

\ +- /

CC+Hot+Cold Scarfing

Potential +Dressing

662

COST

Fig. 2. Potential for reducing the manufacturing cost.

finishing costs, including scarfing after CC, surface

dressing after hot rolling and inspection, are 15o/.. Thebroken line I which is based on energy consumption(discussed in connection with Fig. 1) showsthe decreasing

cost of manufacturing the as-cast strip by the decreasedthicknesses.

The relationship between casting thickness andfinishing cost is based on the surface quality of as-caststrip. Whenthe surface condition of the strip is the sameas that of conventional large section cast slab, finishing

cost increases rapidly with decreasing thickness becauseit is necessary to inspect and condition an increasingly

great surface area for the sameweight of materials, andthe benefit of process integration disappears quite quickly

as the broken line 3shows.

Whenthe surface condition of the as-cast strip is better

than that of hot-rolled strip, both the benefit of processintegration and decreased finishing costs are realized.

Amorphousstrip 2030pmin thickness is an exampleof aproduct which is producedby direct thin strip casting

without finishing.

Thekey point for reducing the cost of cold strip is in

the reduction of finishing costs and not in the reductionof the energy consumption. As can be seen from the

above discussion, there is no overwhelming advantagein simply casting thinner strip as a substitute for slabs.

Substantial benefits are obtained from strip casting only

whenthe as-cast strip is of better surface quality thanas-rolled hot strip, and it is therefore possible to reduce

or even eliminate the cost of finishing.

3. Techniques of Strip Casting

As discussed above, the key to success in strip castingis the surface quality of the as-cast strip. Manytechniques

havebeendevised, but becauseof the importance of rolls

in obtaining the desired shape and surface qualities,

practical development is now centered on only two

ISIJ International, Vol. 31

methods, the single-roll technique and the twin-rolltechnique. Austenitic stainless steel is often used for test-

purposes, since it is easy to obtain good surface qualitywith this materials.

3.1. Single-roll MethodThe production of amorphousalloy strip was first

achieved using a rotating substrate methodinvented byPond.6) Themethodwasmodified to use a slit nozzle soas to produce a wider strip. 11'12) At present, amorphousalloy strip 200mmwide is manufactured for use in electric

power transformers.

The success of the amorphous alloy techniquestimulated the development of strip casting in the steel

industry. A technique called the single-roll method is

under development in the United Statesl3'14) based onamorphousstrip casting technology.

Thestrip produced by the single-roll methodnaturally

has two different surfaces, a roll-side surface and a free

surface (Fig. 3). The methodwas originally devised for

very thin amorphous alloy materials 20-30 ~m in

thickness, so whenthe thickness of the steel strip is onthe order of several millimeters, heat extraction andshapecontrol are in~ufficient, resulting in deterioration of theshapeand surface quality of the free surface. Thecentraltask with the single-roll methodis to ensure control thequality of the free surface. Single-roll method areclassified according to the following three puddle controlmethod. (Detailed explanations given below.)

a. Puddle control 1. Planar fiow castingl3)

with roll andnol"rzzle

(PFC)2. Melt dragl4)

b. Puddle control 3. Melt over-fiow castingl5)

with roll

c. Free puddle 4. Spray depositionl6,17)

Free jet castingl8)

3. I . I . PFCMethodl2,1 3,1 9)

This method, shownin Fig. 4, is characterized by a

r:~

(1 991 ). No. 7

planar fiow generated by a pouring nozzle with a speciallip profile. Thebottom of the nozzle lip is located a shortdistance (0.2-0.3 mm)from the roll surface. Becausethemethod was originally developed for very thin

amorphous alloy strip (20-30~m in thickness), it is

necessary to secure adequate heat extraction whilemaintain the melt puddle until solidification of the endof the free surface whenthis technique is applied to thecasting of steel strips.

Two improvements which have been developed area pouring nozzle with an extended front lip and the useof electromagnetic force to enhance heat extraction.Analysis of the melt flow has also beenuseful in designingthe nozzle profile and stabilizing the melt puddle.Vibration of the puddle has an important effect on surfacequality, but as is the case with thinner strips such asamorphousalloy, if air is trapped between the meltpuddle and roll surface, the resultant air pockets will

cause a surface defect knownas fish-scale. This problemhas been solved by controlling the atmosphere.

In experiments, Iow carbon A1-killed steel and stainless

steel have been cast in strips 0,73.0mmthickness (Theproject of Departmentof Energy in USA), while high-Alspecial stainless steel for exhaust gas converter ofautomobile, a hard-to-roll material, has beencast in thinstrips 30-50 ~m in thickness and 100mmwide. (Thedetails will be published in the proceeding of RQ7.)

3.1.2. Melt Drag Methodl4,20)

A distinguishing feature of the melt drag method is

that no active meansis used to maintain the melt puddle(Fig. 5), which is controlled by the surface tension of thefree surface of the material. The physical properties ofthe melt, mainly its viscosity and surface tension, alongwith speed of casting, play an important rolp in

determining the surface quality of the product. Highviscosity materials such as austenitic stainless steel and

TundiSh

[l~;~~o~C~~~~~~~

tl

Wheel dresser Casting WheelFig. 4. Experimental apparatus of Planar Flow Casting in

D.O.E. project.

stri p\~

argon gas dam

lining

Frg. 3. Solidification structure of strip cast by Single-roll

Method.

663

Frg. 5. Melt Drag Method.

C 1991 ISIJ

ISIJ International, Vol.

Ni3Al strip have showngood as-cast surface quality,

while low viscosity steel such as plain carbon and silicon

steeis producepoor results. Onthe other hand, techniquesfor improving the quality of the roll-side surface include

mat or patterned roll morphologies, which are effective

becausethey apply tension to the solidification front. 21)

Themechanical properties of melt-drag cast austenitic

stainless steels are reportedly as good as those ofcommercial products, and the profile of the as-cast strip

showsa typical thickness deviation of 56 "/..

3.2. Twin-roll MethodThetwin-roll methodis basedon the concept originally

proposed by Bessemer, in which molten metal is fed into

the roll gap from above. Themethodis characterized by

a higher heat extraction capacity than that of thesingle-roll method, since the melt pool is cooled fromboth sides by the twin rolls. A thicker strip can therefore

be cast, and the quality of the two strip surfaces is

essentially the same.However,control of the gapbetweenthe rolls and of rolling force is difficult, so twin-roll

casters generally require more sophisticated control

systems than single-roll casters.

Twin-roll methods maybe broken down into three

pouring methodsand four roll methods, but in spite ofthe variety of possible combinations, only four arecurrently reported to be under development. These aresummarizedbelow.

a. Top feeding l. Equal diameter twmrolls22)

b. Inclined feeding 2. Inclined twin rolls~3)

c Poolfeeding 3, Unequal diameter twin'

rolls24]

4. Inner-ring twin rolls25)

Topfeeding, the basic methodof the twin-roll method,has a drawbackin regard to the stabllity of the melt poolat the roll nip. The cause of this problem is the longdistance betweenthe pouring device and the rolls, whichis an unavoidable result of caster geometry. Inclinedfeeding and pool feeding methodshave been proposedas meansof obtaining a more stable pool, but bothalternatives have their ownunsolved problems.

Figure 6 illustrates the concept of control of the gapbetween the roll in the twin-roll method.22) While the

metal is solidifying betweenthe twin rolls, the parallelism

of the rolls is disturbed by several factors. Omitting the

ideal case, for practical purposes the configuration of therolling- and solidification process is of three types, with

(O

31 (1991), No. 7

combinations of the three observed experimentally.

Type(A) is the ideal case, in which the roll gap is uniformin the axial direction. In Type (B), the rolls are notparallel; this Is called misalignment. In Type(C), the rolls

showheat crowns as a result of thermal expansion, whilein Type (D), the internally cooled ro]Is are deflected

inward at their centers by the rolling load. Except for

the ideal case, all configurations al]ow an area of thestrip to remain unsolidified (indicated by the dottedportions). This unsolidified area maycause breakout andis susceptible to oxidation whenthe strip exits from thecooling rolls. Micron level roll gap control is required

to prevent this problem and ensure the desired thickness

accuracy in the as-cast product.Figure 7 shows the concept of rolling force control.

Case(b) is the ideal case, in which solidific,ation is

completed at the roll-kiss point. In Case(a), the rolling

force is inadequate to bond the shell which forms in-

ward from the cooling-roll surfaces, and the end ofsolidification occurs below the roll-kiss point. Theproblems in this case are breakout and oxidation, andthe strip center showsan equiaxe(} zone, as can be seenin Fig. 8(b).

Conversely, in Case(c) rolling force is excessive and

(a) (C)(b)

Fig. 7. Schematic drawing of the concept of roll force control.

(A)

1mm

co~o(1)

5o)c~U)cV

o

(B) (D)

Frg. 6. Schematic drawing of the concept of roll gap control.

C 1991 ISIJ 664

(b) with equiaxed zoneFlg 8 Solidificatron structure of strip cast by Twin-roll

Method(SUS304).

ISIJ International, Vol, 31 (1 991 ). No. 7

=0 0=

Tundish

Cooling Roll

SecondaryCooling ZonePi chRoll

~~D~!tl

Fig. 9. Equal diameter twin rolls.

o

solidification occurs above the roll-kiss point. Thematerial is squeezedout abovethe roll-kiss point, causing

a type of negative segregation called white band. Thiscase frequently results in heat cracking and damagetothe cooling-roll surface, in addition to structuralabnormalities of the materials. But the effect of rollingforce gives not only negative results, but also im-provement of the strip surface conditions and me-chanical properties in an adequate rolling force.26,27)

The existence of these phenomenawas confirmedexperimentally by observing the material at the outlet ofthe cooling rolls and analyzing the structure of theresultant strips.

3.2.1. Equal Diameter Twin-roll Method22,2830)Figure 9 shows an example of an experimental

apparatus for this method. High alloy stainless steel,

which is used commercially as overlay welding material,

was continuously cast into strip 0,3~).8mm thick and350mmwide at casting speeds of 25m/s. The casting

apparatus has a secondary cooling zone which is usedto prevent oxidation of the strip surface and maintainthe desired cast structure. The device can be used toproduce strip in the order of several millimeters in

thickness whenequipped with side damsat the roll nipto obtain a higher melt height. Large rolls over I OOOmmin diameter have also been introduced as a meansofimproving the surface quality of the cast strip, since thelarger melt pool thus obtained makes it possible tostabilize the meniscus by using an immersion nozzle.

3.2.2. Inclined Twin-roll Method(Fig. 10)23.3i)

The purpose of the inclined twin-roll configuration is

to obtain a laminar fiow at the roll nip by pouring themelt across the roll at one side of the caster. Surfacequality is improved by stabilizing the melt pool, whichenters the roll gap in a laminar flow. Stainless steel, whichnormally requires cold rolling and annealing, can be castto thicknesses of l-1.5 mmand widths of 300mmwiththe samemechanical properties as commercial products.In cast iron, improved ductility and better rollability canbe obtained due to the fine structure produced by rapidsolidification.

3.2.3. Unequal Diameter Twin-roll Method24)This method, shownin Fig. Il, has characteristics of

both the single-roll and twin-roll method. It can also becompared to the melt drag method, which, however,improves on the surface quality of the single-roll method

o

665

Coiler

103

102

E.~EIO

(,)

a)uJzl~~

oi~H

1O-1

1o-2

coiler

10-1

o

Fig.

ladle

//~;roll

/~/'

~~;~~f

'l

~:

i Ii 180~ I jI

)~\>~~~:~~'striP

!f 200~ il l\i 240~ I '/ 1\

guide 1 30o_o'~~~~\~

60 '\

Fig. lO.

guide

Inclined twin rolls.

upper roll

upperroll

nozzle

.~l

ladle

tundish

+ bottomroll

Il]

/ bottom roll

ll. Unequal diameter twin rolls.

(~~s~=~"

NKX

Strip(Double

Fig.

Thinslab

I

LT

HITACHlI~VlE steel

~ship,

NiPPonMetaNj~~:i!~1::kIATJTlc'o

/t~EV?A

NiPPon steel

rolD" 1RIBTEC KAWASAKIsteel

L lAllegheny

l

Strip(Single roll)

/

~~Amorphousmetal striP

1 10 102 103

CASTINGSPEED (m/min.)

12. Activities of steel strip casting,

104

without using a small diameter upper roll. Theproblemwith the unequal diameter method is deflection of thesmall diameter upper roll by thermal stress and rolling

C 1991 ISIJ

ISIJ International, Vol.

force. Stainless steel, silicon steel and cast iron strip havebeen produced experimentally using this method.

3.3. Trends in DevelopmentTrends in the development of strip casting technology

in Japan and the United States are shown in Fig. 12.

Japanesedevelopmenthas focused on twin-roll methods(shown in the shaded squares), while American efforts

have centered on single roll methods(plain squares).

The strip with these machines is typically less thanlO mmin thickness, since a principle aim of the processis to bypass hot rolling and produce a strip suitable for

use as cold rolling material. However, twin-roll deviceshave also been developed as thin slab casters, and sheetbar is produced using strip casting techniques.32,33)

The heat size of these casters is generally under tentons of ladle or melting furnace capacity. 28,29, 31~ 33) Thisis not necessarily a problem, however, since an aim ofdevelopment is not merely to realize cost reductions, butalso to obtain the strategic flexibility neededto meet the

current trend toward small-lot, multi-grade production.Stainless steel is commonlyused as an experimentalmaterial because it is typically a small-lot productcomparedwith plain carbon steel. Moreover, it is easyto obtain good surface quality with austenitic stainless

steel, grade SUS304,using strip casters.

3.4. Problems and Applications

Table 2showsproblems in the commercialization ofthe strip casting process as reported to the Committeeon Rapid Solidification of lron and Steels of the lronand Steel Institute of Japan. It should be noted thatfor reasons of secrecy the results of the questionnairedo not necessarily reflect the latest work of the companiespolled, but someidea of the general direction of devel-

opmentcan be gained from the replies.

The most significant problem, according to all

companies, was surface quality, while the second most

31 (1991 ). No. 7

important was strip profile. Surprisingly, the side dam,which has not yet been perfected, was not considered aserious problem, and most respondents expected asolution in the near future. The answers predictedcommercial use of strip casters by about the turn of thecentury, with stainless steel and special steels such asNi-base alloys as likely applications. Strip casting of lowcarbon steel by that data is not considered a feasible goal.

4. Material Properties

The material properties of an Fe-Ni-Cr system alloy

such as austenitic stainless steel (SUS304), which is atypical strip casting material, are described below.

4. 1. Solidification Structure and Cooling Rate

The solidification structure shownin Figs. 3and 8is

closely related to cooling rate, which in turn is affect-

ed by the latent heat of solidification and recalescence.

To eliminate these effects, the Conference on RapidSolidification of the lron and Steel Institute of Japandefined the cooling rate in the rapid solidification as thecooling rate in the liquid phase immediately prior tosolidification:

U=dTl/dt

where, U: cooling ratedTl: change in temperature at the liquid phase

immediately prior to solidificationdt: time required for dTl'

Threemethodswereused to determine the cooling rate:

direct measurementby thermocouple, indirect measure-ment based on dendrite arm spacing, and calcula-tion.34'35) The indirect method, the results of which areillustrated in Figs. 1336,3 7) and14,38 ~ 42) is generally used.

The relationship between the cooling rate and dendrite

arm spacing is expressed by the following formula:

Table 2. Problems and applications of steel strip casting.

Company Nippon KawasakiSteel Steel NKK Sumitomo Nisshin Hitachi

Metals Ship.SteelKobe NipponSteel Metal Ind.

Heat extraction device

Metal feeding

Heat size (kg)

Thickness (mm)Width (mm)

D.R.M.TOPlOO

l200

D.R.M.TOPl500

0.3~).8

350

D.R.M.TOP2502- 17lOO

D.R.M.TOP

-10

D.R.M.TOPl20

0.82.3

3OO

D.R.M.TOP350

MAX.760

D.R.M.INCLI.

l503~~075

D.R.M.UNEQ.

300

2300

~'~*~o

e*

Thickness vari

Surface quality

TextureInclusionSide damRefractoryHeat crown

**

*

**

*

*

**

*

*

*

*

*

**

*

*

***

**

*

*

s~

o

~,~

Plain carbon steel

Special steel

A

A o

O

O o O

C 1991 ISIJ 666

ISIJ International, Vol. 31 (1991), No. 7

103

~:~

Q)i OOcoC~

~,,)E 10a~

rl)

~~c:e) il:'

~~

Kishitake and Okamoto

(Rapid casting)

~)

oo!

E~(D

l:l

(D1:,

:~(~

o

(Double roll method) ~:,

c:

oe,CD

1Oo I O1 105104103102Cooling rate CKlsec)

Fig, 13, Relationship betweenthe primarydendrite armspacing

and average cooling rate (4.50/0SiFe),

~~~

i02

101

io o

10

Esaka

/,et

~\1 '\Sugiyama,et

-1

Fig.

al.

al

\ \Wolf

/

I Kasamaetal

I This study

O 2Hf=0 65mmA 2H1=i 10mmD 2H1::1.40mme 2H:f=1.70mmJL 2H1=1.92mmI 2H1=220mm

~ ~i-~~~~'~~f2~T\ ~i~~T-_~i~"

\IJ_L 9\.'L '~'~Y*~~~.

\\' \100 iol ioia 2 103

Average cooUngrate ('c/S)

14. Relationship between the secondary dendrite

spacing and average cooling rate (SUS304).

4

arm

iOs

/=kU~"

where, l: dendrite arm spacingk: parametern: exponent.

Thedendrite armspacing was2-1 O,4m in the cast strip;

based on the relationship described above, the cooling

rate wascalculated at 102104(K/s).

4.2. Surface Quality and Thickness Deviation

Problems regarding surface quality and thickness

deviation are at the heart of the development of strip

casting technology. Information in the literature, how-ever, is very slight. The morphology of surface defects

includes surface laps and surface cracks. The averagequality level at present still necessitates dressing before

cold rolling, but in somecases the quality is as good as27,29,30,43)

or better than commercial hot strip.

Typical thickness deviation in as-cast strip is 5-lO "/.,

as shownin Fig. 15.28) Whenthe thickness deviation of

as-cast material for cold rolling is at this level, a solution

from the viewpoint of rolling technique is considereddesirable.

4.3. Mechanical Properties29,43)

Figure 16 shows the mechanical properties of as-cast

annealed at I 050'C in comparison with those of coldrolled and annealed strip (in the figure, L indicates the

rolling direction; Q, a 45' angle from L; and C, the

transverse direction). The tensile strength, 0.2"/, yield

stress, andelongation results of the cast strip werealmostthe sameas those of the conventionally manufacturedSUS304stainless in all measurementdirections. Figure

17 showsthe earing ratio of the conventional CCmaterialin comparison with fully equiaxed and fully columnarzones of the strip, as obtained by etching with acid. Theearing ratio of the strip-cast material was very small

comparedwith that of the conventional CCmaterial,

and that of the columnar zone wasgreater than that ofthe equiaxed zone.

5. Conclusion

Thedevelopmentof strip casting is progressing on the

basis of a combination of two concepts. The first is

600

500

IOD

o

Fig.

~nl

~l~"'1"-" '1'~~ J .."l~,'~

Ave,

S, Dev,

191

15unl

pm

Goo~m

500

IOO

O-2 25 -lOO O 100 225 mm

15. Thickness deviation of as-cast strip (Fe-30Cr-14Ni).

Fig.

UJ

E~O)

:~(

(D

HEEQ)~(

(D

>~~.'

C\!

d

16.

656055

50

454075

70

65

6032

3028262422

~i ~;--

o Strip cast

e conventionally

_-e----c80oo

,*

~OC(~~~~!lL==~:J:~~'O

e•~.__b '---e-- --e

~~--6~~-~L L Q CI

As cast Cold-rolled+annealed+annealed

Mechanical properties (SUS304).L; rolling direction, Q; 45' angle from L,

C; transverse direction.

original concept of steel casting conceived by Bessemer,while the second is the rapid cooling technique, which

was developed for amorphousstrip and later adoptedby the steel industry. Thecombination of these techniques

has given newimpetus to the developmentof strip casting

technology for major steel products such as low carbonsteel and stainless steel, and the development effort has

now entered its most interesting phase. The quality

667 C 1991 ISIJ

ISIJ Internationa[. Vol. 31 (1991), No. 7

EEQD

CQQ)

o~:Q1Q)

I

1

-1

1,o

- I .o

10

-1.

.oequi-axed earing ratio i.096

o ~Ch~~

,o

,ocoiumnar earing ratio 2.1%

o ~~~.o

ccoearing ratio 4.0%

fr 4~Lo ~rc~4'

r~

~~~1>~trJor 4~4n

~no T)

O 45 90 135 180Angle from rolling direction (')

Fig. 17. Earing ratio (SUS304).

requirements applied to commercial products, however,are extremely high, and as-cast strip must therefore offer

excellent properties, since allowable reduction for qualityimprovement is quite limited.

Allegheny Ludlum has recently announced the con-struction of a prototype plant for strips with thick-

nesses of 1-3mmand widths 1220mm,with the goalof commercial production in the first half of the 1990s.

The most significant point will be how the Alleghenyprocess solves the problem of surface quality in mainsteel products, particularly low carbon steel.

Onthe basis of the newconcept described above, thepotential for progress in the developmentof strip castingtechnology is very high. If the steel industry shifts thefocus of its deveiopmentactivities to this field of research,the prospects for a newRenaissance in steelmaking, asHenry Bessemer dreamed, are becoming increasinglybright.

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