F A S T E R

SMARTER

T H I N N E R

B E T T E R

2100 Rexford Road, Charlotte NC 28211

Telephone: 704.972.1820 Facsimile: 704.972.1829

www.castrip.com

Recent Developments in Project M The Joint Development of Low Carbon Steel Strip Casting by BlueScope Steel and IHI By W Blejde and R Mahapatra, BlueScope Steel, Port Kembla, Australia H Fukase, IHI, Yokohama, Japan METEC Congress 99, Düsseldorf, Germany June 1999

RECENT DEVELOPMENTS IN PROJECT M THE JOINT DEVELOPMENT OF LOW CARBON STEEL STRIP CASTING BY BHP AND IHI by W Blejde and R Mahapatra BlueScope Steel, Port Kembla, Australia H Fukase IHI, Yokohama, Japan 1.0 SUMMARY BHP and IHI have been collaborating on the development of strip casting technology since 1989. The main features of the full-scale development strip casting plant at BHP Port Kembla Steelworks are described. Commercial quality low carbon strip 2mm x 1345mm has been produced that has been converted to building products used in actual projects. The properties of cast, inline hot rolled, and cold rolled material are described and are shown to be similar to products from conventional process routes. Strip casting potentially offers a significant reduction in capital and operating costs for the production of thin gauge materials (less than 1.0mm) that currently are produced predominantly by cold rolling mills. 2.0 INTRODUCTION In 1989 BHP and IHI began to collaborate on the development of twin roll strip casting technology with the commissioning of a five tonne pilot plant at Unanderra, NSW, Australia. The initial focus was 304 grade stainless steel and after successfully producing the first crack free strip that could be processed to sink bowls, the emphasis was shifted to low carbon steel casting. By 1993 cast five tonnes coils 2mm thick x 1300mm wide, were successfully pickled, cold rolled, galvanized and roll formed to tile battons which have a tight radius to test the ductility of strip and also adherence of metal coating. This gave the first glimpse of the technical potential for casting low carbon steel. A range of issues such as the long run quality capability, and the service life of side dams and casting rolls could not be resolved on a five tonnes casting scale, hence it was decided in August 1993 to construct a full scale development strip casting plant at Port Kembla, NSW, Australia.

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Commissioning of this plant began in February 1995, and development work on this plant culminated with the production of the first commercial quality coils 2mm x 1345mm in December 1997. Maximum coil mass produced was 25 tonnes, typical mass was 15 - 18 tonnes. These coils were processed to roofing products that were used in building projects. 3.0 FULL SCALE DEVELOPMENT PLANT The full-scale development plant, which embodies all the features necessary for a commercial plant, was constructed in a decommissioned EAF/AOD shop previously used for the manufacture of stainless steel. The site was regarded as ideal because it was centrally located to all of the necessary technical support resources needed for a development project of this magnitude. A cross section of the casting plant is shown in Figure 1.

2100

1300

P.L(F.L+800)

800

1 2 3

4 5

6

7

8 9 10 10

1. Turret 4. Tundish 7, Pinch Roll 10. Coilers 2. Ladle 5. Twin Roll 8. Pinch Roll 3. Plasma torch 6. Rolling Mill 9. Shear

Fig. 1: General Arrangement of the Port Kembla Development Plant

3.1 Process Description The EAF with its current power input of 18MVA is capable of producing 60 tonnes of liquid steel in three hours. A steel ladle arrives from the EAF on a transfer car and is placed onto the turret using a remote controlled crane. During casting, steel flows from the ladle into the main tundish and then through to a metal distributor from whence it flows into the pool via a metal delivery nozzle placed between the two casting rolls. The strip exits the casting rolls through an inert chamber that is used to prevent the formation of scale and is also used to control the strip temperature at the entry to the rolling mill which is capable of about 50% reduction. The strip leaving the mill is cooled, cut to length by a shear and then coiled on one of two coilers. The total line length is 56 meters.

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 2

The plant is fully automated requiring minimal operator intervention. Extensive use has been made of robotics. The machine specification is summarized in Table 1. Table 1: Machine Specification

Twin roll caster with 500mm diameter casting rolls. Casting speed 80m/min. typical 150m/min max Strip thickness 0.9 - 2.0mm. Strip width 1.0 - 2.0m (current width 1.345m) Coil mass 25 tonnes (on 2 x 40 tonne coilers). Target steel grade low carbon steel typically 0.06%,Si killed 60 tonne ladle, 10 tonne tundish Plasma torch for steel temperature control. In-line hot rolling Strip caster capability 300 to 500 kt/a

3.2 Operating Cycle Between February 1995 and September 1998, the development plant was operated on an experimental basis by two operating teams working 12-hour shifts over a 24-hour cycle, 4 days per week. More recently the plant has been operated on a single operating shift, 4 days per week. The total tonnes cast to date is around 30,000 tonnes. 4.0 PRODUCT QUALITY Commercial quality strip produced to date has been in the thickness range of 1.8-2.0mm. This section details the actual methodologies used for assessment and the results obtained. 4.1 Surface Quality Strip surface was routinely examined using a number of techniques, which included:

• on-line inspection of entire cast • visual inspection of cold strip (10m long strip samples from front and back end of each

coil) • pickling of full-width strip samples • dye penetrant testing of all pickled samples

Dye penetrant testing was necessary to reveal microscopic defects, which could not be readily detected on pickled surfaces. Defect-free surfaces, which were suitable for cold rolling, were produced.

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 3

4.2 Internal Quality Numerous strip samples were metallographically examined. In all cases, fine dendritic solidification structures consistent with those reported by others were observed (1). Of particular concern, was the existence of internal porosities. Initial cold rolling trials indicated that this type of defect can cause severe operational problems during cold reduction under tension. During product testing, it was difficult to ensure that strip was totally free of voids using conventional metallographic techniques. To overcome this problem, full-width samples were subjected to X-ray mapping to assess internal soundness. Typical examples of X-ray porosity maps are shown in Figure 2. Figure 2a shows a defect free example, which is typical of good quality cast product, whilst Figure 2b shows the case where internal porosities exist. Porosity is usually associated with uneven solidification, which can be avoided with good control of mould condition and steel chemistry.

ast strips were also subjected to SEM analysis to characterize inclusion size and distribution. ypical SEM results are shown in Fig. 3, which shows that, as expected, the inclusions are very ne.

a) no porosity b) porosity present

Figure 2: X-ray Porosity Maps of full strip width; a) no internal porosity, and b) internal porosity CTfi

ss

1 4 7 10 13 16 19 22 25

Inclusion size µm

0

5

10

15

frequ

ency 20

25

40

30

35

METEC Congre

Figure 3: Typical Inclusion Size Distribution

99, Düsseldorf, Germany, 13-15 June, 1999 4

4.3 Edge Quality Achievement of good edges is one of the significant challenges in strip casting. Effective control of metal flow and solidification is critical to producing good edges. A photograph of a typical coil edge is shown in Figure 4. 4.4 Dimension Control Strip thicknesses were continuously measured throughout each cast using two on-line X-ray gauges. One device was dedicated to measure strip profiles and the other device was utilized to measure centerline thickness. Figure 5 shows a typical cast strip profile which is similar to that produced by Hot Strip Mill (2). The cast strip profiles produced were suitable for cold rolling.

Figure 4: Photograph of a Typical Coil Edge

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

HSM As Cast As Cast &Hot rolled

Sta

ndar

d de

viat

ion

(mm

)

Figure 5: Typical Strip Profiles (As cast vs HSM)

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 5

Centerline gauge performance was characterized from standard deviation values calculated om strip thickness data. Figure 6 shows centerline gauge variation results achieved with cast

roducts and that it is almost halved with the introduction of in-line ot rolling.

frstrip and inline hot rolled product. Also included in Fig. 6 is the corresponding data obtained from a number of hot strip mills (2). Results indicate that the centerline gauge variation of cast strip is comparable to HSM ph Figure 6: Centerline Gauge

6

7

8

9

2

1

As CastHSM

1.

1.

1.

1.

2.

0

900

1000

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1300

Distance From West Edge (mm)

Thic

knes

s (m

m)

100

200

300

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500

600

700

800

Performance of Cast, Inline Hot Rolled and HSM Products.

trip mechanical properties were routinely measured on a per coil basis to determine strength

he mechanical properties of cast product are summarized in Table 2, which also shows the ffect of inl ed compare vorably w

trength of which is redomina product tructure we low sid re. Cast roducts h

able 2: S

4.5 Mechanical Properties Sand elongation values. Cast products were also subjected to ”0T” bending tests. Te ine hot rolling. For both cases, the strength and elongation values obtain

ith those of low carbon Al-killed steel strip produced via the HSM route (3). The the cast material tends to be on the higher side due to the microstructure

ntly a mixture of polygonal and Widmanstatten ferrite (compared to a HSM hich consists of fine equiaxed ferrite). The elongation of cast material tends to be on e, and it improves with inline hot rolling, which refines the cast microstructuave satisfied the requirements of “0T” bend tests.

ummary of Mechanical Properties

Product Yield Strength (MPa)

Tensile Strength (MPa)

Elongation (

300 440 26 t rolled

ill) 385 465 29

band range 250 - 360 320 - 420 22 - 35

faspsthp T

%)

As cast As cast + ho(In-line mTypical hot

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 6

It should be noted that the coarse Austenite grain structure unique to strip cast product can beasily manipulated to produce a wide range of products with varying properties. This potential isdemonstrated in Figure 7, which shows that the use of different cooling regimes can change tstrength from 350 to 900 MPa.

e

he

.6 Quality Repeatability

n extended campaign was undertaken to demonstrate the repeatability of the casting process

of coiled nnage. The remaining 5% was accounted for by start-up and tail-out losses and the

4 Afrom a product quality perspective. This involved a total of 29 separate single ladle casts in May1998. The average prime product success rate (including test samples) was 95%toremaining tundish skull. These losses would be dramatically reduced with sequence casting.

Figure 7: Capability to Control Microstructure/ Strength

0

100

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900

High Moderate Soft Hard

Tens

ile S

treng

th [M

Pa]

Coiling Temperature Run-Out-Table Cooling

PolygonalFerrite

Polygonal+AcicularFerrite

Bainite

Martensite1000

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 7

5.0 PRODUCT PROCESSING The majority of the material cast was 2mm thick x 1345 mm wide which was cold rolled down to 0.42mm thickness as G550 (Grade 80), coated with a 55Al/Zn protective coating and roll formed into a number of roofing profiles such as Custom Orb®, Spandek® and Trimdek® roofing made

produced.

T

from Zincalume® steel. In addition, painted Colorbond® roll formed sections were also The final products were tested in actual building projects. The product processing

flow chart is presented in Figure 8. Figure 9 shows a photograph of the first application.

0.42mm cold rolled full hard product

Cast 2mm

Zincalume®

Colorbond®

Custom Orb®

Custom Orb®Spandek®

Metal coating

Painting

Roll forming

cold rolled

Roll forming

rimdek®

Build

Figure 8: Product Processing Route

ing Projects

Figure 9: Roofing from Strip Cast Product.

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 8

Actual mechanical properties of the final product are presented in Table 3. Properties compare vourably with HSM products (3). fa

Table 3: Properties After Cold Rolling and Annealing.

Product Yield Strength (MPa)

Tensile Strength (MPa)

Elongation (%)

G550/Grade 80 Project M - 850 4.5 HSM - 767 4.7 G550/Grade 80 spec 550 min G300/Grade 40 Project M 315 416 36 HSM 320 390 36 G300/ Grade 40 spec 300 min 340 min 18 min

In addition to sheeting for building products, a limited quantity of as cast material (without subsequent rolling) was converted directly to tubing including 21.3 to 88.9mm round sections and 25 x 25mm and 50 x 50mm square sections. Figure 10 shows a photograph of actual tube

.

sections Figure 10:Tubes processed directly from strip cast product.

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 9

6.0 BUSINESS VISION FOR COMMERCIAL STRIP CASTING OF LOW CARBON STEEL.

.1 Product

he potential product routes for cast strip are presented in Figure 11.

he initial b ills. It as been fo e product apability to al hallenges propriate trip shape capital nd operati

.2

he produc the cast ickness, cnge for a

.3 Costs

rojected capital and operating costs for strip casting are presented in Table 4. Table 4: Projected Capital and Operating Costs

6 T

T usiness vision was for strip cast material to be used as feed for cold rolling m

und that the in-line hot rolling of cast material enables the extension of th areas that currently can only be serviced by cold rolling mills. The additionand complexity associated with the provision of facilities that produce apand surface quality (particularly scale levels) are offset by the reduction inng costs if pickling and cold rolling can be eliminated.

Plant Production Capacity

tion capacity of a single strand strip casting machine will be dependent onasting width and the maximum allowable mould heat flux. The expected production typical plant will be 300kt/a to 500kt/a.

ure 11: Potential Product Routes

M Cas

M PLANT

ter

NAL P

Pr

1.3mRollin “Hot Band” - 1m

Cold Rolled & belowm

FI RODUCT

Cold Rolledoducts

“Hot Band” > m

Pipe Market

Replacement G550 direct

Unique Grades

InlineHot

gMill

ColdRolling

Mill

Fig

hccsa 6 Tthra 6 P

Capital Cost Specific Investment 1. Capital (US$M) US$/a.t) Meltshop 60 150 StripCaster 80 200 Total 140 350 2.Operating Conversion cost (liquid to coil) = US$40/t

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 10

The operating costs which are based on the assumption of achieving 320 tonnes sequence (not

opment plant), are projected to be comparable with effective thin slab aster technologies with the potential for some decrease as refractory and mould technologies

of the current hallenges is to further simplify the plant design to reduce the capital cost.

for three led pickle

possible at the develcfurther develop. The current capital is still considered too high and onec 6.4 Energy Requirements The energy requirements (calculated on a total life cycle basis) have been contrasteddifferent production routes where the material is ultimately processed through a coupline and cold mill (CPCM). These results are presented in Table 5. Table 5: Calculated Energy Requirements

Energy (GJ)/t

†GGE *(t CO2 equiv)/t

Thin Strip Caster ⇒ CPCM (reduced electricity)

1.8 0.16

Caster ⇒ Hot Strip Mill ⇒ CPCM 4.2 0.33 Caster (thin slab) ⇒ Thin Slab Hot 3.5 0.27 Strip Mill ⇒ CPCM These numbers include the generation of electricity from coal, winning natural gas etc but attribute no energy or greenhouse gas emissions to any materials/processes up to and including liquid steel production. † Greenhouse Gas equivalent. * Tonnes of carbon dioxide equivalent per tonne of product.

Not surprisingly the energy consumption and thus the rate of generation of green house gases

much lower for strip casting than other casting technologies.

roducing cold roll replacement material. The initial wed immediately by 0.7mm. The

edium term goal is 0.4mm.

ood progress in solving initial problems associated steer

sulted in the production of the first crack free 1.0mm coils in March 1999. A photograph of this 1.0mm thick coil is shown in Figur

is 7.0 NEXT STEPS The current development program is focused on pgoal is 1.0mm follom Gwith strip ing through the rolling mill has

e 12.

Fi h of 1.0mm Coil

re

gure 12: Photograp

METEC Congress 99, Düsseldorf, Germany, 13-15 June, 1999 11

Work is proceeding to improve strip shape and further reduce strip surface scale levels. It is expected that the first product will undergo market trials during June/July of this year. In parallel to this development activity, a team is developing a commercialization strategy for strip casting that will be announced in the second half of this calendar year. REFERENCES

20A, 1989, pp 1191-1198.

(3) Private Communication, HP Steel, Western Po ip Mill, V Australia

(1) Shiang LT & Wray PJ, “The microstructures of strip-cast low-carbon steels and their response to thermal processing”, Metallurgical Transactions, Volume (2) Internal report, BHP Steel, Australia.

B rt Hot Str ictoria,

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