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Recent Developments in Refractories & Clean Steel Making Technology

Andreas Buhr, Almatis, Frankfurt, GermanyRalf Bruckhaus, AG der Dillinger Hüttenwerke, Dillingen, GermanyReinhard Fandrich, Stahlinstitut VDEh, Düsseldorf, Germany

International Conference on Advances in Refractories and Clean Steel Making, June 26 – 28, 2013, Isphat Bhawan, SAIL, Ranchi, India

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Content

�Trends in steel making technology�Requirements on high purity resp. high quality (HQ)

steel grades�Focus on secondary metallurgy

�Impact of refractories and trends� Interaction between steel and refractories�Refractories as tools for clean steel making�Economics in refractory usage

�Conclusion & Literature

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� Ongoing development of new steel grades with tailore d properties for various very different applications

� High purity steel grades with tight specifications for undesired impurities and alloying elements

� Extended processing of liquid steel in secondary me tallurgy� Zero error strategies with max. productivity and fl exibility� Near net-shape casting technologies in order to red uce the energy

consumption (e.g. thin slab vs. conventional CC -50 %)� Share between oxygen and electrical steel making de pending on

maturity of steel market (availability of scrap) in a region:� Americas, Europe, Japan 40-50% EAF� China <10% EAF� India 60% EAF; limited scrap but HBI/DRI instead

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General trends in steel making technology

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Requirements on HQ steel grades: impurity content

Achievable contents after secondary metallurgical treat ment between 1960 and 2010

Elements:C, S, O, N, H

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Red = Min.

Target

Blue = Max.

Target

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Requirements on HQ steel grades: alloying agents an d relevant aggregates for ladle treatment

Page 6Source: A. Viertauer, Siemens VAI Metals Technologie GmbH, VDEh refractory seminar April 2012

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PageSteel treatment in the ladle defines quality of the steel grades

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Secondary metallurgy for BOF and EAF process routes

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� Scheduling in a steel shop more and more important� Reliable availability of the equipment mandatory (incl. R efractories!)

power outages a challenge in India� Re-heating of steel required due to extended processing ti me 8

Secondary metallurgical process routes – flexibility and d iversity

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PageAbout 350 VD units and 200 RH units in operation ww 2010

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Vaccum treatment plants world-wide 1990 – 2010 RH & VD t ypes

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� Special requirements on steel oxide cleanliness for thin slab casting to avoid clogging

� relatively high share of thin slab in Indian produc tion 10

Technological evaluation of continuous casting processe s

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The steel ladle as a metallurgical reactor

Source: H. Lachmund, AG der Dillinger Hüttenwerke, VDEh steel ladle lining seminar September 2012

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Purging plugs (or lances) as functional refractorie s essential for treatmentWear resistance of sliding gate plates for automate d flow control or Ca-treated steel(thin-slab casting)

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Refractories and clean steel making in secondary metallu rgy

Slag resistance against metallurgical reactive slag composition

Thermodynamic stability of refractory oxides to avoid re-oxidation of steel

Lower carbon content to avoid or limit C-pick up after vacuum treatment

Insulation layer in ladle lining to reduce heat losses during extended treatment times

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Slag resistance of ladle refractories

�Metallurgically reactive top slag, low melting & viscosity

�More aggressive forrefractory linings

�Use of higher qualityrefractories in ladles

Source: A. Viertauer, Siemens VAI Metals Technologie GmbH, VDEh refractory seminar April 2012

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Slag line:� MgO/C bricks based on fused magnesia and higher car bon

content (incl. graphite)� Often bottleneck for balanced lining life, no compr omise on

quality

�Side wall and bottom:� High alumina materials changed from andalusite or b auxite to

higher purity synthetic alumina based materials (ta bular alumina, spinel)

� Doloma replaced by MgO/C in order to achieve higher lining lifein some steel works, but still in use elsewhere

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Slag resistance of ladle refractories

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Slag resistance of high alumina ladle refractories

�Dortmund steelworks (1995):CaO ≈ 30%, C/A = 0.6 OK for andalusiteC/A ≈ 1 andalusite 50 heats (SiO 2!) vs. bauxite 130 heats

� IJmuiden steelworks (2001):direct strip plant (DSP = near net-shape casting)Ca treatment & C/A ratio of slagandalusite bricks -70% lifetime at 20% DSP heats

-90-95% at 100% DSPreplaced by high purity fired spinel bricks

�Today, andalusite and bauxite in back lining but not wear lining

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Decreasing stability with:- increasing temperature- decreasing P O2

- decreasing CO 2/CO- decreasing H 2O/H2

4/3 Al + O4/3 Al + O4/3 Al + O4/3 Al + O2222 = 2/3 Al= 2/3 Al= 2/3 Al= 2/3 Al2222OOOO3333

Si + OSi + OSi + OSi + O2222 = SiO= SiO= SiO= SiO2222

2 SiO + O2 SiO + O2 SiO + O2 SiO + O2222 = 2 SiO= 2 SiO= 2 SiO= 2 SiO2222

The further down a curve, the more stable the oxide.

MgO unstable at high temperature & low P O2

Re-oxidation of steel – thermodynamic stability of oxides

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Replaced by MgO/C, AMC, or synthetic alumina basedcastables or bricks (alumina-spinel) 17

Re-oxidation & steel oxide cleanliness - Decline of bauxi te andandalusite lined steel ladles in Europe 2000 - 2008

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High alumina raw materials

Andalusite Mulcoa 60 Mulcoa 70 BauxiteBrown Fused

Alumina

White Fused

Alumina

Tabular Alumina

Sinter Spinels AR78/AR90

Bonite (dense CA6)

Al 2O3 % 56-59 60 70 85 - 90 94 - 97 99.5 99.6 > 99 (Al2O3+MgO) 90

SiO2 % 38-40 35.8 25.6 5 - 10 0.8 - 1.5 0.02 0.01 0.08 0.9

TiO2 % 0.2-0.5 2.4 3 3 - 4 1.5 - 2.5 0.01 0 0 0

Fe2O3 % 0.8-1.5 1.2 1.2 1 - 2 0.15 - 0.5 0.08 0.04 0.1 0.1

Alkaline Earths % 0.1-0.3 0.2 0.2 0.4 - 0.8 0.4 - 0.6 0.03 0.02 0.2 (CaO) 9.0

Alkalies % 0.2-0.8 0.2 0.15 0.2 - 0.8 0.2 - 0.4 0.3 0.33 0.12 0.15

Bulk Density g/cm³ 3.1 2.78 2.89 3.1 - 3.4 3.8 - 3.9 3.5-3.9 3.55 3.3/3.4 3.0

Apparent Porosity % 5.7 6.2 10-15% 1.5 0 - 9 1.5 1.8 8.5

Water Absorption % 3-5% 0.4 0 - 3 0.5 0.5 2.7

� Silica content in “natural” based materials critical for thermodynamic stability and re-oxidation of steel

� Synthetic alumina based raw materials have high chemical purity

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� Limited C-pick up from carbon bond in bricks (mainly 1. h eat)� Ongoing C-pick up for higher carbon refractories, also v alid for MgO/C

bricks with >10% C (slag line bricks)

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Carbon pick up in laboratory testsSource: H. Lachmund, AG der Dillinger Hüttenwerke, VDEh steel ladle lining seminar September 2012

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Kinetic of decarburisation by use of different material i n the slag zone

Source: H. Lachmund, AG der Dillinger Hüttenwerke, VDEh steel ladle lining seminar September 2012

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� Disadvantageespecially forMgO/C bricks(higher C)

� Low carbon orcarbon-free liningfor side wall andbottom

� Alumina materialscarbon free ascastables orbricks

� Fired dolomitebricks forstainless steelapplications

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Influence of refractory material on achievable carbon co ntent

Source: H. Lachmund, AG der Dillinger Hüttenwerke, VDEh steel ladle lining seminar September 2012

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Steel ladle wear lining – alumina materials

�Synthetic alumina based castables or bricks�AluMagCarbon bricks

�Monolithic ladle with relining technique���� lowest specific refractory consumption

�Spinel castablespre-reacted vs. in situ formed spinel

slag resistancethermo-mechanical properties

(see presentation Shankha Chatterjee)

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�Reliable function, high erosion resistance (hot strengt h) andthermal shock resistance

�Highest performance alumina-spinel materials23

Source: BFI/VDEh presentation at refractory committee meeting Feb. 2010

Temperature changes due to cold stirring gasSteel ladle purging plug

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Evolution of residence time of liquid steel in the ladlefrom tapping to start of casting

Source: H. Lachmund, AG der Dillinger Hüttenwerke, VDEh steel ladle lining seminar September 2012

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�Reduce heat losses duringextended treatment times

�High C refractories havehigher thermal conductivity(heat losses)

�Energy saving, CO 2 reduction gaining importance� Example:6 mio t steel works

-1 K heat losses= 300,000€cost saving per year

�Reduced lining thickness for higher steel capacity of ladle� 200 t ladle: - 10mm lining thickness = steel capacity +2.5 t

� Insulation of steel ladles is standard in Europe25

Ladle insulation Spinel castable Bxbrick

Insulbrick

Microporousboard

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Ladle insulating refractories

Material Thermal conductivity Max. serviceat 300 - 1000 °C [W/mK] temperature [°C]

Insulating fireclay brick 1.2 - 1.4 1260 / 1430Vermiculite board 0.24 - 0.31 (600°C) 800 - 1000Fiber cont. gunning 0.2 - 0.3 1000 - 1100Microporous CA6 gunning 0.37 - 0.36 1500Ceramic fiber board 0.07 - 0.22 1260Microporous board 0.03 - 0.06 800 - 1000for comparison:Fireclay brick 1.2 - 1.4 1500Forsterite brick 1.3 1550

IMPORTANT: STABILITY AND CONTACT REACTIONS!

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Economic aspects� Refractory related operational costs beyond purchas e price &

installation:���� Production losses due to unavailability of vessels (relining, lack of

reliability, unexpected failure – or even worse, inc idents)���� Effect on steel quality���� Energy losses���� Yield���� Environmental, Health & Safety���� etc

� Refractory related operational cost ≈≈≈≈ directly spend refractory cost

� Flexibility in secondary metallurgy process routes requires performance reserves of refractories

� “Refractory is a tool to produce steel” (Rinus Siebring, TATA, VDEh Refractory Seminar part 2)

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�Secondary metallurgy is the key area in clean steel making technology

�Production routes are becoming increasingly complex in order to achieve the metallurgical targets

�Flexibility of the metallurgical equipment is neede d to achieve the desired quality of steel and the performance of refractories is a contributing factor here

�Re-heating of the steel is often required due to lo ng process times

�Higher purity refractories are used for clean steel making and synthetic materials replace natural ones for high a lumina refractories

�Energy and resource efficiency is becoming even mor e important and thermal insulation contributes here 28

Conclusion

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� R. Fandrich, B. Kleimt, H. Liebig, T. Pieper, F. Tr eppschuh und W. Urban: Stand der Pfannenmetallurgie und aktuelle Trends (Status of secondary metallurgy and present trends), stahl und eisen 131 (2011) Nr. 6/7, 75-89

� R. Bruckhaus, R. Fandrich: Trends in Metallurgy 201 2, 55th International Colloquium on Refractories, Aachen, Germany, 19-20 September 2012

� R. Bruckhaus, R. Fandrich: Ist Indiens Stahlindustrie auf dem Sprung? (Indian steel industry leaping forward?), stahl und eisen 133 (2013), Nr. 1, 33-38

� A. Buhr, M. Spreij, J. Dutton: Technical and Econom ic Review of High Alumina Raw Materials for Steel Refractories, IREFCON 2010, Kolkata

� H. Lachmund: Demands on refractory material for sec ondary metallurgy, 7 th

international symposium steel ladle lining, Steel A cademy VDEh, Hannover, Germany, September 2012

� A. Viertauer: Ladle Metallurgical Treatments & Refr actory Stress for a Steel Teeming Ladle, Refractory seminar Steel Academy VDE h, Cologne, Germany, April 2012

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Literature

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Thank you for your attention!

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