mgo-c refractory selection and evaluation for ......the making, shaping and treating of steel, 11th...

The Southern African Institute of Mining and Metallurgy

Refractories 2010 Conference

J Terblanche

________________________________________________________________________

53

MGO-C REFRACTORY SELECTION AND EVALUATION FOR

STEELMAKING VESSELS

J Terblanche

Arcelormittal

Abstract

The challenge for refractory material producers and consumers is to find the optimum

solution between the quality and cost of the product with its value in use.

Magnesia-Carbon (MgO-C) refractories in Steelmaking vessels play an important part to

reach continuous improvement targets. It will remain a focus area to increase campaign

length of vessels and reduce the cost per ton liquid steel produced.

Improvements of 20% can be achieved by using different quality MgO-C refractories.

1. Introduction

The Vanderbijlpark Works of ArcelorMittal, South Africa, consists of the

following:

• Integrated route with 3x 170t Basic Oxygen Furnaces (BOF), 2x Ladle

Furnaces (LF), 1x RH and 2x Twin strand slab casters with capacity of

2.9 mtpa.

• Minimill route with 3x 150t Electric Arc Furnace (EAF), 2x LF’s, 1x

Vacuum Arc Degasser and 1x Twin strand slab caster with capacity of 1.4

mtpa.

The 3 BOF’s are bottleneck units in the Oxygen Steelmaking Route and various

strategies have been implemented to manage the cost, availability and throughput

of this route. These include :

• Extend campaign length with slag splashing

• Maximum utilization of bottom stirring

The selection and properties of the MgO-C refractories used with these different

philosophies and varying operating conditions determine both the length of the

campaign achieved and the cost of the lining.



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2. Background

The following operational conditions affect lining wear1 :

• Slag chemistry - Basicity

- MgO content

- FeO levels

• Size of scrap charged

• End point temperature

• Reblows

• Production Rates (i.e. heats per vessel per day)

• Holding time (blow end to tap start)

• Hot metal quality (limits total mass of fluxes that can be charged)

In order to optimally utilize or consume the refractories, the following maintenance

or repair techniques are utilized with the impact on performance indicated in Fig.1 :

• Gunning of localized high wear areas

• Slag coating : by keeping some slag in the vessel, adding MgO containing

material and tilting the furnace over the tap floor and charge pad areas.

• Slag splashing by blowing high pressure N2 via the top blown lance2 and

coating the complete surface with a slag layer.

The result achieved with such methods is determined by the time available and the

frequency of these activities. In the case of gunning, the durability can be extended

by using improved raw material and binder systems and for slag splashing, low

oxide- and higher MgO levels in the slag.

The drive to improve efficiencies and reduce costs resulted in a change of strategy.

Slag splashing was stopped and the focus changed to ensure bottom stirring

availability and efficiency for the full duration of the campaign. This leads to lower

campaign lengths as indicated in Fig. 1.

The higher refractory cost is countered by savings as a result of lower oxygen

levels in the steel and slag. Higher quality MgO-C bricks are required in order to

improve campaign lengths with little or no refractory maintenance (i.e. gunning and

splashing).



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3. Lining Development

The different areas and wear mechanisms are displayed in Fig. 2 and

Table 11.

Fig 2 : BOF- wear areas

Fig 1 : BOF campaign history for Vanderbijlpark

-

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

2003 2004 2005 2006 2007 2008 2009

Heats

use of slag splashing

no splashing

Topcone

Knuckle

Charg

e P

ad

Charg

e p

ad

Tap p

ad

Tru

nnio

n W

Tru

nnio

n E



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Table 1 : Furnace Area Wear Conditions

Furnace Area Wear Conditions

Cone Oxidizing atmosphere

Mechanical abuse

High temperature

Trunnions Oxidizing atmosphere

Slag corrosion

Slag and metal erosion

Charge Pad Mechanical impact

Abrasion from scrap and hot metal

Tap Pad Slag erosion

High temperature

Mechanical erosion

The Refractory performance can be improved by3:

• Design changes in : knuckle area

: cone area

: use of steel cladding

• Zoning of the furnace according to the different wear mechanisms and

material qualities.

4. Evaluation Process

The following tests were conducted :

• Rotor slag test : 300g slag per cycle, 10 cycles of 20 minutes each after

melting of slag

• Oxidation resistance : 50 x 50 x 75mm sample heated in air at 900°C or

1400°C for 8 hrs.

• 2 step rotor slag test : do 10 cycles, cool down and repeat.

4.1 Rotor slag test

Typical BOF slag was used to compare resistance to chemical attack

(Fig. 3). The depth of slag penetration (Fig 4) is important as this will increase the

wear rate during operation. The thermal expansion properties are different

compared to the virgin material which will lead to cracking of this layer during

thermal cycling.



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4.2 Oxidation Resistance

Oxidation of fixed carbon and the binder system occurs during preheat and

operation. The white decarburized layer can be seen on the bricks during the

demolition process.

Both the depth of the oxidized layer and the condition of the oxidized layer are

compared (Fig 5)

Fig 3 : Rotor Slag Wear Ratio

1

1.61

1.071.00

1.59

1.09

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

B R C

Ra

tio

Ratio 10

Ave 20

Fig 4 : Slag Penetration Ratio 20 Cycles

1.00

1.22

0.81

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

B R C

Pe

ne

tra

tio

n R

atio



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Fig 6 : Condition of oxidized layer

4.3 Two step rotor slag test

Both the global economic slump and normal throughput requirement affect plant

stability. This implies that the golden rule for good refractory performance - “keep

it hot” is not always adhered to. Depending on whether 2 or 3 furnaces are in

operation and with throughput variations from 20 to 54 heats per day, a furnace can

be used for 6 to 27 heats per day. To reduce this effect 1 or 2 furnaces can be

stopped from 8 hrs to a few days at a time. Depending on the production schedule

or maintenance requirement the spare furnace can be on hot or cold standby.

Fig 5 : Oxidation Depth after 4 Cycles @ 1400°C

11.51 12.5

8.61

0

2

4

6

8

10

12

14

B R C

De

pth

(m

m)

B : 2 cycles @ 1400°C R : 2 cycles @ 1400°C



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Table 2 : BOF Operating parameters

2 Furnace Operation 3 Furnace operation

BOF 1 BOF 2 BOF 1 BOF 2 BOF 3

Number Of Casts 18 17 14 7 17

End Point C avg 0.03 0.04 0.04 0.04 0.04

End Point O2 avg 536 532 856 713 906

Slag TFe avg 15.4 15.5 21.9 17.2 20.9

Slag MgO avg 8.2 8.7 6.6 8.0 7.0

End Point Temperature avg 1672 1669 1669 1670 1669

Blow End To Tap Duration

avg 9 11 9 8 16

Tap To Tap avg 57 85 70 220 85

Basicity avg 3.2 3.0 2.9 2.9 3.1

Co-Product avg 19 21 31 26 32

Percentage reblow 5.6 29.4 7.1 14.3 11.8

To simulate this impact the 2 step rotor test was conducted. The result in wear and

condition of the samples after the 2nd

test is displayed in Fig 3.

5. Plant trial

Furnace layout

To evaluate the supplier - material combinations in a reliable trial, it was decided to

do panel tests in 1 furnace rather than to install complete linings in different

furnaces.

Fig 7. BOF Trial Zoning

R

B C



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The life of the furnace will be determined by the highest wear area (material with

the lowest performance) and the campaign may end prematurely as a result of this.

The advantage however is that variations in operational parameters between

furnaces are excluded.

With this layout 2 qualities can be compared to a reference (and each other) on the

trunnion and tap floor area (the highest wear areas during the planning stage of the

trial).

6. Results

Wear profiles can be measured with the laser scanner during operation and results

are displayed in Fig 8 to 11 for the different areas. Extensive gunning maintenance

was started on the high wear areas after 1,000 heats and this is reflected in the data.

Fig 8 : Laser scan profile at heat 1,081



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Fig 9 : Wear rate Tapfloor (mm/heat)

0

0.05 0.1

0.15 0.2

0.25 0.3

0.35 0.4

0.45

753 901 1081 1304

Scanned heats

Tapfloor W : R

Tapfloor W : C

Tapfloor E: R Tapfloor E : B

Fig 10 : Wear rate Trunnion East (mm/heat)

0

0.05 0.1

0.15 0.2

0.25 0.3

0.35 0.4

0.45 0.5

753 901 1081 1304

Scanned heats

Trun E : R

Trun E : B



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Table 3 indicates the expected life of the furnace based on the remaining thickness

and the wear rate since the previous scan. It can be seen that trial quality B

performs better than both the reference and quality C, while quality C compares

well with the reference.

Table 3 : Campaign Forecast

Min Remaining Thickness (mm) = 50

Tap breast East Trunnion West Trunnion

heats

Tapfloo

r W : R

Tapfloo

r W : C

Tapfloo

r E : R

Tapfloo

r E : B

Trunnion

E : R

Trunnio

n

E : B

Trunnion

W : R

Trunnion

W : C

753 1,914 2,076 2,061 3,086 1,628 2,039 1,361 1,448

901 2,356 2,398 2,559 3,375 1,747 2,099 1,504 1,365

1,081 2,045 2,144 2,331 2,950 2,616 3,066 1,547 1,486

Improvement vs

R per area at

901 heats before

gunning started

101.8%

131.9%

120.2%

90.8%

7. Conclusion

Both the Pilot Plant tests and Plant trials indicated a difference in performance of

supplier - quality combinations.

Fig 11 : Wear rate Trunnion West (mm/heat)

0.3

0.4

0.5

0.6

0.7

753 901 1081 1304

Scanned heats

Trun W : R

Trun W : C



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Page 163

It is possible to achieve up to 20% improvement in the life of the BOF at

Vanderbijlpark by using different qualities MgO-C material.

With changing market conditions the impact of availability and opportunity costs

will have an effect on the selection of Refractory materials in the Steelmaking

Vessels.

Acknowledgement

1. J. Victor for conducting the various tests and reporting of the data.

2. R. Nyamane and the reline crews for the installation of the lining.

3. The crew from MTSA for calibration of the scanner, regular scanning and gunning

maintenance.

4. Me I. de Villiers for the typing and layout of the report.

5. ArcelorMittal for the opportunity to grow as an individual by enabling us to do

development work.

Reference

1. The Making, Shaping and Treating of Steel, 11th

Edition, Steelmaking and Refining

volume P227 - 243

2. Everlasting BOF linings at LTV steel, R.O. Russel a.o. LTV steel company,

Independence, Ohio – USA P220-225

3. Refractories performance improvements – meeting the competitive challenge, Ian

N Mackay, Institute of Refractories Engineers Annual conference, 23 Sept 1994.

The Author

Johan Andries Terblanche, Project Manager, Refractories, Operational Excellence,

ArcelorMittal, South Africa

1986 : B Eng in Metallurgy from PU for CHE, Vaal Triangle Campus

1990-1991 : Production Engineer BOF, Iscor, Vanderbijlpark



J Terblanche

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Page 164

1992-1997 : Manager Development, Refractory Services, Iscor, Vanderbijlpark

1998 : Production Manager,v1v2 Continuous Caster, Iscor, Vanderbijlpark

1999-2006 : Plant Manager, Refractory Services, ArcelorMittal, Vanderbijlpark

2007 Project Manager, Refractories,CTO, ArcelorMittal, South Africa

mgo-c refractory selection and evaluation for ......the making, shaping and treating of steel, 11th...

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