PARAMETERS AFFECTING REFRACTORY WEAR - ECOS°D

PARAMETERS AFFECTING

REFRACTORY WEAR

By

MUAMMER BİLGİÇ

PARAMETERS AFFECTING

REFRACTORY WEAR

• OPERATIONAL CONDITIONS

• REFRACTORY LINING AND

BRICK DESIGN

• MATERIAL QUALITY

PARAMETERS AFFECTING

REFRACTORY WEAR

0

20

40

60

80

100

1950 1960 1970 1980 1990 2000

Year

%

Operating conditions

Lining and brick design

Refractory material

New ceramics

OPERATIONAL PARAMETERS

AFFECTING REFRACTORY WEAR • Chemical corrosion, slag attack, oxidation of

graphite

• Hydration,

• Infiltration of steel and slag,

• Atmosphere or slag containing too much

oxygen,

• Mechanical erosion, wear, impact, thermal

shock,

• Thermomechanical stresses and fatıgue,

• Preheating procedure of refractory,

OPERATIONAL PARAMETERS

AFFECTING REFRACTORY WEAR

• Gas stirring conditions,

• Arc radiation and oxygen stream splashing,

• Rate of power input to the vessel,

• Refractory maintanence practice,

• Operation time and temperature,

• CaSi injection, deep desulphurization and

dephosporization,

• Refractory design of vessel, expansion allowances,

lining practice,

•HYDRATION

•CORROSION

•MELT, SLAG INFILTRATION

•DESULPHURIZATION

•ALKALI

•ATMOSPHERE

CHEMICAL

THERMAL •INFILTRATION

•TEMPERATURE LEVEL

•THERMAL SHOCK

•THERMAL FATIGUE

MECHANICAL •EROSION

•ABRASION, IMPACT, SHOCK

•BRICK WORK STRESSES

•MECHANICAL FATIGUE

LADLE

WEAR FACTORS ON LADLE LINING

CHEMICAL CORROSION

• High porosity in hot face and matrix of brick,

• Decarburization and increase in porosity on hot face

of brick, because of high oxygen potential in vessel

atmosphere and slag,

• High amount of SiO2 , Fe2O3 ve B2O3 in refractory

brick,

• Slag, containing high oxygen potential constituents;

such as Fe2O3, SiO2, Cr2O3, MnO,

CHEMICAL CORROSION

• Too fluid slag, high CaF2

• Undersaturated slag to CaO and MgO, low

basicity in slag

• High pressure, flow rate and long time in gas

stirring,

• Long operation time in high temperature.

CHEMICAL CORROSION

• Penetrated zone of hot surface has higher density and lower porosity than main matrix of bricks, the thermomechanical behaviour of this zone is different than main brick structure, during thermal cycling of lining due to above mentioned reasons crack shall occur between brick and penetrated zone, this crack grow and eventually spal from the brick. Figure schematically shows this behaviour. MgO vapour also penetrates to the porous structure of brick under some extreme conditions. Same spalling mechanism is valid for MgO vapour also.

Deposits Infiltrated Zone

GASES

O2 CO CO2 Ar

SO2

Erosion Slabbing Spalling

METALS

Fe Cr Ni

Mn

SLAGS

K2O

CaO SiO2

MnO Cr2O3

Cocked Pitch

Pores

Cracks MgO

CaO

MgO

C2S

WEAR SCHEME OF REFRACTORY

BRICK

INFLUENCE OF SEVERAL MATERIALS

ON SLAGGING IN TREATMENT LADLES

Na2O

CaO / MgO

SLAG

Fe2O3 / MnO /Cr2O3

Al2O3 / SiO2 /CaF2

CaS

COVERING

POWDERS

Rice ashes, Foamed

clay, synthetic

Ca-aluminates,

Ca-silicates, Coke

ADDITIONAL

ELEMENTS

Lime, Dolomite,

Carbide, Fluorspar,

Soda, Ca, CaSi,

FeSi, MnSi

PROSESS GASES

O2, CO, CO2

ELEMENTS IN

THE STEEL

Si, S, P, Mn

LOSSES FROM BRICKS

CaO, MgO, SiO2, Al2O3

REDUCTION MATERIALS

Ca, CaSi, FeSi, Al, MnSi

REPAIR AND FILLING

MASSES

MgO, Cr2O3, CaO etc.

STEEL COMPONENTS Fe, Cr, Mn, Ni, (V, W, Mo)

SLAG ENGINEERING

• There has been continuous acknowledgment that the slag in steelmaking is not an unavoidable part of system, but is a crucial part of modern steelmaking practices. The goals of high quality steel production and low costs can not be realized by poor slag practices. The concept of 'slag engineering' is becoming more and more common in many steel works as the need to implement these concepts is required by more stringent steel quality requirements. Neither the goal of producing high quality steel nor the goal of keeping costs low can be realized by using poor slag practices.

IMPORTANCE OF SLAG

CONTROL

0

25

50

75

100

After slag control Before slag control

We

ar

ind

ex

of

refr

ac

tori

es

MgO SOLUBILITY

• In slag - refractory systems there is a limit for MgO solubility, this point is called as saturation point of slag . Up to that point the MgO coming from refractory is soluble in slag. Above that point MgO is not soluble in slag. This point depends of chemical composition of slag. The difference between saturation point and initial MgO content of slag may come from two sources ; first refractory, second external addition of MgO with a MgO carrier. Obviously the most economical one is the external addition.

EFFECT OF SLAG BASICITY ON

MgO DISSOLUTION

15

20

25

30

35

40

45

0.4 0.6 0.8 1 1.2 1.4

Percent CaO/ Percent SiO2

Percen

t M

gO

in

S

lag 1700 C

1600 C

EFFECT OF Al2O3 ON MgO

SOLUBILITY IN SLAG

EFFECT OF MgO CONTENT OF SLAG ON

BASIC REFRACTORY WEAR

ER

OS

ION

RA

TE

in/h

eat

-0.4

-0.2

0

0.2

0.4

5 6 7 8 9 10 11

FIRST-TURNDOWN SLAG MgO, %

ER

OS

ION

RA

TE

mm

/he

at

EROSION

BUILDUP

-0.016

0.008

0

0.016

-0.008

CaO in LADLE SLAG

• CaO is added externally to slag systems . The main aim is the adjustment of basicity and increase in desulphurization rate. But in usage of Dolomitic refractories, Dolomite Refractory erosion may be a second source for CaO. Slags which is undersaturated to CaO increase the chemical corrosion of Dolomite and MgO-C refractories. Figure 13, gives the optimum range for CaO saturation of ladle treatment slags in ternary phase diagrams. But with Oversaturated slag it is not easy to make metallurgical processes.

FeO IN SLAG

• FeO Decreases the basicity of steelmaking slags. Because of its high oxygen content, oxidize the carbon in MgO-C brick and make it more porous. Its high oxidation capacity acts as a continuous oxygen source for metals and refractories.

• Figure 9 gives the changes in refractory wear with FeO content of slags .

• High FeO content affects the desulphurization capacity of steelmaking slags adversly. Figure 10, gives the changes in desulphurization rate with the FeO+MnO content of ladle treatment slags.

EFFECT OF FeO CONTENT OF

SLAG ON MgO DISSOLUTION

10

20

30

40

0 500 1000 1500 2000

......-MgO from Refractory

FeO

Co

nte

nt

Of

Sla

g, %

SOURCES OF FeO in EAF

• Usage of low yield scrap

• Usage of HBI & DRI

• Insufficient C injection and C boil

• Excessive oxygen consumption

• Usage of low C scrap

• Lack of bottom purging system

• High tapping temperature

• Excessive oxygen in EAF atmosphere

SOURCES OF FeO in LADLE

• Carryover of excessive slags from

primary steelmaking vessels to ladles

• Insufficient slag deoxidation

• Reoxidation because of vigorous bath

movemenet

• FeO coming from Ferro Alloy additions

EFFECT OF FeO+MnO CONTENT OF

SLAG ON DESULPHURIZATION

SiO2 in SLAG

• Slags which contains high SiO2 , form dicalcium and tricalcium silicates. These compounds penetrates into the porous structure of hot face of bricks, freeze there and make a dense penetrated layer on hot face. This dense zone behaves different than main brick matrix during thermal cycling and brick comes out in powder or particle form. SiO2 ,decreases the basicity of slags.. Figure12, Gives the changes in MgO solubility of slag with the changes in basicity.

• Low basicity increases the saturation point of MgO in slag. i.e increases the capability to wash out MgO from refractory. For this reason in all steelmaking slags SiO2 must be kept at minimum level.

SOURCES OF SiO2 IN

STEELMAKING LADLES

• Carryover slags from primary

steelmaking vessels

• FeSi and FeSiMn additions

• Reoxidation of Si in Steel

• SiO2 in CaF2

• SiO2 in other additivies

• SiO2 in cover materials and filling sands

Al2O3 in LADLE SLAG

• Decreases the basicity of slag, but at the same

time decreases the MgO saturation point so it

has the effect of decrease in refractory wear.

Dolomite refractories have higher resistance to

low Al2O3 content slags. Slags undersaturated

to CaO have corrosive effects to the

refractories. Figure 13, gives the changes in

MgO and CaO saturation with the changes in

Al2O3 content of slag .

EFFECT OF CaF2 CONTENT OF

SLAG ON WEAR

ER

OS

ION

RA

TE

INC

RE

AS

E, i

n/h

eat

0

0.5

1

1.5

3 4 5 6

SPAR CHARGED, % OF BURNT LIME

ER

OS

ION

RA

TE

INC

RE

AS

E, m

m/h

eat

0

0

0.04

INFLUENCE OF SPAR ON VESSEL EROSION

0.06

0.02

FOAMY SLAG

• The only way to decrease above mentioned bad effect

of arc radiation is to apply foamy slag.

• Apart from prevention of arc radiation, the most

important benefits of Foamy Slag is reduction of

FeO content of slag, this benefits is extremely

important in cost saving activities at EAF.

• Foamy Slag practice is the most important and

innovative operational parameter in EAF

Steelmaking, in both quality and cost aspects .

FeO REDUCTION

MECHANISM

( FeO ) + CO(g) Fe (s) + CO2

CO2 (g) + C 2CO

----------------------------------------

( FeO ) + C Fe + CO

CO + ½ O2 CO2 ( H= -67.6 Kcal/mol )

CARBON INJECTION

CARBON INJECTION

STABILITY OF OXIDES

REOXIDATION DUE TO

REFRACTORY

Al LOSS IN STEEL and TYPE OF

REFRACTORY

DESULPHURIZATION AND TYPE OF

REFRACTORY