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