study of metadynamic recrystallization phenomena in coarse grained nb microalloyed austenite
DESCRIPTION
Presentation made at Mechanical Working and Steel Processing Conference. Orlando 2002TRANSCRIPT
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
STUDY OF METADYNAMIC STUDY OF METADYNAMIC RECRYSTALLIZATION PHENOMENA IN RECRYSTALLIZATION PHENOMENA IN COARSE GRAINED Nb MICROALLOYED COARSE GRAINED Nb MICROALLOYED
AUSTENITEAUSTENITE
P. Uranga, A.I. FernP. Uranga, A.I. Fernáández, B. Lndez, B. Lóópez and pez and
J.M. RodriguezJ.M. Rodriguez--IbabeIbabe
CEIT and Univ. of Navarra, PCEIT and Univ. of Navarra, Pºº M. LardizM. Lardizáábal 15,bal 15,20018 20018 -- San Sebastian, Basque Country (Spain)San Sebastian, Basque Country (Spain)
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
IntroductionIntroduction
Thin Slab Casting TechnologyThin Slab Casting Technology–– Coarse Grained AsCoarse Grained As--cast Austenite Structurecast Austenite Structure–– Microalloying Elements in SolutionMicroalloying Elements in Solution–– High Deformation in First StandsHigh Deformation in First Stands
Possibility of Dynamic Recrystallization? Possibility of Dynamic Recrystallization? Study of PostStudy of Post--Dynamic Softening Dynamic Softening Microstructural ModelingMicrostructural Modeling
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1000
1020
1040
1060
1080
1100
1120
D0 (μm)
T(ºC
)
0.60.7
0.8
0.9
1.0
1.1
Critical Strain0.035% Nb
Strain rate: 5 s-1
•• Onset of Dynamic Recrystallization for Reductions > 55%, Onset of Dynamic Recrystallization for Reductions > 55%, ε ε > 0.8> 0.8
•• Softening Mechanisms for Strains Higher than Critical StrainSoftening Mechanisms for Strains Higher than Critical Strain
Dynamic Recrystallization in First Stand?Dynamic Recrystallization in First Stand?
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Usually when:Usually when:
ε > εcDynamic Dynamic RecrystallizationRecrystallization
Metadynamic Metadynamic RecrystallizationRecrystallization
Recently, Recently, BaiBai et al. (2000):et al. (2000):
Metadynamic Metadynamic RecrystallizationRecrystallization εε >> εεTT With With εεTT = 1.5= 1.5·· εεpp
Transition between different regionsTransition between different regions
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
C Mn Si S P Nb N0.1 1.42 0.31 0.008 0.018 0.035 0.0053
Material and Experimental ProcedureMaterial and Experimental Procedure
T
t
1400 ºC
ε1 tip1100ºC
ε2
Strains between εc and ε = 4
s 1t s 1 ip1 =→= −ε&
s 3.0t s 5 ip1 =→= −ε&
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Influence of Strain on Softening
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5
StrainFr
actio
nal S
ofte
ning
εT = 1.7
εC = 0.75
Strain rate = 5 s-1
t = 0.3 sT = 1100ºC
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5
Strain
Frac
tiona
l Sof
teni
ng
εT = 1.3
εC = 0.6
Strain rate = 1 s-1
t = 1 sT = 1100ºC
εεTT == 2.22.2··εεcc
•• Strain dependent softening for strains higher than Strain dependent softening for strains higher than εεcc
•• Strain independent behaviour for strains higher thanStrain independent behaviour for strains higher than εεTT
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Modeling Softening Kinetics
0
50
100
150
200
0 1 2 3 4 5Strain
Stre
ss (M
Pa)
T = 1100ºCStrain rate=1 s-1
εc εT
I II III
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Modeling Softening Kinetics
0
50
100
150
200
0 1 2 3 4 5Strain
Stre
ss (M
Pa)
T = 1100ºCStrain rate=1 s-1
εc εT
I II III
••Range I: (Range I: (ε ε << εεcc))
Static RecrystallizationStatic Recrystallization
••Range III: (Range III: (εεTT < < εε))
Metadynamic RecrystallizationMetadynamic Recrystallization
••Range II: (Range II: (εεcc <<ε ε << εεTT))
Static and Metadynamic Static and Metadynamic RecrystallizationRecrystallization
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
εεTT : Critical Value to achieve the minimum : Critical Value to achieve the minimum dynamic recrystallized fraction for a complete dynamic recrystallized fraction for a complete postpost--dynamic softening by metadynamic dynamic softening by metadynamic recrystallizationrecrystallizationCoarse Grained Austenite: Coarse Grained Austenite: εεcc HighHighIndustrial Conditions:Industrial Conditions:
–– εεTT much higher than applied strainmuch higher than applied strain–– Deformation and Softening Mechanisms: Ranges I / IIDeformation and Softening Mechanisms: Ranges I / II
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Range I (Range I (ε ε << εεcc): ): Static RecrystallizationStatic Recrystallization– Initial Grain Size– Strain– Strain Rate– Temperature
Different Softening MechanismsDifferent Softening Mechanisms
Grain RefinementGrain Refinement
[ ]( )T,Nb,,,Dft 0SRX5.0 εε &=
( )T,ft MDRX5.0 ε&=
Range III (Range III (εεΤΤ < < εε): ): Metadynamic RecrystallizationMetadynamic Recrystallization– Strain Rate– Temperature
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Modeling Softening Kinetics
SRXMDRX XXX +=
cT
cMDRXfX
εεεε
−−
= MDRXf
SRXf X1X −=
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛−−=
MDRX5.0
MDRXfMDRX t
t693.0exp1XX
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛−−=
SRX5.0
SRXfSRX t
t693.0exp1XX
Region II (Region II (εεcc < < εε < < εεTT): Static and Metadynamic Recrystallization): Static and Metadynamic Recrystallization
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Modeling Softening Kinetics
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5Strain
Frac
tiona
l Sof
teni
ng
Strain rate = 1 s-1
t = 1 s
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5Strain
Frac
tiona
l Sof
teni
ng
Strain rate = 5 s-1
t = 0.3 s
εc
XSRX
εc
XSRXXMDRXεT XMDRXεT
XX
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
0
0.2
0.4
0.6
0.8
1
0.01 0.1 1 10 100Time (s)
Frac
tiona
l Sof
teni
ng
Strain = 0.9Strain rate = 1 s-1
XSRX
XMDRX
ModelingPost-Dynamic Softening with Time
•• Applied Strain in Range IIApplied Strain in Range II
•• Sum of Individual Sum of Individual Components: Overall Components: Overall SofteningSoftening
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
ModelingDependence of t0.5 with Applied Strain
0.1
1
10
100
0.1 1 10Strain
t 0.5
(s)
T = 1100ºCStrain rate = 1 s-1
D0 = 806 μm
•• Below Below εεcc: Strong dependence : Strong dependence on strainon strain
ε c
•• εε > > εεTT: Strain independent: Strain independentε Tε p
•• εεcc<< εε < < εεTT: Correct Prediction: Correct Prediction
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Modeling Microstructural EvolutionModeling Microstructural Evolution
Thin Slab Casting and Direct Rolling TechnologyThin Slab Casting and Direct Rolling Technology– Heterogeneous Initial Grain Size
– Solid Solution
Recrystallization delayedRecrystallization delayed
Need of a Model taking into account these Need of a Model taking into account these singularitiessingularities
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Modeling Microstructural EvolutionModeling Microstructural Evolution
Initial variables:Initial variables:– Processing variables: Strain, strain-rate, temperature…– Initial Grain Size Distribution
Static and Metadynamic SofteningStatic and Metadynamic SofteningInteraction with PrecipitationInteraction with PrecipitationGrain Size EvolutionGrain Size EvolutionOutputs:Outputs:– Recrystallized and Unrecrystallized Grain Size
Distributions at the entry of any rolling pass
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
T
t
1100 ºC (20 min)
1400 ºC
ε = 0.93strain rate = 5 s-1
T = 1080ºC
T = 1000ºC
Model Validation
Torsion Test Schedule
0
5
10
15
20
25
30
0 500 1000 1500 2000 2500 3000
Grain Size (μm)Fr
eque
ncy
(%)
Initial Grain Size Distribution
Mean Grain Size: 806 μm
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Model Validation ResultsModel Validation Results
0
0.1
0.2
0.3
0.4
20 100 180 260 340 420 500Grain Size (μm)
Are
a Fr
actio
n
ModelExperimental
XXSRXSRX = 0.86= 0.86
XXMDRXMDRX = 0.12= 0.12
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
0
0.1
0.2
0.3
0.4
20 100 180 260 340 420 500Grain Size (μm)
Are
a Fr
actio
n
ModelExperimental
a)
0
0.1
0.2
0.3
0.4
20 100 180 260 340 420 500Grain Size (μm)
Are
a Fr
actio
n
ModelExperimental
b)
New ModelClassical
Approach
Comparison betweenbetween models
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
ConclusionsConclusionsResults show that once the applied strain is higher than Results show that once the applied strain is higher than the critical value the critical value εεcc, there is a transition regime , there is a transition regime between between εεcc and and εεTT where both classical static and where both classical static and metadynamic recrystallization softenings intervene.metadynamic recrystallization softenings intervene.
In the analyzed 0.035%Nb microalloyed steel, for the In the analyzed 0.035%Nb microalloyed steel, for the case of coarse initial grain sizes, a value of the case of coarse initial grain sizes, a value of the transition strain equal to transition strain equal to εεTT == 2.22.2··εεcc has been obtained.has been obtained.
Taking into account the typical reductions of the first Taking into account the typical reductions of the first rolling passes, real situations will correspond to fully rolling passes, real situations will correspond to fully classical static recrystallization (classical static recrystallization (εε << εεcc) or to mixed ) or to mixed conditions (conditions (εε >> εεcc).).
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite
Conclusions (II)Conclusions (II)The model considers a mean recrystallized The model considers a mean recrystallized microstructure combining both classical static and microstructure combining both classical static and metadynamic grains through the law of mixtures. metadynamic grains through the law of mixtures. The model predictions have been validated with The model predictions have been validated with specific tests. The model leads to good predictions when specific tests. The model leads to good predictions when both static and metadynamic softening are included for both static and metadynamic softening are included for applied strains applied strains εε >> εεcc. Some important divergences are . Some important divergences are observed if only metadynamic softening is considered.observed if only metadynamic softening is considered.
Study of Metadynamic Recrystallization PhenomenaStudy of Metadynamic Recrystallization Phenomenain Coarse Grained Nb Microalloyed Austenitein Coarse Grained Nb Microalloyed Austenite