Microstructure evolution during recrystallization of dual-phase steels

N. Perannio*, M. Calcagnotto, B. Springub**, M. Feucht***, D. Raabe, F. Roters, D. Ponge, S. Zaefferer

Düsseldorf, GermanyWWW.MPIE.DEd.raabe@mpie.de

RX&GG iV 5, July 2010 Sheffield, UK

* Inst. f. Physik, Universität Tübingen, Germany** Salzgitter Mannesmann Forschung, Salzgitter, Germany*** Daimler AG, Sindelfingen, Germany

Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

Overview

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High-strength ductile C-Mn DP steels for weight reduction

Microstructure evolution in hot rolled, cold rolled, and annealed DP

Intercritical annealing: recovery, recrystallization, phase transformation

Parameters: heating&cooling rates, temperature, time

Through-thickness inhomogeneity (texture, phases, grain size,….)

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Motivation, outline and strategy

Overview

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738 4

Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

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hot band: 70% ferrite, 30% pearlite; 0.147 wt% C, 1.9 wt. % Mn, 0.4 wt.% Al cold band: 43%, 50%, 63% Annealing: salt bath, conductive, hot dip galvanizing

temperature 740°C≈Ac1, 860°C≈Ac3, 920°C time 100 s, 200 s, 300 s cooling rate 7 K/s, 15 K/s, 22 K/s heating rate 10 K/s, 20 K/s, 30 K/s

Experiments

Peranio et al: Mater Sc Engin A 527 (2010) 4161

Fe C Si Mn P N N

bal. 0.147 0.403 1.868 0.01 0.0056 0.0056

Cr Ni V Ti Nb Al Al

0.028 0.044 0.098 0.005 0.047 0.037 0.037

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Intercritical deformation and isothermal holding

PF

Ar3

Hot Deformation

T

t

Large Strain Warm Deformation

e=1.6

Annealing (2h)

air cooling

Intercritical Annealing

UFG F/M DP

Ac1

e = 0.1, 0.3, 0.5

Intercritical Annealing

UFG F/M DP

Ac1

t = 1 min, 10 min, 30 min

6Peranio et al: Mater Sc Engin A 527 (2010) 4161

Overview

Peranio et al: Mater Sc Engin A 527 (2010) 4161 7

Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

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Texture and microstructure–rolled, annealed, through thickness

Peranio et al: Mater Sc Engin A 527 (2010) 4161

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Texture and microstructure–rolled, annealed, through thickness

Peranio et al: Mater Sc Engin A 527 (2010) 4161

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Results - EBSD – cold rolled

cold rolled, center of sample

pearlite

ferrite

unfiltered

image quality signal allows separate

analysis of the constituents

ferrite volume fraction 74%

grain size 4.8 mm, aspect ratio 0.26

large grains are deformed

TD

ND

TD

ND

TD

ND

Peranio et al: Mater Sc Engin A 527 (2010) 4161

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inverse pole figures and ODF, cold rolled, center

<110> parallel RD (a-fiber), {111} parallel ND (g-fiber)

typical texture for bcc-materials

TD

ND

TD

ND

ND RD

large grains are closer to the a-fiber

EBSD – cold rolled

Peranio et al: Mater Sc Engin A 527 (2010) 4161

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Microstructure and texture evolution – hot band through thickness

Recrystallization dual phase steels

phase changes in dual phase steels

intercritical annealing

deformed ferrite pearlite

strain freeaustenite

recrystallizedferrite

recoveredferrite

room temperature

recrystallized/strain free

ferrite

recovered/strainedferrite

martensite

cold rolled

13Peranio et al: Mater Sc Engin A 527 (2010) 4161

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Texture evolution –rolled, annealed, through thickness

Peranio et al: Mater Sc Engin A 527 (2010) 4161

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Texture: recrystallization-transformation, through thickness

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Competition: recrystallization -transformation, through thickness

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738

annealing time

Effect of annealing time on martensite contentEffect of annealing process / rates on martensite contentEffect of through-thickness inhomogeneity

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Competition: recrystallization -transformation, through thickness

Peranio et al: Mater Sc Engin A 527 (2010) 4161

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Microstructure evolution

Calcagnotto, Ponge, Raabe: ISIJ 48 (2008) 1096

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Competition: recrystallization -transformation, through thickness

Peranio et al: Mater Sc Engin A 527 (2010) 4161

Overview

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Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

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Instrument overview

• Scanning electron microscope (SEM) – observation of microstructure

SEM & FIB:Zeiss

Crossbeam 1540

EBSD system:TSL with

Hikari camera

• Quantitative images with EBSD and EDX– quantitative characterisation of

microstructure

• Scanning Ga+-ion microscope (FIB = focused ion beam)– sputtering of material for serial

sectioning

Zaefferer et al., Met. Mater. Trans. 39A (2008) 374

sample in cutting position

(36° tilt)

e-

x-ra

ys

e-

sample in EBSD position

(70° tilt)

ion milling

to EBSD detector

electron beam

tilt 34 °

alignment marker

FIB column

EBSD camera

EDX

detector

SEM objective lens

Ga+

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Principle of serial sectioning & orientation microscopy

Konrad et al. Acta Mater. 54 (2006) 1369

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3D EBSD: joint FIB-EBSD tomography (Zeiss; FEI)

• Increase phase space of microstructure analysis

6D (j1, ,f j2,x,y,z): Crystallography and texture with morphology

8D (j1, ,f j2,h,k,x,y,z): Interface crystallography (interface texture)

• Spatial texture and phases (connectivity, percolation, correlations)• FIB, EBSD, EDX

Review: Zaefferer et al., Met. Mater. Trans. 39A, (2008) 374

Konrad et al. Acta Mater. 54 (2006) 1369

GND (Kröner-Nye)

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From local misorientations to GNDs

misorientation

orientation gradient(spacing d from EBSD scan)

Demir, Raabe, Zaafarani, Zaefferer: Acta Mater. 57 (2009) 559

orientation difference

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From local misorientations to GNDs

distortion(sym, a-sym)

dislocation tensor (GND)

J. F. Nye. Some geometrical relations in dislocated crystals. Acta Metall. 1:153, 1953.E. Kröner. Kontinuumstheorie der Versetzungen und Eigenspannungen (in German). Springer, Berlin, 1958.E. Kröner. Physics of defects, chapter Continuum theory of defects, p.217. North-Holland Publishing, Amsterdam, Netherlands, 1981.

Demir, Raabe, Zaafarani, Zaefferer: Acta Mater. 57 (2009) 559

T TT

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From local misorientations to GNDs

Frank loop through area r

18 b,t combinations

9 b,t combinations

Demir, Raabe, Zaafarani, Zaefferer: Acta Mater. 57 (2009) 559

T TT

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martensiteferrite

111

001 101

3D EBSD analysis of DP microstructure and texture

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738

3D EBSD experiment

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Image Quality Kernel Average Misorientation (martensite highlighted in black)

3D EBSD analysis of DP microstructure and texture

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738

3D EBSD experiment

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GND analysis of DP microstructure and texture

Calcagnotto, Ponge, Raabe: ISIJ 48 (2008) 1096

Zaefferer, Wright, Raabe: Metal. Mater. Trans. A 39A (2008) 374 Demir, Raabe, Zaafarani, Zaefferer: Acta Mater. 57 (2009) 559

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ferrite-ferrite interfaces

ferrite-martensite interfaces

3D GND analysis of DP microstructure

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738

Overview

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Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

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Ultrafine grained DP steels

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738

all with ca. 30% martensite

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Effect on microstructure

effect of deformation

effect of holding time

a) ε = 0, t = 1 min

b) ε = 0.5, t = 1 min

c) ε = 0, t = 30 min

RD

ND

1 µm

1 µm

1 µm

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Effect on retained austenite fraction

effect of deformation

effect of holding time

RD

ND

b) ε = 0.3, t = 1 min

γ = 3.4 %

γ = 0.2 %

c) ε = 0, t = 10 min

a) ε = 0, t = 1 min

γ = 2.6 %

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Coarse grained DP (12.4 µm)

Berkovich 50 nmConstant load 500 µN

3D GND analysis of DP microstructure

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738

Overview

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738 38

Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

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Simulation of recrystallization (CA & Calphad & DICTRA)

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Simulation of recrystallization (CA & Calphad & DICTRA)

Java based

Windows Linux Apple OS X

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Simulation of forming (CPFEM, virtual lab, yield surface)

Kraska, Doig, Tikhomirov, Raabe, Roters, Comp. Mater. Sc. 46 (2009) 383

Together with Mercedes, FhG, Volkswagen, Audi, Inpro Roters et al. Acta Mater.58 (2010)

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Simulation of forming (CPFEM, virtual lab, yield surface)

Kraska, Doig, Tikhomirov, Raabe, Roters, Comp. Mater. Sc. 46 (2009) 383

Together with Inpro, Berlin

Tension 0° (RD)

Tension 90° (Querrichtung) Tension biaxial

Tension 45°

RVE from annealed DP

Overview

Calcagnotto et al. Mater. Sc. Engin. A 527 (2010) 2738 43

Motivation

Experiments

Microstructure and texture evolution

3D tomographic analysis of interface regions and correlation to mechanical properties

Ultra-fine grained DP

Simulations

Conclusions

Conclusions

Strong through-thickness gradients inherited from hot rolling

Competition between RX and PT depends strongly on heat treatment conditions

3D tomographic analysis of texture and micromechanics

Correlation of microstructure, texture, orientation gradients and interface strenght

Enabling CA/Thermocalc and CPFEM / YS simulations for industrial applications

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