Calculation of high temperature parent orientation maps application to low carbon steels

Transcription

1 LABORATOIRE D ETUDE DES MICROTEXTURES ET DE MECANIQUE DES MATERIAUX Calculation of high temperature parent orientation maps application to low carbon steels L. Germain, N. Gey, R. Mercier, M. Humbert 1

2 What's is a reconstruction? Temperature? γ α high temperature microtexture Reconstruction time Post-transformation EBSD map Application in Ti, Zr, Steels, TiAl, Zirconia

3 Outline Principle of reconstruction Challenges in reconstruction of steels Application examples Conclusions 3

4 Principle of reconstruction Example: Burger OR in Ti, Zr (110) 111 // 1120 //(00.2) Involves geometrically Rotation Δg 0 1 Parent 12 variants 1 Variant 6 Parents g v ij=d j. Δg 0.P i.g p Orientation of all variants Symetry elements Orientation of a parent 4

5 Principle of reconstruction Requirements: 1. OR known 2. Enough variants 3. Spread OR - (tolerance ω0 around the strict OR) Potential Parents P 1 2 P 2 1 ω 0 P 1 1 P i 1 P 1 2 P 2 2 P 2 1 P 2 i P 2 1 V 3 Variants of the same parent V 1 V 2 5

6 Principle of reconstruction Initial Clusters Starting from a variant + neighborhood Is it possible to find at least one parent common to at least 4 variants? (Within a tolerance : w0) Propagation of the clusters Tolerance w1 To account for larger spread Gey, et al., Solid State Phenomena Vols (2011) pp Restitution of the shapes and orientations of the prior austenitic grains from inherited alpha' orientation maps in steels Blaineau, thèse de doctorat, Université Paul Verlaine de Metz, (2010). 6 Restitution de la microtexture parente à partir de la microtexture héritée mesurée par EBSD, application aux aciers faiblement alliés

7 Principle of reconstruction Initial map (BCC phase) Validation on a Steel with retained γ Reconstructed map Initial map (FCC phase) 85% of correct pixels Blaineau, Germain, Humbert, Gey, Solid State Phenomena, (2010), Vol. 160, pp A new approach to calculate the γ orientation maps in steels, 7

8 Challenges in reconstruction of steels Multiple ORs High fraction of ambiguous situations Spread around OR Number of variants 8

9 Multiple ORs Bain KS NW GT Pitsch Close variants OR choice influence reconstruction OR % reconstructed KS 70% NW 71% GT 92% Deduced from EBSD 97% 9

10 angle between [1-11]α and [1-10]γ ( ) Multiple ORs Determination of the OR from EBSD data 5 4 NW Microstructure %C %Mn %Si %Cr bainite + martensite martensite martensite bainite bainite KS GT bainite bainite 1 yes bainite + martensite 1 yes bainite 1 yes bainite + martensite 1 yes angle between (110)α and (111)γ ( ) M. Humbert, P. Blaineau, L. Germain, N. Gey, Scripta Mat. 64 (2011)

11 Challenges in reconstruction of steels Multiple ORs High fraction of ambiguous situations Spread around OR Number of variants 11

12 High fraction of ambiguous situations Case of twinning 6 common variants Bainite structure : etched to reveal prior austenite grains Courtesy of Dr Hell Twin boundaries may be wrongly reconstructed Some annealing twins may not be seen by reconstruction methods Strategy: Track ambiguities 12

13 High fraction of ambiguous situations 13

14 High fraction of ambiguous situations Reality? 14

15 High fraction of ambiguous situations Reality? 15

16 Challenges in reconstruction of steels Multiple ORs High fraction of ambiguous situations Spread around OR Number of variants 16

17 Spread around OR Bainitic Steel 0.17%C 1.2%Mn 1.2%Cr 1%Si Bainitic Steel 0.3%C 2.2%Mn 1.5%Si Trip Steel (Deformed =0.3) 0.6%C 1.5%Mn 1.5%Si 17

18 Spread around OR Deformed materials = gradient of parent orientation Local approach: Locally spread is lower lower ω 0 less ambiguities less avialable variants microstructure dependent 18

19 Challenges in reconstruction of steels Multiple ORs High fraction of ambiguous situations Spread around OR Number of variants 19

20 Number of variants How many variants to find a unique parent? Number of variants >6 Probability to find KS a unique parent [%] NW Variants with a common {111}γ Very likely situation in lower bainite 20

21 Conclusion Multiple ORs High fraction of ambiguous situations Spread around OR Number of variants 21

22 Application of the reconstruction toolbox Bainite Original orientation map Automated reconstruction Final reconstruction Black: non indexed pixels White: non reconstructed pixels misorientations > 5 > 10 > 15 22

23 Conclusions Steels are challenging materials for automated reconstructions Many OR Twin increase ambiguous situations Spread Correct orientations can be calculated with automated reconstructions Some boundaries may difficult to define due to ambiguity Topological information is helping Combined tools are able to reconstruct the parent microtextures Germain, et al. accepted in acta mat 2012 An advanced approach for reconstruction of parent orientation maps in case of approximate orientation relations - Application to steels, 23

24 Thank you for your attention 24