Characterization of the micromechanical behavior of advanced high-strength bainitic steels

Characterization of the micromechanical behavior of advanced high-strength bainitic steels

This project deals with the phase quantification by nanoindentation and electron back scattered diffraction (EBSD), as well as a detailed analysis of the micromechanical compression behaviour, to understand deformation processes within an industrial produced complex bainitic microstructure.

The combination of high strength and ductility is vital for industrial products like line pipe or structural steels. Increasingly, such products are made of bainitic steels with complex microstructures [1-3]. Since such complex microstructures often consist of granular bainite and polygonal ferrite, and both phases are very difficult to distinguish under the light optical microscope, two different approaches have been applied [4-5].

As a first approach, nanoindentation tests and extreme property mapping (XPM) were used, which were additionally analysed using k-means clustering. In addition, an automatised MATLAB MTEX tool was created to determine the misorientation angle within each grain, which enables the differentiation between both phases [5-7]. Furthermore, micropillar compression tests were applied on both constituents to understand the deformation process by mechanism-based models. The critical resolved shear stress (CRSS) and the corresponding activated slip systems will be used as a decisive criterion.

Subsequently, the relevant parameters to describe the representative behaviour of real microstructures can be used as an input for a computational material model to be implemented in the crystal plasticity simulation tool DAMASK [8].  

This project is in cooperation and supported by Dillinger (AG der Dillinger Hüttenwerke).

Fig. 1: The granular bainite has been separated by the kernel average misorientation threshold. a) the detected granular bainite grains (the low angle grain boundaries are displayed as red lines) show also a higher kernel average misorientation compared to polygonal ferrite grains in b).

Fig. 2: According to the crystallographic orientation of the tested grain, the slip planes are predicted for all three slip families which can be active due to the highest Schmid factor a). In comparison with a) the {112} slip plane was activated in b) during this microcompression test.

References

1.
S. Zajac, V. Schwinn, and K. H. Tacke
Characterisation and Quantification of Complex Bainitic Microstructures in High and Ultra-High Strength Linepipe Steels
Mater. Sci. Forum, vol. 500–501, pp. 387–394, 2005
2.
B. M. Huang, J. R. Yang, H. W. Yen, C. H. Hsu, C. Y. Huang, and H. Mohrbacher
Secondary hardened bainite
Mater. Sci. Technol., vol. 30, no. 9, pp. 1014–1023, 2014
3.
K. Hickey
The Value of Mass Benchmarking - AHSS Insights
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K. Zhu, D. Barbier, and T. Iung
Characterization and quantification methods of complex BCC matrix microstructures in advanced high strength steels
Journal of Materials Science, vol. 48, no. 1. pp. 413–423, 2013
5.
Y. W. Chen et al.
Y. W. Chen et al., “Phase quantification in low carbon Nb-Mo bearing steel by electron backscatter diffraction technique coupled with kernel average misorientation
Mater. Charact., vol. 139, no. September 2017, pp. 49–58, 2018
6.
Y. W. Chen, B. M. Huang, Y. T. Tsai, S. P. Tsai, C. Y. Chen, and J. R. Yang
Microstructural evolutions of low carbon Nb/Mo-containing bainitic steels during high-temperature tempering
Mater. Charact., vol. 131, no. March, pp. 298–305, 2017
7.
F. Bachmann, R. Hielscher, and H. Schaeben
Texture Analysis with MTEX-Free and Open Source Software Toolbox
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8.
Franz Roters, Martin Diehl, Pratheek Shanthraj, Philip Eisenlohr, Jan Christoph Reuber, Su Leen Wong, Tias Maiti, Alireza Ebrahimi, Thomas Hochrainer, Helge-Otto Fabritius, Svetoslav D. Nikolov, Martin Friák, Noriki Fujita, Nicolò Grilli, Koenraad G.F. Janssens, Nan Jia, Piet Kok, Duancheng Ma, Felix Meier, Ewald Werner, Markus Stricker, Daniel M. Weygand, and Dierk Raabe, "DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale," Computational Materials Science 158, 420-478 (2019).

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