Selective role of bainitic lath boundary in influencing slip systems and consequent deformation mechanisms and delamination in high-strength low-alloy steel

Abstract

We elucidate here the deformation behaviour and delamination phenomenon in a high-strength low-alloy bainitic steel, in terms of microstructure, texture and stress evolution during deformation via in situ electron back-scattered diffraction and electron microscopy. Furthermore, the selective role of bainitic lath boundary on slip systems was studied in terms of dislocation pile-up and grain boundary energy models. During tensile deformation, the texture evolution was concentrated at {1 1 0}<1 1 1> and the laths were turn parallel to loading direction. The determining role of lath on the deformation behaviour is governed by length/thickness (l/t) ratio. When l/t > 28, the strain accommodates along the bainite lath rather than along the normal direction. The delamination crack initiated normal to (0 1 1) plane, and become inclined to (0 1 1) plane with continued strain along (0 1 1) plane and lath plane. This indicated that the delamination is not brittle process but plastic process. The lack of dimples at the delaminated surface is because of lack of strain normal to the direction of lath. The delaminated (0 1 1) planes were associated with cleavage along the (1 0 0) plane.

Keywords:

• High-strength low-alloy steel
• deformation mechanism
• delamination fracture
• slip system

Acknowledgements

R.D.K. Misra also acknowledges continued collaboration with the University of Science and Technology, Beijing, as an honorary professor providing guidance to students in research.

Author contributions

S. Liu and X. Li did the experiments. S. Liu wrote the manuscript. H. Guo, S. Yang, X. Wang, C. Shang, R. D. K. Misra contributed to the discussion.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was supported by the National Natural Science Foundation of China [grant number 51371001]. S. Liu acknowledges the award of scholarship from China Scholarship Council to pursue study at the University of Texas at El Paso, USA.