Micro-tensile Behaviour of Low Alloy Steel with Bainite/martensite Microstructure

Micro-tensile testing combined with analysis using a crystal plasticity finite element method (CPFEM) was employed to elucidate the deformation behaviour of bainite/martensite structures of a low alloy steel. The bainite single phase specimens exhibited habit-plane-orientation-dependent yielding similar to the martensite single phase specimens. In the bainite/martensite specimen, deformation concentrated in the bainite region oriented favourably for the in-habit-plane slip, leading to low ductility fracture. With consideration of the habit-plane-orientation-dependent yielding, the present CPFEM analysis successfully reproduced the anisotropic plastic deformation behaviour of the single phase steels obtained in the experiments. The numerical result for the bainite/martensite specimen showed slip localization in the bainite region and stress concentration near the interphase boundary. This suggests that the interphase boundary can be a site for the fracture origin.