The mechanical behaviour of metastable austenitic steels in pure bending

Metastable austenitic steels exhibit remarkable mechanical properties, that to a large extend can be attributed to the martensite phase transformation taking place during (thermo)mechanical loading. Although the behaviour of these materials under homogeneous monotonic and cyclic deformation has intensively been studied in the literature, non-homogeneous stress and strain states have received significantly less attention.In this work, pure bending experiments have been performed on a metastable austenitic stainless steel to characterise the intrinsic interaction between the through thickness non-homogeneous martensite transformation and the resulting mechanical behaviour and the springback response. The moment-curvature response and the springback have been measured and related to the overall martensite content recorded in-situ using the magnetic induction technique. In addition, micrography has been used to study the through thickness tension–compression asymmetry of the martensite formation, which leads to a complex internal stress distribution resulting in a non-trivial springback behaviour, as compared to non-transforming materials. Three stages in the deformation and transformation under pure bending have been identified, each characterised by distinct moment-curvature loading and unloading responses.

► Pure bending and springback characterization of metastable austenitic steels.
► Martensite formation initially softens and finally hardens the moment-curvature response.
► Martensite formation begins in tensile region and is delayed in compressive region.
► Strongly non-linear springback response due to non-homogeneous martensite formation.
► Three distinct behaviour stages identified in pure bending of metastable austenitic steels.