Experimental and numerical investigation of V-bent anisotropic 304L SS sheet with spring-forward considering deformation-induced martensitic transformation

Highlights: • Spring-forward of 304L steel sheet was examined using a novel V-bending die and verified by finite element analysis. • Martensitic transformation was affected by austenite grain size and orientation, deformation mode and anisotropy factor. • An empirical equation was proposed to correlate residual magnetic field and fraction of transformed α′-martensite. • The amount of spring-forward increased by raising the fraction of α´-martensite in V-bent samples. Spring-back/forward phenomenon usually occurs during various kinds of bending tests of sheet metals. In this study, using a digital image correlation (DIC) technique coupled with uniaxial tensile test, mechanical properties of AISI 304L austenitic stainless steel were determined and the results were applied into finite element analysis (FEA) for further investigations. In order to examine various parameters affecting spring-forward in V-bending, a novel V-bending die equipped with data acquisition system was designed and used to perform V-bending tests of the AISI 304L stainless steel samples. For investigating crystallographic texture evolution in the bent sample, electron backscatter diffraction (EBSD) analysis was conducted. Furthermore, microstructural characterization, micro-hardness test and residual magnetic field measurement were utilized to investigate the transformation of austenite to α′-martensite in the bent samples. The results revealed that spring-forward angle raised by increasing sample thickness and lowering bending angle and anisotropy parameter. The fraction of transformed α′-martensite was affected by mode of deformation (stress state). An empirical model was suggested to relate residual magnetic field to volume fraction of α′-martensite for bent samples. In order to control the spring-forward efficiently, the contribution of microstructural evolution in V-bent samples was discussed.