In-situ Observation of Dislocation Evolution in Ferritic and Austenitic Stainless Steels under Tensile Deformation by Using Neutron Diffraction

To investigate the characteristics of dislocation evolution in ferritic and austenitic stainless steels under tensile deformation, neutron diffraction line-profile analysis was carried out. The austenitic steel exhibited higher work hardening than the ferritic steel. The difference in the work hardening ability between the two steels was explained with the dislocation density estimated by the line-profile analysis. The higher dislocation density of the austenitic steel would originate from its lower stacking fault energy. Dislocation arrangement parameters indicated that the strength of interaction between dislocations in the austenitic steel was stronger than that in the ferritic steel. This would mainly originate from the difference in dislocation substructures; while dislocation tangle, which can be prompted by the cross slip, was expected in the ferritic steels, highly dense dislocation walls induced by planar glide of dislocations as well as the tangle were expected in the austenitic steel. It was confirmed that the stronger interaction between dislocations in the austenitic steel resulted in the smaller strain field of dislocation. Consequently, the coefficient for the root square of dislocation density in the Bailey-Hirsh equation became smaller in the austenitic steel. X-ray diffraction line-profile analysis was also carried out for the tensile-deformed specimens. The dislocation arrangement parameter evaluated by X-ray diffraction was smaller than that evaluated by neutron diffraction. This would be caused by the difference in the relationship between the loading direction and the scattering vector. On the other hand, the dislocation density evaluated by both methods was almost identical.