Neutron strain scanning in straightened eutectoid steel rods

Neutron strain scanning has been performed on a neutectoid steel rod at a reactor-based source (REST diffractometer, at NFL) and at a pulsed source (ENGIN diffractometer, at ISIS). The rod is primarily obtained from a drawing process and has been subject to bending and straightening procedures, which induce residual stress. The material exhibits a pearlitic microstructure, with alternating ferrite (90 vol %) and cementite (10 vol %) layers. Strain profiles for the ferritic phase were measured on REST. Both phases were measured on ENGIN and analysed by single-peak (ferrite) and Rietveld refinement (ferrite and cementite) methods. The agreement between REST and ENGIN data is excellent for the three measured directions in the ferritic phase. Total stress profiles have been evaluated by combining phase stresses using the rule of mixtures. The experimental results compare well with analytical models for a two-phase material subject to bending and straightening operations under pure bending and unbending moments with perfect elastic behaviour up to the yield point and plastic Voce behaviour above.