(a) The microstructure of the cast iron used in the experiment comprised ferrite, pearlite (layered structure of ferrite and cementite), and spheroidal graphite. (b) The in situ neutron diffraction experiment during cyclic tensile-compressive deformation was performed using the Engineering Materials Diffractometer TAKUMI at J-PARC. The diffraction lines in the loading direction (+90°) and the direction perpendicular to the loading direction (-90°) were measured simultaneously. (c) The obtained results revealed that the contribution of ferrite to the external stress increased as the number of cycles increased, thereby increasing the overall strength of cast iron. Meanwhile, the contributions of cementite and spheroidal graphite were minor.