Internal Strain Measurement of Carburized Gear by Neutron Diffraction

Abstract

Internal strain and stress distributions of carburized transmission gear was non destructively measured by neutron diffraction in order to understand deformation behavior after carburizing. The material used in this study was chromium-molybdenum steel, SCM 420 H. The carburized case depth was determined by microscope and measuring hardness distribution. The diffractions from Fe-110 and 211 planes were used, and internal strain was obtained from the lattice spacing change. Reference coupon specimens were cut from the same carburized gear, and then lattice spacing was measured as stress-free one. As the results, the carburized case depths of shift fork groove and dog clutches were relatively deeper than that of gear wheel. From measured axial, radial and hoop residual strains near the internal spline, large tensile residual strain parallel to the axial direction was generated in the shift fork groove. Furthermore, tensile residual strains parallel to the axial and hoop directions were also generated in the gear wheel. Residual strains of carburized gear were found to be not uniform, and be balanced by local deformation through the whole gear including the shift fork groove and dog clutches.