Load partitioning between ferrite and cementite during elasto-plastic deformation of an ultrahigh-carbon steel

An ultrahigh-carbon steel was heat-treated to form an in situ composite consisting of a fine-grained ferritic matrix with 34 vol.% submicron spheroidized cementite particles. Volume-averaged lattice elastic strains for various crystallographic planes of the α-Fe and Fe₃C phases were measured by synchrotron X-ray diffraction for a range of uniaxial tensile stresses up to 1 GPa. In the elastic range of steel deformation, no load transfer occurs between matrix and particles because both phases have nearly equivalent elastic properties. In the steel plastic range after Lüders band propagation, marked load transfer takes place from the ductile α-Fe matrix to the elastic Fe₃C particles. Reasonable agreement is achieved between phase lattice strains as experimentally measured and as computed using finite-element modeling.