Grain size dependence of intergranular lattice strain generated by plastic deformation in ferritic steel

The uniaxial deformation behavior of low-carbon ferritic steels with grain sizes of 0.47 μm and 1.5 μm was investigated using in situ neutron diffraction measurements under both tensile and compressive loading. The analysis focused on the evolution of <hkl> lattice (elastic) strains, originating from anisotropy in <hkl> elastic moduli and differences in plastic flow among grains. Such plastic strain incompatibilities produce <hkl> intergranular lattice strains (or stresses). The experiments revealed substantial residual <hkl> intergranular lattice strains following both tensile and compressive plastic deformation. Transmission electron microscopy confirmed the grain-size dependence of dislocation structures formed during plastic flow, suggesting that plastic relaxation near grain boundaries becomes increasingly constrained with grain refinement. Overall, the results demonstrate that the magnitude of residual <hkl> intergranular lattice strains increases as grain size decreases from several tens of micrometers down to 0.5 μm.