In situ neutron diffraction study of IF and ultra low carbon steels upon tensile deformation

Abstract Tensile behavior of an interstitial-free (IF) and an ultra low-carbon (ULC) steel bearing similar concentrations of carbon and nitrogen was studied by means of an in situ neutron diffraction technique. The (110), (200) and (211) lattice plane strains were determined as a function of the applied stress, revealing three deformation stages; (1) elastic deformation, (2) grain to grain yielding and (3) the stage III deformation. The microstrain associated with dislocation density (ρ) was increased with tensile straining and the increasing rate was higher in the ULC steel than in the IF steel, resulting in higher flow stress in the ULC steel due to dynamic strain aging. The estimated ρ was summarized as a function of strain (e); ρ = ρ0 + AeB, leading to the description of flow stress (σ); σ=120+0.89μb A1/2eB/2 MPa, where ρ0, A and B were constants, μ shear modulus, and b the magnitude of Burgers vector. The above constants were influenced by dynamic strain aging through the Bailey–Hirsch relation.