Evolution of dislocation structure determined by neutron diffraction line profile analysis during tensile deformation in quenched and tempered martensitic steels

Effects of Dislocation Arrangement and Character on the Work Hardening of Lath Martensitic Steels

“…Asquenched lath martensitic steels have an extremely high workhardening rate. The dislocation densities of the as-quenched martensitic steels hardly change during their deformation; however, the dislocation arrangement changes from a random arrangement to a correlated configuration during the deformation at room temperature [2][3][4]. The change in the dislocation arrangement can be expressed using the dimensionless parameter M*, a product of the radius of the strain field produced by the dislocation (R * e ) and ̅̅ ̅ ρ √ (i.e., M * = R * e ̅̅ ̅ ρ √ ) [5].…”

“…( 1) is affected by the dislocation structure and arrangement. Thus, the variation of M* is a factor that can be used to explain the work-hardening behavior, as indicated by the variation of α [2][3][4]. The variation of α during deformation of the steels has been demonstrated using in situ neutron diffraction measurements combined with line profile analysis [3,8,9] and can be explained using the Mughrabi's composite model [10]; α changed with deformation as dislocation cells formed and the heterogeneity of the dislocation distribution changed.…”

“…The Vickers hardness of steels increases when the fraction of edge dislocations (f edge ) becomes larger than that of screw dislocations (f screw ) [14]. Thus, the evolution of the dislocation character in lath martensitic steels during deformation [4] may also affect α. However, detailed…”

“…The full martensite condition was kept in the T573, but in the T773, the presence of a tiny amount of austenite with 1.5 mass% was confirmed from the neutron diffraction pattern and the microscopy observations. The tiny austenite is likely because of the reverted austenite transformation during tempering at 773 K [4]. The effect of the austenitic phase on the strength in the T773 can however be neglectable owing to the quite small amount of austenite because no significant changes were detected in terms of both the volume fraction and microstructural evolution [4].…”

“…The tiny austenite is likely because of the reverted austenite transformation during tempering at 773 K [4]. The effect of the austenitic phase on the strength in the T773 can however be neglectable owing to the quite small amount of austenite because no significant changes were detected in terms of both the volume fraction and microstructural evolution [4]. In situ neutron diffraction measurements were performed at room temperature during the tensile deformation of the specimens using the engineering materials diffractometer TAKUMI available at Japan Proton Accelerator Research Complex [15].…”