Changes of Dislocation Density and Dislocation Arrangement during Tensile Deformation in Lath Martensitic Steels

Abstract

To understand high work hardening behavior in lath martensitic steels, in situ neutron diffraction studies during tensile deformation for 22SiMn2TiB steel (contained 0.22 mass% of carbon) and carbon–free Fe–18Ni alloy were performed using a high–resolution and high–intensity time–of–flight neutron diffraction. Profile analyses were conducted using the Convolutional Multiple Whole Profile (CMWP) procedure and the Williamson–Hall (W–H) method. As results, the dislocation densities as high as 10¹⁵ m^–2 in the undeformed states of both steels were observed hardly to change or slightly increase by the CMWP procedure. The reliability of the dislocation density obtained by the W–H method was low, because the whole profile was not considered for the analysis. In the former method, the values of parameter M related to dislocation arrangement were found to decrease rapidly in both steels at the beginning of plastic deformation, regardless of the solution of carbon atom. Hence, the high work hardening in the lath martensitic steel was considered by taking into account not only the increase of the dislocation density but also the change in dislocation arrangement.