Modeling Dislocation Interactions with Grain Boundaries in Martensitic Steels

Abstract

Martensitic steels are widely used as a structural material in critical components found fossil fuel and nuclear power plants, such as boilers, pipes, and fittings. Martensitic steels are known to have a hierarchical microstructure that follows the Kurdjumov – Sachs (K – S) orientation relationship, where a prior austenite grain is composed of packets separated by high angle grain boundaries or packet boundaries, which are in turn divided into blocks or variants segregated by high angle grain boundaries called block boundaries. Blocks themselves are an agglomeration of laths divided by low angle grain boundaries named lath boundaries which have precipitates scattered on them. This work seeks to examine, using a couple dislocation dynamics – continuum mechanics approach called Multiscale Dislocation Dynamics Plasticity (MDDP), the interactions between dislocations and packet, block, lath boundaries and precipitates under uniaxial tension loading and their effect on the mechanical response of the material. The simulations are conducted at a strain rate of 105 s-1 at room temperature. The main crystallographic features that arise during the deformation process were extracted and analyzed in terms of their contribution to the mechanical response of the material. The orientation relationship governing the microstructure of martensitic steels, namely the K – S orientation relationship was incorporated in MDDP in an effort to accurately capture the deformation behavior of the material in question. The strength of lath martensitic steel was analyzed as a function of the lath width, block size, and packet size to determine the appropriate effective grain size.