Diametral strain response and microstructural yielding mechanisms of a bainitic pressure vessel steel

Unexpected trends of diametral strain range response have been recorded for annealed bainitic Cr-Mo-V-pressure vessel steel at room temperature and moderate strain amplitudes. Stress and diametral strain response were also recorded for three harder heat treatment variants, but they behaved as expected. The alloy is strengthened by a carbide dispersion and a dislocation network, both of variable density. The unexpected diametral strain response is suggested to be associated with yet unknown macroscopic effects of particular observed microscopic mechanisms of slip. These mechanisms of slip can be analyzed with a model for dispersion strengthening which expresses the connection between nominal dislocation activity and the plastic and elastic components of elongation. The necessity for a differentiation between effective obstacles to slip consisting of stable carbides or cyclically unstable dislocation networks is arrived at.
Observation of slip mechanisms by scanning electron microscopy is presented.