Deformation effects on the development of grain boundary chromium depletion (sensitization) in type 316 austenitic stainless steels

Deformation induces an acceleration in the kinetics and a reduction in the thermodynamic barrier to carbide precipitation and grain boundary chromium depletion (GBCD) development of a high carbon Type 316 stainless steel (SS). This was observed in a study on strain effects on GBCD (or sensitization) development in the range of 575;The alterations in thermodynamics and kinetics of GBCD development with strain were found to result in a systematic increase in degree of sensitization (DOS) of the material. The acceleration in DOS with strain was, however, more prominent at temperatures between 550 to 700;Strains above 20% also yielded the presence of a time-temperature-strain dependent transgranular (TG) attack during EPR testing. This was induced by precipitation of carbides on the deformation structure of the material.;Analytical methods developed to quantify chromium diffusivity from EPR test data indicated that a decrease in the activation barrier to diffusion, (Q;Examination of the (ambient temperature) deformation microstructure showed that the GBCD kinetic effects were due to increased dislocation pipe diffusion of chromium with increasing strain. Thermodynamic changes were attributed to a change in the ledge structure, and energetics, of the grain boundary, while TG attack was considered to occur due to creation and increase in energy of intra-grain sites during the straining process.;Comparison of predictions of deformation effects on GBCD using an empirical sensitization model with experimental data obtained in this work indicated the model overpredicted DOS values at all strain and heat treatment schedules. Modifications to the model using the thermodynamic and kinetic data developed in this work resulted in an improvement in the predictive capability of this model.