Plasticity assessment based on Schmid factor in deformed 9Cr-1Mo steel

Chromium alloyed Ferritic/Martensitic steels are widely used as structural materials in power plants, and considered for core applications of fast and fusion reactors. Characterization and fundamental interpretation of deformed microstructure through crystal plasticity principles are useful for tailoring desired microstructure by optimal processing methods. This study reports the characterization of plastic strain distribution in cold rolled 9Cr-1Mo steel using Electron back scatter diffraction (EBSD) technique. Small orientation changes within the individual grains were studied to gauge the accumulation of ‘geometrically necessary’ dislocations in deformed material, and correlate with the load geometry. The correlated misorientation angle distribution showed a significant presence of low angle boundaries in the deformed microstructure as compared to the annealed specimen. Crystal orientation map of deformation bands indicated significant intra-grain rotation, and the extent of rotation was distinctly different for different grains. A heterogeneous accumulation of plastic strain distribution is inferred from the grain maps of local misorientation angle (0.5º-5º) and orientation spread parameters. Analysis by Schmid factor criteria (0.4-0.5) showed more than 50% of the grains to exhibit favorable orientation for {110} <111> slip activity, whereas higher stress would be required for plastic deformation of remaining grains. Copyright © 2017 VBRI Press.