MEASUREMENT OF PLANAR FAULT PROBABILITIES IN AUSTEMPERED DUCTILE IRON AND 304L STAINLESS STEEL

During plastic deformation both stacking and twin faults can be generated in face-centered cubic materials, including iron-based metals that contain thermally stable austenite. These planar faults are a critical component of the austenite to martensite transformation, forming shear bands that can act as nucleation sites. The measurement of these faults via x-ray diffraction has been long established, however it has not been applied widely to austempered ductile irons. The ability to measure these faulting probabilities could give insights into the transformation as a function of deformation. In this work both planar fault densities were measured in austempered ductile iron to test the feasibility of the x-ray diffraction peak-shift (stacking) and centroid-shift (twin) techniques in these materials using a traditional laboratory diffractometer and synchrotron beamline source. Experimentation was also performed with 304L stainless steel as a baseline material for comparison. The errors associated with this technique are also discussed and highlighted. Errors in the laboratory diffractometer measurement were shown to be significant and therefore the experimental setup should be carefully considered when performing these types of analyses