Twins or the omega phase: Which is it in high carbon steels?

© 2020 Acta Materialia Inc. Electron diffraction coupled with aberration-corrected (AC) scanning transmission electron microscopy (STEM) is used to image, identify and confirm the structure producing double diffracted spots seen in electron diffraction patterns in twinned high-carbon steels. The experimental and simulated data show that regions comprising: (i) overlaps between a twin and the matrix or, (ii) overlapping twins, create projected structures that are similar to the ω phase observed in other metastable bcc systems. Thus, AC STEM is proficient in the definitive identification of twins in bcc high carbon steels or nanoscale phases in metastable bcc systems.