“…Between stages I and II, there is a processing window period, which lasts from 0 min to 3 h, depending on the austempering temperature and alloying elements content (i.e., Cu, Ni, and Mo). [32][33][34][35] The change of the phase fractions of austenite and ferrite as well as the carbon redistribution, as encoded in the crystal lattice expansion of austenite, can be extracted from the diffraction profiles and length change curves (Figure 4 and 5). [20,21] At the beginning/end of stage I (Figure 4a,c), the reflections are symmetric and can be fitted using a single Gaussian peak shape function.…”