Therefore, we can safely assume that SIM due to the sample-cutting process adopted in the present investigation is negligible and, in addition, that the magnetic signal in the as-received material is due to δ-ferrite. Concerning the as-received material, Fig. 6(a) shows that magnetization presents a noticeable drop around 550 °C, as evidenced in the inset of this figure. So, we can also infer that the Curie temperature of δ-ferrite is ∼550 °C. It must be stressed that, according to Thermo-calc© predictions, the residual δ-ferrite is expected to be stable until 600 °C. Concerning the 60% cold-rolled steel, from Fig. 6(b) it is observed that the magnetization decreases progressively with temperature until a sharp drop to zero in the range 550–600 °C, as evidenced in the inset of this figure. These results suggest that the reversion of the SIM occur between 550 and 600 °C. Furthermore, the sharp drop to zero observed for magnetization can be related
to the Curie temperature of the remaining martensite. It must be stressed that the amount of carbon in the investigated steel is low
and, in consequence, the structure of martensite is expected to be
BCC [35]. Therefore, since δ-ferrite and SIM are BCC, according to
Fig. 6(a) and (b), they have practically the same Curie temperature,
i.e. in the range 550–600 °C.