In the present study, high silicon (6.4 wt%) -iron microcrystalline ribbons (25 mm;38 m) were obtained directly from its melted state by rapid quenching. The material thus obtained was then submitted to heat treatment. This soft magnetic material is mainly used as cores in high-performance electric machines (50-400 Hz.). At this stage of the heat treatment, the effect of the vacuum level (10-30 Pa) and temperature range (950-1250Β°C) on grain size and developed texture as well as the resulting influence on the amount of total core losses (1.0 T, 10-1000 Hz) were studied. The obtained results show two types of recrystallization, primary and tertiary, which are both controlled by vacuum level and temperature range. The process of tertiary recrystallization is further divided into three differentiated subtypes, according to the developed texture and core losses obtained. In the case of tertiary recrystallization (1-20 Pa, 1050-1100Β°C), which also shows the highest percentage (70-90%) of texture +1 0 0,10 k l2 and a grain size between 800 and 1100 m, the minimum amount of magnetic core losses is obtained. These core losses (1.0 T, 50 Hz) are lower (60-65%) than those obtained with the top grade (FeV-240-35HA) of conventionally processed (+3 wt% Si) non-oriented magnetic steel sheets. This difference in the amount of core losses increases as the work frequency rises.