A transformer core includes two stacks, each of first thickness with ≥1 flat parts, the cutting directions rectilinear and parallel or perpendicular to one another, the stacks facing across a gap, the flat parts made of an austenitic FeNi alloy 30-80% Ni and 10% alloying elements, with a sharp {100} cubic texture, the cutting directions of the flat parts parallel to the rolling or transverse direction, the flat parts having magnetic losses, for a maximum induction of 1 T,