Magnetic and Mechanical Properties of Newly Developed High-Strength Nonoriented Electrical Steel

New, nonoriented electrical steel featuring great strength and low core loss has been developed. The strengthening mechanism that was mainly applied was dislocation strengthening. The typical properties of developed steel of 690 and 780 MPa grades in tensile strength with a thickness of 0.35 mm were 46 and 51 W/kg in
W

_10/400
, respectively. The core loss of the 780 MPa grade developed steel was a third part of that of a 980-MPa grade dual-phase steel in
W

_10/400
. Furthermore, the fatigue strength of the 780-MPa grade developed steel was found to be superior to that of the 980-MPa grade dual-phase steel. These excellent characteristics were ascribed to the specific microstructure of the steel, in which dislocations introduced by cold rolling were rearranged and a few recrystallized grains were formed within the dislocation-reduced deformed matrix. Solute Nb would be responsible for this favorable microstructure evolution through moderate suppression of dislocation annihilation and consequent retardation of recrystallization during annealing. Another outstanding characteristic of the developed steel was its nickel-free chemical composition, by which a rise in alloying costs could be minimized.