Stress annealing effects on magnetic properties of grain oriented electrical steel under compressive stress

There is a strict relation between Gross National Product and electric energy consumption; consequently, the improvement of electrical machines efficiency is highly desired. Regarding power transformers, power loss of magnetic core sheets increases due to compressive stresses appearing during its operation, decreasing power transformer performance. In this article, the effects of tensile stress annealing on power loss of grain oriented electrical steel under compressive stress are evaluated. To do that, the power loss of two uncoated sheets was measured before and after tensile stress annealing for several magnetic inductions (0.7, 1.0, 1.3, 1.5, and 1.7 T) and compressive stress (0, 2, 4, 6, 8, and 10 MPa). This thermomechanical procedure was performed at 500°C, 40 MPa for 10–20 min. Although the tensile stress annealing performance depends on crystallographic texture, a power loss reduction occurs for both samples when compressive stresses were higher than 6 MPa, regardless of magnetic induction. In summary, tensile stress annealing could reduce the deleterious effects of compressive stress on power loss, making commercial grain oriented electrical steel more magnetic uniform and improving power transformer efficiency.