Nonoriented Electrical Steels FERNANDO JOSE GOMES LANDGRAF 1,2 1.—Escola Polite´cnica, Universidade de Sa˜o Paulo and Instituto de Pesquisas Tecnolo´gicas (IPT), 05508-901 Sa˜o Paulo, SP, Brazil. 2.—e-mail: f.landgraf@usp.br The physical origins of the magnetic properties of nonoriented electrical steels; its relations to microstructural features like grain size, nonmetallic inclusions, dislocation density distribution, crystallographic texture, and residual stres- ses; and its processing by cold rolling and annealing are overviewed, using quantitative relations whenever available. Nonoriented electrical steels are the most eco- nomical choice of material used in electrical machines to transform electricity in movement, as in the electric car motors, or to transform movement into electricity, as in the wind mills generators, due to their capacity to amplify several thousand times the magnetic field generated by electric currents. They have been in use since the beginning of com- mercial electricity, around 1850. The name was coined in the 1930s to differentiate them from the newly invented grain-oriented electrical steels, a class of steels with 3% silicon in which a very strong (110)[001] crystallographic texture is developed by abnormal grain growth. The world market for nonoriented electrical steels reached 14 million tons per year 1 in 2008, keeping its niche position as 1% of total steel pro- duction. It is reasonable to admit that its growth rate should follow the increase in electricity demand, which had a yearly average of 3.5% in the first decade of the 21st century, after a 2.5% average in the last decade of the 20th century. New products for new applications are blooming, led by their use in wind generators and electric car motors. No radical innovation was introduced since the last review paper about the subject in this magazine 2 in 1986: The dream of a science wish list of the 1980s, three tesla saturation magnetization material, is yet to be discovered. The processing steps to achieve the ideal crystallographic texture (100)[uvw] in steels for electrical motors application have not been developed; despite the success in the modeling of texture evolution in cold rolling, 3 recrystallization texture still lacks a better understanding. The promise of significant cost reduction and better tex- ture by strip casting has not reached mass produc- tion scale. 4 The commercial introduction of 6.5% silicon strips is a significant innovation of the period. 5 Nevertheless, the ever present energy conservation effort 6 led to significant incremental innovations that will be discussed. The Materials Science Tetrahedron 7 suggests that we look for the relations between its four ver- tices: performance, properties, processing, and microstructure. Materials scientists like to focus on the relationships between property and micro- structure and between process and microstructure, but we need to start by discussing the relation be- tween component performance and properties, magnetic properties. Taking an electric motor as the main application, its torque is proportional to the magnetic flux (the unit is weber, Wb) in the air gap between the stator and the rotor. The flux intensity is directly connected with the ability of the material to amplify the magnetic field, somewhat inappro- priately called magnetic permeability. As the mag- netization curve has an S shape, magnetic permeability is not constant, and for quality control purposes, it is specified at certain points of the curve. The properties expressed in the magnetiza- tion curve are magnetic induction (also known as flux density B, in units of weber [volt second] per square meter, known as tesla, T) and the magnetic field (H field, in ampere per meter). Permeability in electrical steels is addressed in two different ways: ASTM defines the relation between specified values of magnetic induction and the magnetic field needed to achieve it (as in magnetic permeability l 1.5 = 1.5/ l o H), while IEC specifies the magnetic induction to be achieved at a certain value of magnetic field (as in B 50 , the induction obtained with H = 50 A/cm). Flux performance is so sensitive to the size of the air gap that small differences in magnetic permeability are accepted. On the other hand, the concern with JOM, Vol. 64, No. 7, 2012 DOI: 10.1007/s11837-012-0356-7 Ó 2012 TMS 764 (Published online July 4, 2012)