Tests to measure the effects of the precipitating size of Cu on the magnetic properties of nongrain-oriented (NGO) electrical steel were carried out. The hysteresis loss had a maximum value when the diameter of the precipitates was around the thickness of the domain wall and decreased rapidly with decreasing size of the precipitates. Alternatively, yield point (YP) rose steeply with reduction in the size of Cu precipitates. It can be confirmed that the precipitating Cu has an ability of rising over 100 MPa in YP without deteriorating core loss. Regarding the effects of Cu precipitates on the hysteresis loss, the surface tension effect might be dominant for the case in which precipitates are smaller than the domain wall thickness, and internal magnetic poles are effective for the larger precipitates.Index Terms-Domain wall pinning, high tensile strength steel, precipitation hardening, Si-Fe.
Synopsis : Deformation microstructures developed in cold-rolled ultra low carbon (ULC) steel as well as those in low carbon (LC) steel have been investigated by using TEM and SEM-EBSD techniques. Particular attention has been paid to the effect of solute carbon on the development of those microstructures. Dislocation structures characteristic to the preferred orientations such as γ-fiber (ND//<111>) and α-fiber (RD//<011>) have been revealed by the same area observation employing the above two techniques. TEM images of dislocation cell boundaries observed in ULC are sharper than those in LC structures. Images of dislocation line segments were separately distinguished in cell structures in ULC, while in LC they were indistinguishable because of high density of dislocations. This indicates that dislocation density increases with increasing the amount of solute carbon, which was confirmed also by XRD measurement. In grains of ND//<111>, fine microbands and/or shear bands (SBs) were developed while in RD//<011> grains such remarkable inhomogeneous microstructures were not observed, which suggests that work-hardening in ND//<111> grains is more prominent than that in the other preferred orientations. In {111}<211> grains of LC steel, the same kinds of shear bands as observed in Fe-Si steels were formed as the most characteristic microstructure, where elongated fine-grained structures with the orientation scattering of 35° between the {111}<211> and {110}<001> Goss orientation were found.
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