Karl Foster

Loss separation measurements for several electrical steels

Loss separation measurements were made on regular grain oriented 3% Si steels of four sheet thicknesses, one thickness of high permeability oriented 3% Si steel, two grades of nonoriented Si steel, a low carbon steel, a primary recrystallization oriented low alloy iron sample, and an amorphous metal sample. The Bn dependence of hysteresis loss Ph for all samples except the oriented Si steels was close to n=1.6, in good agreement with the Steinmetz value. All the oriented Si steels had n values close to 2.

Magnetic properties of (110) [001] oriented low alloy iron

Magnetic characteristics have been determined for several 6 mil thick samples of low alloy iron with strong (110)[001] orientations. These textures have been obtained by primary recrystallization and normal grain growth in iron base alloys with small additions of Si, Cr, and Mn. This presentation will discuss how highly oriented specimens were obtained by the control of chemical composition, processing, and final annealing. Both the texture and magnetic properties of these alloys will be described. The strong (110)[001] textures were confirmed by torque measurements, magnetic properties, reflective X‐ray pole figures, and quantitative domain analyses.

Factors affecting core losses in oriented electrical steels at moderate inductions (invited)

The effects of sheet thickness, orientation, grain size, silicon content, stress, domain control, and surface condition on core losses of both regular grain oriented (RGO) and high permeability (HGO) silicon steels in the induction range of 1.0 to 1.5 T were reviewed. Where possible, the effects of these factors were discussed in terms of total loss PT hysteresis loss Ph eddy current loss Pe and eddy current loss anomaly factor η. The effect of decreasing sheet thickness t is dependent on Pe∼t, while for increased silicon content, Pe∼1/ρ. Improvements in orientation are shown mainly to decrease Ph, with the effect being larger at 1.5 T and above than at lower inductions. Grain size reductions, applied tensile stress, and other domain control methods are mainly aimed at reducing the 180° domain wall spacing 2L which in turn decreases η. Improved surface condition decreases both Ph and Pe, but mainly above 1.5 T.

Effect of anneal coatings and surface condition on magnetic properties of grain oriented 3% Si - Fe

Reductions in high induction losses were obtained by annealing cold rolled, decarburized 3% Si-Fe samples with an Al 2 O 3 separator coating rather than MgO to obtain the final texture and properties. Reduced coercive force values were associated with the lower losses, and MgO coated samples exhibited subsurface oxide particles, while samples annealed with Al 2 O 3 had smooth surfaces. Similar low losses could be obtained in fully processed grain oriented samples by removing the mill coating by pickling and annealing at 1050°C with an Al 2 O 3 coating. Minimum losses were obtained in high permeability grain oriented samples by applying tension after a high temperature anneal with Al 2 O 3 coating.

Enhanced domain imaging techniques

In this paper we present three techniques which provide improved permanent ferromagnetic‐particle images of domain structures. A normal field, supplied by flexible permanent magnet strip, is used for all three. The first method employs a pigmented strippable coating which is peeled from the specimen after drying. The result is a high‐resolution mirror image of the domain structure; the method can be used to study parts of large specimens nondestructively. In the second method, the coating is examined while still in place; its contrast can be increased by adding more white pigment and by painting the specimen white before application. The third method uses noncolloidal Fe3O4 powder in artist’s matte medium to provide domain images, on a white‐painted specimen, with higher contrast but lower resolution.

Effect of Coating Induced Stresses on Properties of Cube Textured 3% Si???Fe Sheets

Glass coatings having varying coefficients of thermal expansion were applied to Epstein strips cut in the rolling direction from cube textured 3% Si‐Fe having two levels of directional orientation. A low expansion glass resulted in substantial reductions in loss and magnetostriction. Allowing coated samples to cool under applied tensile stress resulted in further loss and magnetostriction reductions.

Temperature dependence of loss separation measurements for oriented silicon steels

Loss separation measurements were made over the temperature range of 20 to 200°C for 0.22-mm and 0.29-mm thick regular grain oriented (RGO) and 0.31-mm thick high permeability oriented (HGO) Epstein samples. The 0.22-mm thick RGO sample had only a forsterite coating, while the thicker samples had secondary high stress coatings. Over the temperature range of 20 to 100°C the change in hysteresis loss P h with temperature was negligible for all samples. Since the total core loss P T decreased with increasing temperature over this range, almost all the loss reduction was due to a reduction in the eddy current loss component P e which was inversely proportional to the resistivity. The eddy current loss anomaly factors η exhibited little variability with increasing temperature, indicating that domain wall spacings did not change with increasing temperature.

Effect of tensile stress on magnetic properties of oriented alloys with residual sulfur

Applied tensile stress was shown to reduce core loss in two types of experimetal (110) [001] oriented alloys with residual sulfur contents: continuously strip annealed 3% Si‐Fe and iron‐base alloys containing less than 2% Si textured by a primary recrystallization and normal grain growth mechanism. Application of 700 psi (5 MPa) to a 3% Si‐Fe sample containing 0.018% S resulted in a decrease of Hc from 0.17 to 0.13 Oe and a decrease in 60 Hz, 15 kG core loss from 1.40 to 1.26 W/kg. Similar reductions in Hc and loss were obtained by the application of a ’’high stress’’ glass coating to the same sample. Reductions of Hc and core loss were observed in primary textured iron‐base alloys with additions of 0.005% S. In highly textured material, loss decreases with tension included both reductions in hysteresis loss and domain loss.

Stress and induction dependence of hysteresis losses in electrical steels

Hysteresis losses Ph were measured for several electrical steels over an induction range of 0.4–1.7 T as a function of stress coatings and applied tensile stress. The Bn dependence of Ph was determined, where n is the Steinmetz coefficient. Removal of stress coatings from high permeability oriented (HGO) steel samples decreased n from about 2 to 1.6, while application of stress coatings to uncoated regular grain oriented samples increased n from 1.6 to 1.9–2. An applied tensile stress of about 7 MPa increased n from about 1.6 to 2 for both RGO and HGO samples. A similar tensile stress level increased n from 1.6 to about 1.8 for a nonoriented silicon steel sample.

The effect of manganese and sulfur on the development of orientation (110) [001]‐oriented low‐alloy iron

An investigation was made to determine the role of manganese and sulfur concentration on the development of (110) [001] orientation in low‐alloy iron specimens by primary recrystallization and normal grain growth. Fifteen heats, containing nominally 0.8% Si and 0.6% Cr with varying Mn and S contents, were used for the study, with three‐stage processing to 0.15 mm thick strip. The manganese content was varied between 0 and 0.15% with nominal sulfur contents of 0.001, 0.006, and 0.012%. Torque and magnetic properties, as well as X‐ray pole figures, were used to evaluate the orientation after final annealing. The low‐sulfur alloys (0.001% S) did not develop the best (110) [001] orientations. Those specimens containing the higher sulfur concentrations (0.012% were poorly oriented, except for one specimen which contained essentially zero Mn (<0.01%). All the specimens with nominal 0.006% S content developed strong (110) [001] textures with B10 values of up to 1.93 T and 60 Hz core losses at 1.7T as low as 1.5 ...