The Effects of Pre-annealing Temperature and Final Thickness Reduction on Goss Texture in C- and Al-free Grain-oriented Electrical Steel

Abstract

Electrical steel is a soft magnetic material having excellent electromagnetic character and grain-oriented electrical steel has a strong Goss texture {110}<001>. Among the various <uvw> crystal directions on the {110} plane, the strongest intensity of the <001> direction arises from the intrinsic formation mechanism of the {110}<001> cold-rolling texture. And then, through the competitive selective growth process between {100}, {110} and {111} grains which is governed by the primary grain size and the surface segregation concentration of sulfur, the sharp {110}<001> annealing texture can be developed in a C- and Al-free Fe-3%Si-0.1%Mn steel. The selective growth of a {hkl} grain is possible, when the {hkl} grain size is larger than the critical grain size linearly proportional to the strip thickness. From these theories, effects of pre-annealing temperature on development of {110}<001> Goss texture after final annealing have been investigated in a C- and Al-free Fe-3%Si-0.1%Mn-x%S steel. In the first case of Fe-3%Si-0.1%Mn-0.012%S steel which were final reduced at 87.9%, the total number of {110} grains in a fixed strip dimension after final annealing decreases with decreasing pre-annealing temperature in the temperature range of 1073K(800˚C)~1373K(1100˚C). In the second case of Fe-3%Si-0.1%Mn-0.002%S steel which were final reduced at 69.7%, however, the increase in primary grain size with increasing pre-annealing temperature causes the transition in annealing texture after final annealing from {110}+{100} to {110} in the temperature range of 1073K(800˚C)~1223K(950˚C). From those results, the magnetic induction of the first case decreases with increasing pre-annealing temperature, however that of the second case is inverse tendency. The final thickness reduction effect of Fe-3%Si-0.1%Mn-0.012%S steel was also investigated. In this case, the final thickness reduction was changed from 69.7 to 90.8% and they were pre-annealed for 1 min at a 900˚C under a pure hydrogen gas. The primary grain size decreases with increasing final thickness reduction, while the magnetic induction shows a convex profile. An excellent magnetic induction, B10(T), of 1.99 T, 1.938T and 1.95T in each case are comparable to that of the conventional electrical steels, 1.94T. ODFs (orientation distribution functions) which are obtained from the Gaussian spread of 5 degrees and an etch-pit method were used for texture analyses of the cold-rolled and annealed strips. The surface segregation behavior of sulfur and the final annealing texture were investigated using Auger electron spectroscopy (AES). After final annealing, magnetic induction (B10(T)) and core loss (W17/50(W/kg)) were measured under an external magnetic field of 1000 A/m and 1.7T and 50Hz using a single strip dc flux-meter, respectively.