Abstract Lab experiments were carried out to check the effect of some process parameters of nitriding, performed simultaneously with decarburization, on magnetic properties of 3%Si Grain-oriented silicon steel produced by a low slab reheating technology. The samples of (GO) 3% Si steel collected as 0.27mm cold-rolled were submitted to a continuous annealing process at two temperatures, 860 and 900ºC; three annealing times, 63.6, 95.4, and 119.25s; and three ammonia flows 0.1, 0.2, and 0.4Nm3/h. The nitrogen content obtained after the treatments was much higher than those obtained by the currently used process, and it increased as the ammonia flow rates and soaking times were increased, hindering the primary grain growth that adversely affected the magnetic properties. The increase of annealing temperature improved the decarburization and the magnetic properties. The best magnetic properties were found in the sample with the highest primary grain size and the lowest amount of absorbed nitrogen. The success of this practice, in terms of magnetic properties, was pointed out to be based on a drastic reduction on strip nitrogen increase.

The effect of carbon content on the magnetic ageing index and Vickers hardness evolution on annealed samples of 2%Si non-oriented grain electrical steel was studied. Samples with 40 and 60ppm carbon content were subjected at ageing temperatures of 200 and 225ºC, respectively. During the ageing treatment, the cycle was interrupted on several time intervals in order to obtain the core loss and to determine Vickers hardness. The precipitates were characterized using scanning electron microscope (SEM). Using the software MatCalc, computer simulations of ε-carbide precipitation were performed and compared with experimental data from literature. The results for both carbon contents showed that the maximum hardness value was achieved in shorter time than that to achieve the maximum magnetic ageing, indicating that the critical size of precipitates more harmful to the magnetic properties is larger than the ones that maximize the hardness.

The processing of 3% Si steel is characterized by the use of MnS particles as a normal grain growth inhibitor. Experiments were carried out to investigate the grain growth in this material during heat treatments at low temperature. Industrial decarburized samples were annealed in the range 825-845 °C and a detailed study of grain size and texture was made by EBSD measurements. The primary grain size and texture were related to the secondary structure obtained after high temperature final annealing. The heat treatments for grain growth led to an increase in the mean grain size by 1.2 to 3 times, depending on the stability of MnS particles distribution. The increase of the primary grain size increased the core loss and decreased the magnetic induction of the fully processed material.