Effect of annealing atmosphere on secondary recrystallization in thin-gauge grain-oriented silicon steel: evolution of inhibitors

Thin-gauge cold-rolled grain-oriented (TG-CRGO) silicon steels were fabricated using the acquired inhibitor method, in which the behaviors of inhibitor are strongly influenced by the final annealing atmosphere and differ from that of the TG-CRGO silicon steel. In this study, macrostructures, grain orientations, and evolution of inhibitors in two gauges of thickness (0.23 and 0.18 mm) of steels were studied and compared in five different annealing atmospheres. The second-phase particles in samples were observed by field-emission scanning electron microscopy. Distribution densities and mean diameter of particles were statistically calculated to illustrate the effect of Zener factor. Results indicated that the inhibitor behaviors in the two thickness samples are similar with the change of N-2 proportion in annealing atmosphere, i.e., nitrogen loss, decomposition, coalescence, and ripening of particles would be strongly suppressed with the increase of N-2 content. However, in comparison with the 0.23-mm samples, the nitride precipitation, decomposition and inhibitor coarsening of the 0.18-mm specimens are more likely to occur at a lower temperature because of the thinner thickness. Furthermore, the value of Zener factor implies that for thinner samples, more N-2 should be employed when nitrides are used the main inhibitor; this condition would inhibit the development of undesirable deviated Goss grains. This study showed that the 0.23-mm sample could achieve the best magnetic properties (B-8) at 1.92 T in the atmosphere containing 25% N-2. The 0.18-mm sample could achieve the best magnetic properties (B-8) at 1.93 T in the atmosphere containing 75% N-2.