It has been silicon steel sheet that we use as electric materials in machinery such as motors, power generators, and transformers. Though 3 wt% silicon steel has been used most widely till now, silicon content is increased up to 6.5 wt% to reduce iron loss due to hysteresis curve and eddy current. But the production of thin steel sheet by rolling become difficult because the hardness get increased and the brittleness become serious through the process. It is thought that the increase of brittleness is due to the existence of ordered phase. Thus the investigation of microstructure was tried through TEM varying the conditions of heat treatment and composition to annihilate the ordered phase in this study.
At first, the microstructures of 6.5% silicon steel were investigated varying heat treatment conditions and it was concluded that it is impossible that the ordered phase disappear completely. Secondly, the microstructures were observed varying the contents of silicon with the interval of 0.5% and the composition in which the ordered phase do not exist could be found. After that, the efforts were concentrated on finding the exact contents in which the ordered phase disappear and succeeded in confirming the composition. Moreover, the observation of the effects of addition of manganese on the existence of the ordered phase was performed.
