Study On Low Slab Reheating Temperature Technique For Grain-Oriented Silicon Steel

Efficient manufacturing processes of grain-oriented silicon steel considering energy conservation and environmental protection requirements have been developed recently in the world, as important methods of reducing production cost and increasing competitiveness on the market. And the production process by reducing slab reheating temperature has been attracted more attention in the field of electrical steel. In this dissertation, the grain-oriented silicon steel (0.30mm) prepared in the laboratory by low temperature slab reheating technique was studied. Reasonable chemical composition and producing processes were determined according to magnetic properties after experimental research with different compositions and a series of process schemes. The producing processes of low temperature slab reheating method were researched in detail. The characteristic of inhibitors in grain-oriented silicon steel, and the evolution of microstructure and texture during producing as well as their influence on magnetic properties were analyzed systematically, so that the mechanism of low temperature slab reheating technique for grain-oriented silicon steel was explored.It’s known that the composition must be fully corresponded with the producing processes, because of limited range of composition and strict process parameters in grain-oriented silicon steel production. Grain-oriented silicon steel with definite composition was prepared as followed:the slab was hot rolled to 2.3mm thickness after being reheated at 1250℃for 30 minutes; the hot rolled band was cold-rolled to 0.65mm thickness for the first time and then decarburization annealed at 840℃; then the decarburized strip was cold-rolled to 0.30mm thickness for the second time and then recovered at 550℃; after being applied by MgO preparation, the high temperature batch annealing was employed, heating up from room temperature to 1200℃at 50℃/h warming-up velocity, and the other process parameters were the same as those of conventional procedures of CGO steel. Then ideal magnetic properties were obtained by the process.It’s shown that inhibitors influence the magnetic properties of grain-oriented silicon steel by grain growth inhibition, which is a key requirement in the development of sharp Goss texture via secondary recrystallization during the high temperature batch annealing. It has been investigated from second phase particles that the inhibitors in grain-oriented silicon steel prepared by low slab reheating temperature method were mostly Cu2S, and some (Cu, Mn)S and (Mn, Cu)S precipitates. They were precipitated from hot rolled band with considerable amount. Typical inhibitor Cu2S particles have some advantages such as smaller grain size, higher distribution density and have more inhibition ability than those of CGO steel produced by conventional process. They are competent in grain-oriented silicon steel production by the process mentioned.The evolution of microstructure and texture in steel from decarburization annealing was different obviously from that of conventional high slab reheating temperature technique. In the production mentioned, decarburization happened during the intermediate annealing. Cold rolled microstructure and texture inherited after recovery treatment. Primary recrystallization and grain growth course of low slab temperature grain-oriented silicon steel were prolonged at the stage of high temperature batch annealing at slow warming-up velocity. It benefited to the development of secondary recrystallization, so that grain-oriented silicon steel strip had more proportion of sharp Goss texture and quite larger size grains than those of CGO steel, which determined fine magnetic properties of product.