Study Of Microstructure And Properties Of Mid-grade Non-Oriented Electrical Steel Produced In Twin-roll Strip Casting

Eliminating the continuous casting and hot rolling processes in the traditional technology for producing non-oriented silicon steels, the twin-roll strip casting, which can supply the strip with a thickness about2.0mm directly from molten steel, is a new efficient, energy saving and low cost technology.The microstructure, texture and magnetic properties of non-oriented1.2%silicon steel processed by the twin-roll strip casting was investigated in this work, especially under the different secondary cooling, normalizing and hot leveling conditions. Appropriate casting condition for the production of1.5mm ultra-thin slab by twin-roll casting is explored.A number of micrographs, EBSD and X-RD results about the cast strips show that water cooling can avoid the phase transition of αâ†'γâ†'α which produces small grains, and improve the average grain size and structural homogeneity of the casting strip, thereby optimize the microstructure of the products and reduce iron loss. Although there was no obvious columnar grain in water-cooled strip, the texture is still influenced by the temperature gradient, strong {001} texture was formed in the strip, and the magnetic induction of the product increased.After normalizing and hot leveling, the strip shape is adjusted and the average grain size is increased. Low temperature normalizing could save energy after hot leveling deformation, thereby annealing temperature is reduced and the magnetic properties are improved. The product which normalized at800℃for5minutes, hot leveled by hot mill, cold rolled and annealed at950℃for5minutes shows an excellent magnetic properties, the iron loss is reduced to4.592W/kg and the magnetic induction is rose to1.796T, so it can be used in high efficient motors.Reducing the thickness of the casting strip increased the temperature gradient, and the pouring temperature and rolling speed should be rose appropriately. With a thinner strip, the cold rolling reduction and the deformation energy decreased, the grain rotation decreased so that the accumulation of γ texture is reduced, the texture of the casting strip can be reserved to improve the magnetic induction. Reducing the cold rolling reduction will cut down the nucleation sites and increase grain size to reduce iron loss. The product which cast in1570℃,cold rolled and annealed at950℃for5minutes shows an excellent magnetic properties, which can be used in high efficient motors.By TEM observation, AlN precipitations above100nm were found in water-cooled strip and ultra-thin sheet. The morphology and size of the coarse AlN precipitations in the subsequent process almost unchanged. MnS precipitations about40nm were found in all products, which inhibit grain growth and should be controlled.Generally speaking, the twin-roll strip casting1.3%Si non-oriented silicon steel has obvious advantages. The products show bettor magnetic propenics and can be used in efficient motors.