Development of Through-Thickness Cube Recrystallization Texture in Non-oriented Electrical Steels by Optimizing Nucleati
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INTRODUCTION
NON-ORIENTED electrical steels (NOES) are widely used in iron cores with alternating magnetic flux, such as generators and motors. The various fabricating methods of NOES have been reported, including conventional rolling and annealing, powder metallurgy, selective laser melting, CVD, PVD, rapid solidification, spray forming, hot dipping, strip casting, etc.[1,2] The conventional rolling and annealing process is the most common method for fabricating NOES sheets and widely used for large-scale industrial production. The magnetic properties of NOES are highly sensitive to the texture, and h100i is the easy magnetization direction. In order to achieve a high magnetic flux density at weak magnetic field, it’s beneficial to form a cube texture which contains two h100i along rolling direction (RD) and transverse direction (TD), respectively. However, through-thickness c fiber (h111i//normal direction [ND]), which has no h100i in the rolling plane, usually dominates the recrystallized sheets of NOES after final annealing[3,4] due to the orientation-dependent stored strain energy.[5] Currently, texture optimization in NOES mainly focuses on two issues, reducing c texture and enhancing NING SHAN, JINLONG LIU, YUHUI SHA, FANG ZHANG, and LIANG ZUO are with the Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang 110819, China; Contact e-mails: [email protected]; [email protected] Manuscript submitted September 22, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
k texture (h100i//ND) including cube texture. As c recrystallized grains mainly nucleate at grain boundaries,[6,7] modifying the nucleation environment at grain boundaries is a considered way to control c texture. Park et al.[8] reduced the number of c nuclei at grain boundaries in 2.0 wt pct Si NOES by increasing grain sizes of hot bands from 115 to 460 lm. And Cunha et al.[9] weakened the strain-stored energy of grain boundaries which provide activation energy of c recrystallized grains using a two-stage cold rolling process. In addition, temper rolling and pre-annealing was also proved to effectively suppress c recrystallization texture by Gre´gori et al.[10] But it is difficult to completely eliminate c texture through all these methods. On the other hand, cube texture has won a high degree of attention not only in NOES but in grain-oriented electrical steels (GOES). Actually, cube is difficult to develop as a dominant recrystallization texture in virtue of the disadvantages of the size or quantity in the early stage of recrystallization produced by the conventional rolling method.[7] It is easy to form strong Goss and a (h110i//RD) textures in bands after conventional hot rolling under heavy deformation at high temperature. These textures have an important effect on texture evolution. In NOES, they convert to c or Goss recrystallized grains after cold rolling and primary recrystallization annealing, while i
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