Optimum Magnetic Properties of Non-Oriented Electrical Steel Produced by Compact Strip Production Process

Optimum grain size and effects of crystallographic textures on magnetic properties of Fe-0.65%Si non-oriented electrical steel produced by compact strip production (CSP) process were investigated by optical microscope, electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) techniques. Magnetic induction and core loss show a decreasing trend with the increase of grain size, and grain sizes for optimal magnetic properties are in the range of 26–30 μm. Core loss would be mainly affected by grain size, whereas crystallographic texture would primarily affect magnetic flux density. Magnetic properties increase with increasing of texture factor (volume fraction ratio of {100}/{111}) and magnetic texture factor (volume fraction ratio of <100>/<111>), and increasing with the decrease of A-parameter (minimum angle between magnetization direction and the closest <100> direction) and A(h→), respectively. Simultaneously, with increasing of A-parameter and A(h→), a linear decrease of B50 was obtained.

Texture Evolution during Recrystallization and Grain Growth in Non-Oriented Electrical Steel Produced by Compact Strip Production Process

Evolution of texture and α*-fiber texture formation mechanism of Fe-0.65%Si non-oriented electrical steel produced by Compact Strip Production (CSP) process during all the thermo-mechanical processing steps were investigated using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) techniques. Columnar crystal structure of cast slab is fine and well-developed. Textures of the hot-rolled band are quite different in the thickness direction. During annealing of cold-rolled sheet, γ-fiber texture grains would nucleate and grow preferentially, and α*-fiber texture grains mainly nucleate and grow in the shear zone of α-fiber texture of cold-rolled sheet. During the recrystallization process, γ-fiber texture gradually concentrated to {111}<112>, and γ and α*-fiber texture increased significantly. {111}<112> texture priority nucleation at the initial stage of recrystallization. Due to the advantages of nucleation position and quantity, the content of α*-fiber texture is greater than {111}<112> texture in the mid-recrystallization. During grain growth process, {111}<112> oriented grains would grow selectively by virtue of higher mobility, sizes and quantity advantages than that of {411}<148 > and {100}<120>, resulting in the gradual increase of γ-fiber texture and the decline of α *-fiber texture.

Effect of Solidifying Structure on Centerline Segregation of S50C Steel Produced by Compact Strip Production

Medium-high carbon steels having a high quality are widely used in China. It is advantageous to produce high value-added hot-rolled plates with the crystal refined and chemical composition homogenized in the casting slabs. However, element segregation occurs easily during high-medium carbon steels’ production. Generally, the centerline segregation is improved by enlarging the equiaxed zone with low-superheat casting and electromagnetic stirring (EMS). Studies were conducted on centerline segregation of S50C steel slabs with a thickness of 52 mm produced by the compact strip production (CSP) process in China without EMS equipped. By sampling along the width at different position, the secondary dendrite arm spacing (SDAS) was measured after etching and picture processing, based on which the cooling rate was calculated. It was found that the cooling rate increased from the center to the surfaces of the slabs ranging in 1~20 K/s, 10 times faster than that of a conventional process. The faster cooling rate led to a refined solidifying structure and columnar dendrite through the center of the slabs. The SDAS tended to increase from surfaces to the center, ranging only 32~120 μm smaller than that of a conventional process in 100~300 μm, indicating a finer solidifying structure by the CSP process. Results by EPMA indicated that elements C, Si, and Mn distribute in dispersed spots, increasing towards the center, and the centerline segregation changed in a narrow range: for C mainly in 1.0~1.1, Si in 0.98~1.08, Mn in 0.96~1.02, respectively, meaning a more chemical homogenization than that of thick slabs. Elements’ segregation originated from solute redistribution between solid and liquid. According to thermodynamic calculation, δ region of S50C is so narrow that the solute redistribution mainly occurred between γ-Fe and liquid during solidification. As the equilibrium partition coefficient of element C was the smallest, it was easy for C to be rejected to the residual liquid in the inter-dendritic space, leading to obvious segregation, relatively. Besides, as a result of high-cooling intensity, the solidifying structure became so fine that the Fourier number increased and the volume of the residual liquid decreased, making centerline segregation alleviated effectively both in volume and degree. Although bulging was observed during the industrial experiment, the centerline segregation was still inhibited obviously as the refining solidifying structure with permeability ranged only in 0.1~2.3 μm2 from the surfaces to centerline, which showed a good resistance on the residual flow towards the centerline.

Precipitates in Compact Strip Production (CSP) Process Non-Oriented Electrical Steel

Nitrogen and Sulfur in non-oriented electrical steel would form precipitates, which would severely affect its magnetic properties. Precipitates in compact strip production (CSP) process non-oriented electrical steel were investigated using a transmission electron microscope (TEM) and scanning electron microscopy (SEM). The precipitation mechanism and influence on grain growth were analyzed experimentally and theoretically. The results showed that the main particles in steel were AlN, TiN, MnS, Cu2S, and fine oxide inclusions. The spherical or quasi-spherical of MnS and Cu2S were more liable to precipitate along grain boundaries. During the soaking process, the amount of MnS precipitated on the grain boundary was much larger than that of Cu2S. AlN and TiN in cubic shape precipitated inside grains or grain boundaries. Precipitates preferentially nucleated at grain boundaries, and TiN, MnS mainly precipitated during soaking. In the subsequent processes after soaking, AlN and Cu2S would precipitate unceasingly with the decrease in the average size. The distribution density, the volume fraction, and the average size of the precipitates in the annealed sheets were 9.08 × 1013/cm3, 0.06%, and 54.3 nm, respectively. Precipitates with the grain size of 30–500 nm hindered the grain growth, the grains with 100–300 nm played a major role in inhibiting the grain growth, and the grains with the grain size of 70–100 nm took the second place.