Yasuyuki Hayakawa

Influence of heat treatment before secondary recrystallization on magnetic properties of 3% Si grain-oriented steel containing Sb

Abstract The secondary recrystallization of 3% Si grain-oriented steel containing Sb has been investigated. The mechanism of the improvement of the magnetic properties under the conditions of Sb addition and a constant temperature treatment during secondary recrystallization has been clarified by three experiments. It has been found that (1) Sb segregation in grain boundaries during decarburization annealing retards decarburization and grain growth, so that the {110} intensity increases and the grain size decreases with increasing Sb; (2) the constant temperature treatment for final annealing enhances the Sb segregation in grain boundaries, and therefore maintains the {110} intensity in the specimen with the addition of Sb; and (3) the addition of Sb increases the inhibiting force. These three effects enable secondary recrystallization such that many (110)[001] nuclei grow rapidly, surrounded by small primary grains, leading to high B 8 values.

Effect of Cold Rolling Reduction Rate on Secondary Recrystallized Texture in 3 Pct Si-Fe Steel

The phenomenon of secondary recrystallization in 3 pct Si-Fe electrical steel subjected to relatively high cold rolling reduction rates has been investigated. The texture of the secondary recrystallized sample that has a cold rolling reduction rate of 97.2 pct consists mainly of {110}〈112〉 component, which is quite different from the ideal Goss ({110}〈001〉) texture obtained after lower cold rolling reduction rates. The grain boundary character distribution (GBCD) analysis on the primary recrystallized sample with a cold rolling reduction rate of 97.2 pct indicates that the {110}〈112〉 component has the highest frequency of high energy (HE) boundary with a misorientation angle between 20 and 45 deg, whereas the Goss component in the sample subjected to lower cold rolling reduction rates has the highest frequency of HE boundary. These results indicate that the component with the highest frequency of HE boundary surrounding it after primary recrystallization has the privilege to outgrow other components during secondary recrystallization. However, the GBCD analysis for coincidence site lattice (CSL) boundary points out that the Goss component has the highest frequency of CSL boundaries in the primary recrystallized texture irrespective of the cold rolling reduction applied. These results suggest that the HE model can predict the orientation relationship between the primary and secondary recrystallized textures better than the CSL model.

Influence of Carbon Content and Rolling Temperature on Rolling Texture in 3 Pct Si Steel

Effects of carbon and rolling temperature up to 453 K (180 °C) on rolling texture of 3 pct Si steel at a reduction of 66 pct were investigated using a single crystal with an initial orientation of {110}〈001〉. With residual-level carbon, uniform slip deformation was observed in the specimen cold rolled at room temperature and most of initial orientation {110}〈001〉 rotated to {111}〈112〉 during the rolling. With carbon addition, the formation of the deformation twins and the shear bands were promoted in the specimen cold rolled at room temperature. Regions with {110}〈001〉 were observed inside the shear bands. Warm-rolled specimen with residual-level carbon had microbands containing tiny {110}〈001〉 regions. Warm-rolled specimen with carbon addition had both the shear bands and the microbands but no deformation twin. Additionally, there were unique band structures with rotated crystal orientation around the rolling direction from initial orientation {110}〈001〉. These experimental results suggest that the carbon addition inhibits dislocation migration by the increase of the critical resolved shear stress (CRSS) and that the high deformation temperature activates multiple slip systems by the reduction of CRSS and further that the carbon addition and high deformation temperature superimposed bring about the activation of symmetrical {110} slip systems additionally.

Investigation of secondary recrystallization kinetics in grain-oriented electrical steel using the ultrasonic interferometry

Measurements of the growth rate for the individual secondary recrystallized Goss grain in Fe–3%Si containing AlN and MnSe as grain growth inhibitors were made by the ultrasonic interferometry. It was found that the growth rates in the rolling direction for secondary recrystallized grains varied from 0.3 to 0.6 mm/min, and that the growth rate in the rolling direction is 1.2–1.9 times higher than that of the cross-rolling direction. The set of results were explained in terms of the concept of the “growth advantage” which is defined as the fraction of high-energy grain boundaries having the misorientation angles between 20° and 45° with respect to the specific secondary recrystallized grain in the primary recrystallized grains.

Effect of Cold Rolling Reduction Rate on Secondary Recrystallized Texture in 3%Si-Fe

The phenomenon of secondary recrystallization in 3%Si-Fe under relatively high cold rolling reduction rate condition has been investigated. The texture of the secondary recrystallized sample under 97.2% cold rolling reduction rate condition consists of {110} orientation, which is quite different from Goss ({110}) orientation obtained under lower cold rolling reduction rate conditions. As a result of Grain Boundary Character Distribution (GBCD) analysis on primary recrystallized texture, {110} orientation has the highest frequency of High Energy (HE) boundary with misorientation angle between 20° and 45°. This result demonstrates that the orientation, which has the highest frequency of HE boundary in primary recrystallized texture, is selected during secondary recrystallization. However, as a result of GBCD analysis based on Coincidence Site Lattice (CSL) boundary, Goss orientation has the highest frequency of S9 (CSL) boundary in the primary recrystallized texture throughout all cold rolling conditions.

Influence of High-Mobility Boundaries on the Selective Growth of Goss Grain in Grain-Oriented Electrical Steel

Behavior of the selective growth of Goss grains in grain-oriented electrical steel was investigated by controlling the heating rate in secondary recrystallization annealing．It was clarified that the important factors on the selective growth of Goss grains were the frequency and the mobility of grain boundary. It was demonstrated that boundaries having misorientation angle between 30 degree and 35 degree had the greatest influence on the selective growth, and the change of crystal orientation of secondary recrystallized grains expected by analyzing the change of primary recrystallized texture during secondary recrystallization annealing showed good agreement with the experimental result.

Cold-Rolled Micro-Texture in Polycrystalline 3%Si-Fe

Cold-rolled micro-texture of polycrystalline 3%Si-Fe was investigated using high-resolution Electron BackScattering Patterns (EBSP) method. There were deformation bands near grain boundaries. The orientation relationship between the deformation bands and the surrounding deformed grains is explained by the orientation rotation around a <211> axis. The activated slip to generate these deformation bands is estimated from the <211> rotation. The S-value, which is a geometrical index of slip operation against applied stress, of this slip system was not maximum value of all, but it had a common slip plane with an adjacent grain. A hypothesis that the slip system having a common slip plane with an adjacent grain is activated was proposed from the present results.

Effect of grain orientation on magnetic properties in secondary recrystallized 3% Si steel

Abstract The influence of continuous changes in crystal orientation inside grains of grain-oriented 3% Si steel sheets on their magnetic properties was investigated. It was demonstrated that the changing rate of β (tilt angle of [001] out of the sheet plane) inside a grain is determined by the the radius of curvature ( R ) in coils at the secondary recrystallization annealing, and that the average β over the whole sheet increases as R decreases. The increase in β strongly affected the domain structure and hence the magnetic properties. A minimum iron loss was obtained at the value of R at which the average β was about 2°, even when β changed inside grains.