Papers by Keyword: Si Steel

Abstract: During abnormal grain growth, a few Goss grains grow exclusively fast and consume the matrix grains. The Goss abnormally-growing grain (AGG) has peculiar features which are irregular grain boundaries and very high frequency of peninsular grains nearby the growth front of AGG and island grains trapped inside AGG. These features might provide a clue for clarifying the mechanism of Goss AGG. The experimentally-observed microstructural feature and grain boundary characterization of Goss were approached by the solid-state wetting mechanism. In this study, observing the three-dimensional wetting morphology in serial section images of Goss AGG by EBSD, we report some direct microstrucrual evidence supporting solid-state wetting mechanism for Goss AGG. The solid-state wetting mechanism for the evolution of the Goss AGG in Fe-3%Si steel explains the microstructural features evolved during secondary recrystallization, which cannot be approached by the conventional theories based on the grain boundary mobility.

Abstract: The static continuous cooling transformation (CCT)curves of 3.15 Si-0.036 C-0.21 Mn-0.008 S-0.008 N-0.022 Al are measured on Gleeble-3500 thermal mechanical simulator, the evolution of microstructure and the tendency of hardness are investigated by optical microscope (OM) and hardness tester. The results show that there is no evident change in microstructure which mainly are ferrite and little pearlite under different cooling rates, but the transition temperature of ferrite is gradually reduced with the increase of cooling rate. When the cooling rate is increased from 0.5°C/s to 20°C/s, the ending temperatures of phase transformation are decreased by 118°C, when cooling rate reaches to 10, Widmanstatten ferrite appears. The hardness of the steel turns out gradual upward trend with the increase of cooling rate.

Abstract: The selective abnormal grain growth (AGG) of Goss grains in Fe-3%Si steel was investigated using a parallel Monte-Carlo (MC) simulation based on the new concept of sub-boundary enhanced solid-state wetting. Goss grains with low angle sub-boundaries will induce solid-state wetting against matrix grains with a moderate variation in grain boundary energy. Three-dimensional MC simulations of microstructure evolution with textures and grain boundary distributions matched to experimental data is using in this study.

Abstract: In order to verify the origin of Goss nuclei for secondary recrystallization in Fe-3%Si steel, the effect of cold-rolling direction on the secondary recrystallization was examined in this study. The cold-rolling direction was rotated through 0 ~ 90 degrees about the hot-rolling direction on normal direction axis of hot-rolled sheet. In spite of the different initial texture before cold rolling, the 88% cold rolled texture was formed by similar α and γ fiber regardless of the rotation of cold rolling direction. Likewise, regardless of the cold rolling direction, the primary recrystallized sheets had a similar texture. In particular, the area fraction of Goss component (tolerance angle within 15º) in the primary recrystallized sheets was increased in the cold rolling condition of rotating through 60, 90 degrees from the hot rolling direction. After high temperature annealing at 1200°C, the secondary recrystallized grain was fully evolved in the all conditions. The sharpness of Goss texture in secondary recrystallized sheet was decreased as increasing the rotation angle of cold rolling direction.

Abstract: The process of hot rolling Fe-3.15% Si steel is simulated by Gleeble-3500 thermal mechanical simulator, the influence of finishing temperature, coiling temperature and cooling rates after rolling on microstructure of Fe-3.15% Si steel are mainly researched, and the influence of hot rolled microstructure on Goss texture, secondary recrystallization and magnetic property are analysed. The results show that the nonuniform microstructures of hot rolled strip play an important role in developing the perfect secondary recrystallization. Fe-3.15% Si steel is rough rolled at 1110°C, finished rolled at 880°C, subsequently cooled to 550°C for coiling at rate of 10°C/s, then air cooled to room temperature. The above mentioned process could produce hot-rolled microstructure which are benefit to formation of Goss texture and the development of perfect secondary recrystallization.

Abstract: Fracture behaviour transitions due to change in the strain rate in steels with various Si content ranging from 2% to 5 wt% were studied. Room-temperature tensile tests were conducted over wide range of strain rates ranging from 10-3 s-1 to 103 s-1. Concerning of the steels with low Si content (no more than 3%), the nominal stress - nominal strain curves represented both uniform and local elongations at all strain rates. On the other hand, in 4% Si steel at a strain rate higher than 101 s-1, the tensile sample broke down without local elongation (necking). The stress at breaking was found to be nearly equal to its work hardening rate. The strain rate at which fracture behaviour transition took place in 5% Si steel (10-1s-1) was lower than that in 4% Si steel. TEM observations clarified the existence of deformation twins in the sample that fractured without necking. These results indicated that Si addition is subject to the brittle fractures and that the fracture mechanism transition is closely related with the deformation twinning behaviour.

Abstract: In order to investigate the feasibility of spray forming process for production of high Si steel sheets, 4.8~6.4%Si steels were prepared by spray forming process using N2 and Ar gases and their cold workability was compared with that of conventional ingot cast samples. Atomizing gas affected significant effect on deposit features, microstructural characteristics and mechanical properties of the spray formed high Si steels.