Three-Dimensional Morphologies Of Goss Oriented Grains In Hi-B Steel Formed During Secondary Recrystallization Annealing

Microstructure and texture evolution of Hi-B steel have been extensively studied in the past decades,and the microstructural features are ordinarily characterized only using a single two-dimensional plane of polished or thin foil specimen.Much information on the morphologies is lost owing to the fact that a large part of microstructure is embedded beneath the polished surface,or removed during specimen preparation.Recently,computer-aided three-dimensional morphologies have been developed that can visualize microstructure in metals.In this paper,three-dimensional morphologies of different oriented grains which include Goss,Brass,{411}<148> and {111}<112> oriented grains in Hi-B steel formed during secondary recrystallization annealing were investigated by a combination of serial sectioning,computer-aided reconstruction and visualization,and electron back-scattered diffraction technique.The results show:(1)During the early secondary recrystallization annealing,Goss oriented grains mainly exhibit pagoda shape,brass oriented grains are similar to inverted taper shape,which the grain sizes reduce gradually from the surface of the sample to the internal along normal direction,and {411}<148> oriented grains also exhibit pagoda shape and inverted taper shape.However,the morphologies of {111}<112> oriented grains show irregular shape.Compared with other oriented grains,Goss oriented grains have no size advantages on three-dimensional scale,and the growth of Goss oriented grains is mainly controlled by curvature before they grow up abnormally.(2)During the late stage of the secondary recrystallization annealing,abnormal growth Goss oriented grains appear mainly in the three-dimensional morphology "gully-like" and "twin-peaked".Goss oriented grains size along ND direction dimension has reached the plate thickness,but far smaller than in the size of RD and TD direction;Goss oriented grains which are not grown abnormal are similar to the inverted taper shape and pagoda shape,the difference in the three-dimensional size is very small,the size along the RD,TD,ND is basically close to 1: 1: 1.(3)The solid-state wetting effect is not obvious in the early stage of abnormal Goss grain growth instead of the medium and late stage of abnormal growth.(4)The formation of island and peninsula grains have a completely or partiallywetted morphology,indicating that they are formed by solid-state wetting.Near the growth front of abnormal growth Goss grains,grains with the negative curvatures are three-dimensionally connected to the abnormal growth Goss grain.These grains may be island or peninsula grains in three-dimensional.