Origin and development of through-the-thickness variations of texture in the processing of grain-oriented silicon steel

In the production of high-permeability grain-oriented silicon steel, through-the-thickness variations of texture in the hot-rolled sheet make an important contribution to the perfection of secondary recrystallization. In particular, large grains at a depth of 20 to 25 Pct of the thickness are thought to provide the nuclei for secondary recrystallization. In this report, formation of the Goss orientation in the subsurface to intermediate layer of hot-rolled sheets has been studied by rolling with a variety of draft schedules and also by rolling in a high-speed laboratory mill equipped with a means for quenching at predetermined times as short as 10 msec after rolling. Formation of a texture gradient in the hot-rolled sheet is shown to be controlled by the sequence of deformation and recrystallization during rolling. The Goss grains are found to originate from a shear deformation of ferrite crystals due to the high friction in hot rolling and to grow by a coalescence process. The effects of through-the-thickness variations of the hot-rolling texture, together with the inhomogeneities originating from the history of partial phase transformation in the hot-rolling stage, are discussed in connection with optimal selection of the processing variables leading to the perfection of secondary recrystallization, in terms of the sites providing the source of potential nuclei and those preparing the favorable surroundings for an extensive growth of the viable nuclei in the final annealing. This paper is based on a presentation made at the symposium “Physical Metallurgy of Electrical Steels” held at the 1985 annual AIME meeting in New York on February 24–28, 1985, under the auspices of the TMS Ferrous Metallurgy Committee.