Metallurgy of Oriented Silicon Steels

Abstract

For the past twenty‐five years, a single oriented silicon steel containing 3% silicon has been commercially produced. The crystallographic description of this material is usually given as (110)[001]. It is now generally agreed that this texture occurs because of a preferred type of secondary recrystallization occurring at temperatures above 950°C. The primary recrystallization texture contains only a small fraction of the (110)[001] component which forms from a (111)[112] deformation texture. In order to complete the orientation process by secondary recrystallization, various impurities have been suggested. These impurities are in the form of a second phase. However, manganese sulphide has been found to be the most effective for providing conditions for selective growth of the (110)[001] component. Furthermore, at the desirable annealing temperatures, sulfur is rapidly lost by diffusion, thus, the final product is highly oriented and has excellent properties because of the low impurity level. More recently, a cube texture (001)[100] has also been made by at least two techniques. By controlled columnar freezing of the ingot, a type of 〈001〉 fiber texture can be produced. If this structure is carefully cold rolled and annealed, eventually a primary recrystallization (100)[001] texture will result. Alternately the cube texture can also be achieved by a controlled surface energy reaction causing a secondary recrystallization. The primary recrystallization texture necessary for the production of a highly oriented product is obtained by rolling and annealing a (110)[001] type of orientation. The secondary growth of the (100)[001] grain is controlled by surface and grain boundary energies. A critical amount of sulfur is required in the steel to initiate the cube grains. However, an excess of either sulfur or oxygen will prevent the growth process. Elimination of oxygen to the lowest possible levels will favor cube growth providing that the sulfur content is in a critical concentration range. If the sulfur content drops to too low a level, cube grain growth will also cease. The range of sulfur required for cube growth is orders of magnitude below the reported level of solid solubility.