Decarburization of 3%Si-1.1%Mn-0.05%C Steel Sheets by Silicon Dioxide and Development of 100< 012> Texture

Abstract

Decarburization of silicon steel sheets by annealing with oxide separators has been found to cause a high degree of {100}-texture development. Cold-rolled Fe–3%Si–1.1%Mn–0.05%C sheets of 0.35 mm thickness were laminated with separators containing SiO2. They were then annealed under a reduced pressure at about 1300 K in a ferrite and austenite two phase region. It has been observed that carbon concentration notably decreases down to 0.001% during the lamination annealing. Thus an almost complete decarburization of sheet steels was possible, whereas no oxidation of silicon as well as manganese and iron occurred. Associated with decarburization, columnar ferrite grains grew inward from sheet surfaces due to the phase transformation from austenite to ferrite. A {100}〈012〉 texture dramatically developed in the columnar grains. Fully decarburized materials consisted of grains of 0.6 mm diameter, more than 90% of which were closely aligned with {100}〈012〉 orientation. Another aspect of great interest in the grain structure after decarburization was that there existed convoluted domains of a few mm in width, in which dozens of grains were oriented in a single variant of the texture, (100)[012] or (100)[021]. The decarburization is considered to be caused by the thermo-chemical reaction, 2C+SiO2→Si+2CO. The texture development is most likely to be due to the orientation dependence of surface free energy under an oxidation-free surface condition.