Promotion of Cubic Grain Growth in 3% Silicon Iron by Control of Annealing Atmosphere Composition

Abstract

Under certain special conditions of processing and annealing,silicon iron can be made to have cubic orientation. This phenomenon was first reported by Assmus et al. The driving force for the growth of the cubic grains has been determined by several investigators to be surface energy. We have found that by controlling the concentration of impurities in the annealing atmosphere the growth of grains having the (100) plane parallel to the sheet surface can be greatly improved. Calculations of the surface energies in the body-centered system show that the surface energy of atomic planes are (110), (100) and (111) in order of ascending values. From this orientation dependency of the surface energy, there results a discrepancy between theory and the observed fact of (100) surface energy growth. It is proposed that adsorption by the metal surface of atmosphere constituents in a very special manner can accomplish a change in relative surface energy so that the (100) plane becomes the lowest energy crystal plane. Data on some atmosphere composition effects on transformation to cube texture of silicon iron 2 to 14 mils thick were obtained. The degree of transformation was found to be closely related to the concentration of certain compounds that are added to the atmosphere. The degree of cube growth reaches a maximum at a certain small concentration of impurity. These effects were studied in both metal and ceramic annealing tubes. With proper additives excellent cube growth can be obtained in either type annealing tube.