In order to better understand the formation mechanism of tertiary oxide scale in high-strength steel during hot rolling, the microtexture of the oxide layer has been characterized and analyzed by the electron backscatter diffraction (EBSD) method. The results show that the Fe₃O₄ phase in the oxide layer has a two-phase heterogeneous morphology, Fe₃O₄ in the oxide layer comprises columnar grains, and Fe₃O₄ near the substrate comprises spherical grains. As the reduction rate increases, the Fe₂O₃ layer is gradually wedged into the surface of the Fe₃O₄ layer. Fe₃O₄ forms a fiber texture at a reduction rate of 10%. The inner layer of the oxide scale comprises spherical grains, and Fe₃O₄ is preferentially nucleated and precipitated in the direction of Fe surface grains texture. With the increase in the reduction rate, the {112}<−1−21> directional slip system shows the lowest Schmidt factor value, so the grains with a low Schmidt factor exhibit higher stored strain energy. The formation of the spherical Fe₃O₄ seam layer close to the steel matrix is the result of the combined effect of the stress state at the matrix and ion diffusion.

Rotary ultrasonic machining (RUM), a hybrid machining process that combines diamond grinding and ultrasonic machining, has been utilized as a cost-effective material removal method for hard-to-machine materials such as advanced ceramics. In this study, the stress and deformation fields in a ceramic workpiece (92% Al2 O3 ) and the formation of edge chipping during RUM process are investigated using finite element method. Based on a simplified model of RUM process, a three-dimensional finite element model is constructed using axisymmetric eight-node quadrilateral element. In the finite element model, the areas of the workpiece bottom surface that are in contact with the fixture are defined as boundaries of zero displacement in normal direction. A static load is applied to the cutting zone, which is the contact area between the tool’s end face and the bottom surface of the machined slot in the workpiece. The value of the load is calculated from experimental measurements using a dynamometer. Using this model, the maximum von Mises stresses are computed. Initiation and location of the crack, which leads to chipping in RUM process, are also analyzed and compared with experimental results observed under a microscope.