Tkachuk E. Physical basis of the anisotropy of fracture of the metal polycrystals in an aggressive environments

The thesis was first carried out a comprehensive study on the causes and patterns of emergence and development of the anisotropy of fracture of structural steels in corrosive environment due to the crystallographic texture and anisotropy of the coercive force of sheets and tubes. Found that the crystallographic texture, formed in sheets and tubes made of structural steel used in oil and gas transportation, is inhomogeneous over the cross section. In the near-surface layers formed tend the torsion texture of the {011} <100>. In the middle layers at the same time develops the typical deformation texture with the main component of the {001} <110> and additional {112} <110> + {111} <110>. It is shown that the main cause of the anisotropy of layered brittle fracture in sheets and tubes of low carbon and alloy steel is the component of deformation texture {001}<110> due to the fact that the {001} cleavage planes are the principal, along which facilitated the spread of laminated brittle cracks and corrosion. Emergence of corrosion cracks is caused by increased solubility of interstitial elements - primarily hydrogen and carbon - in a highly distorted crystallites texture component {111} <110 - 112> and the formation of methane. It was found that the inhomogeneity of plastic deformation through the wall thickness of pipe of steel 15Kh5M promotes of forming of heterogeneous texture, an additional distortion of the crystal lattice, which leads to the acceleration of local corrosion attack. For steel coils 05kp and made of it piece of pipe and tube samples deformed by internal pressure by 8% and 18%, established a linear correlation between the coercive force Hc in the rolling direction (RD) and the transversal direction (TD) and of pole density of inverse pole figures and a broadening of the diffraction lines with increasing deformation. The increase of the coercive force is caused by the work of reversal of crystals (that prior to the application of a magnetic field are oriented along the easy magnetization axes <100>) by applying an external magnetic field in the hard magnetization directions <110> oriented in the RD, and <222> and <211> oriented in the direction perpendicular to it, and as a result of comminuting of regions of coherent scattering and growth of micro stresses in the corresponding crystallographic directions.