Tishkevich D. Formation of fine-grained structure and improving the properties of medium-carbon steels by severe plastic deformation

Object of study - the formation of structure and properties of steel during severe plastic deformation and subsequent heating. The aim of the thesis: increasing complex of mechanical properties and corrosion resistance of steel using new technologies to produce high-quality oil and gas pipe grades. Methods: X-ray analysis, optical, raster transmission diffraction and electron microscopy; definition of complex of mechanical properties; atmospheric corrosion tests on laboratory and field methods, determining electrochemical characteristics of steel. Theoretical and practical results: the corrosion rate of steel grade 45 was determined after severe plastic deformation (SPD) by equal channel angular pressing; the dependence of the corrosion rate of the steel was determained on heating temperature; phase and structural transformations during severe plastic deformation and subsequent heating were determined; the influence of severe plastic deformation and subsequent low temperature heating into mechanical properties of steel grade 45 were determined; technical and technological solutions which could increase lifetime of oil and gas pipe grades were developed and improved. Scientific novelty: idea of the structure formation during severe plastic deformation by equal channel angular pressing of steel grade 45 has got further development; ideas of dislocation restructuring and softening at the afterdeformation heating in low temperature area have got further development for steel grade 45 with ultra-fine grade structure formed by equal channel angular pressing; corrosive properties of steel grade 45 with ultra-fine grade structure formed by equal channel angular pressing at 400°C were identified in the first time; in the first time it has obtained the quantitive assessment of the corrosion rate depending on after deformation heating temperature of steel grade 45 with ultra-fine grade structure formed by equal channel angular pressing. Degree of implementation: Results of the thesis introduced in the educational process at the Department of Technological Design of National Metallurgical Academy of Ukraine at teaching discipline "Technological features of metal forming processes". It had been formulated the recommendations for rolling of tubes in a continuous mill with the new organization of deformation zone. The formulated recommendations submitted to the JSC "Interpipe NTZ" and taken to the introduction at the designing of section of the tube rolling on continuous mill. Scope: tubes production on continuous mill.