The corrosive-aggressive downhole environment and cyclic loads are among the most common factors that affect running condition and service life of tubing pipes. Long-term operation in these settings causes aging processes, accompanied by metal degradation and a decrease in the level of its properties. In our present study we investigate microstructure of low-carbon steel AISI 1020 which is widely used in tubing pipes manufacture and establish the influence of plastic deformation (stretching) on a significant change in coercive force. The scientific novelty of our paper consists in the way the degradation of the pipe steel is investigated: we experimentally model the development of diffusion processes in the structure under cyclic stretching similar to that in operation under the load of an entire column. We use both optical-mathematical and EDS structure analyses in order to identify the degradation. The observed structural changes determine the level of coercive force, which can be effectively used to evaluate the degradation degree of the pipe material in operation. The surface extrusion zones have been detected, which include carbide-type phases with different carbon content, solid non-metallic inclusions, oxides, and, presumably, areas where spontaneous transformation of metal into powder occurred. Such zones appear due to plastic deformation in the original and deformed samples. In the near surface region post deformation, a quasi-homogeneous structure without pearlite is observed with an equal amount (~7.0%) of point carbides and a transition phase of the ferrite type that is maximally saturated with carbon (colour 155). Carbon content within the main ferrite (86%) varies. Based on the obtained results, for the effective use of pipe material in operation, we discuss the importance of taking into account both the initial state of the material and the degree of its initial deformation when developing further technological processes, which brings additional practical value to our study.