Effect of Impact-Oscillatory Loading on the Variation of Mechanical Properties and Crack Resistance of Pipe Steel

To study a full range of the mechanical properties on small-sized flat specimens from the pipe steel, including the characteristics of crack resistance after the realization of certain loading modes, the authors used the method of complete stress–strain diagrams. This method was previously substantiated both theoretically and experimentally by professors A. A. Lebedev and M. G. Chausov for assessing the fracture kinetics of plastic materials on small specimens subjected to various types of preliminary loading. The effect of preliminary plastic deformation under static tension on changes in the crack resistance and mechanical characteristics of the pipe steel is extreme at a strain level ε_pl = 6.3%. Test results were compared at identical levels of the preliminary plastic deformation under static tension and impact-oscillatory loading at strain levels of 4.5–8.8%. The comparison showed significant differences in the effect of impact-oscillatory loading on changes in the mechanical properties and crack resistance of the pipe steel. Nanotechnologies were used to analyze the original results on the effect of preliminary plastic deformation under static tension and identical levels of dynamic deformations caused by impact-oscillatory loading on changes in the mechanical properties and crack resistance of the 17G1S-U pipe steel in the initial state. This was especially noticeable when tungsten carbide and carbon nanoparticles were used under impact-oscillatory loading. To confirm the revealed mechanical effects, detailed fractographic studies of specimen fractures were conducted along with investigations into the surface macrohardness of the steel.