Investigation into the Influence of Jet Cavitation Impact on Changes in Characteristics of the Surface of Structural Steel 30L and 20GL

The work is devoted to the study of the dynamics of changes in the surface roughness of structural steels 30L and 20GL under the cavitation effect of a liquid jet during tests according to the ASTM G134-17 standard. The research method was based on the study of the parameters of the relief and the dynamics of destruction of the near-surface layer of steel samples using metallographic analysis and the construction of 3D maps of worn surfaces. The kinetic curves of wear are presented, the change in fractograms and surface topography with increasing testing time is analyzed. Based on the change in the surface profile and the evaluation of the roughness parameters, the wear kinetics of the studied steels is revealed. It is shown that, in the period of time characterized by the maximum wear rate, there is a sharp increase in roughness after the end of the incubation period and a slowdown in growth upon reaching fluctuating, almost constant values of its parameters at a steady wear rate. The obtained range of roughness parameters in the region of the cavitation cavity of 15–20 µm for steel 30L and 20–25 µm for steel 20GL during the period with a steady wear rate can be due to the removal of a layer of constant thickness, depending on the microstructure of the materials under study. The results of the work can be used to predict the cavitation destruction of elements of hydraulic turbines and centrifugal pumps made of cast steels, based on fixing changes in the roughness parameters of their functional surfaces during operation.