The effect of ultrasonic impact-frictional treatment on the surface roughness and hardening of 09Mn2Si constructional steel

Abstract

The paper compares the strengthening of constructional steel 09Mn2Si achieved by traditional ultrasonic impact treatment (UIT), and, the new method of ultrasonic impact-frictional treatment (UIFT), proposed by the authors. UIT is usually performed normally on the surface of the part with lubrication in the contact zone. The idea of UIFT is based on plastic shear deformation, activated by the friction effect of impulse impacts at a certain angle to the surface to be processed. In order to raise the friction coefficient, UIFT is performed without lubrication. It is shown that a decrease in the load application angle to the sample surface (α) increases the depth and hardness of the deformed surface layer of 09G2S structural steel. At the same time, the strengthening effect of treatment in the range of angles of 90 -70° mainly manifests itself in a thin (a few microns) near-surface layer, and the surface roughness remains almost unchanged. A further decrease in the angle increases the contribution of the friction component. Thus, UIFT at α = 50° gives the depth of the deformed layer 1.5 times, and the surface hardness is 2.5 times higher than after the traditional UIT. It was found that the profile of the pile-ups behind a moving instrument changed from symmetrical after UIT to shifted in the impact direction after UIFT, which led to a twofold increase in surface roughness for α = 50°. It was established that reduction of the UIFT scanning step from 0.2 mm to 0.1 mm (load of 149 N and processing speed of 600 mm/min), improved the surface roughness R a by a factor of 5 from 3.9 μm to 0.7 μm. A further decrease in the scanning step resulted in a surface coarsening due to fatigue degradation.