Errosion-corrosion critical performance of surface nanocrystalline 20 carbon steel in condensate water

In this paper, the ultrasonic shot peening (USSP) technology was used to obtained surface nanocrystalline of 20 carbon steel. The grain size of test surface and the thickness of nanocrystallization layer were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The three electrode electrochemical measurement was employed to investigate the electrochemical corrosion performance and the critical character of USSP surface nanocrystallization samples in different impact strength. The results showed that the USSP surface nanocrystallization could obtain the nanocrystalline grain. The thickness of nanocrystallization layer increased and grain sizes reduced with the increase of the impact strength. Nanocrystallization layer took the way to expand concentric circles with impact crater as the center. The corrosion current of nanocrystallization sample was much larger than as-received. The controlled step of corrosion process was turned from cathodic process to anodic process by USSP surface nanocrystallization. The sample surface formed two layers corrosion product films in condensate water, which were compact Fe₃O₄ membrane as inner corrosion product film and loose Fe₃O₄ membrane or Fe₂O ₃ membrane as outer layer. With the increase of the impact strength, critical velocity of the outer corrosion product film increased gradually. The critical velocity of inner corrosion product film had an increasing trend, but the critical velocity tended to be a constant value when impact strength was more than 1.9904min/cm²