Surface Nanocrystallization of 35# Type Carbon Steel Induced by Ultrasonic Impact Treatment (UIT)

A nanostructured surface layer was fabricated on 35# type carbon steel plate by using ultrasonic impact treatment (UIT) technique. The micro-structural features of the surface layer produced by UIT were characterized by optical microscopy (OM) observations, X-ray diffraction (XRD) and transmission electron microscopy (TEM), and hardness measurement was carried out in order to examine the hardness variation along the depth. Experimental results showed that the thickness of the plastic deformation layer varies from a few to about 100μm depending on the duration of UIT. Obvious grain refinement was observed and the gain size was about 10nm in the top surface layer. After UIT, the micro-hardness of the surface layer was enhanced significantly compared with that of the original sample, and the hardness increased when the duration of UIT increased.