低碳钢超声喷丸表面纳米化的研究

A nanocrystalline surface layer was fabricated on a 20 steel plate by using an ultrasonic shot peening (USSP) technique. The USSP induced surface nanocrystallization products were characterized by means of XRD and TEM. Experimental evidences showed that after the USSP treatment for a short period of time, the initial coarse-grained structure in the top surface layer was refined into ultrafine grains. The mean grain size in the surface layer is about 10 nm and the mean microstrain about 0.02%-0.04%. The thickness of the nanocrystalline surface layer is about 10 μm, which is dependent on the treatment duration. It was also found that the metastable phase Fe₃C in the surface layer decomposes into nanometer-sized graphite and α-Fe phases after the USSP treatment.