Study on the Surface Stainless-Steel-Like Alloying of Commercial Iron

By means of high energy shot peening (HESP) to a commercial iron cylinder, a nanocrystalline surface layer without oxidation, porosity and contamination was obtained. And at 500 degrees C Cr and Ni was diffused to the nanocrystalline surface layer under 50 MPa pressure in a vacuum furnace 12 h, which lead to an alloying layer with composition closed to stainless steel formed on commercial iron. The microstructure and corrosion properties of the nanocrystalline surface layer and alloying layer was characterized through microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical measurement system. Experimental results show that under the condition of 0.6 MPa shot pressure and 10 min shot time, a self-nanocrystallized layer with an average grain size of 34.6 nm and a 0.0273% microstrain is obtained by HESP. Because of large number of grain boundaries, Cr and Ni are diffused into commercial iron to form stainless-steel-like alloying layer. The corrosion potential of the layer is -0.565 V which is larger than that of commercial iron and nanocrystalline surface layer, indicating that the corrosion properties of the commercial iron is enhanced due to stainless-steel-like alloying treatment.