Investigation On The Corrosion Behavior Of Low Carbon Steel Induced By Surface Mechanical Attrition Treatment

The failure of metallic engineering materials mostly originated from the surface of the material. If the surface grain of metal materials can be refined to nano-scale, the overall mechanical properties and environmental service behavior of the materials can be improved by making the most of the advantages of nanocrystalline. Surface nanocrystallization was brought up in recent years, such as surface mechanical attrition treatment (SMAT), high energy shot peening (HESP) and severe plastic deformation (SPD). These technologies can all generate a nanostructured surface layer on metal materials.The nanocrystalline microstructure and properties in the surface of low carbon steel induced by surface mechanical attrition treatment has been characterized by optical microscopy (OM), X-ray diffractometry (XRD), surface rough-meter, and the effects of surface nanocrystallization technology on the surface of materials have been investigated. Then, the corrosion resistance of nanocrystalline has been measured by electrochemical test, salt spray corrosion and stress corrosion experiments. The difference of corrosion resistance of as-received and SMAT samples between the two kinds of low carbon steel (their carbon content are0.08%and0.02%, respectively) can be revealed and explained through the comparative analysis. The main experimental results are as follows:(1) The surface of low carbon steel0.08sample is relatively flat under the neutral salt spray, and etch pits on which are very few and trivial. While the corrosion degree of the surface layer of low carbon steel0.08SMAT samples is very serious, there are lots of deep corrosion ravines on it, which distribute unevenly. It shows that SMAT can reduce the salt spray corrosion resistance of low carbon steel0.08seriously. However, it can be seen that there is no difference in corrosion behavior between low carbon steel0.20sample and low carbon steel0.20SMAT sample. It can be concluded that SMAT contribute little to the corrosion resistance of low carbon steel0.20.(2) In electrochemical testing, whether in0.05mol/L H2SO4+0.05mol/L Na2SO4or in0.05mol/L H2SO4+0.05mol/L Na2SO4+0.5mol/L NaCl solution, the corrosion resistance of low carbon steel0.08all reduced greatly in the processing of SMAT, while SMAT causes no significant decrease to the corrosion resistance of low carbon steel0.20. Further experiments indicate that grain size can be the main factor for the huge gaps of the corrosion resistance of low carbon steel in the processing of SMAT.