The Research On Stress Corrosion Cracking Mechanism Of Ustenitic Stainless Steel Under Marine Environment

At the beginning of the12thFive-Year Program(2011-2015)on NationalEconomic and Social Development, Shandong Peninsula blue economic zonedevelopment plan was adopted to be the national development strategy. A lot ofinfrastructure construction along the seashore will be built for the exploitation andutilization of marine resources. More and more stainless steel products haveapplication in shipbuilding, seawater desalination, off-shore oil platform, port and pierand so on. Stainless steel will corrode inevitably as the result of severe corrosionenvironment and stress. Besides the uniform corrosion, stress corrosion cracking(SCC) is apt to occur and brings extensive damage. So it is urgent and necessary toinvestigate the SCC of stainless steel under marine environment.The changing process of corrosion liquid film on the surface of stainless steelwas simulated in this work. The hydrogen permeation behaviors were researched byusing Devanathan-Stachurski's hydrogen permeation technique the results showedthat obvious hydrogen permeation behaviors can be observed as the development ofcorrosion liquid film. The hydrogen permeation current observed in the experimentsincreased with the rising of concentration of corrosion products.SCC sensibility of stainless steel was studied by using slow strain rate test (SSRT)and SEM. The results showed with the increasing of corrosion film concentration,SCC sensibility also increased. SCC sensibility of stainless steel was also affected byapplied potential and temperature. SCC sensibility could be repressed when cathodicpolarization potential was applied. Meanwhile SCC sensibility was obviously increased when the temperature reached to55℃.The hydrogen permeation behaviors in crack tip and crack side of stainless steelwas also studied at the process of crack propagation. The results showed thathydrogen produced by electrochemical reaction absorbed at crack side and thenmoved to crack tip under load. At last, the metal in crack tip ruptured in the style ofhydrogen embrittlement. A patent named empirical approach of detecting hydrogenpermeation current in crack tip and crack side was applied.The corrsive reactions are easy to occur in thin film than in the solution. That isbecause the oxygen in the atmosphere dissolves into the film and diffuses to thereaction interface easily. With the proceeding of the reaction, diffusion controllingprocess appears in the cathodic polarization curves. It may be the result of mass ofcorrosive production blocking the oxygen diffusing to the reaction interface.