Effect of fluctuant load frequency on stress corrosion cracking behavior of X70 steel welded joint

The stress corrosion cracking(SCC)behavior of X70 steel welded joint was investigated in a near-neutral pH solution by fluctuant slow strain rate test(F-SSRT).The test results indicate that X70 steel has certain SCC sensitivity in specific near-neutral pH solution under fluctuant tension load and cathodic potential(-850 mVSCE).Under fluctuant slow strain rate test(F-SSRT),the mechanism of crack growth of the steel is obviously different from that of slow strain rate test(SSRT).The SCC crack in F-SSRT is able to initiate from the tiny hole in the surface,and when the fluctuation frequency is up to some extent,the SCC cracks propagate along 45 degree direction to the maximum shear stress plane.Overheated zone of X70 welded joint is SCC sensitive zone under cathode potentials in the near-neutral solution.The effect and mechanism of hydrogen in the SCC initation and growth are analyzed.