Studying The Effect Of Cathodic Polarization On The Susceptibility Of 907 Steel To Hydrogen Embrittlement

High strength steels are applied in weeks of airplane, boat, marine structure for its excellent capability. The susceptibility to hydrogen embrittlement increases with intensity inhancement of high strength steel. Cathodic protection is always used to contral general corrosion of high strength steel in marine. The application of cathodic protection can lead to the formation of hydrogen at the metal surface,this can result in hydrogen embrittlement. The application of high strength steels is more and more wide as the ocean stratagem is carried out.The question cathodic protection induces hydrogen embrittlement stands out increasingly。Cathodic protection is always used uniforming with organic coating and it is useful. Hence, there is more important practical signification to study the effect of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel with epoxy coating. So it's necessary to study effect of cathodic polarization on the susceptibility to Hydrogen Embrittlement of high strength steels and confirm appropriate potential of cathodic protection for a particular high strength steel-environment combination.It is studied in this work that effect of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel with and without epoxy coating , by means of slow strain rate test method and electrochemical study. Fractography is made by Three-dimension Microscope and SEM. The rule of polarizing impedance and current in different phases and characters of fracture face are studied too.Base on this effect of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel with and without epoxy coating is comparede and effect mechanism of cathodic polarization and epoxy coating on the susceptibility to hydrogen embrittlement of 907 steel is investigatied.The investigation of effect of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel without epoxy coating shows that the elongation, time-to-fracture, and fracture energy decreased and hydrogen embrittlement coefficient increased with shifting potential in the negative direction, the susceptibility to hydrogen embrittlement boost up. But intensity criterions don't present disciplinarian variation with shifting potential. Polarizing impedance of four deforming phases monish with shifting potential in the negative direction. When applying potential is -1.01V versus a saturated calomel electrode., fracture face presents the character of cleavage brittle; when it is -1.06V, hydrogen embrittlement coefficient enter danger zone of HE during service, the fracture is brittle.The effect of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel with perfect coating and 5% coating defect is studied. The results show that the law of mechanics criterion and polarizing impedance of everyr deforming phase is same with that of 907 steel without coating. For 907 steel covered with perfect coating when applyied potential is -0.91V, fracture face presents the character of cleavage brittle; when it is -0.96V, hydrogen embrittlement coefficient enter rapidly danger zone of HE during service, 70% of fracture face is the character of cleavage brittle.For 907 steels with 5% coating defect it's -1.01V that hydrogen embrittlement coefficient enters rapidly danger zone of HE.Compare and contrast effects of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel with and without coating, it shows that the susceptibility to hydrogen embrittlement and loop current enhance when shifting potential in the negative direction.Applied potential range from -0.91V, at the same potential, the current of 907 steel with perfect and defect coating is less than that of 907 steel without coating, but the susceptibility to hydrogen embrittlement is higher. Hence,effect of cathodic polarization on the susceptibility to hydrogen embrittlement of 907 steel with coating is more distinct and 907 steel with perfect coating is easier to hydrogen embrittlement. It's likely that concentration of stresses where coating is defect and the perfect part of coating blocking hydrogen diffusion outside, they accelerate hydrogen diffusion into matal. So the concentration of hydrogen in metal arrive at critical value, crake gestatesand enlarge until hydrogen embrittlement occers.