Hydrogen Permeation Behavior Of Hot-dipped Steels In Seawater And Its Effect On The Mechanical Properties Of Steel Substrate

The security of hot-dip steels was imperiled by the synergistic action ofhydrogen permeation and stress in marine environment. In this thesis, threekinds of hot-dipped steels (Galvanized, Galfan and Galvalume) were used asinvestigative object. Potential and current density distribution around coating'sdefect in seawater were calculated by boundary element method. Hydrogenpermeation curves of these hot-dip steels were measured using a specialbipolar cell which had been designed for steel plating. The inhibition ability forhydrogen permeation and the possibility of self hydrogen permeation werecompared among these three materials, and analyzed combined with thesematerial's chemical composition and structure. Also the expressions related tohydrogen permeation process have been established. Thus the model namedas TANG-LI was developed, which adapts to evaluate the hydrogenpermeation behavior of material with coating. The kinetic parametersconcerning hydrogen permeation for the three kinds of hot-dip steels werecalculated via TANG-LI model. At last, the stress-strain behaviors of thesematerials for with and without charging hydrogen were contrasted by SSRT.Fractography were also carried out to investigate the effect of hydrogenpermeation for hot-dip coating with defect in seawater on the mechanicalproperties of steel substrate. The results showed that:⑴ Potentials around coating defect in seawater were so negative thathydrogen evaluation reaction could happen easily and hydrogen atoms couldcome into being.⑵ Hydrogen permeation inhibiting efficiency of Galvanized coating is low,and that of Galfan coating is higher a little. And when these two kinds ofcoating have defect, they can produce hydrogen atoms in seawater. On thecontrary, Galvalume coating can resist most hydrogen permeation, and it hasno self hydrogen permeation behavior even with defect. With the highercontent of aluminum and compacter structure, the coating has finer hydrogenpermeation inhibitory ability and less self permeation possibility.⑶ Self hydrogen permeation behavior of Galvanized coating in seawatercan reduce the strength of steel substrate and shift its fractured character fromductile fracture to quasicleavage fracture, thus can cause embrittlement ofmaterials. The behavior of Galfan coating can only reduce the strength but notalter the ductile fracture. Galvalume coating neither reduce strength norchange fracture property.