Studies On Effect Of Cathodic Polarization On The Susceptibility To Hydrogen Embrittlement Of590High-strength Steel And Welded Pieces

590high-strength steel with high strength and good weldability is widely appliedin the field of marine engineering and shipbuilding.590high-strength steel which isserviced in the marine environment is imposed cathodic protection to suppresscorrosion.However,cathodic protection is so negative that it can generate hydrogen onmetal surfaces,enter into the interior of materials and lead to the occurrence ofhydrogen-induced embrittlement even broken.Therefore,it is important to studysensitivity to hydrogen embrittlement of590high-strength steel in seawater.Theelectrochemical properties and the hydrogen diffusion coefficient of590high-strengthsteel are studied under different cathodic protection through the use of weightlessnessexperiments, slow strain rate test, hydrogen permeation experiments, electrochemicalexperiments and surface analytical tools.Susceptibility to hydrogen embrittlement ofweldments(submerged arc welding,manual welding,gas welding with argon as aprotective gas)of590high-strength steel is studied in seawater by the evaluation indexof the elongation and hydrogen coefficients.The study of electrochemical properties of590high-strength steel under differentcathodic polarization potentials in seawater shows that a layer of white protective filmis generated on the metal surface when the cathodic polarization potential is-0.85V~-1.1V.With the increasing polarization potential(Ecorr~-0.95V),the whiteprotective film is more dense and more stable.The corrosion of590high-strength steelis inhibited for the white protective film which makes the potential of corrosionnegative shift and has the current of cathodic polarization reduced.Study of hydrogenpermeation test results shows that polarization current density and apparent solubilityof590high-strength steel increase with cathodic protection potential negative shift while the diffusion coefficient which is2.8×10-6mm2/s or so on is slightly changed inseawater.The study of the reasonable potential range of cathodic protection of590high-strength steel by testing protection degree and coefficient of hydrogenembrittlement shows that the corrosion rate with cathodic protection potentialnegative shift becomes smaller while protection degree becomes larger.When thepotential is-0.758V,protection degree of590high-strength steel is90%,so the mostpositive protection potential is-0.758V.With cathodic protection potential negativeshift, elongation and reduction rate of area of590high-strength steel reduced.Whencathodic protection potential is-0.945V, hydrogen embrittlement coefficient of590high-strength steel is25%and the fracture type is mainly brittle fracture,so the mostpositive protection potential is-0.945V.The study of susceptibility to Hydrogen embrittlement of three590high-strengthsteel weldments under different polarization potentials in seawater shows thatcathodic polarization has little affected on yield strength, tensile strength and tensilestrength while cathodic polarization has significantly affected on the elongation andhydrogen embrittlement coefficient.With cathodic protection potential negative shift,the elongation reduced,but the sensitivity to hydrogen embrittlement and hydrogenembrittlement coefficient both increased.When cathodic protection potential is-0.907V, hydrogen embrittlement coefficient of submerged arc welding of590high-strength steel is25%and materials are in the danger zone of hydrogenembrittlement. Polarization potential of manual welding and gas shielded arc weldingentering into the danger zone of hydrogen embrittlement respectively are-0.958Vand-0.937V.