Research On Effect Of Plastic Deformation On Hydrogen Damage Behavor Of High Strength Steel

As a kind of serious defects of high strength steel and ultra high strength steelgenerated in the welding process, hydrogen induced cracking made the weldmaterial occurred in the period of time after the low stress brittle fracture. Studyon the hydrogen diffusion and aggregation behavior in material, was conducive tothe prevention and control of hydrogen induced crack. The hydrogen in steel wasdistributed in irreversible defect, reversible defects and lattice space. Plasticdeformation made the dislocation and reversible defect density increased. It helpedto deepen the understanding of hydrogen induced cracking through the hydrogenconcentration after the plastic deformation in the material.30CrMnSiNi2A of high strength steel after plastic deformation was moresensitive to hydrogen induced cracking and hydrogen bubbling while hydrogendiffusion and aggregation in steel. The more hydrogen filled in steel, the enhancedtrend was more obvious, and from ductile to brittle fracture more quickly.Hydrogen made fracture position transfer from the base metal to heat affected zoneof30CrMnSiNi2A steel joint under the condition of tensile, as the residual stressdeformation were concentrated in he weld zone and heat affected zone.The electrochemical experiments about hydrogen permeation of compressionsamples in high temperature and tensile samples in room temperature of30CrMnSiNi2A steel were carried out and the critical hydrogen concentration andthe average reversible hydrogen concentration in different compression rate andelongation of high strength steel after hydrogen permeation were calculated. Theresults showed that the hydrogen pressure converted from the critical hydrogenconcentration of cold crack was much lower than the fracture strength of30CrMnSiNi2A steel, and the relationship between the average hydrogen pressureand plastic deformation rate was not clear.The stress effect of hydrogen pressure in the defects surrounding of hole andcrack in the linear elastic conditions were obtained by using the finite elementmethod respectively. The stress intensity factor near the crack tip when the cracklength was2mm or1.8mm and the crack tip had the effect of hydrogen pressure or no effect of hydrogen pressure was calculated. The idea that let the outer tensilestress instead of hydrogen pressure at the crack tip and the calculation of stressintensity factor was proposed. It was verified that the idea was feasible, as thestress intensity factor was proportional to the applied tensile stress and hydrogenpressure, and the proportional coefficient was fixed in the same conditions ofcrack size.