Study On Corrosion And Hydrogen Embrittlement Of Dissimilar High Strength Steel Welded Joints

Nowadays,dissimilar steel welded parts are often used as structural materials to meet the application requirements and reduce the production costs in many engineering fields such as ship,and the cathodic protection technology is widely used to restrain the steel corrosion in sea water.But inappropriate protection potential would lead to hydrogen induced failure of material.In this paper,the welded joints of dissimilar highstrength steel with yield strength of 800~1000 MPa was studied using the hydrogen permeation test,electrochemical measurement,slow strain rate test and fracture morphology analysis,combined with metallographic observation,scanning kelvin probe test and full immersion corrosion test,and its hydrogen permeation,hydrogen embrittlement sensitivity and corrosion behavior of materials in sea water were investigated.The analysis results of dissimilar steel welded joints corrosion performance showed that the corrosion resistance of high-strength steel base metal(1000 MPa grade steel)was the best in the welded joints,and the corrosion resistance of the weld zone was between the two kinds of base materials,while the HAZ were more vulnerable to corrosion,which may be related to carbide precipitation and increase of lattice defects caused by the heat input in HAZ.Then the electrochemical and hydrogen permeation experiment of dissimilar steel welded joints were carried out.There was little difference in the hydrogen diffusion coefficient of the each region of the welded joints.However,the hydrogen evolution potential was the most positive and the hydrogen solubility was the largest in the HAZ,which indicated that the HAZ was easier to hydrogen evolution,and had a greater tendency to absorb hydrogen.In addition,the effect of the cathodic polarization potential on the hydrogen diffusion coefficient of the high strength steel was small,but the hydrogen solubility increases linearly with the negative shift of the polarization potential.When the sample was hydrogen charged,the self corrosion potential of each micro zone was significantly negative shifted,while the hydrogen evolution potential was positive shifted,which indicated that the corrosion resistance of the welded joints was weakened and the hydrogen evolution tendency was intensified after hydrogen charging.From the study results of hydrogen embrittlement sensitivity,it can be concluded that the polarization potential had a significant effect on the fracture property of high strength steel.With the negative shift of polarization potential,the tensile strength and yield strength of the 1000 MPa high strength steel and dissimilar steel welded joints did not change significantly.But the rate of elongation and the shrinkage of the section gradually decreased.The fracture morphology gradually changed from ductile fracture to cleavage and intergranular fracture.And the risk of hydrogen embrittlement of materials increased.The assessment results of hydrogen embrittlement coefficient showed that the most negative cathodic protection potential of 1000 MPa-grade high strength steel should not be more than-910 mV,the most negative cathodic protection potential of 0.8 strength ratio and 0.9 strength ratio dissimilar steel welded joints were-940 mV and-945 mV,respectively.At the same time,it can be concluded that dissimilar steel welding will not increase the susceptibility to hydrogen embrittlement of 1000 MPa grade high strength steel.