Hydrogen permeation of two kinds of ferritic steel with different level of 2nd phase particles are compared utilising electrochemical permeation technique evaluated under various loads. This study indicates that tensile stress in plastic domain induces expansion of the interface between the 2nd phase particles and steel matrix, and formation of blister crack. Such microstructuraldiscontinuity provides additional hydrogen traps, resulting in slower diffusion and lower steadystate permeation flux. These phenomena appear predominantly in steel containing coarse-sized inclusion and precipitate having sharp extremities. The numerical analysis also supports that the steel containing coarse-sized 2nd phase particles with sharp extremities exhibits higher parameters of hydrogen capture rate per irreversible traps and blister crack formation rate than the steel containing fine-sized ones with spherical shape.

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