Effect Of Pearlite Tailored On HIC Sensitivity And Hydrogen Diffusion Behavior Of Pipeline Steel

Hydrogen-induced cracking(HIC)is one of the main failure modes of pipeline steel in service.In this paper,electrochemical hydrogenation technology,electrochemical hydrogen charging,hydrogen microprint technique,SSRT and other experimental methods are used to investigate the hydrogen capture behavior of pipeline steel.Hydrogen capture effect and HIC crack propagation was observed by OM?SEM/EBSD and TEM tests.The effect of pearlite on the initiation and propagation of hydrogen induced cracks in pipeline steel at different strain rates was discussed.The results showed that:(1)The hydrogen capture efficiency of F/P and F/Fe3 C interfaces will be affected by volume of pearlite.The larger volume fraction of pearlite in the sample is,the more F/Fe3 C interface and F/P interface are.At the same time,the concentration of irreversible hydrogen will increase,which would reduce the hydrogen diffusion coefficient in pipeline steel.Due to the large number of small angle grain boundaries and dislocations near the F/P interface,the hydrogen capture efficiency of F/P interface is higher than that of F/Fe3 C interface.(2)Different morphology of pearlite leads to different hydrogen induced crack initiation and propagation mode.The interface between lamellar pearlite and ferrite had higher interface energy and stress concentration contributes to the initiation of hydrogen induced crack at ferrite/pearlite interface and the propagation along F/P interface.Because of the discontinuous distribution of cementite in the degenerated pearlite,the hydrogen pressure is dispersed,the nucleation of hydrogen induced crack and HIC sensitivity decreases.(3)According to the dynamic hydrogen charging experiments,when the strain rate is large,the action time of stress on the movement of hydrogen atom is shorter,the content of diffusing hydrogen atoms are less.Resulting in the lower concentration of hydrogen in pearlite and the weaker elongation loss of the material.When the strain rate is small,the action time of stress on the movement of hydrogen atom is longer,more hydrogen atoms move to ferrite/pearlite interface through dislocation,and are trapped by it.As a result,the strength of the interface decreases,and the crack propagates along the ferrite/pearlite interfaces and exhibits a brittle mode.