| With the developing of oil and gas pipeline engineering construction in China, the demand of pipeline steel increases. Since X80 pipeline steel has high strength and good tough, it is considered as the first choice of gas pipeline steel in 21 century. It has been wildly used in West-East Gas Pipeline Project in China. In the plumbing engineering, the pipeline is mainly connected by welding, which induces the forming of heat-affected zone nearby the welding joint region. Compared with the original microstructure, the crystal grain in heat-affected zone getting coarsens, the mechanical property and the anti-hydrogen induced cracking performance also changes. Therefore, the study on HIC performance of weld heat-affected zone has certain necessity and pressing.In this paper, different heat treatment were done to simulate the heat affected zone of X80 pipeline steel, based on the investigation of heat affected zone of X80 pipeline steel, CCT curve and literature. Optical microscope and scanning electron microscope were used to analyze the microstructure, inclusions and precipitates of the three different microstructures X80 pipeline steel. Hydrogen induced cracking and hydrogen permeation in H2S environment was studied to explore the relationship of microstructure and hydrogen trapping efficiency. Polarization curves and AC impedance is also used to study the electrochemical behavior of X80 pipeline steel in H2S environment. Since H2S is a toxic gas,in order to get a safe and effective method of hydrogen permeation, we simulate it by using electrochemical method based on H2S environment hydrogen permeation. The research indicated that:⑴By the heat treatment method of heat original steel to 1300oC, then air cooled and water quenched respectively, those two specimens could simulate the HAZ of X80 pipeline steel. The original microstructure is acicular ferrite, air cooling microstructure is polygonal ferrite and water quenching microstructure is lath martensite-based. The inclusion hasn't changed after the heat treatment, it mainly contains MgO,Al2O3,CaO,TiO2 and duplex inclusion. The precipitate is mainly Nb and Ti carbon nitrude.⑵The HIC test of different microstructure indicated that the HIC susceptibility of X80 steel increased after heat treatment. The crack initiated nearby the inclusions and for original and air cooled specimen, the dominant mode of crack propagation is transgranular cracking, while intergranular cracking, accompanied by little transgranular cracking, is the main cracking mode of crack propagating in the quenched specimen.⑶Hydrogen trapping efficiency of X80 steel, one of the main factors of HIC susceptibility, indicated the same pattern as HIC susceptibility. The more the value of hydrogen flux J∞, hydrogen diffusion coefficient Deff, the less pipelines steel is prone to HIC.⑷The polarization curves and AC impedance spectroscopy of water quenched X80 pipeline steel showed that, with the immersion time increased, the corrosion acceleration, it also indicated that with the increase of immersion time, the hydrogen evolution reaction at surface is easier, it will produce more H atoms into the steel matrix, promote hydrogen induced crack initiation and growth. ⑸It's a reasonable and practicable method of electrochemical hydrogen permeation by electrolyzing 0.5mol/L H2SO4 + 3.1×10-3 mol/L Na4P2O7 solutions with cathode current density of 30mA/cm2 to substitute hydrogen permeation test in NACE solutions which contained saturated H2S.
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