Effect of Microstructures on Hydrogen Induced Cracking Behavior of Ultra-low Carbon X80 Pipeline Steel

Normalizing and quenching treatment were carried out on ultra-low carbon X80 pipeline steel, and then the influence of microstructures on the hydrogen-induced cracking behavior of the steel was investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction (EBSD) technology. The results show that the tested steel before heat treatment owned acicular ferrite structure, and its HIC resistance was better than the HIC resistance of polygonal ferrite structure after normalizing and bainite ferrite structure after quenching. The uniform distribution of high and low angle grain boundaries was of benefit to the improvement of HIC resistance of the test steel,meanwhile high density low-angle grain boundaries could prevent the extend of hydrogen induced crack.