Investigation on the hydrogen induced cracking behaviour of heat-treated pipeline steel.

• Heat treatments reduced the hydrogen induced cracking sensitivity (HIC) of pipeline steel, increasing the ductility of steel and decreasing the number and the size of surface HIC microcracks. • Compared with water cooling, air cooling promoted the formation of precipitated phase in steel, which promoted the formation of deep hydrogen trap. • Air cooling process reduced concentration of diffusible hydrogen and the degree of local distortion of steel. In this paper, the hydrogen induced cracking (HIC) sensitivity of the austenitized Cu-containing pipeline steels after cooling processes in air and water conditions was evaluated. Microstructural test, as well as hydrogen-charging slow strain rate tensile test and hydrogen concentration tests were conducted. Results indicated that steels after both cooling processes exhibited lower HIC sensitivity compared to the untreated steel. Elongation and percentage reduction of area after the hydrogen-charging slow strain rate tensile tests were increased. This was related to the formation of strong hydrogen trapping sites and the decrease of weak hydrogen trapping sites such as high-angle grain boundaries. Moreover, the TDS test results confirmed the presence of more stable hydrogen trapping sites in air-cooled steel than water-cooler steel. The latest phenomenon effectively hindered the diffusion behaviour of hydrogen in steel and reduced the HIC sensitivity. [ABSTRACT FROM AUTHOR]