Effect of hydrogen on the corrosion behavior of X80 pipeline steel joints with high-power laser welding

Abstract A single-pass laser welding process was conducted on a 20 mm thick X80 pipeline steel plate utilizing a 30 kW ultra-high-power fiber laser. The study investigated the effects of various welding process parameters on the microstructure, mechanical properties, and corrosion resistance of the welded joints. The electrochemical method was employed to assess the hydrogen absorption capacity of both X80 pipeline steel and its welds under electrochemical hydrogen charging conditions. Additionally, the corrosion behavior of X80 steel and its welds in a 3.5% NaCl solution following electrochemical hydrogen charging was examined by x-ray diffraction and x-ray photoelectron spectroscopy. The results indicate that the microstructure of weld zone primarily consists of ferrite and bainite. The hardness value in this region decreases progressively with increasing laser power, exhibiting the highest hardness at the bottom section along the thickness direction. Additionally, tensile strength diminishes as laser power increases, with peak values observed in the middle section of the thickness direction. Notably, the mechanical properties of these joints are significantly enhanced compared to those of the base metal. In terms of corrosion resistance, welds demonstrate slightly inferior performance relative to that of the base metal; furthermore, their corrosion resistance declines with rising laser power. Both diffusible hydrogen concentrations in the base metal and welds exhibit a similar upward trend as hydrogen charging time extends. A saturation level for diffusible hydrogen concentration is reached after 12 h of charging. Under identical hydrogen charging conditions, larger grain sizes and an increased number of hydrogen traps within the weld render it more susceptible to hydrogen absorption than its base metal counterpart. In terms of the impact of hydrogen on corrosion behavior, an increase in both the hydrogen charging current density and the duration of hydrogen charging exacerbates the corrosion characteristics of both the base metal and weld. Furthermore, it is observed that the corrosion resistance exhibits minimal variation with prolonged hydrogen charging time. Moreover, under equivalent conditions, electrochemical responses reveal that welds are less affected by hydrogen charging compared to base metals; thus indicating superior corrosion resistance for welds over their corresponding base metals. The corrosion products observed before and after hydrogen charging are primarily composed of α -FeOOH, α -Fe 2 O 3 , and γ -FeOOH. Following hydrogen charging, the welds exhibit a relatively higher content of α -FeOOH, which serves to impede matrix corrosion to some extent.