Influence Mechanism of Different Heat-Treated Microstructures on the Hydrogen Permeation Behavior and Hydrogen Diffusion Paths in X52 Pipeline Steel

Electrochemical hydrogen permeation tests were employed to evaluate the hydrogen permeation behavior of X52 pipeline steel (for hydrogen-blended natural gas service) under different heat treatment temperatures, and hydrogen microprint technique was used to observe hydrogen diffusion paths. The results indicate that hydrogen primarily diffused along nonmetallic inclusions, pearlite, and grain boundaries in X52 steel. For slowly cooled specimens, the pearlite content decreased with increasing temperature, leading to a corresponding reduction in hydrogen permeability, solubility, and reversible hydrogen trap density. In contrast, for rapidly cooled specimens, the increase in heat treatment temperature raised the size and volume fraction of martensiteaustenite (MA) constituents in the microstructure, which significantly enhanced the hydrogen trap density.