Microstructural characteristics of hydrogen-exposed P355NH steel and welded joints

It is known that microstructure of materials, such as material structure, grain size, orientation, crystallographic texture and dislocation density, change the mechanism and intensity of hydrogen diffusion, contribute to an increase or decrease in solubility, which significantly changes the mechanical properties of steels and leads to brittleness. In the present study, the microstructure of welded joints of steel P355NH, a typical material grade in domestic transmission lines, and GMAW and hybrid GTAW /GMAW welded joints were investigated and exposed to high pressure pure hydrogen with exposure times of 41 and 92 days. The investigations were carried out to find out the characteristic microstructural details of the base material and welded joints, and the mechanical property changes that can be observed, which can be used to infer the hydrogen susceptibility of both the base material and the welded joints.