Effect of microstructure on hydrogen embrittlement of weld-simulated HSLA-80 and HSLA-100 steels

HSLA-80 and HSLA-100 steels have been subjected to weld-simulated grain-coarsened heat-affected zone (GCHAZ) and grain-refined heat-affected zone (GRHAZ) treatments at peak temperatures of 1350degreesC and 950degreesC, respectively, followed by varying cooling rates to approximate the weld heat inputs of 10 to 50 kJ/cm. Subsequent slow strain rate testing in synthetic seawater has been employed to assess the hydrogen embrittlement (HE) propensity of the materials. It is indicated that in spite of an increase in strength after weld simulation, further ductility deterioration, compared to the base material under similar testing conditions, did not occur in GCHAZ HSLA-100 steel and for low heat input condition of GRHAZ HSLA-80. This has been attributed to their HE resistant microstructures. Predominant acicular ferrite or lath martensite or a combination of both imparts resistance to HE, as observed in the case of grain-coarsened HSLA-100 and for the low heat input grain-refined HSLA-80 steels. The deleterious effect of bainitic-martensitic microstructure has been reflected in the ductility values of grain-coarsened HSLA-80, which is in agreement with the observation of higher susceptibility of the as-received HSLA-100 steel having a similar structure. However, contrary to its beneficial effect in the as-received HSLA-80, an acicular ferrite structure has shown vulnerability toward HE for high heat input grain-refined HSLA-80. This has been attributed to the presence of polygonal ferrite and to the development of an HE susceptible substructure on GRHAZ weld simulation.