Effect of Microstructure and Trapping on the Hydrogen Embrittlement Susceptibility of a Ti-Bearing HSLA Steel

摘要

The general hydrogen embrittlement susceptibility of a titanium-bearing HSLA steel has been characterized and correlated with detailed transmission electron and field ion microscopic studies of various microstructures. The hydrogen permeability and trapping in the same microstructures has also been studied through the use of electrochemical polarization and potentiostatic detection. The trapping character of the various microstructures has been determined by comparison with the TEM and FIM results. Hydrogen embrittlement susceptibility has been determined by the use of cathodically precharged cylindrical tensile specimens and hydrogen induced cracking of double cantilever beam type fracture mechanics specimens. The hydrogen permeability studies showed that austenitized and quenched microstructures were composed of essentially low interaction energy reversible trap sites for hydrogen including but not restricted to grain boundaries, solute elements and dislocations. Aging at temperatures between 400 deg C and 500 deg C still resulted in a reversible trap population, although the character of trapping was inferred to have shifted to higher capture-to-release rates from examination of the form of the transient hydrogen exit flux. The introduction of cementite in these microstructures was assumed to be responsible. At aging temperatures of 600 deg c and higher, irreversible trapping of hydrogen was found to occur concurrently with the direct precipitation of the alloy carbide, TiC.