Influence of internal hydrogen on fatigue thresholds of HSLA steel

The effect of internal hydrogen on the near-threshold fatigue crack growth behavior is investigated for an HSLA microalloyed steel with a view to separating true hydrogen effects from any closure effects. It is found that the effect of hydrogen on near-threshold fatigue crack growth is largely determined by the availability of hydrogen ahead of the growing crack. The apparent absence of enhanced cracking in gaseous hydrogen may reflect hydrogen availability, as controlled by the rate of hydrogen adsorption and by the diffusion distance in front of the crack tip. Once hydrogen becomes available at the crack tip through cathodic charging prior to testing or by an increase in triaxial stress at the crack tip, increased susceptibility to cracking is observed. 13 references