Cathodic charging of notched 304 austenitic stainless steel specimens was carried out in aqueous solution of 1N H.$O, containing 250 mg/l NaAsO, at room temperature and 70 *2 C while undergoing tensile straining over a wide range of crosshead speed (833 urn/s, 83 urn/s, 8.3 urn/s, 833 nmis, 83 nmfs and 9.8 rims).. Test at room temperature 22 X! C resulted in a marked reduction in the elongation to fracture ratio (Esol/Eair) by reducing the crosshead speed. However, little reduction was observed in the stress to fracture ratio (osol/oair). Quasi cleavage and intergranular fractures where the predominant failure modes when tests were carried out at low crosshead speeds, The extent of these modes of fracture was observed to increase by reducing the crosshead speed.
Cathodic charging of 304 austenitic stainless steel at 70 f2 C caused less reduction in the elongation to fracture ratio compared to the tests carried out at room temperature. Consistent with the room temperature test results, the reduction in the elongation to fracture ratio was found to increase with reduced crosshead speed. However, restoration in the elongation to fracture ratio was exhibited by 304 austenitic stainless steel specimens tested at the lowest crosshead speed (9.8 nm/s). These results are in good agreement with the finding that hydrogen embrittlement is temperature and strain dependent.
Quasi cleavage fracture associated with the plastic deformation was the predominant failure mode exhibited by 304 austenitic stainless steel specimens tested at 70 *2 C at low crosshead speeds.
Austenitic stainless steels have good resistance to hydrogen embrittlement and therefore they are frequently chosen as suitable materials in environments containing hydrogen. However, a number of studies have shown that austenitic stainless steels are susceptible to hydrogen embrittlement, though not to the extent of ferritic stainless steels. This is due to the differences in solubilities and difisivities of hydrogen within these two alloy (1) classes.
For austenitic stainless steels, it has been established that the degree of embrittlement in tensile tests increases as the time of hydrogen charging increases and is dependent on strain rate and temperature.(?) The most severe embrittlement was observed to occur at (2) low strain rates and at temperatures below or at room temperature. Despite many previous studies on hydrogen induced cracking in austenitic stainless steels, there are no reliable, consistent or uniform data about the effect of hydrogen on the mechanical properties as function of strain rate and temperature.
The effect of hydrogen on the mechanical properties (ductility and strength) and change of the fracture morphology for 304 austenitic stainless steel as function of temperature and strain rate (crosshead speed) will be presented and discussed.
Experiment
A commercial 304 austenitic stainless steel specimens with the required dimensions were machined from 0.8 mm thick sheet supplied in the annealed condition. A 60 V notch were machined at the middle of all tested specimens in order to promote the initiation and propagation of a single crack to enable convenient investigation of the tested specimens as seen in Figure 1. In order to remove the stresses induced during sp
