Interaction between hydrogen and defects in AISI 304 stainless steel was investigated by positron annihi- lation lifetime and coincidence Doppler broadening (CDB) measurements. Hydrogen was electrochemically charged into the annealed stainless steel samples in 0.5 mol/L H2SO4 solution for 1h at different current density. Experimental results show that mean lifetime τ

second lifetime component τ2 and its intensity I2 increase with current density. This means that hydrogen-induced defects are created in the annealed stainless steel samples. Furthermore

the CDB ratio curves (ratio to annealed sample) show that the enhancement in the low-momentum region (less than 5×10-3 m0c) af- ter hydrogen-charging denotes that the positrons are trapped in hydrogen-induced defects

which is consistent with the result of positron lifetime. It is interestingly found that an obvious peak appears in the high-momentum region after hydrogen-charging

and the peak site doesn’t vary with current density. This suggests that hydrogen might interact with vacancy and become the center of vacancy accumulation

leading to the formation of vacancy-hydrogen com- plexes

which results in the change of chemical environment of defects.