Hydrogen Evolution of 17-4PH Stainless Steels

The hydrogen evolution transforming potential and current density of hydrogen evolution at -1.10 V (vs. SCE, the same below) polarization potential of 17-4PH stainless steels with two distinguishing strength were studied using electrochemical test method. Hydrogen charging test was used to study the hydrogen contents of the alloys after 15 days of hydrogen charging at -1.1 V polarization potential. The slow strain rate tests were used to evaluate the hydrogen embrittlement susceptibility of 17-4PH alloys with or without hydrogen charging. The results show that the hydrogen evolution transformed potentials of both 17-4PH stainless steels in seawater were about -0.90 V. The low strength 17-4PH strainless steel had a hydrogen content of only 2.55×10-4mass%, while the high strength stainless steel had a hydrogen content as high as 6.84×10-4mass%. The strainless steel with high strength showed a significant increase in brittleness after hydrogen charging, while the change in low-strength stainless steel was much smaller. The high strength stainless steel had a hydrogen embrittlement coefficient more than 25%, which means the steel is among the risky range of hydrogen embrittlement; while the low strength stainless steel had a hydrogen embrittlement coefficient about 18%, which means the steel is in riskless range of hydrogen embrittlement.