EFFECT OF HYDROGEN ON THE MECHANICAL BEHAVIOR OF AISI 4340 AND SA372 STEELS

摘要

This work addresses selection of candidate materials for use as pipelines and storage tanks at distribution systems to support developing the infrastructure necessary to promote sustainable energy management via the hydrogen economy. Air and vacuum-melted AISI 4340 (containing 1.65-2.00% Ni) and SA372 Grade J Class 70 (no nickel) alloy steels, which were first copper plated and annealed, were analyzed to study the effects of hydrogen-charging on its mechanical properties. Hydrogen-charging results in significant decrease in strength of air-melted 4340 steel, increase in strength of vacuum-melted 4340 steel, and no significant change in the strength of SA372 alloys; while it always leads to reduced ductility as measured by the reduction in area. Results show that statistically there is no significant change in the modulus of elasticity. However, on an average, it appears that hydrogen charging increases the stiffness of 4340 steels by 3.4 to 7.8% for vacuum and air-melted steels, respectively, where as it tends to decrease the stiffness of SA372 alloy steel by 5.2%. While copper-plating does not affect the UTS, yield strength, strain to failure or the reduction in area, it has the ability to retain hydrogen concentration within the specimen. Although techniques have been developed to diffuse the samples with hydrogen, it is not clear where the hydrogen gas is stored: at the grain boundaries of the copper-metal interface or at the defects. Finally, air-melted 4340 alloys were found to hold significantly more hydrogen than vacuum-melted 4340 while SA372 alloys tend to retain minimal amounts of hydrogen gas.