| Air-melted and vacuum-melted 4340 alloys along with SA372 Class 70 Grade J alloys were examined through tensile testing to explore the effects of hydrogen charging, annealing, and copper plating on the mechanical properties of the specimens. Results show that there was no change in modulus of elasticity throughout all the specimens, including the air-melted and vacuum-melted 4340 alloys as well as the SA372 alloys, and that annealing and hydrogen charging have similar effects on the aforementioned samples as there was a slight decrease in the yield and ultimate tensile strength. More significant changes in mechanical properties, due to hydrogen charging and annealing, were experienced in the vacuum-melted 4340 alloys in comparison to the air-melted 4340 alloys. Copper plating did not affect the ultimate tensile strength, yield strength, strain to failure or the reduction in area of the samples, thus implying the validity of copper plating to retain hydrogen concentration within the specimen. Although techniques have been developed to diffuse the samples with hydrogen, studies indicate that it is unclear as to just where the hydrogen gas is stored, whether it be at the grain boundaries of the copper-metal interface or at the defects. Results suggest that air-melted 4340 alloys are able to hold significantly more hydrogen than the vacuum-melted 4340 and the SA372 alloys tend to retain minimal amounts of hydrogen gas. As it is known that hydrogen is a very mobile gas, more control is needed on the copper coating techniques and annealing processes to ensure more repeatable and accurate results. |
