Heat Treatment Effects on Hydrogen Exposure Mitigation for 304 Stainless Tensile Specimens

Hydrogen changes the mechanical properties of a wide range of materials, especially metallic surfaces exposed to gaseous hydrogen or hydrocarbons. Diatomic hydrogen molecules become adsorbed onto metal surfaces and dissociate into hydrogen atoms, which then dissolve into the metal and can manifest as a proton locally trapped near a dislocation. Noticeable effects of hydrogen embrittlement include a reduction in the elongation at failure, a reduction in strength, and a loss in fatigue life. The extent of the reduction in these mechanical properties depends on microstructure, stress intensity factor, diffusivity, and duration and type of hydrogen exposure. It may be possible to mitigate against some of the deleterious effects. My research goal is to investigate and characterize the effects of gaseous hydrogen exposure on the tensile properties of 304 stainless steel sheet and possible effects of heat treatment to out-gas dissolved hydrogen. Specimens will be tested in the following six conditions: as-cut from the sheet; heat treated only at 500 degrees Celsius for 30 minutes; hydrogen exposed only at 1 atm pressure for 1 week; hydrogen exposed and then heat treated; heat treated and then hydrogen exposed; heat treated, hydrogen exposed and then re-heat treated. So far my findings have shown no major difference in ultimate tensile strength in specimens that are exposed to hydrogen compared to those exposed to hydrogen and then heat treated. This could possibly be due to lack of adequate enough exposure to hydrogen to produce any noticeable weakness or simply that heat treatment does not dissolve out those particles well enough to increase strength. I will continue to research specimens heat treated and then exposed to hydrogen and heated treated both before and after to see if order makes a difference in strength