Publications

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The objective of this project is to measure the hydrogen-affected fracture properties of structural welded metals exposed to hydrogen isotopes. The main goal of FY16 was to evaluate low-temperature effects on fracture properties of stainless steel welds pre-charged with hydrogen. Forged stainless steels consisting of 316L, 304L, and 21-6-9 welded with 308L filler metal were pre-charged and tested at 223 K at select displacement rates to evaluate fracture behavior over the lower STS temperature range. Reductions in fracture thresholds were observed for all stainless steel welds when samples were precharged with hydrogen; however, temperature effects were not observed in the 304L and 21-6-9 welds. Only 316L exhibited enhanced degradation at 223 K. In addition to fracture testing, tensile specimens were extracted from the weld region and tested at 296 K and 223 K in the hydrogen pre-charged condition. A slight increase in yield strength was measured in the pre-charged condition at 296K and 223 K for the three different welds. A reduction in total elongation of 3-11% was observed at 296 K, whereas reductions in total elongation from 50-64% were observed at 223 K. Microhardness and ferrite numbers were measured in the weld regions to try to elucidate the factors affecting fracture. Lastly, in collaboration with Savannah River National Laboratory (SRNL), weld and heat-affected zone bend specimens extracted from forged 304L and 21-6-9 stainless steel were supplied to SRNL and are in the final stages of sample preparation for subsequent tritium exposure, aging, and fracture testing. The collection of testing completed and planned between Sandia and SRNL contributes to the development of a comprehensive database of properties for materials as a function of hydrogen-isotope concentrations.

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The primary objective of this effort is to identify alloys to replace type 316/316L in hydrogen service for balance of plant (BOP) applications onboard fuel cell electric vehicles (FCEVs). Type 316/316L austenitic stainless steels are used extensively in hydrogen systems for their resistance to hydrogen embrittlement, which is attributed to the relatively high nickel content of type 316/316L alloys. Nickel content, however, drives the cost of austenitic stainless steels, thus type 316/316L alloys impose a cost premium compared to similar alloys with lower nickel content. Since the cost of BOP components is a large fraction of the cost of hydrogen fuel systems (even dominating the cost at low production volumes [1]), alternative materials are desired. In addition, type 316/316L alloys are relatively low strength, thus high-pressure components tend to be heavy to accommodate the stresses associated with the pressure loads. Higher-strength materials will reduce weight of the components (an added benefit for onboard components) and contribute to lower cost since less material is needed. However, engineering data to justify selection of lower cost and higher strength alloys for high-pressure hydrogen service are currently unavailable. Moreover, alloy design could enable low cost solutions to the specific needs of onboard hydrogen storage.

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