ABSTRACT

Stainless steels such as grade 316 are commonly used in various hydrogen applications, and the hydrogen embrittlement (HE) resistance of these steels is well-established. However, the high degree of alloying, particularly nickel, required to achieve the stable austenitic microstructure drives their relatively high cost and is a potential barrier to future implementation of a broad hydrogen infrastructure. The objective of a program including the efforts reported here is to develop lower cost steel alloys with high performance, through novel microstructural design, for use in hydrogen refueling infrastructure such as storage, compressors, and dispensing components. We are employing manganese (Mn) substitutions for nickel to produce both fully austenitic and duplex austenite-ferrite microstructures and evaluating potential alloy and microstructure design alterations through thermomechanical processing to enhance the HE resistance of the designed high Mn alloys. HE sensitivity of the high Mn (20-30 wt pct) steels in comparison to commercial 316L austenitic and 255 duplex stainless steels was investigated by means of rising displacement testing of circumferentially notched tensile specimens during in situ electrochemical hydrogen charging. Both austenitic and duplex microstructures produced in high Mn alloys exhibited promising toughness in hydrogen results, as compared to the stainless steels.

INTRODUCTION

Stainless steels, e.g. 316 austenitic stainless steel, are commonly used in various hydrogen (H) delivery and storage applications, and the H embrittlement (HE) resistance of these steels is well-established. However, the alloying, particularly nickel (Ni), required to achieve the stable austenitic microstructure drives their relatively high cost and is a potential barrier to broad implementation of extensive infrastructure for the H economy. Figure 1 shows a plot of fracture toughness in H, KIH or KJH, versus yield strength for both austenitic stainless steels and lower alloy ferritic steels. For a given yield strength, austenitic steels have a greater fracture toughness in hydrogen than the ferritic counterparts. The gap between the two trend lines represents a development opportunity to produce lower cost alloys compared to more costly austenitic stainless steels with enhanced performance compared to ferritic steels.

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