Role of Twinning and Transformation in Hydrogen Embrittlement of Austenitic Stainless Steels

摘要

Internal hydrogen embrittlement may be viewed as an extreme form of environmental embrittlement that arises following prolonged exposure to a source of hydrogen. Smooth bar tensile specimens of three stainless steels saturated with deuterium (approximately 200 mol D sub 2 /m exp 3 ) were pulled to failure in air at 200 to 400 exp 0 K or in liquid nitrogen at 78 exp 0 K. In Type 304L stainless steel and Tenelon ductility losses are a maximum around 200 to 273 exp 0 K; Type 310 stainless steel is not embrittled at this hydrogen concentration. A distinct change in fracture mode accompanies hydrogen embrittlement, with fracture proceeding along coherent boundaries of pre-existing annealing twins. This fracture path is observed in Tenelon at 78 exp 0 K even when hydrogen is absent. There is also a change in fracture appearance in specimens with no prior exposure to hydrogen if they are pulled to failure in high-pressure hydrogen. The fracture path is not identifiable, however. Magnetic response measurements and changes in the stress-strain curves show that hydrogen suppresses formation of strain-induced alpha '-martensite at 198 exp 0 K in both Type 304L stainless steel and Tenelon, but there is little effect in Type 304L stainless at 273 exp 0 K. (ERA citation 03:001148)