Shigeo Nomura1 and Masayoshi Hasegawa1
1Department of Metallurgical Engineering, School of Science and Engineering, Waseda University, Tokyo
Behavior of Fe-N alloys containing 66∼402 ppm of nitrogen under hydrogen (380°C, 200 atm) was studied by the tensile test, SEM-fractography and mass-spectroscopy. The results obtained were as follows:
(1) With increasing nitrogen content in Fe-N alloys, degradation of the tensile properties was observed at the earlier stage of holding time in hydrogen. This damage showed no recovery with a dehydrogen treatment in vacuum.
(2) The damage was accelerated with a precipitation of iron nitride, but not observed in the alloy in which nitrogen was stabilized by chromium.
(3) Many spherical voids like gas-bubble were observed at the grain boundary in hydrogen damaged Fe-N alloys.
(4) In hydrogen damaged alloys, a removal of nitrogen was observed remarkably and NH3 and H2 were detected in residual gas extracted at the intergranular brittle fracture surface. It was concluded from above results that the damage in Fe-N alloys was analogous to ``hydrogen attack'' in Fe-C alloys.
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