EFFECT OF NITROGEN ON HYDROGEN EMBRITTLEMENT OF AUSTENITIC STAINLESS STEELS BASED ON TYPE 316LN

The effect of nitrogen on hydrogen gas embrittlement (HGE) in 1 and 70 MPa hydrogen and internal reversible hydrogen embrittlement (IRRE) of austenitic stainless steels of 17Cr1 1Ni2Mo(0.4 in max.)N alloys, based on type 316LN, was investigated by slow strain rate technique tests at room temperature in comparison with the effect of Ni on HGE and IRHE of Ni-added type 316 stainless-steel-alloys. For the nitrogen-added alloys, HGE and IRHE decreased with increasing nitrogen content, where alpha' martensitic transformation occurred. HOE was not observed but IRHE was observed above the nitrogen content, where austenite is completely stabilized by nitrogen. Hydrogen-induced fracture related to the strain-induced alpha' martensite structure was observed in HGE specimens and that together with brittle transgranular fracture was observed in IRHE specimens. HGE of the nitrogen-added alloys is larger than that of the Ni-added alloys in the Ni-eq range, where alpha' martensitic transformation occurred. No HOE was observed in both the nitrogen-added alloys and the Ni-added alloys, but IRHE was observed in not the Ni-added alloys but the nitrogen-added alloys above the Ni-eq, where no martensite is identified in both alloys. It is discussed that the alpha' martensite and the austenite of the nitrogen-added alloys were