Microstructure and mechanical properties of Ni-free high nitrogen austenite stainless steels fabricated by mechanical alloying method

摘要

Particular attention is called to nickel-free or lower nickel austenitic stainless steels containing high nitrogen from the viewpoint of protections against earth resources and Ni allergy for human being. We have made high nitrogen steels (HNS) that were containing 0.7-2.0mass%N and 23Cr-2Mo by mechanically alloying method and the microstructure and mechanical properties have been examined. HNS containing 1.0-1.6mass%N have nearly full austenite phase and the mean grain diameter was about 2-3μm for every HNS. The strength and work hardening rate increased and the elongation decreased with increasing nitrogen content. Especially, HNS containing 1.0mass%N exhibited superior balance of strength-ductile properties, that is, yield strength of 1200MPa and fracture elongation of 36%. The yield point phenomena and ductile-brittle transition behavior can be seen in spite of austenitic stainless steels. The planar dislocation arrays were seen on the deformed structure. These results suggest that the formation of planar dislocation structure, high work hardening rate for high nitrogen steels and temperature dependence of mechanical properties might be caused by the formation of the Mo-N interstitial-substitutional atom couples.