Precipitation sequence and its effect on age hardening of alumina-forming austenitic stainless steel

Abstract

The precipitation sequence during ageing of Fe-14Cr-20Ni-0.9Nb-2.5Al based alumina-forming austenitic (AFA) steel was explored through a transmission electron microscopy analysis and a small angle neutron scattering experiment. The samples were aged at 700 degrees C for up to 504 h. Particles of NbC, M23C6 and Ni3Al-type L1(2) were observed in the early stage of ageing. Metastable L1(2) particles were-formed both in grain interior and along grain boundary. M23C6 carbides precipitated along grain boundary accompanied with precipitation of L1(2) particles. After ageing for longer than 48 h, particles of B2-NiAl and Laves-Fe2Nb were newly formed. We suggest the possibility of phase transition from L1(2) to B2 with increase in ageing time. Finally, this study examined the change of mechanical properties during ageing through a Gleeble hot tension test and a Vickers hardness test, and then the relationship between precipitation behavior and mechanical properties was carefully investigated and discussed in terms of precipitation behavior. (C) 2015 Elsevier B.V. All rights reserved.