Development of the high-strength ductile ferritic alloys via regulating the intragranular and grain boundary precipitation of G-phase

A typical G-phase strengthened ferritic model alloy (1Ti:Fe-20Cr-3Ni-1Ti-3Si, wt.%) has been carefully studied using both advanced experimental (EBSD, TEM and APT) and theoretical (DFT) techniques. During the classic "solid solution and aging " process, the superfine (Fe, Ni)(2)TiSi-L2(1) particles densely precipitate within the ferritic grain and subsequently transform into the (Ni, Fe)(16)Ti6Si7-G phase. In the meanwhile, the elemental segregation at grain boundaries and the resulting precipitation of a large amount of the (Ni, Fe)(16)Ti6Si7-G phase are also observed. These nanoscale microstructural evolutions result in a remarkable increase in hardness (10 0-30 0 HV) and severe embrittlement. When the "cold rolling and aging " process is used, the brittle fracture is effectively suppressed without loss of nano-precipitation strengthening effect. Superhigh yield strength of 1700 MPa with 4% elongation at break is achieved. This key improvement in mechanical properties is mainly attributed to the pre -cold rolling process which effectively avoids the dense precipitation of the G-phase at the grain boundary. These findings could shed light on the further exploration of the precipitation site via optimal processing strategies. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.