Precipitation behavior in G-phase strengthened ferritic stainless steels. (15th February 2021)

• Record Type: Journal Article
• Authors: Yang, Mujin; King, Daniel.J.M.; Postugar, Ivan; Wen, Yuren; Luan, Junhua; Kuhn, Bernd; Jiao, Zengbao; Wang, Cuiping; Wenman, M.R.; Liu, Xingjun
• Is Part Of: Acta materialia. Volume 205(2021)
• Publication Date: 2021-02-15
• Subjects: Ferritic stainless steel -- Aging hardening -- Nano-precipitation -- G-phase -- Atom probe tomography; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2020.116542
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: A series of G-phase strengthened ferritic stainless steels Fe-20Cr-3Ni-3Si-X (X = 2Mn, 1Mn-2Ti, 1Mn-2Nb and 1Mn-2Ta) are characterized after aging using experimental (microhardness, TEM and APT) and theoretical (DFT) techniques. The results indicate that the Ni16 Mn6 Si7 G-phase shows sluggish precipitation during aging treatment. This was attributed to the small difference in the enthalpy of formation between the Ni16 Mn6 Si7 G- and BCC phase and the requirement of high Ni:Fe ratio. A superfine Ni16 Ti6 Si7 G-phase was found to precipitate as a core accompanied with an "envelope" of Fe2 TiSi-L21 Heusler phase during early aging (≤24 h) in the Ti containing alloy. This morphology is predicted to occur due to early Ni clustering in ferrite and a negative Ni concentration gradient away from the cluster that favors Fe2 TiSi formation. The G-phases show only particle coarsening without obvious chemical composition evolution for further aging up to 96 h. A prominent hardness increase of 100-275 HV was also observed during aging. These findings provide valuable insight into methods for precipitating low lattice mismatch silicide phases for the development of future high strength steels. Graphical abstract: Image, graphical abstract