Crystallographic details of precipitates in Fe-22Cr-21Ni-6Mo-(N) superaustenitic stainless steels aged at 900 degrees C

Citation
Th. Lee et al., Crystallographic details of precipitates in Fe-22Cr-21Ni-6Mo-(N) superaustenitic stainless steels aged at 900 degrees C, MET MAT T A, 31(7), 2000, pp. 1713-1723
Citations number
44
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science",Metallurgy
Journal title
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN journal
1073-5623 → ACNP
Volume
31
Issue
7
Year of publication
2000
Pages
1713 - 1723
Database
ISI
SICI code
1073-5623(200007)31:7<1713:CDOPIF>2.0.ZU;2-T
Abstract
Crystallographic features of second phases and the effect of nitrogen addit ion on the microstructural evolution in superaustenitic Fe-22Cr-21Ni-6Mo-(N ) tall in wt pet) stainless steels during isothermal aging at 900 degrees C were investigated using scanning electron microscopy (SEM) and transmissio n electron microscopy (TEM). Both alloys with and without nitrogen containe d sigma phase and M23C6 carbides in the solution treated condition. While f our phases (sigma, M23C6, M6C, and chi) of intermetallics and carbides appe ared sequentially as a function of aging time in the nitrogen-free alloy, t wo nitrides (Cr2N and AIN) were additionally observed after long time aging of the nitrogen-containing alloy. The addition of nitrogen into Fe-22Cr-21 Ni-6Mo steel promoted a finer and more uniform distribution of precipitates during isothermal aging. The exact identification and crystallography of v arious second phases were confirmed from the analyses of selected area diff raction patterns from various orientations, stereographic projection, and e nergy dispersive spectroscopy. The orientation relationships between the pr ecipitates and austenite matrix can be summarized as follows: (1) two carbi des (M23C6 and MBC): cube-on-cube orientation relationship; (2) chi phase: Kurdjumov-Sachs (K-S) orientation relationship; (3) two nitrides (Cr2N and AlN): (11 (2) over bar 0)(nitrides) //(211)(gamma) and [0001](nitrides) //[ (1) over bar 11](gamma), and (4) sigma phase: (1) ((1) over bar 11)(gamma)/ /(00 (1) over bar)sigma and [<(11)over bar>0](gamma)//[<(11)over bar>0](sig ma) or (2) ((1) over bar 10)(gamma)//((1) over bar 10)(sigma) and [<(11)ove r bar>2](gamma)//[113](sigma). For the sigma phase, the former orientation relationship was predominant throughout aging, and the latter orientation r elationship was occasionally observed under limited aging conditions.