475 degrees C Embrittlement of Duplex Stainless Steel-A Comprehensive Microstructure Characterization Study


Oernek C. , Burke M. G. , Hashimoto T., Lim J. J. H. , Engelberg D. L.

MATERIALS PERFORMANCE AND CHARACTERIZATION, vol.6, no.3, pp.409-436, 2017 (Journal Indexed in ESCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 6 Issue: 3
  • Publication Date: 2017
  • Doi Number: 10.1520/mpc20160088
  • Title of Journal : MATERIALS PERFORMANCE AND CHARACTERIZATION
  • Page Numbers: pp.409-436
  • Keywords: duplex stainless steel, 475 degrees C embrittlement, microstructure characterization, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, spinodal decomposition, electron energy loss spectroscopy, secondary phases, G-PHASE PRECIPITATION, STRESS-CORROSION CRACKING, DEGREES-C EMBRITTLEMENT, R-PHASE, IMPACT TOUGHNESS, FERRITE-PHASE, DECOMPOSITION, TEMPERATURE, NITROGEN, AUSTENITE

Abstract

The effect of 475 degrees C embrittlement on microstructure development of grade 2205 duplex stainless steel was investigated. Spinodal decomposition products and associated precipitates in ferrite, austenite, and at interphase boundaries were characterized using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Microanalyses confirmed the presence of Cr-enriched alpha'' and Cr-depleted alpha' spinodal structures in the ferrite after 5 h of aging at 475 degrees C. Long-term aging for 255 h resulted in heavily-faulted R-phase precipitates with sizes of similar to 50-400 nm, chi-phase, and epsilon-Cu in the ferrite, TiN and Cr2N precipitates in the austenite, and a continuous network of M23C6-carbides at interphase boundaries. A significant hardness increase was observed after 255 h of aging, which was accompanied by a reduction of ferrite fraction. X-ray diffraction (XRD) stress measurements showed a general reduction of residual stresses in both ferrite and austenite with aging. Electron backscatter diffraction (EBSD) showed increased local misorientations, primarily close to precipitate interfaces within the ferrite, indicating the development of strain heterogeneities in the microstructure. The data presented provided a better understanding of 475 degrees C embrittlement in duplex stainless steel, suggesting that not only the ferrite alone is responsible for embrittlement. A comprehensive microstructure characterization study has been provided and the explanation for 475 degrees C embrittlement of duplex stainless steel has been discussed.