EBSD investigation of microstructure evolution during cryogenic rolling of type 321 metastable austenitic steel

Ainur Aletdinov, S. Mironov, G. Korznikova, Tatyana Konkova, Rida Zaripova, Michail Myshlyaev, S. Lee Semiatin

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Abstract

Electron backscatter diffraction (EBSD) was employed to establish microstructure evolution in type 321 metastable austenitic stainless steel during rolling at a near-liquid-nitrogen temperature. A particular emphasis was given to evaluation of microstructure-strength relationship.As expected, cryogenic rolling promoted strain-induced martensite transformation. The transformation was dominated by the γ→α′ sequence but clear evidence of the γ→ε→α′ transformation path was also found. The martensitic reactions were found to occur almost exclusively within deformation bands, i.e., the most-highly strained areas in the austenite. This prevented a progressive development of deformation-induced boundaries and thus suppressed the normal grain-subdivision process in this phase. On the other hand, the preferential nucleation of martensite within the deformation bands implied a close relationship between the transformation process and slip activity in parent austenite grains. Indeed, the martensite reactions were found to occur preferentially in austenite grains with crystallographic orientations close to Goss {110}<100> and Brass {110}<112>. Moreover, the martensitic transformations were governed by preferential variant selection which was most noticeable in ε-martensite. The sensitivity of the martensitic reactions to the crystallographic orientation of the austenite grains resulted in re-activation of the transformation process after development of a deformation-induced texture in the austenitic phase at high strains. Both martensitic phases were concluded to experience plastic strain which resulted in measurable changes in misorientation distributions. Cryogenic rolling imparted dramatic strengthening resulting in a more-than-sixfold increase in yield strength. The main source of hardening was the martensitic transformation with lesser contributions from dislocations and subboundary strengthening of the austenite.
Original languageEnglish
Pages (from-to)460-473
Number of pages14
JournalMaterials Science and Engineering: A
Volume745
Early online date27 Dec 2018
DOIs
Publication statusPublished - 4 Feb 2019

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Keywords

  • electron microscopy
  • iron alloys
  • nanocrystalline materials
  • plasticity methods
  • grains and interfaces
  • phase transformation

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