THE EFFECT OF INTERSTITIAL N ON GRAIN BOUNDARY COHESIVE STRENGTH IN Fe

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Increased nitrogen levels have been correlated with decreased ductility and elevated ductile-to-brittle transition temperature in pressure vessel steels [1]. However, the exact role played by nitrogen in the embrittlement of steels remains unclear. Miller and Burke have reported atom probe ion microscopy findings from neutron-irradiated low-alloy pressure vessel steel showing the presence of a 1 to 2 ruonolayer thick film of Mo, N, and C at prior austenitic grain boundaries (GB's) [2], suggesting a role for nitrogen as an intergranular embrittler. It is of interest for the development of mitigation strategies whether nitrogen must combine with other impurities to form ... continued below

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Miyoung, Kim; Gellar, Clint B. & Freeman, A. F. September 22, 2003.

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  • Bettis Atomic Power Laboratory
    Publisher Info: Bettis Atomic Power Laboratory (BAPL), West Mifflin, PA
    Place of Publication: West Mifflin, Pennsylvania

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Increased nitrogen levels have been correlated with decreased ductility and elevated ductile-to-brittle transition temperature in pressure vessel steels [1]. However, the exact role played by nitrogen in the embrittlement of steels remains unclear. Miller and Burke have reported atom probe ion microscopy findings from neutron-irradiated low-alloy pressure vessel steel showing the presence of a 1 to 2 ruonolayer thick film of Mo, N, and C at prior austenitic grain boundaries (GB's) [2], suggesting a role for nitrogen as an intergranular embrittler. It is of interest for the development of mitigation strategies whether nitrogen must combine with other impurities to form nitride precipitates in order to exert an embrittling effect. Briant et al [1] have associated the embrittling effect of N in steels exclusively with intergranular nitride formation. This association suggests that high nitrogen levels may be acceptable if nitride precipitation at grain boundaries is suppressed. To address whether precipitate formation is indeed essential to the N embrittlement process in pressure vessel steel, a computational study was undertaken to ascertain whether the presence of interstitial nitrogen alone could embrittle an Fe GB. If so, nitrogen in any form must be kept completely away from the grain boundaries, if not out of the material altogether. The effect of interstitial N on the cohesion of an Fe {Sigma}3[110](111) grain boundary (GB) was investigated by ab-initio electronic structure calculations to reveal that free interstitial N produces a large strengthening energy, reduces the magnetic moments of the GB Fe atoms and is embrittling at the GB's.

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6 pgs / 705 KB

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  • Report No.: B-T-3517
  • Grant Number: DE-AC11-98-PN38206
  • Office of Scientific & Technical Information Report Number: 940235
  • Archival Resource Key: ark:/67531/metadc898777

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  • September 22, 2003

Added to The UNT Digital Library

  • Sept. 27, 2016, 1:39 a.m.

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  • Feb. 20, 2017, 2:54 p.m.

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Miyoung, Kim; Gellar, Clint B. & Freeman, A. F. THE EFFECT OF INTERSTITIAL N ON GRAIN BOUNDARY COHESIVE STRENGTH IN Fe, report, September 22, 2003; West Mifflin, Pennsylvania. (digital.library.unt.edu/ark:/67531/metadc898777/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.