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

Abstract

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 ofmore » 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.« less

Authors:
Publication Date:
Research Org.:
Bettis Atomic Power Laboratory (BAPL), West Mifflin, PA
Sponsoring Org.:
USDOE
OSTI Identifier:
940235
Report Number(s):
B-T-3517
TRN: US200825%%791
DOE Contract Number:
DE-AC11-98-PN38206
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ATOMS; DUCTILITY; ELECTRONIC STRUCTURE; EMBRITTLEMENT; GRAIN BOUNDARIES; IMPURITIES; INTERSTITIALS; ION MICROSCOPY; MAGNETIC MOMENTS; MITIGATION; NITRIDES; NITROGEN; PRECIPITATION; PRESSURE VESSELS; PROBES; STEELS; TRANSITION TEMPERATURE

Citation Formats

Miyoung, Kim, Geller, Clint B., Freeman, A.F. THE EFFECT OF INTERSTITIAL N ON GRAIN BOUNDARY COHESIVE STRENGTH IN Fe. United States: N. p., 2003. Web. doi:10.2172/940235.
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Miyoung, Kim, Geller, Clint B., Freeman, A.F. THE EFFECT OF INTERSTITIAL N ON GRAIN BOUNDARY COHESIVE STRENGTH IN Fe. United States. doi:10.2172/940235.
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Miyoung, Kim, Geller, Clint B., Freeman, A.F. Mon . "THE EFFECT OF INTERSTITIAL N ON GRAIN BOUNDARY COHESIVE STRENGTH IN Fe". United States. doi:10.2172/940235. https://www.osti.gov/servlets/purl/940235.
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@article{osti_940235,
title = {THE EFFECT OF INTERSTITIAL N ON GRAIN BOUNDARY COHESIVE STRENGTH IN Fe},
author = {Miyoung, Kim, Geller, Clint B., Freeman, A.F.},
abstractNote = {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.},
doi = {10.2172/940235},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Sep 22 00:00:00 EDT 2003},
month = {Mon Sep 22 00:00:00 EDT 2003}
}
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DOI:  10.2172/940235
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