The Evolution of the Segregation Behavior of Alloying Elements in a Low-Alloy Steel

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The segregation of alloying and impurity elements to prior austenite grain boundaries (PAGBs) in low-alloy steels controls temper-embrittlement although the precise microchemical and microstructural interactions are, as yet, unclear because of the many variables involved. Competing segregation and de-segregation phenomena are observed. For example, Auger analyses of fracture surfaces indicate that brittle fracture is caused by the segregation of P to the PAGB. The addition of small amounts ({approx} 0.5 wt%) of Mo appears to regard, but not stop, temper-embrittlement, possibly due to Mo{sub 2}C precipitates that form at elevated temperatures causing de-segregation of Mo from the PAGB. The relationship ... continued below

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378 Kilobytes pages

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Papworth, A.J.; Knorr, D.B. & Williams, D.B. August 21, 2002.

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The segregation of alloying and impurity elements to prior austenite grain boundaries (PAGBs) in low-alloy steels controls temper-embrittlement although the precise microchemical and microstructural interactions are, as yet, unclear because of the many variables involved. Competing segregation and de-segregation phenomena are observed. For example, Auger analyses of fracture surfaces indicate that brittle fracture is caused by the segregation of P to the PAGB. The addition of small amounts ({approx} 0.5 wt%) of Mo appears to regard, but not stop, temper-embrittlement, possibly due to Mo{sub 2}C precipitates that form at elevated temperatures causing de-segregation of Mo from the PAGB. The relationship between segregation and temper embrittlement is further complicated in commercial alloys by both the number of segregating elements and the complex, multi-stage heat treatments. Auger analysis pre-selects the most embrittled boundaries and so the complete distribution of segregants across all PAGBs cannot be determined by this technique. Previous work has shown how X-ray mapping (XRM) in a field-emission gun scanning transmission electron microscope (FEG-STEM) offers a more complete view of the distribution of segregants on both non-embrittled and embrittled PAGBs. XRM was used to observe the evolution of the segregation and desegregation of five elements during four successive heat-treatment stages of commercial low-alloy steel forging. In the last and crucial temper-embrittlement stage, increases in the degree and frequency of Ni segregation occur while other elements either segregate, remain constant or desegregate from the PAGBs.

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378 Kilobytes pages

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OSTI as DE00820718

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  • Other Information: PBD: 21 Aug 2002

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  • Report No.: LM-02K058
  • Grant Number: AC12-00SN39357
  • DOI: 10.2172/820718 | External Link
  • Office of Scientific & Technical Information Report Number: 820718
  • Archival Resource Key: ark:/67531/metadc740021

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  • August 21, 2002

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  • Oct. 18, 2015, 6:40 p.m.

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  • March 24, 2016, 9:16 p.m.

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Papworth, A.J.; Knorr, D.B. & Williams, D.B. The Evolution of the Segregation Behavior of Alloying Elements in a Low-Alloy Steel, report, August 21, 2002; United States. (digital.library.unt.edu/ark:/67531/metadc740021/: accessed July 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.