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

DE2004820718

Publication Date	2002
Personal Author	Papworth, A. J.; Knorr, D. B.; Williams, D. B.
Page Count	10
Abstract	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.
Keywords	Low alloy steels Segregation Alloys Steels Impurities Embrittlement Grain boundaries Fractures Heat treatment Temper embrittlement
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Lehigh Univ., Bethlehem, PA. Materials Research Center.; Department of Energy, Washington, DC.; Lockheed Martin Electronics Labs., Syracuse, NY.
Supplemental Notes	Prepared in cooperation with Lockheed Martin Electronics Labs., Syracuse, NY. Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200413

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

Evolution of the Segregation Behavior of Alloying Elements in a Low-Alloy Steel.
DE2004820718

Publication Date	2002
Personal Author	Papworth, A. J.; Knorr, D. B.; Williams, D. B.
Page Count	10
Abstract	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.
Keywords	Low alloy steels Segregation Alloys Steels Impurities Embrittlement Grain boundaries Fractures Heat treatment Temper embrittlement
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Lehigh Univ., Bethlehem, PA. Materials Research Center.; Department of Energy, Washington, DC.; Lockheed Martin Electronics Labs., Syracuse, NY.
Supplemental Notes	Prepared in cooperation with Lockheed Martin Electronics Labs., Syracuse, NY. Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200413