Abstract
AISI 316 stainless steel, which is frequently employed in the power industry, shows considerable increases in high-temperature creep ductility when small quantities of boron are added to it. However, considerable effort by a number of researchers has failed to reveal the exact location of the boron and the mechanism by which it enhances the creep properties. The work presented herein involved the study of two casts of 316 steel with varying boron concentrations. Low-resolution location of the boron was performed by secondary ion mass spectrometry. The boron was mostly segregated to the grain boundaries of the steel. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the grain boundaries were heavily coated with precipitates of the carbide M23X6 (M = metal, X = C, B, N). These precipitates were identified by X-ray energy-dispersive spectroscopy, in both the TEM and SEM, and convergent-beam electron diffraction in the TEM. Electron energy loss spectroscopy was employed to locate the boron within the carbides. The visibility of the boron K edge was enhanced by a digital filtering technique. Detection of boron in the M23X6 precipitates has made it possible to re-evaluate previous work on this subject and the role of boron in the improvement of the creep ductility of stainless steel is suggested.
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Mansfield, J.F. Identification of boron in M23X6 precipitates in 316 stainless steel using electron energy loss spectroscopy. J Mater Sci 22, 1277–1285 (1987). https://doi.org/10.1007/BF01233121
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DOI: https://doi.org/10.1007/BF01233121