Feb/March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 2 1 2 2 which include casting the molten metal in a workable form, followed by the nec- essary hot and/or cold work processes. The resulting compositional variations could influence steel characteristics such as precipitation behavior, phase transformation temperature and rates. In extreme environmental conditions such as in power plants, segregation of elements may negatively affect local corrosion properties or enhance the de- velopment of creep damage. Micro-XRF mapping is an ideal tool for investigating segregation of elements at a macro-scale. Figure 5 shows a longitudinal cross section of tube of an advanced austenitic 18Cr-9Ni-CuNbN steel (e.g., Super 304H) and results from µ-XRF analysis. Re- sults from the scan show Ni, Nb, and Cu rich bands formed along the tube axis. Using a µ-XRF line-scan performed Micro-XRF is an invaluable tool in the current suite of macro-based lab- oratory characterization. As briefly described in this article, the results ob- tained from this technology are routine- ly used to: • Perform quality assurance or op- timize welding procedures where dilution can be a significant, long- term concern to corrosion and/or high temperature performance • Inform failure analysis investiga- tions • Assess the potential heterogeneity in final product forms commonly used in the fabrication of complex components EPRI and its extended network of collaborative organizations are taking advantage of µ-XRF to better inform weld procedures, root cause, and im- prove materials or component spec- ifications. In a research setting, the routine use of µ-XRF provides a practi- cal means to interrogate a large library of samples and determine those which are most relevant for a more rigorous evaluation. Tools like µ-XRF may be in- valuable well into the future as they continue to supplement existing mi- croscopy equipment with semi-quan- titative results in the quest to solve the power generation industry’s most com- plex materials challenges. ~AM&P For more information: Tapasvi Lolla, technical leader, Electric Power Research Institute, 1300 West W.T. Harris Blvd., Charlotte, NC 28262, tlolla@epri.com . References 1. T. Lolla, et al., Delamination Failures of Stellite Hardfacing in Power Plants: A Microstructural Characterisation Study, Science and Technology of Welding and Joining, 19 (6), p 476- 486, 2014. 2. 30-Plus Years of Long-Seam Weld Failures in the Power Generation Industry—Perspective and Continuing Challenges with Life Management. EPRI, Palo Alto, CA, 3002011587, 2017. 3. S. Jabar, et al., The Effect of Micro- Segregation on the Quantification of Microstructural Parameters in Grade 91 Steel, Metallurgical and Materials Transactions A, 52, p 426- 437, 2021. Fig. 5 — Through-thickness µ -XRF elemental distribution maps from region “a” of longitudinal tube section. Fig. 6 — Line scan results showing variation in alloying elements with distance of scan. perpendicular to these bands (location identified by the yellow arrow), the dis- tribution of elements at these bands are plotted in Fig. 6. The plot suggests that bands with lower concentration of Fe appear to correspondingly have higher Ni, Nb, and Cu concentrations (marked by black arrows for convenience). In this example, µ-XRF mapping was used to determine regions with significant el- emental segregation and line scan was then used to determine the concentra- tion of alloying elements at such sites. Because local variation in compositions could influence formation and/or stabi- lization of specific phases, these results highlight the need to seek representa- tions of the actual composition range instead of simply the average (or bulk) composition for reliable thermodynam- ic predictions.