Publication Date:
2012-10-13
Description:
A centrifugally cast 20Cr32Ni1Nb stainless steel manifold in service for 16 years at temperatures ranging from 1073 K to 1123 K (800 °C to 850 °C) has been characterized using scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), auger electron spectroscopy (AES), and X-ray diffraction (XRD). Nb(C,N), M 23 C 6 , and the silicide G-phases (Ni 16 Nb 6 Si 7 ) were all identified in a conventional SEM, while the nitride Z-phase (CrNbN) was observed only in AES. M 23 C 6 , Z-phase and G-phase were characterized in XRD. Thermodynamic equilibrium calculations using ThermoCalc Version S, with the TCS Steel and Fe-alloys Database (TCFE6), and Thermotech Ni-based Superalloys Database (TTNI8) were validated by comparing experimental phase fraction results obtained from both EPMA and AES. A computational study looking at variations in the chemical composition of the alloy, and how they affect phase equilibria, was investigated. Increasing the nitrogen concentration is shown to decrease G-phase formation, where it is replaced by other intermetallic phases such as Z-phase and π -phase that do not experience liquation during pre-weld annealing treatments. Suppressing G-phase formation was ultimately determined to be a function of minimizing silicon content, and understabilizing the Nb/(C + 6/7N) ratio. Content Type Journal Article Pages 1-13 DOI 10.1007/s11661-012-1457-1 Authors Matthew P. Dewar, Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2V4, Canada Adrian P. Gerlich, University of Waterloo, Waterloo, ON, Canada Journal Metallurgical and Materials Transactions A Online ISSN 1543-1940 Print ISSN 1073-5623
Electronic ISSN:
1543-1940
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
