Effect of Al Addition on the Microstructure and Phase Stability of P91 Ferritic-Martensitic Steel
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This paper presents the results of an experimental and computational study carried out to elucidate the effect of Al on the microstructure and phase stability of P91 F/M steel in as-cast, homogenized and normalized conditions. Al-added steels followed ‘Ferritic-Austenitic’ mode of solidification and the as-cast microstructures consisted of δ-ferrite + α′-martensite, the volume fraction of ferrite and hardness of martensite increased with Al concentration. Heat treatments and DSC experiments confirmed increased stability for δ-ferrite with Al addition. Systematic change in the phase transformations temperatures and volume fraction of equilibrium phases due to Al addition was estimated with the help of Thermo-Calc®. Al addition promoted the formation of AlN which was confirmed through electron microscopy-based investigations. AlN dissolution temperature was always above γ-loop which made it impossible to dissolve during austenization. With the help of Scheil and equilibrium simulations using Thermo-Calc®, elemental partitioning between δ-ferrite and α′ phases was found to be the reason for higher hardness of martensite. Based on experimental evidences, it is concluded that except in the case of 0.48 wt pct Al-added steel it is impossible to obtain single phase γ-field (without ferrite) at high temperature thereby a fully martensite structure on cooling.
The authors thank Dr. A.K. Bhaduri, Director, IGCAR and Dr. G. Amarendra, Director, Metallurgy and Materials Group and Materials Science Group for their encouragement and sustained support. The authors also thank UGC-DAE-CSR, Kokkilamedu for the FE-SEM support.
- 1.C. Behar: Technology Roadmap Update for Generation IV Nuclear Energy Systems, OECD Nuclear Energy Agency for the Generation IV International Forum, 2014.Google Scholar
- 3.A.J. Romano, C.J. Klamut, and D.H. Gurinsky: The investigation of container materials for Bi and Pb alloys Part I Thermal convection Loops No BNL-811, Brookhaven National Laboratory, Upton, 1963.Google Scholar
- 6.C. Fazio: Handbook on Lead-bismuth Eutectic Alloy and Lead Properties, Materials Compatibility, Thermal-hydraulics and Technologies, 2015th edn, OECD/NEA, Paris 2015, pp. 445-47.Google Scholar
- 9.M.E. Angiolini, P. Agostini, F. Di Fonzo, F. García Ferré, L. Pilloni, and M. Utili: Towards a New Approach for Structural Materials of Lead Fast Reactors. https://www.iaea.org/NuclearPower/Downloadable/Meetings/2017/2017-12-12-12-12-NPTDS-test/FR17_WebSite/papers/FR17-227.pdf. Accessed 26 June 2018.
- 15.J. Lim: PhD dissertation, MIT, 2006. http://hdl.handle.net/1721.1/41288. Accessed 26 July 2018
- 22.B.D. Cullity, and S.R. Stock: Elements of X-ray Diffraction. 3rd ed, Pearson Education Limited, Harlow, 2014, pp. 376-95.Google Scholar
- 24.D.A. Porter, K.E. Easterling, and M. Sherif: Phase Transformations in Metals and Alloys, (Revised Reprint). CRC Press, Boca Raton, 2009, pp. 202–203.Google Scholar
- 27.R.L. Klueh and D.R. Harries: High-Chromium Ferritic and Martensitic Steels for Nuclear Applications, ASTM Monograph-3, ASTM International, West Conshohocken, 2001, p. 28.Google Scholar