Abstract
When high Al containing Fe alloys such as TRIP steels are exposed to atmospheres that contain N2 during re-heating, sub-surface nitrides form and these can be detrimental to mechanical properties. Nitride precipitation can be controlled by minimizing the access of the gaseous atmosphere to the metal surface, which can be achieved by a rapid growth of a continuous and adherent surface scale. This investigation utilizes a Au-image furnace attached to a confocal scanning microscope to simulate the annealing temperature vs time while Fe-Al alloys (with Al contents varying from 1 to 8 wt pct) are exposed to a O2-N2 atm with 10−6 atm O2. The heating times of 1, 10, and 100 minutes to the isothermal temperature of 1558 K (1285 °C) were used. It was found that fewer sub-surface nitride precipitates formed when the heating time was lowered and when Al content in the samples was increased. In the 8 wt pct samples, no internal nitride precipitates were present regardless of heating time. In the 3 and 5 wt pct samples, internal nitride precipitates were nearly more or less absent at heating times less than 10 minutes. The decrease in internal precipitates was governed by the evolving structure of the external oxide-scale. At low heating rates and/or low Al contents, significant Fe-oxide patches formed and these appeared to allow for ingress of gaseous N2. For the slow heating rates, ingress could have happened during the longer time spent in lower temperatures where non-protective alumina was present. As Al content in the alloy was increased, the external scale was Al2O3 and/or FeAl2O4 and more continuous and consequently hindered the N2 from accessing the metal surface. Increasing the Al content in the alloy had the effect of promoting the outward diffusion of Al in the alloy and thereby assisting the formation of the continuous external layer of Al2O3 and/or FeAl2O4.
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References
J. Gao and M. Ichikawa: Proc. Int. Conf. on Advanced High Strength Sheet Steels for Automotive Applications, Winter Park, CO, June 6–9, 2004, AIST, Warrendale, PA, 2004, pp. 107–15.
T.L. Baum, R.J. Fruehan, and S. Sridhar: Metall. Mater. Trans. B, 2007, vol. 38B, pp. 287-97.
M. De Meyer, D. Vanderschueren, and B.C. De Cooman: ISIJ Int., 1999, vol. 39, pp. 813-22.
J. Bott, H. Yin, J. Zhu, S. Sridhar: Mater. Corros., 2014, vol. 65, pp. 296-304.
J. Bott, H. Yin, and S. Sridhar: AISTech 2013 Proceedings, Pittsburgh, PA, May 6–9, 2013, AIST, Warrendale, PA, 2013, pp. 1–11.
L.S. Darken, R.P. Smith, and E.W. Filer: Trans. AIME, 1951, vol. 191, pp. 1174-9.
Z.G. Zhang, F. Gesmundo, P.Y. Hou, and Y. Niu: Corros. Sci., 2006, vol. 48, pp. 741-65.
R. Prescott and M.J. Graham: Oxid. Met., 1992, vol. 38, pp. 73-87.
R. Prescott and M.J. Graham: Oxid. Met., 1992, vol. 38, pp. 233-54.
B.A. Pint, J. Leibowitz, J.H DeVan: Oxid. Met., 1999, vol. 51, pp. 181-97.
P. Tomaszewicz and J.R. Wallwork: Oxid. Met., 1983, vol. 19, pp. 165-85.
P. Tomaszewicz and G.R. Wallwork: Rev. High Temp. Mat., 1978, vol. 4, pp. 75-105.
H.J. Grabke, M.W. Brumm, and B. Wagemann: in Oxidation of Intermetallics, Wiley-VCH Verlag GmbH, Weinheim, 2007, pp. 79–83.
J.L. Meijering: Advances in Materials Research, vol. 5, Wiley-Interscience, New York, NY, 1971, pp. 1-81.
W.S. Rasband: ImageJ: U. S. National Institutes of Health, Bethesda, MD, http://imagej.nih.gov/ij/, 1997–2012. Accessed 25 Nov 2012.
C. Wagner: Z. Elektrochem, 1959, vol. 63, pp. 772-82.
A. Boumaza, L. Favaro, J. Lédion, G. Sattonnay, J.B. Brubach, P. Berthet, A.M. Huntz, P. Roy, and R. Tétot: J. Solid State Chem., 2009, vol. 182, pp. 1171-1176.
P. Kofstad: Nonstoichiometry, Diffusion, and Electrical Conductivity in Binary Metal Oxides, Robert E. Krieger Publishing Company, Malabar, FL, 1983, p. 229.
L. Himmel, R.F. Mehl, and C.E. Birchenall: Trans. AIME, 1953, vol. 197, pp. 822-43.
I.A. Akimova, V.M. Mironov, and A.V. Pokoyev: Phys. Met. Metallogr., 1983, vol. 56, pp. 1225-7.
Acknowledgments
The authors acknowledge ArcelorMittal Global R&D for their financial support and other in-kind support of this project. They would like to thank E. Mantle at ArcelorMittal Global R&D EC Center for making the lab ingots. The discussions with Drs. O. Lanzi, S. Atreya, and S. Bhat, all at ArcelorMittal Global R&D EC Center, were very valuable in the present study. The authors would also like to thank J. Wolf and N.T. Nuhfer at Carnegie Mellon University for their assistance with characterization methods.
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Manuscript submitted July 10, 2013.
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Bott, J., Yin, H. & Sridhar, S. The Effect of Heating Rate on Subsurface AlN Formation in Fe-Al Alloys in N2-O2 Atmospheres. Metall Mater Trans B 45, 2222–2231 (2014). https://doi.org/10.1007/s11663-014-0116-x
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DOI: https://doi.org/10.1007/s11663-014-0116-x