Metallurgical Engineering

Metallurgical Engineering

Cr-rich precipitates impact on microstructure and mechanical properties of Fe-23Cr-2.4Mo ferritic stainless steel

Document Type : Research Paper

Authors
Khadijeh Farjam Hajiagha
Alireza Akbari
Roghayeh mohammadzadeh
Abstract
In this study, Influence of formation of Cr-rich precipitates on microstructure and mechanical properties of Fe-23­Cr-2.4­Mo ferritic stainless steel has been investigated. In this regard, samples of this steel were homogenized at 1100°C for 48 hours and then were cooled in furnace. Microstructure, phase composition, and hardness of the samples were investigated using optical and scanning electron microscopes, X-ray diffraction and micro-hardness measurements. Results of microstructural observations and thermodynamic evaluations showed that Cr-rich precipitates are formed in the steel microstructure due to slow cooling after homogenizing treatment. In order to dissolve the Cr-rich precipitates; formed during slow cooling, a number of samples were subjected to solution treatments at 1100°C, 1150°C for 5 hours and then were quenched in water. Results showed that at temperature of 1100°C precipitates are not dissolved entirely but at 1150°C they are dissolved completely. After solution treatment at 1150°C followed by water quenching no longer precipitation is took place due to the fast cooling rate. Results of phase analysis and microhardness measurements showed that solution treatment at 1150°C lead to increase of ferrite lattice parameter from 2.880 Åto 2.893Å and also enhancement hardness from 211 to 317 Vickers despite an increase in ferrite grain size. These results confirm dissolution of Cr-rich precipitates in the ferrite matrix.
Keywords
Ferritic stainless steel
Cr-rich precipitates
Lattice parameter
Hardness
Grain size
1-       Chun, C. H., & Polonis, D. H. (1992). Metallurgical stability and the fracture behavior of ferritic stainless steel. Journal of Materials Engineering and Performance, Vol. 1(3), Pp. 371-382.
2-       Cullity, B.D. (1978). Elements of x-ray diffraction. London: Addison-Wesley.
3-       Dieter, G. E. (1988). Mechanical metallurgy. London: McGraw-Hill.
4-       Grobner, P. J. (1973). The 885°F (475 °C) embrittlement of ferritic stainless steels. Metallurgical Transactions,Vol. 4, Pp. 251-260.
5-       Guimarães, A. A., & Mei, P. R. (2004). Precipitation of carbides and sigma phase in AISI type 446 stainless steel under working conditions. Journal of Materials Processing Technology, Vol. 155, Pp. 1681-1689.
6-       Mohammadzadeh, R., & Akbari, A. (2013). Effect of pressurized solution nitriding on phase  changes and mechanical properties of ferritic Fe-22.7Cr-2.4Mo stainless steel. Materials Science and Engineering A, Vol. 81, Pp. 239-243.
7-       Park, C-J., & Ahn, M-K. (2006). Influences of Mo substitution by W on the precipitation kinetics of secondary phases and the associated localized corrosion and embrittlement in 29% Cr ferritic stainless steels. Materials Science and Engineering A, Vol. 418, Pp. 211-217.
8-       Qu, H. P., Lang, Y. P., Chen, H. T., Rong, F., Kang, X. F., Yang, C. Q., & Qin, H. B. (2012). The effect of precipitation on microstructure, mechanic properties and corrosion resistance of two UNS S44660 ferritic stainless steels. Materials Science and Engineering A, Vol. 534, Pp. 436–445.
9-       Sawatani, T., Minamino, S., & Morikawa, H. (1982). Effect of laves phase on the properties of Ti and Nb stabilized low C, N-19%Cr-2%Mo stainless steel sheets. Transactions ISI Journal, Vol. 22, Pp. 172-180.
10-   Sello, M. P., & Stumpf, W. E. (2010). Laves phase embrittlement of the ferritic stainless steel type AISI 441. Materials Science and Engineering A, Vol. 527, Pp. 5194-5202.
11-   Sello, M.P., & Stumpf, W.E. (2011). Laves phase precipitation and its transformation kinetics in the ferritic stainless steel type AISI 441. Materials Science and Engineering A, Vol. 528, Pp. 1840-1847.
12-   Smith, W. F. (1993). Structure and properties of engineering alloys. New York: McGraw-Hill.
13-   Song, R., Ponge, D., Raabe, D., Speer, J. G., & Matlock, D. K. (2006). Overview of processing, microstructure and mechanical properties of ultrafine grained bcc steels. Materials Science and Engineering A, Vol. 441,Pp. 1-17.
14-   Steigerwald, R.F. (1977). The effect of metallic second phases in stainless steels. Corrosion, Vol. 33, Pp. 338-343.
15-   Tavares, S. S. M., Souza, J. A. de., Herculano, L. F. G., Abreu, H. F. G. de, & Souza Jr, C. M. de. (2008). Microstructural, magnetic and mechanical property changes in an AISI 444 stainless steel aged in the 560°C to 800°C range. Materials Characterzation, Vol. 59, Pp. 112 – 116.
16-   Van Zwieten, A. C. T. M., & Bulloch, J. H. (1993). Some considerations on the toughness properties of ferritic stainless steels - a brief review. International Journal Press Vessels and Piping, Vol. 56, Pp. 1-31.
17-   Yamamoto, K., Kimura, Y., Wei, F-G., & Mishima, Y. (2002). Design of laves phase strengthened ferritic heat resisting steels in the Fe–Cr–Nb(–Ni) system. Materials Science and Engineering A, Vol. 329-331, Pp. 249-254.

  • Receive Date 21 March 2013
  • Revise Date 21 March 2014
  • Accept Date 21 March 2014