This study performs a precipitation examination of the phase using the general diffusion equation with comparison to the Vitek model in dissimilar stainless steels during multipass welding. Experimental results demonstrate that the diffusivities ( , , and ) of Cr, Ni, and Si are higher in -ferrite than ( , , and ) in the phase, and that they facilitate the precipitation of the σ phase in the third pass fusion zone. The Vitek diffusion equation can be modified as follows: . 1. Introduction ASSs (austenitic stainless steels) are used widely in high-temperature conditions such as energy conversion systems. For instance, to ensure economy in central power systems, sections of boilers subjected to lower temperatures are constructed from FSS (ferritic stainless steel) for economic reasons [1]. However, ASS and FSS composites have acid, alkali, and high-temperature resistances, and so have many applications in a wide variety of industries, such as chemical, oil refining, artificial fiber, food, and medicine [2]. When stainless steels are heated to temperatures between 700°C and 1000°C for prolonged periods of time, several harmful second phases, such as , , and , can precipitate [3–6]. While the phase was first observed in the Fe-Cr system, it has also been observed in Fe-Mo, Fe-V, and Cr-Mo-Ni alloy systems [7]. The crystallographic lattice of the phase is a tetragonal structure with 30 atoms per unit cell. The phase is the most important of these intermetallic phases due to its impact on the mechanical properties, corrosion resistance or weldability of stainless steels, as well as other properties [8–11]. Previous studies on the properties of stainless steels containing the phase have focused on microstructural observation and the mechanical property in the fusion zone (FZ) of similar stainless steels [12–18]. Very few researchers have discussed the precipitation of the phase through the diffusion theory in the fusion zones (FZ) of dissimilar stainless steels. The precipitation behavior of the phase in fusion zones during the welding process is unclear for ferritic and austenitic stainless steels. Hsieh and Wu [19] first reported the precipitation of the phase using the Vitek diffusion model in the multipass fusion zone of dissimilar stainless steels. Autogenous GTAW (gas tungsten arc welding) was used to manufacture dissimilar stainless steels for this present study. The precipitation behavior of the phase in the multipass fusion zone of dissimilar stainless steels taking place during the multipass GTAW process has been discussed via a calculation of the
References
[1]
S. Missori and C. Koerber, “Laser beam welding of austenitic-rerritic transition joints,” Welding Journal, vol. 76, no. 12, pp. 125S–134S, 1997.
[2]
B. Sun, Y. J. Li, Q. Chi, and X. S. Zhang, “Analysis of the microstructure in the weld zone of 0Cr18Mo2 and 1Cr18Ni9Ti dissimilar stainless steel,” Chemical Engineering and Machinery, vol. 31, no. 1, pp. 17–23, 2004.
[3]
P. Michael, S. Oliver, and G. Thomas, “Effect of intermetallic precipitations on the properties of duplex stainless steel,” Materials Characterization, vol. 58, pp. 65–71, 2007.
[4]
R. F. Steigerwald, “Effects of metallic second phases in stainless steels,” Corrosion, vol. 33, no. 9, pp. 338–343, 1977.
[5]
H. Kiesheyer and H. Brandis, “Investigation of phase equilibria in the ternary system Fe-Cr-Mo in the solid state,” Zeitschrift fuer Metallkunde, vol. 67, no. 4, pp. 258–263, 1976.
[6]
C. J. Park, M. K. Ahn, and H. S. Kwon, “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, 2006.
[7]
M. Raghavan, G. A. Mueller, G. A. Vaughn, and S. Floreen, “Determination of isothermal sections of nickel rich portion of Ni-Cr-Mo system by analytical electron microscopy,” Metallurgical Transactions A, vol. 15, no. 5, pp. 783–792, 1984.
[8]
L. Karlsson, L. Ryen, and S. Pak, “Precipitation of intermetallic phases in 22% Cr duplex stainless weld metals,” Welding Journal, vol. 74, pp. 28S–40S, 1995.
[9]
T. H. Chen, K. L. Weng, and J. R. Yang, “The effect of high-temperature exposure on the microstructural stability and toughness property in a 2205 duplex stainless steel,” Materials Science and Engineering A, vol. 338, no. 1-2, pp. 259–270, 2002.
[10]
J. O. Nilsson, P. Kangas, and T. Karlsson, “Mechanical properties, microstructural stability and kinetics of σ-phase formation in 29Cr-6Ni-2Mo-0.38N superduplex stainless steel,” Metallurgical and Materials Transactions A, vol. 31, pp. 35–45, 2000.
[11]
L. Jinchun, W. Tuyan, and R. Yves:, “δ phase precipitation and its effect on the mechanical properties of a super duplex stainless steel,” Materials Science and Engineering A, vol. 174, pp. 149–156, 1994.
[12]
A. Turnbull, P. E. Francis, M. P. Ryan, L. P. Orkney, A. J. Griffiths, and B. Hawkins, “A novel approach to characterizing the corrosion resistance of super duplex stainless steel welds,” Corrosion, vol. 58, no. 12, pp. 1039–1048, 2002.
[13]
D. Y. Lin, G. L. Liu, T. C. Chang, and H. C. Hsieh, “Microstructure development in 24Cr–14Ni–2Mn stainless steel after aging under various nitrogen/air ratios,” Journal of Alloys and Compounds, vol. 377, pp. 150–154, 2004.
[14]
C. C. Hsieh, D. Y. Lin, and W. Wu, “Precipitation behavior of σ phase in 19Cr–9Ni–2Mn and 18Cr–0.75Si stainless steels hot-rolled at 800°C with various reduction ratios,” Materials Science and Engineering A, vol. 467, pp. 181–189, 2007.
[15]
C. C. Hsieh, T. C. Chang, D. Y. Lin, and M. C. Chen, “Dispersion strengthening behavior of σ phase in 304 modified stainless steels during 1073？K hot rolling,” Metals and Materials International, vol. 13, pp. 359–363, 2007.
[16]
C. C. Hsieh, D. Y. Lin, and W. Wu, “Precipitation behavior of σ phase in fusion zone of dissimilar stainless steel welds during multi-pass GTAW process,” Metals and Materials International, vol. 13, pp. 411–416, 2007.
[17]
C. C. Hsieh, D. Y. Lin, and T. C. Chang, “Microstructural evolution during the δ/σ/γ phase transformation of the SUS 309LSi stainless steel after aging under various nitrogen atmospheric ratios,” Materials Science and Engineering A, vol. 475, no. 1-2, pp. 128–135, 2008.
[18]
C. C. Hsieh, X. Guo, and W. Wu, “Dendrite evolution of delta (δ) ferrite and precipitation behavior of sigma (σ) phase during multipass dissimilar stainless steels welding,” Metals and Materials International, vol. 16, pp. 349–356, 2010.
[19]
C. C. Hsieh and W. Wu, “Discussing the precipitation behavior of σ phase using diffusion equation and thermodynamic simulation in dissimilar stainless steels,” Journal of Alloys and Compounds, vol. 506, pp. 820–825, 2010.
[20]
E. Folkhard, G. Rabensteiner, E. Perteneder, H. Schabereiter, and J. T？sch, Welding Metallurgy of Stainless Steels, Springer, New York, NY, USA, 2004.
