Influence of isothermal aging on σ precipitation in super duplex stainless steel

Abstract

The time-temperature-transformation (TTT) curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on σ precipitation was studied by metallographic observation, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750–1000°C, especially in the range of 800–900°C. The longer the aging time, the higher the amount of σ precipitation. The area fraction of various phases remains at a certain value upon the completion of ferrite deformation. The temperature of 850°C is the most sensitive transaction temperature, the incubation time for the formation of σ precipitation is less than 1 min, and aging for 20 min leads to the complete transformation of ferrite. The σ phase is formed preferentially at the α/α/γ junction, and then grows along the α/α boundary in the matrix.

Keywords

super duplex stainless steel / isothermal aging / precipitation / area fraction

References

[1] Park Y.H., Lee Z.H. The effect of nitrogen and heat treatment on the microstructure and tensile properties of 25Cr-7Ni-1.5Mo-3W-xN duplex stainless steel castings. Mater. Sci. Eng. A, 2001, 297, 78.

[2] Hänninen H., Romu J., Ilola R., et al. Effects of processing and manufacturing of high nitrogen-containing stainless steels on their mechanical, corrosion and wear properties. J. Mater. Process. Technol., 2001, 117, 424.

[3] Nilsson J.O., Wilson A. Influence of isothermal phase transformations on toughness and pitting corrosion of super duplex stainless steel SAF 2507. Mater. Sci. Technol., 1993, 9(7): 545.

[4] Chen T.H., Weng K.L., Yang J.R. The effect of high temperature exposure on the microstructure stability and toughness property in a 2205 duplex stainless steel. Mater. Sci. Eng., A, 2002, 338, 259.

[5] Wharton J.A., Wood R.J.K., Mellor B.G. Wavelet analysis of electrochemical noise measurements during corrosion of austenitic and super duplex stainless steels in chloride media. Corros. Sci., 2003, 45, 97.

[6] Chiu P.K., Weng K.L., Wang S.H. Low-cycle fatigue-induced martensitic transformation in SAF2205 duplex stainless steel. Mater. Sci. Eng. A, 2005, 398, 349.

[7] Jiménez J.A., Frommeyer G., Carsí M. Superplastic properties of δ/γ stainless steel. Mater. Sci. Eng. A, 2001, 307, 134.

[8] Nilsson J.O. Super duplex stainless steels. Mater. Sci. Technol., 1992, 8, 685.

[9] Martins M., Casteletti L.C. Heat treatment temperature influence on ASTM A890 GR 6A super duplex stainless steel microstructure. Mater. Charact., 2005, 55, 225.

[10] Chen T.H., Yang J.R. Effects of solution treatment and continuous cooling on σ-phase precipitation in a 2205 duplex stainless steel. Mater. Sci. Eng. A, 2001, 311, 28.

[11] Angelini E., Bennedetti B.D., Rosalbino F. Microstructure evolution and localized corrosion resistance of an aged super duplex stainless steel. Corros. Sci., 2004, 46, 1351.

[12] Sato Y.S., Nelson T.W., Sterling C.J., et al. Microstructure and mechanical properties of friction stir welded SAF2507 super duplex stainless steel. Mater. Sci. Eng. A, 2005, 397, 376.

[13] Li J.C., Wu T.Y., Riquier Y. σ phase precipitation and its effect on the mechanical properties of a super duplex stainless steel. Mater. Sci. Eng. A, 1994, 174, 149.

[14] Dobranszky J., Szabo P.J., Berecz T., et al. Energy-dispersive spectroscopy and electron backscatter diffraction analysis of isothermally aged SAF2507 type super duplex stainless steel. Spectrochim. Acta B, 2004, 59, 1781.

[15] Smuk O., Jagodzinski Y., Tarasenko O., Smuk S. Internal friction study of decomposition kinetics of SAF2507 type duplex stainless steel. Scripta Mater., 1999, 40(3): 321.