日本金属学会誌

J. Japan Inst. Metals, Vol. 63, No. 12 (1999),
pp. 1503-1509

Compositional Evolution of Ferrite in Cast Duplex Stainless Steelduring Thermal Aging

Takayuki Miura1, Hisashi Kuwano1,Kiyohiko Itoh2 and Yuichi Ishikawa3

1Department of Materials Science and Engineering, Faculty of Engineering, Muroran Institute of Technology, Muroran 050-8585
2Kure-Norton Co. Ltd., Kure 737-8518

3Mechanical Engineering Research Laboratory, Hitachi Ltd., Tsuchiura 300-0000

Abstract:

A cast duplex stainless steel practically used in the intermediate temperature range of 280 to 330°C was investigated in terms of its aging behavior in the temperature range of 350 to 450°C for aging times up to 20000 h. A change in ferrite composition with increasing aging time was detected at room temperature by M\"{o}sbauer spectroscopy. The characteristic changes in internal magnetic field distribution and its full width at half maximum revealed that the ferrite phase decomposes by the spinodal process. The change in ferrite composition with time during aging was analyzed and the corresponding equation proposed was that of the sum of two hyperbolic tangent curves. The activation energy for the compositional change during decomposition was about 200 kJ/mol, which is comparable to that for volume diffusion of Cr or Fe in ferrite. An aging parameter p(t, T) calculated from the above activation energy was introduced to estimate the decomposition behavior at temperatures lower than 350°C. The time required for the ferrite phase to reach completion of phase decomposition was estimated to be about 1700000 h at 320°C.


(Received March 31, 1999; In Final Form September 16, 1999)

Keywords:

M\"{o}ssbauer spectroscopy, spinodal decomposition, internal magnetic field, phase decomposition, duplex stainless steel, composition fluctuation


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