Microstructural influences on the decomposition of an Al-containing ferritic stainless steel

The behaviour of as-received and recrystallised (homogenised) MA 956, a Cr-rich ferritic stainless steel, aged at 475°C for up to 588 h has been investigated. The convolution of recovery and phase separation results in aged as-received material contrasting with hardening due to phase separation only in homogenised material. Atom probe microanalysis of the decomposition products reveals that Al does not partition significantly to the Fe-rich phase, as calculated by phase diagram modelling. The wavelength of the decomposition is found to be significantly larger in aged as-received material compared to aged homogenised material. The spinodal decomposition of the MA 956 supersaturated solid solution is possibly a paraequilibrium transformation with respect to Al. The behaviour of Al is discussed in terms of competing chemical and stress gradients in the nanophase material and the influence of a such a structure on its thermodynamic description.

[1]  Rachel C. Thomson,et al.  The partitioning of substitutional solute elements during the tempering of martensite in Cr and Mo containing steels , 1995 .

[2]  P. J. Grobner,et al.  The 885° f (475° c) embrittlement of ferritic stainless steels , 1973 .

[3]  M. Loretto,et al.  The stability of the oxide dispersion in INCONEL alloy MA6000 , 1989 .

[4]  J. E. Brown,et al.  Atom probe studies of spinodal processes in duplex stainless steels and single- and dual-phase Fe-Cr-Ni alloys , 1990 .

[5]  Toshio Sakurai,et al.  APFIM studies on martensite tempering of Fe-C-Si-Mn low alloy steel , 1993 .

[6]  P. Camus,et al.  Phase separation and coarsening in FeCrCo alloys , 1984 .

[7]  L. Lundin,et al.  Atom-probe study of phosphorus segregation to the carbide / matrix interface in an aged 9% chromium steel , 1995 .

[8]  J. Stringer,et al.  Interdiffusion in ternary Fe-Cr-AI alloys , 1989 .

[9]  P. Haasen,et al.  Atom probe field ion microscopy of a FeCrCo permanent magnet alloy , 1982 .

[10]  A. Yavari.  Phase transformations in nanocrystalline alloys , 1994 .

[11]  D. Blavette,et al.  An atom-probe investigation of some correlated phase transformations in Cr, Ni, Mo containing supersaturated ferrites , 1992 .

[12]  J. Weissmüller.  Some basic notions on nanostructured solids , 1994 .

[13]  M. Miller,et al.  APFIM and AEM investigation of CF8 and CF8M primary coolant pipe steels , 1990 .

[14]  W. Tofaute,et al.  Die Versprödung von hochlegierten Chromstählen im Temperaturgebiet um 500 , 1942 .

[15]  A. Cerezo,et al.  Comparison of low temperature decomposition in FeCr and duplex stainless steels , 1995 .

[16]  H. Bhadeshia,et al.  Crystallographic texture in mechanically alloyed oxide dispersion-strengthened MA956 and MA957 steels , 1993 .

[17]  H. W. King.  Quantitative size-factors for metallic solid solutions , 1966 .

[18]  K. Binder,et al.  Unmixing of binary alloys by a vacancy mechanism of diffusion: a computer simulation , 1991 .

[19]  M. Miller,et al.  Spinodal decomposition of iron-32 at.% chromium at 470°C☆ , 1982 .