Intermediate phases of the alpha - sigma phase transition in the Fe-Cr system.

(Fe 100-x Cr x ) 100-y Sn y alloys with 42.0≤x≤44.7 and 0≤y≤5.6 were annealed at 700 o C for a period of up to 1000 h in order to cause a transformation of the a phase into the a phase. Room temperature 57 Fe Mossbauer spectra registered on the samples consist of a magnetic subspectrum, related to the a phase, and a nonmagnetic subspectrum, related to the a phase. Evidence is found that the isomer shift of the nonmagnetic subspectrum changes continuously with the amount of its relative contribution in the spectrum and it reaches the value characteristic of a pure a phase only when its contribution in the two-phase sample is larger than about 30%