γ → α-transformation in Fe–15Ni

Abstract

Although M _s for Fe–C alloys varies linearly with carbon content extrapolating to 550°C in pure iron, Bibby and Parr reported a rapid rise in supposed M _s extrapolating to ∼700°C in pure iron for carbon contents less than 0·005%. They concluded that at these very low carbon contents the supposed M _s of pure iron rises to ∼700°C. However, Wilson suggested that Bibby and Parr may have observed a bainitic-type transformation at 700°C and that the true M _s for lath martensite in pure iron is 550 ± 10°C. Such a bainitic reaction could give rise to surface tilts on a prepolished surface and be mistaken for a martensitic reaction.