High‐Pressure α⇄ε Martensitic Transformation in Iron

A study of the high‐pressure transformation in iron using an opposed‐anvil x‐ray diffraction apparatus and high‐pressure light metallography has shown that the 130‐kbar transformation is martensitic. The bcc and hcp phases were found to coexist over a large pressure range, and there is a large hysteresis between the forward and reverse transformation‐start pressures. A room‐temperature equilibrium pressure for the bcc and hcp phases of 107 ± 8 kbar is proposed, and discrepancies in the current P‐T equilibrium diagram for iron are discussed.

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