Identification and characterization of a novel intermetallic compound in a Fe-22 wt % Cr-5 wt % Ni-3 wt % Mo-0.03 wt % C duplex stainless steel

A new intermetallic compound labelled the τ-phase with an orthorhombic structure (a = 0.4044 nm, b = 0.3436 nm and c = 0.2867 nm) is formed throughout the ¯ matrix during isothermal heat treatment in the temperature range below 650°C. The face-centred orthorhombic Bravais lattice and Fmmm space group are established by electron microdiffraction in conjunction with group theory analysis. The τ-phase crystal lattice is oriented with respect to the surrounding δ matrix according to the Bain orientation relationship. The defects inside τ particles were analysed as sequence faults.