The alloy composition limits for transformation of the ordered bcc β₁ Cu–Sn phase to the β₁′ and γ₁′ martensites during quenching to 20°C and subsequent cooling to −196°C have been determined by optical metallography. It is shown that the limits are imposed by the variation with composition of the initial β₁ phase of the M_s and M_F temperatures for the transformations. In duplex structures the transformation behaviour changes with quenching temperature probably as a consequence of the temperature dependence of the Sn concentration in the β₁ phase.
An additional product, termed β′, formed in all alloys quenched from above some minimum temperature and was identified as martensite from relief effects which accompanied the transformation.