Tetragonality of martensite crystal lattice and hysteresis of γreversibleα transformation in alloys

Method of X-ray diffraction analysis with the use of a low-temperature accessory was applied to study changes in tetragonality of crystal lattice of thermoelastic martensite in Fe-Ni-Co-Ti carbon-free alloys depending on chemical composition and heat treatment conditions. An evaluation of γ- and α-phase specific volumes and transformation hysteresis was made with austenite ageing. It was confirmed that martensite lattice tetragonality increase correlated with hysteresis decrease, the latter could reach 20K. The value of γreversibleα transformation hysteresis when the transformation occured through reversible motion of martensite crystal boundaries was found to be determined by degree of coherent stress relaxation of interfaces