Based on the experimental observation of cubic-to-tetragonal transition of low-carbon martensite, we perform a long-wavelength approximation for the stress-induced elastic interaction in the theory of microscopic elasticity. Taking into account the elastic anisotropy and the tetragonal character of the octahedral interstices in α-iron, we consistently obtain the cubic-to-tetragonal transition of first-order nature at the carbon concentration of 0.18 wt %, using the order-disorder transition theory formulated by Khachaturyan with the method of static concentration waves. The detailed variation of the lattice parameters and axial ratio is also given compatibly with our results. The difference in experimental results between single crystals and polycrystals is emphasized, and a phenomenological two-dimensional internal strain is proposed to explain the transition in thin-plate samples. The results are in good agreement with experimental observations.

• Received 7 February 1995

DOI:https://doi.org/10.1103/PhysRevB.52.9979