Effect of solutes on the lattice parameters and elastic stiffness coefficients of body-centered tetragonal Fe

We compute changes in the lattice parameters and elastic stiffness coefficients C_ij of body-centered tetragonal (bct) Fe due to Al, B, C, Cu, Mn, Si, and N solutes. Solute strain misfit tensors determine changes in the lattice parameters as well as strain contributions to the changes in the C_ij. We also compute chemical contributions to the changes in the C_ij, and show that the sum of the strain and chemical contributions agree with more computationally expensive direct calculations that simultaneously incorporate both contributions. Octahedral interstitial solutes, with C being the most important addition in steels, must be present to stabilize the bct phase over the body-centered cubic phase. We therefore compute the effects of interactions between interstitial C solutes and substitutional solutes on the bct lattice parameters and C_ij for all possible solute configurations in the dilute limit, and thermally average the results to obtain effective changes in properties due to each solute. The computed data can be used to estimate solute-induced changes in mechanical properties such as strength and ductility, and can be directly incorporated into mesoscale simulations of multiphase steels to model solute effects on the bct martensite phase.