Magnetic properties of BCC, FCC and HCP Fe and the effects of the Sigma 3 < 0<(1)over bar>0 > {111} grain boundary (GB) and the alloying elements of Cr, Ni, Ta and Zr are investigated by first-principles calculations. The FCC Fe changes continuously from the non-magnetic state at low volumes to the ferromagnetic state at high volumes. It is observed that Sigma 3{111} type GBs in FCC Fe have a negative formation energy since the formation of Sigma 3 GB is attributed to the local FCC-HCP transformation. Moreover, consistent with the variation of equilibrium volume caused by TM solute atoms, the magnetic moment of FCC Fe70TM2 is decreased with alloying Ni while increased with alloying Cr, Ta and Zr. Due to the difference in the valence electrons and atomic radius among those solute atoms, the chemical and mechanical effects on the bond structure of Sigma 3{111} GB in Fe and Fe70TM2 are respectively characterized by deformation electron density and plots of spin alignments. It is understood that the variation of the spin state of Fe70TM20 is dominated by the electron redistributions, as illustrated by the spin-flipping and the change of the bond structure. This work provides an insight into the effect of lattice distortion on ferromagnetism of FCC Fe and Fe70TM2 (C) 2015 Elsevier B.V. All rights reserved.