Considerations of size can help to

Considerations of size can help to decide where the formation of an interstitial solid
solution is likely to occur. Thus, the largest solute atom that can enter a close-packed solid
without distorting the structure appreciably is one that just fits an octahedral hole, which
as we have seen has radius 0.414r. For small atoms such as B, C, or N the atomic radii of
the possible host metal atom structures include those of the d-metals such as Fe, Co, and
Ni. One important class of materials of this type consists of carbon steels in which C atoms
occupy some of the octahedral holes in the Fe bcc lattice.