When L∕F is an unramified
extension of Henselian fields, we analyze the underlying division algebra cD of the
corestriction corL∕F(D) of a tame division algebra D over L with respect to the
unique valuations on cD and D extending the valuations on F and L. We show that
the value group of cD lies in the value group of D and for the center of residue
division algebra, Z(cD) ⊆𝒩(Z(D)∕F)1∕k, where 𝒩(Z(D)∕F) is the normal closure
of Z(D) over F and k is an integer depending on which roots of unity lie in F and
L.