We have test data to show that if an austenitic stainless steel (Types 304, 316, 321 or 347) normally FCC have transformed to BCC, which some people call alpha prime martensite (myself included) then the fracture toughness shows a clear DBTT.   

I know this is not an answer to your question but I thought you might be interested.  We have not published our own work, if I find some relevant publication from other researchers then I will add a link to this answer.  

As for the question are there any BCC metals that don't show a DBTT?  I can't think of any BCC steels that don't show a DBTT.   I don't know about other metals.  

https://en.wikipedia.org/wiki/Periodic_table_(crystal_structure)

FCC materials don't show any DBTT, because of the many slip systems with low activation energies for dislocation motion. But it is common in BCC materials regardless of the presence of solute atoms. The transition occurs because the fracture toughness is relatively independent of temperature, but the energy needed for dislocation motion typically exhibits an Arrhenius dependence on temperature. Thus, at high temperatures dislocations begin to move and relieve stress before fracture can occur, resulting in plastic deformation (ductile behavior). At temperatures below the DBTT, the fracture toughness is exceeded before the stress is sufficient to induce dislocation motion and brittle fracture is observed.

All BCC steels show DBTT, but can't say about other materials.