Addition of non-metals like B and C to the interstitial sites of a transition metal results the metal:

Ductability, malleability, and hardness are the three qualities under question. We are extremely aware of how the arrangement of the atoms in the crystal affects these qualities.
The interstitial position is the void between the atoms.
The crystal will become harder and less flexible once B and C have filled the pores or interstitial position.
Metal that is less malleable, ductile, and flexible
More forceful; more toughness