This study reports on a successful deposition of adherent nanocrystalline diamond films on Fe-9Cr steel which is free of interlayer and pre-treatment, but has been alloyed with a small fraction of Al and Si (2.2 wt% each). High nucleation density and enhanced adhesion of diamond films have been achieved on the modified steel substrate. We have clarified the mechanism regarding the chemical nature of the steels and the diamond films formed. (c) 2006 Elsevier B.V. All rights reserved.