Free-standing diamond films have been successfully deposited on stainless steel substrates using microwave plasma-assisted chemical vapor deposition. Although iron, which is the main element of stainless steel, is known to inhibit the nucleation of diamond and enhance the formation of graphite, we were able to grow relatively thick films (～ 1.2 mm). The films were easily detachable from the substrates. The poor adhesion made it possible to obtain free-standing diamond films without chemical etching. Raman spectroscopy showed the 1332 cm-1 characteristic Raman peak of diamond and the 1580 cm-1, 1350 cm-1 bands of graphite on the growth surface and backside of the films, respectively. By energy dispersive X-ray spectroscopy it was only possible to detect iron on the back of the films, but not on the surface. The role of iron in the film growth is discussed.