The microstructure and mechanical integrity of protective multilayered oxide films grown in liquid metal on F/M steel HCM12A was investigated utilizing Raman spectroscopy, nanoindentation and micro-cantilever testing methods. The Raman spectra showed a Fe3O4 outer layer and a Cr-rich spinel structure inner layer. The nanoindentation results showed a higher hardness value for the inner layer than for the outer layer. In addition, the hardness of the diffusion layer in between the inner layer and the bulk steel was measured. Quantitative fracture properties were obtained of the steel/oxide interface and within the oxide layers utilizing micro-cantilever testing. Furthermore the strength and elastic properties of the multilayered oxide film were measured and it was found that the porous structure in the inner Fe–Cr oxide limits the integrity of the steel/oxide interface.