Amorphous Fe1−xCx coatings as carbon reservoirs for diffusion strengthening of steel sheets

In situ transmission electron microscopy–electron energy loss spectroscopy heating experiments were carried out to study the composition, structure and thermal stability of physical-vapour-deposited amorphous-Fe1−x-Cx films. Compositionally graded interstitial-free steel sheets were then produced by diffusion annealing specimens coated with thin layers of amorphous-Fe0.4C0.6. After annealing at 425 °C, tensile samples exhibited a + 86 MPa increase in yield strength and + 41 MPa in ultimate tensile strength with no significant reduction in elongation compared to the unannealed condition. Furthermore, specimens annealed at 425 °C did not show any yield point elongation.