2015 T.C. Graham prize winner: High-strength interstitial-free steel obtained using FeC amorphous films and induction heating for packaging applications and cladding with lighter metals for car body panels

A new solution to strengthen interstitial-free (IF) steel is proposed. The main innovation is to use FeC films to diffuse carbon into the IF substrate. This film can be applied on one side or on both sides of the steel sheet by using a physical vapor deposition (PVD) process. Once the coating has been applied to the steel, it can be annealed to diffuse carbon into the substrate. Depending on the heat treatment, on the carbon amount present in the FeC film and on its thickness, the mechanical properties can be properly tailored. The main advantage of these films is their versatility. The carbon content inside the FeC film can be regulated and even 100% carbon films could potentially be used as well. Once the specimen is coated, it can undergo the heat treatment to obtain the diffusion from the carbon coating. If middle yield strength is required, an annealing at temperatures lower than 800°C for 1 hour in a high-vacuum furnace can be used. The formation of martensite or bainite would increase markedly the strength of the steel sheet and would also improve the hardness surface of the IF sheet.