Effect of Nb Contents on Size of Ferrite Grain in Ultra-low Carbon Steel for Cans

Fineness of ferrite grain is desirable for good surface quality of film laminated steel for drawn cans. And softness of steel is suitable for drawn cans from the view point of high formability. Generally, ultra low carbon steel (ULC) is soft, but it has coarse ferrite grains. On the other hand, low carbon steel (LC), which has fine ferrite grains, is hard and has poor formability, and therefore it is not suitable for drawing. In order to improve these contradictory properties, the amount of carbon and niobium in ULC steel is varied to control the size of precipitates of niobium carbide, which contribute to reduction of grain size. The study suggested that the newly developed steel has a potential to have an excellent balance of both properties.