Effect of Nb Contents on Size of Ferrite Grains and Nb Precipitates in Ultra-low Carbon Steel for Cans

Soft-tempered, fine-grained ferritic steel is preferred for film-laminated steel for drawn cans from the viewpoints of surface quality and high formability. Generally, ultra-low carbon steel (ULC) is soft but has coarse ferrite grains. On the other hand, low carbon steel (LC) has a fine ferrite grain size but is hard and has inferior formability, and thus is not suitable for drawing. In order to solve this problem, the contents of carbon and niobium in ULC steel were varied in order to control the size of niobium carbide precipitates. This study suggested that the newly-developed steel has the potential to have an excellent balance of ferrite grain size and formability.