New developments in the production of ultra low carbon steel for automotive applications at CST Arcelor Brasil

摘要

The ultra low carbon (ULC) steels are essential for the production of complex parts for automotive industry with an excellent balance between strength level and formability. Two different groups of ULC can be distinguished for automotive applications. The first group is represented by soft IF grades (Interstitial free steels). For these materials the C and N interstitial atoms must be fully combined either with Ti or Nb (single stabilized) or with both Ti + Nb (double stabilized). The level of solid solution strengthening elements shall be as low as possible in order to afford product properties of high formability and surface quality. The second group is represented by the Bake Hardening (BH) steel grades, in which the additions of Ti, Nb or combination of these elements are used for partial C stabilization. The BH steels are characterized by excellent mechanical properties, a high tensile strength level in particular, which is obtained after painting the final parts. To achieve this, it is necessary to optimize the chemical composition and the processing parameters during BH steel production (1).