IF Steels 2000 Proceedings

ULC steel grades are increasingly gaining importance for the production of thin sheet material for the automotive industry with an excellent balance between strength level and formability. Soft IF gradees, high-strength IF steel grades and partially stabilized ULC grades can be dstinguished. The own research work on the three different groups of ULC grades is summarized and critically compared with available results from the literature. Particular attention is paid to the precipitation state investigated with TEM. These results are compared with thermodynamic calculations and the data used for the solubility products or Gibbs energy values for the precipitates form the literature are critically evaluated from an industrial point of view. The impact of the different alloying elements (Ti, Nb, V or combinations) - which are used for stabilizing - on the precipitation sequence is discussed. Additionally, the microstructure is related to the mechanical properties, and the parameters with the strongest impact on the properties are selected. In a last step the further research and development work is discussed for each ULC group. Finally, precipitation sequence and mechanical properties of the different ULC grades are compared critically.