Effect of Mn and P on precipitation behavior and solute distribution in ultra-low carbon bake hardening steels

The effect of Mn and P on types of precipitates as well as solute distributions in ultra-low carbon bake hardening (ULC-BH) steels was originally investigated in this paper. Three samples of hot-rolled ULC-BH steels (Ti–V, Ti–V–Mn, and Ti–V–P) were prepared. The types of precipitates in the three samples were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and further calculated by Thermo-Calc. The different types of nanometer sized vanadium carbides are clearly characterized by SEM and TEM, and results of calculation and experiments are generally in agreement. Besides, the solute distributions in Ti–V–Mn and Ti–V–P steels were detected by three-dimensional atom probe (3DAP). It is found that no Ti, N, or S elements are present in both of the two steels, and the distribution patterns of the solute elements in the two steels are completely determined. Results show that SEM, TEM combining with 3DAP can well detect the existence of elements added into the bake hardening steels, and are very useful techniques for the base of the further investigation of mechanical properties and bake hardening phenomenon in bake hardening steels.