Titanium alloyed interstitial free (Ti-IF) steels, widely known for their excellent formability, are commonly used in deep drawing applications for the automotive industry. However, these steels are susceptible to cold work embrittlement. This phenomenon results from the segregation of tramp elements such as P, Sn, or Sb to grain boundaries, causing a weakening of these interfaces. Since increased scrap usage in the future will most likely lead to elevated contents of tramp elements, a fundamental understanding of their segregation behavior is essential for maintaining the high formability of these steels.

In this work, a ferritic Ti-IF steel is used to analyze the effect of different heat treatment parameters on the segregation levels of the alloying elements. For this reason, atom probe tomography and transmission electron microscopy are employed to measure local grain boundary concentrations and calculate the interfacial excess to determine the segregation tendencies. Furthermore, an alternative heat treatment approach is proposed to facilitate the measurement of changes in grain boundary chemistry caused by the different heat treatments. For this purpose, the grain size is initially increased through a high-temperature annealing process. The resulting high-angle grain boundaries are observed to have lengths of several hundred micrometers compared to twenty micrometers in standard industrial material. They are, therefore, long enough to probe the segregation at one specific high-angle grain boundary multiple times after consecutive heat treatments of the same sample. Electron backscatter diffraction is used in this case to characterize the grain boundaries and confirm that the same boundary is targeted every time.

Preliminary atom probe tomography measurements revealed the possibility of measuring changing segregation tendencies towards a high-angle grain boundary caused by different cooling rates after annealing. The interfacial excess of Sn showed a twofold increase after slow cooling compared to quenching. Ti exhibited the opposite behavior, as its segregation to the grain boundary was much stronger in the quenched state. This indicates an interplay between precipitation and segregation of the alloying elements at different cooling rates.