Effects of Occurrence States of Nitrogen on Tensile Properties and Bendability in Dual‐Phase Steels

Herein, the occurrence states of nitrogen (N) in dual phase (ferrite and martensite) with different N contents (30, 60, 90, 120, and 140 ppm wt%) and its influence on tensile properties and bendability are investigated combining with internal friction spectrum. The results demonstrate that the occurrence states of N are mainly consumed by nanoscale and micron‐scale TiN precipitates, interstitial solid solution, and segregation at crystallographic defects, which account for ≈74–85%, 2.3–4.5%, and 11–21% of the total N content, respectively. Furthermore, the formed nanoscale TiN precipitation enhances the yield strength without damaging ductility, while the micron‐scale complex TiN‐Al 2 O 3 /MnS (TiN‐MA) inclusions deteriorate ductility and bendability. These micron‐scale TiN‐MA inclusions mainly originate from heterogeneous nucleation of TiN during solidification process, and their number density and size increase with the increase of N content, which induces their interface debonding with the matrix and itself fragmentation during deformation, and accelerates microcrack/microvoid nucleation and coalescence. The present results show new insight into the effect of occurrence states of N on tensile properties and bendability in steels and provide important guidance for electric arc furnace steelmaking, which inevitably introduces excessive N.