Quantitative research on effects of Nb on hot deformation behaviors of high-Nb microalloyed steels

► The amount of Nb in solution and/or in precipitates was determined. ► The Nb cannot be completely dissolved during the reheating process. ► The precipitates cannot effect on dynamic recrystallization. ► The Q def presents a perfect linear correlation with the amount of Nb in solution. ► Each addition of 1 wt% Nb in solution adds 1599.9 ± 137.7 kJ/mol to Q def. The hot deformation behaviors of six high-Nb steels were investigated by hot compression methods on a Gleeble-3500 thermo-mechanical simulator. The amount of Nb in solution and/or in precipitates of the specimens deformed at different conditions was determined by inductively coupled plasma–atomic emission spectrometry (ICP–AES). The effects of dissolved Nb and precipitates on hot deformation behavior were discussed. The results show that Nb cannot be completely dissolved in the high-Nb steels during the reheating process, and the undissolved precipitates do not influence the dynamic recrystallization due to their larger size. Moreover, the undissolved precipitates more effectively influence the peak stress instead of peak strain. Strain induced precipitation occurs during the hot deformation process. However, the precipitates cannot delay the dynamic recrystallization because of the longer induction period. The deformation activation energy presents a perfect linear correlation as a function of the amount of Nb in solutions, and each addition of Nb by 1 wt% would lead to an increase of the deformation activation energy by 1599.9 ± 137.7 kJ/mol.