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Abstract: The effects of Nb on strain-induced precipitation and softening were quantified by means of the Gleeble-3500 thermo-mechanical simulator and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results show that Nb cannot completely dissolve during the reheating processes in the high Nb steels. The undissolved precipitates act as heterogenous nucleation sites for the precipitates induced by the strain, and prolong the strain-induced precipitation start time shown in the stress relaxation curves. The strain-induced precipitation start time is linearly related to the content of supersaturated Nb (the difference between dissolved Nb content after soaking and dissolved Nb content in equilibrium at corresponding deformation temperature). Increasing the content of supersaturated Nb can shift the nose of the precipitation C-curve to shorter time and higher temperatures. The effect of content of supersaturated Nb on precipitation increases along with the decrease of temperature. The softening ratio is linear with dissolved Nb content before the strain-induced precipitation and with precipitable Nb content after the strain-induced precipitation. The precipitates induced by strain have more strong retarding effect on the static recrystallization than the solid solution of Nb atoms. However, with the increase of the average precipitate radius, the retarding effect of precipitate rapidly decreases. [Copyright &y& Elsevier]

Abstract: 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 1wt% would lead to an increase of the deformation activation energy by 1599.9±137.7kJ/mol. [Copyright &y& Elsevier]