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<p>Quantitative knowledge of austenite recrystallization is essential for designing the thermo-mechanical controlled processing (TMCP) routes of high-strength low-alloyed (HSLA) steels. Among the experimental tools available for recrystallization studies, laser ultrasonics has proven to be efficient for monitoring austenite recrystallization in situ through changes in the grain size. However, its potential for quantifying recrystallization kinetics, particularly under partial recrystallization conditions, has not been fully explored. In this study, a Gleeble 3500 thermo-mechanical simulator coupled with a laser ultrasonics for metallurgy (LUMet) system was used to investigate static recrystallization in austenite for selected low-carbon C–Mn and Nb-microalloyed steels over a range of deformation conditions. An approach based on the law of mixtures is proposed to determine recrystallized fractions from LUMet measured grain sizes. The results are consistent with those from softening-based double-hit compression tests. In cases of complete recrystallization, the recrystallization kinetics can be described with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) approach, and the time for 50 pct recrystallization can be represented by an empirical function of the solute Nb concentration, initial austenite grain size, deformation temperature, and applied strain. For partial recrystallization in Nb-microalloyed steels below 1000 °C, the recrystallized fractions feature a plateau that is interpreted by the precipitation of Nb(C, N) using a physically based model. This study extends the capability of laser ultrasonics from grain size monitoring to quantitative analysis of static recrystallization kinetics under both complete and partial recrystallization conditions. By simultaneously providing grain size and recrystallized fraction, two key parameters describing the recrystallization process, the technique offers a unique opportunity for accelerated evaluation of recrystallization behavior for different alloy designs and TMCP processing parameters.</p>

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Quantification of Austenite Recrystallization Kinetics from Laser Ultrasonic Measurements

  • 期刊论文

  • 发表日期：

    2026年7月23日

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  • Minghui Lin,
  • Matthias Militzer

摘要

Quantitative knowledge of austenite recrystallization is essential for designing the thermo-mechanical controlled processing (TMCP) routes of high-strength low-alloyed (HSLA) steels. Among the experimental tools available for recrystallization studies, laser ultrasonics has proven to be efficient for monitoring austenite recrystallization in situ through changes in the grain size. However, its potential for quantifying recrystallization kinetics, particularly under partial recrystallization conditions, has not been fully explored. In this study, a Gleeble 3500 thermo-mechanical simulator coupled with a laser ultrasonics for metallurgy (LUMet) system was used to investigate static recrystallization in austenite for selected low-carbon C–Mn and Nb-microalloyed steels over a range of deformation conditions. An approach based on the law of mixtures is proposed to determine recrystallized fractions from LUMet measured grain sizes. The results are consistent with those from softening-based double-hit compression tests. In cases of complete recrystallization, the recrystallization kinetics can be described with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) approach, and the time for 50 pct recrystallization can be represented by an empirical function of the solute Nb concentration, initial austenite grain size, deformation temperature, and applied strain. For partial recrystallization in Nb-microalloyed steels below 1000 °C, the recrystallized fractions feature a plateau that is interpreted by the precipitation of Nb(C, N) using a physically based model. This study extends the capability of laser ultrasonics from grain size monitoring to quantitative analysis of static recrystallization kinetics under both complete and partial recrystallization conditions. By simultaneously providing grain size and recrystallized fraction, two key parameters describing the recrystallization process, the technique offers a unique opportunity for accelerated evaluation of recrystallization behavior for different alloy designs and TMCP processing parameters.