The metadynamic recrystallization (MDRX) behavior of Super304H austenitic heat-resistant steel was systematically investigated, and its hot processing parameters were optimized by integrating processing maps with microstructural analysis. Double-pass hot compression tests (temperature: 950-1150 °C, strain rate: 0.01-5 s−1, inter-pass time: 5-30 s) were conducted to develop an Avrami-type kinetic equation, which is quantified by: \(X_{{{\text{MDRX}}}} = 1 - exp\left[ { - 0.693\left( {t/t_{0.5} } \right)^{0.623} } \right]\) , \(t_{0.5} = 3.18 \times 10^{ - 9} \dot{\varepsilon }^{ - 0.264} exp\left( {252330/RT} \right)\) , where XMDRX is the MDRX fraction, t is the inter-pass time, t0.5 is the time for 50% recrystallization, \(\dot{\varepsilon }\) is the strain rate, Q is the activation energy of MDRX, R is the universal gas constant, and T is the deformation temperature. The results demonstrate that MDRX progression exhibits a strong positive correlation with deformation temperature, strain rate, and inter-pass time, and the proposed kinetic equation accurately predicts MDRX behavior. Nano-sized Nb-rich MX-type precipitates hinder grain boundary migration via the Zener pinning effect, leading to a significant increase in MDRX activation energy (Q = 252.3 kJ/mol) compared to conventional 304 austenitic steels. The established processing maps reveal that prolonged inter-pass time shifts instability zones from low-temperature/high-strain-rate regions to high-temperature/high-strain-rate regions. By combining microstructural evolution analysis with model predictions, the optimal processing window was identified as 1100-1150 °C/0.1-1 s−1. This study provides a theoretical foundation for optimizing high-temperature forming processes and microstructure control in Nb-microalloyed austenitic steels.
