Static recrystallization characteristics and kinetics of austenitic stainless steels under development for LH2 storage applications

Abstract

Developing high-strength austenitic stainless steel (ASS) grades for lightweight cryogenic storage tanks, particularly for liquefied hydrogen (LH<inf>2</inf>), demands precise microstructure control achievable via optimized thermomechanically controlled processing (TMCP). In recrystallization–controlled regime of TMCP, successive rolling passes facilitate microstructural refinement through dynamic and static restoration mechanisms. This work illustrates static recrystallization (SRX) characteristics and kinetics in three ASS alloys designed by varying N, Mn and Nb contents. Interrupted (double–hit) compression tests were conducted to characterize the flow behaviour and microstructural evolution across different deformation conditions. SRX kinetics were formulated using a fractional–softening framework, where the time to 50 % recrystallization was correlated with strain, strain rate, temperature, and initial grain size. While the exponents of strain (−3.1) and strain rate (−0.3) were consistent across all compositions, the apparent activation energies of SRX varied in the range 251.5–298 kJ·mol⁻¹, with 7 wt% Mn showing a more noticeable effect in comparison with 0.1 wt% Nb. Detailed metallographic analysis confirmed the accuracy of the derived models. Suitable semi-empirical relations were established enabling prediction of statically recrystallised grain size across various processing conditions. These results define the processing windows needed to design TMCP schedules for advanced ASSs for LH<inf>2</inf> and cryogenic environments.