Hot deformation behavior and dynamic recrystallization of Fe-24Mn steel: Influence on cryogenic hardness

Fe-24Mn steel has attracted attention as a promising material with excellent mechanical properties for cryogenic applications. Understanding the high-temperature deformation behavior and microstructural characteristics of this material is essential for process optimization and performance improvement. This study evaluated the high-temperature deformation behavior and microstructural characteristics of Fe-24Mn steel under temperature conditions ranging from 700 to 1000 °C and strain rates between 0.01 and 10 s -1 . Analysis of the flow curves revealed that dynamic recrystallization (DRX) occurred at temperatures above 900 °C, contributing to stress relaxation, whereas at 700 °C and 800 °C, DRX was suppressed, leading to sustained deformation resistance. To explain the complex interaction between temperature and strain rate, a constitutive equation with high accuracy was established using the Zener-Hollomon parameter. The validation results indicated an R-value of 0.980 and an average absolute relative error (AARE) of 7.83%. Processing map analysis confirmed that stable deformation conditions were achieved at strain rates below 0.1 s -1 , temperatures above 900 °C, and strain levels exceeding 0.4. Microstructural analysis showed that at higher temperatures, DRX reduced dislocation density and formed a uniform grain structure, while at lower temperatures, dislocation accumulation and localized deformation were dominant. Additionally, cryogenic hardness tests conducted at -179 °C demonstrated that under conditions where DRX was suppressed, hardness increased due to high dislocation density. In contrast, under conditions where DRX was actively occurring, deformation twinning (TWIP) was activated, resulting in reduced hardness.