Hot Deformation Characteristics and Dynamic Recrystallization Mechanisms of a Newly Developed Austenitic Heat-Resistant Alloy

Abstract

The hot deformation characteristics, microstructure evolution, and dynamic recrystallization (DRX) mechanism of the newly developed austenitic heat-resistant steel Fe–18Cr–10Ni–0.3Nb–2.5Cu were systematically investigated by thermal compression tests combined with microstructure characterizations. The activation energy (Q) map, Zener–Hollomon parameter (Z) map, and processing map were plotted according to the stress–strain curves to reveal the inherent connection between the three maps and the hot deformation characteristics of this alloy. The high η region in the processing map does not precisely correspond to the region where DRX developed. Nevertheless, the flow instability map accurately predicts the microstructure. The variation pattern of Z corresponded more closely to the hot deformation microstructure evolution than did the variation pattern of Q. The degree of DRX increases with decreasing Z. The optimal process parameters are 1000 °C/0.01 s−1/0.8 and 1100 °C/10 s−1/0.8 (temperature/strain rate/strain), and they result in complete DRX and a narrow range of Z values. The DRX mechanism at high strain rate is characterized by the combined enhancement of discontinuous DRX (DDRX), continuous DRX (CDRX), and twin-DRX (TDRX). The dominance of the particle-stimulated nucleation (PSN) mechanism at intermediate strain rate results in the formation of incompletely recrystallized microstructures with approximate orientation. Sufficient time at low strain rate promotes the development of DDRX and CDRX.