A modified kinetics model and softening behavior for static recrystallization of 12Cr ultra-super-critical rotor steel

Abstract

In this paper, the static recrystallization (SRX) of 12Cr ultra-super-critical (USC) rotor steel was investigated by a series of hot compression tests on a Gleeble1500D thermal simulator. Double-hit hot deformation tests were conducted at temperatures of 1223K–1323 K and strain rates of 0.001 s ^−1 –0.1 s ^−1 with inter-pass times of 10s–180 s. A conventional kinetics model of SRX was established based on flow curves obtained by regression analysis under different deformation conditions. However, a significant deviation resulted between predicted and experimental values for the SRX fraction, and therefore a modified kinetics equation was proposed by analysing the SRX characteristics and possession of the capability to accurately predict SRX softening behaviour was confirmed. Effects of hot deformation parameters on SRX softening behaviour and SRX grain size were discussed. Furthermore, microstructure deforming was observed at different inter-pass times with an optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Analysis showed that recovery was the main softening mechanism and the fundamental nucleation mechanism for SRX was bulging at the grain boundary.

Keywords

• 12Cr USC rotor steel
• double-hit hot compression tests
• Static recrystallization
• kinetics model
• microstructure