Effect of carbides and ∑CSL grain boundaries on the recrystallization behavior of Hastelloy X superalloy

Abstract

In this paper, the recrystallization mechanism of Hastelloy X and the grain boundary character distribution (GBCD) are investigated. The effects of carbides and ∑ coincident site lattice (∑CSL) grain boundaries on the recrystallization behavior of Hastelloy X were investigated in detail by hot compression tests. The purpose is to improve the understanding of the microstructural evolution during hot deformation and to understand the role of carbides in the hot deformation process. The hot compression test employs a strain rate of 1 s⁻¹, a temperature range of 1110°C ∼ 1170°C and a strain of 20∼50 %. Discontinuous dynamic recrystallization (DDRX) was the main dynamic recrystallization (DRX) mechanism. When the forming temperature increased to 1170°C, due to the high deformation temperature, the grains grew further and random grain boundaries replaced ∑ coincident site lattice (∑CSL) grain boundaries. Consequently, the ∑CSL grain boundaries ratio was decreased, which was unfavorable to the GBCD in Hastelloy X alloy. Ti, Mo, and Cr-rich carbides, which are M₆C, M₂₃C₆, and TiC, were found in Hastelloy X. The results indicated that these carbides were preferential nucleation sites for the DRX process, which can serve as particles to stimulate nucleation and promote the DRX process.