Microstructure evolution and hot deformation characteristics of a novel 15Cr-30Ni-2Ti-3Cu engine valve alloy

Abstract

The flow behavior, dynamic recrystallization (DRX), and microstructure evolution during the hot deformation of a newly developed 15Cr-30Ni-2Ti-3Cu valve alloy were studied. A constitutive model after strain compensation was established to predict the flow behavior of the alloy. A DRX kinetic model was proposed to predict dynamic recrystallization behavior during hot deformation. Both the fraction of DRX and the recrystallized grain size increases as the deformation temperature is increased from 950 ℃ to 1150 ℃, and decreases with increasing the strain rate from 0.01 s−1 to 10 s−1. A complete recrystallization structure of the alloy is obtained at the hot deformation temperature of 1150 ℃ and the strain rates smaller than 0.1 s−1. The optimal processing parameters of the valve alloy are determined as 1050 ℃− 1150 ℃/0.01 s−1-0.1 s−1. The Laves phase and (Ti,Nb)C particles precipitate during hot deformation, and hinder the dynamic recrystallization process by pinning dislocations and grain boundaries. Fine γ' particles provide nucleation sites for the formation of dynamically recrystallized grains due to its ordered cubic L12 structure.