Microstructure evolution modeling of titanium alloy large ring in hot ring rolling

摘要

Exploration of microstructure evolution is of significance for manufacturing the large ring with high performance and high reliability in hot ring rolling. In the study, the microstructure evolution model and the rate-/temperature-/microstructure-dependent constitutive model of titanium alloy are implemented in ABAQUS/Explicit through the user material subroutine VUMAT. The developed subroutine is validated by single-element models and isothermal upsetting experiments of Ti-6Al-4V cylinder. The subroutine is imbedded into a coupled thermomechanical three-dimensional finite element (3D-FE) model for hot rolling of Ti-6Al-4V large ring. The evolution characteristics of β phase volume fraction and grain size of Ti-6Al-4V during the process are revealed, and the final microstructures of the large ring under different processing conditions are explored. The results obtained show that (1) microstructure evolution follows the trend with the process progressing: the fine grain zone transfers from the surface layer (SL) to the middle layer (ML) of the ring; the poor β zone extends from the outside of the SL to the end-plane of the ML, and the rich β zone always locates at the SL. (2) decreasing the rotational velocity of the driver roll n_1, or increasing the feed rate of the idle roll v or the initial temperature of the ring T_0 contributes to more uniform distributions of β phase and its grain size, but results in the increase of the β phase volume fraction and grain size.