A modified Hansel-Spittel constitutive equation of Ti-6Al-4V during cogging process

•The isothermal compression of four typical microstructures for Ti-6Al-4V is studied.•A modified H-S CE considering the alpha/beta structure is proposed and calibrated.•Compared with the H-S and S-C-A CEs, the W and Δ% of the modified CE are smaller and more concentrated.•The modified H-S CE is embedded in the finite element code, and good agreement with the experimental results. The isothermal compression of four typical microstructures in the cogging process for Ti-6Al-4V was conducted at strain rates ranging from 0.01 to 1 s−1 with varying temperatures. The flow behavior of different microstructures was compared. The Hansel-Spittel (H-S) and strain compensated Arrhenius (S-C-A) constitutive equations (CEs) were calibrated. To improve prediction ability, a modified H-S CE considering the evolution of microstructure was proposed and embedded in the finite element code. The original, modified H-S, and S-C-A CEs were evaluated based on the average absolute error (W) and relative error ratio (Δ%). Compared with the original H-S and S-C-A CEs, the W (−2.5%~2.5%) of the modified CE was found to be smaller and the Δ% was more concentrated. Furthermore, hot forging experiment and finite element simulation (FES) at different speeds were performed. The average relative error (AARE) of load-stroke for the H-S and modified H-S CEs is 13.51% and 3.67%, respectively. The comparisons between the FES and hot forging experiment indicate that the modified CE is more accurate for the simulation of the cogging process.