Influence of deformation path on microstructure evolution during multi-step deformation of a high strength steel: experiments and FE analysis

This study aims to investigate the effect of deformation path on deformation and microstructure evolution during the multi-step deformation of a high strength steel. The deformation paths were illustrated by flat and concave surface anvils. Multi-step deformation experiments were conducted on high strength steel specimens using thermomechanical simulator, Gleeble 3800 equipped with MaxStrain module, a special purpose attachment. All tests were performed at a strain rate and temperature of 0.01 s⁻¹ and 1150 °C respectively, considering two deformation paths. A total true strain of 0.84 was imparted over four steps, with approximately 0.21 strain applied per step. The results were used to analyze the influence of varying deformation paths on microstructure evolution and hardness distribution. A finite element (FE) model was developed using Forge NxT 3.2 FE code to simulate the multi-step deformation process. The strain distribution obtained via FE model was correlated to the average grain size and hardness distribution after the multi-step deformation experiments for validation. This validated FE model was capable of predicting strain distribution, dynamic recrystallization (DRX) volume fraction, and grain size evolution during the multi-step deformation process. A comparative study of results obtained from two deformation paths was conducted to determine the optimal deformation path, aiming homogeneous strain and grain size distribution. The Coefficient of Variation (CoV) was used to assess the heterogeneity of the hardness distribution. The results suggest that concave anvils promote a higher and more uniform strain distribution, leading to a homogeneous distribution of grain size and hardness. An increased and more uniform strain distribution promotes complete dynamic recrystallization (DRX) with finer grain size leading to homogeneous hardness distribution.