Influence of deformation path on microstructure evolution during the open die forging of large size ingot of high strength steel: experiments and FE analysis.

The inhomogeneity present in the deformation and microstructure during the open die forging of large size ingot significantly influences the mechanical properties of the final part. This study aims to develop a microstructure-based finite element (FE) model and investigate the influence of deformation path on microstructure evolution during the upsetting process of large size ingot of a high strength steel. The difference in deformation path is achieved by modification in anvil shape such as flat, v shape, convex, and concave die. To achieve this goal, hot compression tests were carried out using the Gleeble 3800 thermomechanical simulator. Utilizing the acquired and corrected flow stress data, a material model and a microstructure model were established, and both formulated models were then integrated into the Forge NxT 3.2 finite element simulation software through the inclusion of a dedicated user subroutine. The predictions from the FE analysis were validated with experimental results on standard size hot compression specimens, which allowed for the accurate prediction of the dynamic recrystallized average grain size at the end of hot deformation. Afterwards, the validated FE model was scaled up to simulate the industrial upsetting process, making it possible to investigate the effect of deformation path on inhomogeneity of strain and microstructure evolution at the end of upsetting process for large sized forged ingots. An evaluative analysis of four die geometries, aimed at identifying the optimal die shape for minimizing inhomogeneity in strain and grain size across a large size forged ingot, was conducted. It was found that the convex die provokes the lowest deformation, while the concave die induces the highest deformation values at the center of the ingot. Utilizing the coefficient of variation as an indicator of heterogeneity, it was determined that the v-die and concave die resulted in a more consistent grain size distribution compared to the flat and convex dies. [ABSTRACT FROM AUTHOR]