Inhomogeneity of microstructure and mechanical properties in compression-type bulk formed specimens

Abstract

The effect of elongation and spreading in a material on strain and microstructure inhomogeneity during compression-type bulk forming processes was investigated to improve the strain homogeneity of the materials. For systematic investigation, four different compression-type forming processes, namely wire flat rolling, plate flat rolling, wire caliber rolling, and uniaxial compression, were compared. Strain inhomogeneity and macroscopic shear bands (MSBs) were clearly observed during the compression-type bulk forming processes based on a comparative study on the shape change, effective strain and hardness distributions, and microstructural evolution in twinning-induced plasticity steel. The flat-rolled wire had the largest strain inhomogeneity, followed by the caliber-rolled wire, compressed specimen, and flat-rolled plate in the listed order. The inhomogeneity of the strain distribution along the horizontal direction tended to increase with the pure spreading during the forming process. Meanwhile, the inhomogeneity of the strain distribution along the vertical direction increased with decreasing elongation during the process. Therefore, a small pure spreading and large elongation of the specimen result in more homogeneous and higher quality products in the compression-type bulk forming process. For instance, the flat-rolled plate exhibited weak MSBs and low strain inhomogeneity because of the small pure spreading and large elongation during the forming process.