Effect of Advanced Processing on the Development of Nano Bainite

Prantik Mukhopadhyay

Abstract

A comprehensive report has been tried to address associating the advanced processes to develop high performance bainitic steel. The effect of novel processing like iso-thermal processing, thixoforming, quenching-partitioning and ausforming has been justified on the development of carbide free nano bainite. The single-variable stage iso-thermal holding of 0.34C-1.52Mn-1.48Si-0.93Ni-1.15Cr-0.40Mo-0.71Al steel at the temperature range of 668K-563K has revealed that the bainite, which formed at just above martensite start temperature, was associated with both high strength and toughness. The iso-thermal banitic processing of steel with composition 0.74C-1.64Si-1.82Mn-1Ni-0.36Mo-0.21Cr-0.047Al at 513K, 543K and 573K, performed just after the thixotropic flow of prior 50% deformed feedstock, produced globular grain with size 115 µm containing mixture of ferrite plate (0.063 µm) and austenite plate (0.040 µm). High carbon steel with composition 0.79C-1.98Mn-1.51Si-0.98Cr-0.24Mo-1.06Al-1.58V deformed 15% in 10 second during ausforming at 573K, enhanced the nano bainite development throughout the process. An equivalent process to quenching and partitioning process revealed that the pre-existing martensite plate enhanced the nano bainite kinetic. However, the effect of ausforming was found to be stronger than the effect of pre-existing martensite.