Exploring Variations in Toughness Contributions Across Different Types of High-Angle Grain Boundaries in Bainitic Steels

Abstract

Generally, the toughness of steel is greatly influenced by the density of high angle grain boundaries (HAGBs). However, in bainitic steel, various types of boundaries can exhibit high angles, potentially leading to differences in their contributions on toughness. In this research, two steel samples with same chemical composition, similar strength and elongation, and comparable HAGBs densities demonstrated varying absorption energies in Charpy impact tests conducted at room temperature and -40°C. Crystallographic analysis revealed that although both samples have similar density of HAGBs, prior austenite boundaries and packet boundaries contribute more to impact absorption energy by enhancing plasticity compared to block boundaries. The discrepancy was particularly notable due to the high proportion of V1/V2 variant interfaces within the block interfaces. The findings underscore the significance of understanding the nuanced contributions of different HAGB types to the toughness of bainitic steels.

Keywords: bainitic steel, toughness, high angle grain boundaries, variant selection, slip-transfer geometric factor