Unusual relationship between impact toughness and grain size in a high-manganese steel

• 作 者: Pan Xie Shucheng Shen Cuilan Wu Jiehua Li Jianghua Chen
• 机 构: Center for High Resolution Electron Microscopy,College of Materials Science and Engineering,Hunan Un
• 出 处: 材料科学技术（英文版）
• 发表日期: 2021年30期
• 关键词: Toughness Grain size Twinning induced plasticity Transformations induced plastic

The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excel-lent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,εhcp-martensite and α\'bcc-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate that εhcp-martensite becomes more stable than α\'bcc-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80 C,εhcp-martensite transformation,α\'bcc-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.