OH Yoonsuk Research Institute of Science and Technology

Spoluautoři YANG Heok, LEE Young Joo, LEE Soon Gi, JANG Wookil, CHOI Jong K.

High manganese steels have been widely used since the mid-19th century as they have high toughness and excellent wear-resistant. The mechanical properties of high manganese steels are sensitive to the microstructure and impurity behavior in the grain boundaries(GBs). When the impurities segregate inside GBs, the cracks are easily found during hot rolling. Moreover the impurities on GBs do the detrimental effects on the ductility and toughness at both room temperature and low temperature. Impurity segregation frequently plays a role in GB decohesion. In some cases, segregation to GBs can actually be beneficial for macroscale material properties, e.g., strengthening GB cohesion, or preventing grain growth. Despite the continuing effort to understand impurity-induced properties of the material, the physics and chemistry underlying the phenomenon is not still fully understood. Previous experimental and theoretical studies showed that impurities within iron GBs significantly affect the intergranular cohesion. For example, interstitial carbon and boron impurities enhance cohesion, while sulfur and phosphorous interstitials weaken. Regarding substitutional transition metal impurities, molybdenum was shown to enhance intergranular cohesion, while palladium weakens the cohesion strength. In this work, the effects of the impurity atoms such as boron and phosphorus on symmetrical tilt GBs for high manganese steels are investigated by using first-principle calculations. As an aid in establishing an understanding on the electronic level, the influence of impurity on the cohesion of an iron GB was determined using density functional theory with the generalized gradient approximation. Through precise calculations on both GB and bulk alloy, we found boron, carbon and some other elements enhance the GB while the others act as embrittling effect. Analysis of the results in terms of structural relaxation, bonding character, and magnetic interactions shows that charge-transfer and local atomic environment is found to play a dominant role for the chemical bond between the impurity atom and iron and the cohesion across the iron GB. These results provide a quantitative explanation from first principles for the technologically important phenomenon of embrittlement.