Effect of Thermomechanical Treatment on the Grain Boundary Character Distribution in a 9Cr-1Mo Ferritic Steel

摘要

Grain boundary embrittlement due to segregation of impurities to high-energy grain boundaries causing an increase of ductile-brittle transition temperature poses a major obstacle in the development of ferritic steel for nuclear reactor core applications. Various types of thermomechanical treatments were carried out on the modified 9Cr-1Mo steel, and the nature of grain boundaries was evaluated using electron backscattered diffraction (EBSD); the “effective grain boundary energy” (EGBE) was also computed. The minimum EGBE was obtained in a specimen that was deformed in the austenite phase field at 1323 K and further normalized and tempered. This condition also gave a high fraction of coincident site lattice boundaries compared to the normalized and tempered modified 9Cr-1Mo steel.