FRACTURE AND DUCTILE-TO-BRITTLE TRANSITION CHARACTERISTICS OF MOLYBDENUM BY IMPACT AND STATIC BEND TESTS

In order to investigate the relationship between the impact and static bending behaviors at low temperatures for molybdenum having different grain structures and different grain boundary strengths, the impact a nd static bend tests were performed for miniaturized specimens of five kinds of molybdenum. The pure molybdenum with or without carbon addit ion and the TZM alloy had a fine and equiaxed grain structure, and the doped-molybdenum with or without carbon addition had a coarse and elo ngated grain structure. The total absorbed energy, total deflection, y ield and maximum stresses by the impact bend test, and the bend angle, yield and maximum stresses by the static bend test were calculated an d compared with each other. The fracture and ductile-to-brittle transi tion characteristics by both tests were discussed from the viewpoints of the grain structure and the grain boundary strength. The results ar e summarized as follows. (1) Fracture characteristics by the impact an d static bend tests are essentially the same. The difference in critic al stress representing the low-temperature fracture strength between t he materials is due to the difference in grain structure and grain bou ndary strength. (2) DBTT by the impact bend test depends apparently on the critical stress of the material, whilst DBTT by the static bend t est depends not only on the critical stress but also on the yield stre ss. (3) DBTT by the impact bend test is higher by 90-175 K than that b y the static bend test. This result is principally due to the increase of the yield stress at a given temperature which results from the inc rease of the strain rate. The degree of the DBTT increase differs betw een materials. This result is due to the difference in yield stress re sulting from the difference in grain structure.