Tensile properties and fractography of aged hastelloy B2 (550–850°C for up to 1200 H)

Abstract

The 0.2% yield strength and elongation at fracture have been measured at 25°C for Hastelloy B2 samples that were aged for up to 1200 h from 550 to 850°C. This alloy is very similar in composition to the binary Ni-20 at.% Mo alloy. At 550 and 750°C, the strength increased significantly (approximately tripling after 1200 h at 550°C). Upon aging at 750°C, the strength passed through a maximum (of about twice that of the solution-annealed condition) then decresed. In the solution-annealed condition, the ductility is approximately 60%, but after aging at 550 and 850°C for 400 h or more, the ductility was <5%. Upon aging at 750°C, it was <5% for aging 200 h or more, even though the strength decreased.

In the ductile condition, the fracture surface topology was dimpled. As aging increased and ductility decreased, the fracture became increasingly intergranular and transgranular. The fracture surface topology is related to the microstructural changes that occur upon aging.