The mechanical properties and microstructure evolution of domestic Incoloy 800H during aging in high purity helium at 675 ℃ 7 for 3 000 h were investigated. By scanning electron microscope(SEM)

energy diffraction spectrum(EDS) of X-ray

transmission electron microscope(TEM) and mechanical properties tests

the effects of microstructure change on mechanical properties of the alloy was studied. The results indicated that

the mechanical properties of alloy Incoloy 800H were excellent after aging

which met the requirements of ASME SB163—2015. Both the room temperature tensile strength and micro-Vickers hardness increased with extension of the aging time. After 3 000 h aging

the room temperature tensile strength and micro-Vickers hardness increased by 7.1% and 16.9%. The M_(23)C_6 carbides were mainly distributed along the grain boundaries and in the matrix

the second Ti(C

N) phases distributed in the matrix after aging. The size of the discontinuous M_(23)C_6 carbides along the grain boundaries increased slightly with the extension of the aging time. After 3 000 h aging

the size of the M_(23)C_6 carbides along the grain boundaries was about 400～700 nm. The number of M_(23)C_6 and secondary Ti(C

N) phases in the matrix increased significantly

however their sizes changed little

which were about 120～160 nm and 200～ 250 nm respectively. No harmful phase like the σ phase and G phase was found