The microstructure, micro-hardness, and tensile properties of interface between hot isostatic pressing densified low alloy steel and Inconel 690 cladding were investigated during the aging process at 600 ℃. The results show that the interface region can be divided into four zones from base metal to deposited metal: carbon-depleted zone (CDZ), partial melting zone (PMZ), planar growth zone (PGZ), and brownish feature zone (BFZ). Dimensions of these zones do not significantly change during aging. However, type I carbides noticeably increase in size in the PMZ, and precipitates clearly occur in the PGZ. The main reason for their growth and occurrence is continuous carbon migration. The highest micro-hardness appears in the PGZ and BFZ regions, which is related to carbon accumulation and precipitates in these regions. Tensile failure occurs on the base metal side due to the high strength mismatch between these two materials. The CDZ, composed of only ferrite, has lower strength and fractures at the boundary between CDZ and base metal. The ultimate tensile strength decreases by only 50 MPa after aging for 1500 h, and the interface region maintains high strength without significant deformation.