Abstract
Limited studies have evaluated the creep behavior of additively manufactured (AM) ferritic-martensitic (FM) steels. This work investigated the creep behavior of a 9Cr FM steel fabricated by powder blown directed energy deposition (DED) technique. The creep testing at 550–650 °C and 150 MPa for the specimens along the deposition direction in the as-built condition, together with corresponding microstructural characterization, revealed a threshold temperature between 600 and 625 °C, below which the steel has creep resistance comparable with Grade 91 cross-welds and noticeably greater than 9Cr-1Mo steel. The threshold temperature distinguishes the creep behavior in two regimes differentiated in creep activation energy, creep deformation, and failure mechanism. Unlike the creep rupture surface ∼45° from the loading direction when tested above the threshold temperature, the creep rupture for testing below the threshold temperature resembles type IV failure in the cross-welds of ferritic steels. The DED-induced layer structure in the as-built steel played a significant role on the change of creep behavior.
