High Temperature Aging Structures of Ni-20Cr-20W Alloys

Abstract

High temperature aging structures and age hardening of Ni-20Cr-20W alloys developed as the superalloys for the nuclear energy steelmaking, and effects of C and Zr additions to the alloys and the effect of preheat treatment on these properties were studied.
M₆C, α-W and two kinds of M23C6 having different lattice parameters were found as precipitates in the alloys. M₂₃C₆ whose lattice parameter was around 10.7A precipitated in the early stage of aging at 700°C-1150°C, and the carbide changed to M₆C at higher temperature than 1000°C, but it remained as a stable carbide at lower temperature than 900°C.
α-W precipitated at 800°C-1100°C after precipitation of M₂₃C₆ and it disappeared with increase of M₆C. M₂₃C₆ having the larger lattice parameter (10.9Å) precipitated transitionally in aging stage of 26×10³ in Larson Miller parameter at 900°C and 1000°C.
Age hardening corresponded to the precipitation of M₂₃C₆ and it was reduced by the double pre-heattreatment.
Zr addition and amount of C influenced on the aging structure and age hardening. Zr seemed to be a favorable element to stabilize the carbide.